Dr Alexandra J Spencer

Research Area: Immunology
Technology Exchange: Cell sorting, Cellular immunology, Flow cytometry, Immunohistochemistry, In vivo imaging, Microscopy (Confocal) and Vaccine production and evaluation
Scientific Themes: Immunology & Infectious Disease and Tropical Medicine & Global Health
Keywords: Cell-mediated immunity, Malaria, Vaccines and Immunology
Malaria development in mosquitoes

Malaria development in mosquitoes

CD8+ T cells play a significant role in protection from liver-stage malaria, but due to the short time-interval between injection of sporozoite from the bite of an infected mosquito and invasion of hepatocytes, exceptionally high number of circulating T cells are required. While traditional vaccination with heat-killed or attenuated vaccines has proved highly effective against pathogens controlled by neutralising antibodies, no vaccine has yet been licensed against pathogens in which cell mediated immunity plays an important role. Viral vaccines have shown a remarkable capacity to induce and boost T cells responses and are therefore the primary focus for our development of vaccines against malaria, influenza and tuberculosis. 

The primary focus of my research is to understand the immune response induced by vectored vaccines and in response to liver-stage malaria. I am particularly interested in the type of T cell response induced in terms of effector capacity (cytokines), phenotype (effector/memory) and tissue specificity. I am interested in determining ways to increase the size of the immune response induced by vectored vaccines be that through altering vaccination regimens or through the co-expression of molecular adjuvants. This is complemented by work to identify new or more efficacious antigenic targets for a liver-stage malaria vaccine by combining measurements of T cell function with transgenic parasite technology. 

Name Department Institution Country
Professor Adrian VS Hill Jenner Institute Oxford University, Old Road Campus Research Building United Kingdom
Dr Paulo Bettencourt Jenner Institute University of Oxford United Kingdom
Professor Ronald N Germain NIH United States
Professor Sarah C Gilbert Jenner Institute Oxford University, Old Road Campus Research Building United Kingdom
Dr Teresa Lambe Jenner Institute Oxford University, Old Road Campus Research Building United Kingdom
Associate Professor Katie Ewer Jenner Institute Oxford University, Old Road Campus Research Building United Kingdom
Associate Professor Shahid M Khan LUMC Netherlands
Associate Professor Chris J Janse LUMC Netherlands
Dr George M Warimwe MRCVS Tropical Medicine Oxford University, Kilifi Kenya
Rodríguez-Galán A, Salman AM, Bowyer G, Collins KA, Longley RJ, Brod F, Ulaszewska M, Ewer KJ, Janse CJ, Khan SM et al. 2017. An in vitro assay to measure antibody-mediated inhibition of P. berghei sporozoite invasion against P. falciparum antigens. Sci Rep, 7 (1), pp. 17011. | Show Abstract | Read more

A large research effort is currently underway to find an effective and affordable malaria vaccine. Tools that enable the rapid evaluation of protective immune responses are essential to vaccine development as they can provide selection criteria to rank order vaccine candidates. In this study we have revisited the Inhibition of Sporozoite Invasion (ISI) assay to assess the ability of antibodies to inhibit sporozoite infection of hepatocytes. By using GFP expressing sporozoites of the rodent parasite P. berghei we are able to robustly quantify parasite infection of hepatocyte cell lines by flow cytometry. In conjunction with recently produced transgenic P. berghei parasites that express P. falciparum sporozoite antigens, we have been able to use this assay to measure antibody mediated inhibition of sporozoite invasion against one of the lead malaria antigens P. falciparum CSP. By combining chimeric rodent parasites expressing P. falciparum antigens and a flow cytometric readout of infection, we are able to robustly assess vaccine-induced antibodies, from mice, rhesus macaques and human clinical trials, for their functional ability to block sporozoite invasion of hepatocytes.

Ewer K, Sebastian S, Spencer AJ, Gilbert S, Hill AVS, Lambe T. 2017. Chimpanzee adenoviral vectors as vaccines for outbreak pathogens. Hum Vaccin Immunother, 13 (12), pp. 3020-3032. | Show Abstract | Read more

The 2014-15 Ebola outbreak in West Africa highlighted the potential for large disease outbreaks caused by emerging pathogens and has generated considerable focus on preparedness for future epidemics. Here we discuss drivers, strategies and practical considerations for developing vaccines against outbreak pathogens. Chimpanzee adenoviral (ChAd) vectors have been developed as vaccine candidates for multiple infectious diseases and prostate cancer. ChAd vectors are safe and induce antigen-specific cellular and humoral immunity in all age groups, as well as circumventing the problem of pre-existing immunity encountered with human Ad vectors. For these reasons, such viral vectors provide an attractive platform for stockpiling vaccines for emergency deployment in response to a threatened outbreak of an emerging pathogen. Work is already underway to develop vaccines against a number of other outbreak pathogens and we will also review progress on these approaches here, particularly for Lassa fever, Nipah and MERS.

Longley RJ, Halbroth BR, Salman AM, Ewer KJ, Hodgson SH, Janse CJ, Khan SM, Hill AVS, Spencer AJ. 2017. Assessment of the Plasmodium falciparum Preerythrocytic Antigen UIS3 as a Potential Candidate for a Malaria Vaccine. Infect Immun, 85 (3), pp. e00641-16-e00641-16. | Show Abstract | Read more

Efforts are under way to improve the efficacy of subunit malaria vaccines through assessments of new adjuvants, vaccination platforms, and antigens. In this study, we further assessed the Plasmodium falciparum antigen upregulated in infective sporozoites 3 (PfUIS3) as a vaccine candidate. PfUIS3 was expressed in the viral vectors chimpanzee adenovirus 63 (ChAd63) and modified vaccinia virus Ankara (MVA) and used to immunize mice in a prime-boost regimen. We previously demonstrated that this regimen could provide partial protection against challenge with chimeric P. berghei parasites expressing PfUIS3. We now show that ChAd63-MVA PfUIS3 can also provide partial cross-species protection against challenge with wild-type P. berghei parasites. We also show that PfUIS3-specific cellular memory responses could be recalled in human volunteers exposed to P. falciparum parasites in a controlled human malaria infection study. When ChAd63-MVA PfUIS3 was coadministered with the vaccine candidate P. falciparum thrombospondin-related adhesion protein (PfTRAP) expressed in the ChAd63-MVA system, there was no significant change in immunogenicity to either vaccine. However, when mice were challenged with double chimeric P. berghei-P. falciparum parasites expressing both PfUIS3 and PfTRAP, vaccine efficacy was improved to 100% sterile protection. This synergistic effect was evident only when the two vaccines were mixed and administered at the same site. We have therefore demonstrated that vaccination with PfUIS3 can induce a consistent delay in patent parasitemia across mouse strains and against chimeric parasites expressing PfUIS3 as well as wild-type P. berghei; when this vaccine is combined with another partially protective regimen (ChAd63-MVA PfTRAP), complete protection is induced.

Spencer AJ, Longley RJ, Gola A, Ulaszewska M, Lambe T, Hill AVS. 2017. The Threshold of Protection from Liver-Stage Malaria Relies on a Fine Balance between the Number of Infected Hepatocytes and Effector CD8+ T Cells Present in the Liver. J Immunol, 198 (5), pp. 2006-2016. | Show Abstract | Read more

Since the demonstration of sterile protection afforded by injection of irradiated sporozoites, CD8+ T cells have been shown to play a significant role in protection from liver-stage malaria. This is, however, dependent on the presence of an extremely high number of circulating effector cells, thought to be necessary to scan, locate, and kill infected hepatocytes in the short time that parasites are present in the liver. We used an adoptive transfer model to elucidate the kinetics of the effector CD8+ T cell response in the liver following Plasmodium berghei sporozoite challenge. Although effector CD8+ T cells require <24 h to find, locate, and kill infected hepatocytes, active migration of Ag-specific CD8+ T cells into the liver was not observed during the 2-d liver stage of infection, as divided cells were only detected from day 3 postchallenge. However, the percentage of donor cells recruited into division was shown to indicate the level of Ag presentation from infected hepatocytes. By titrating the number of transferred Ag-specific effector CD8+ T cells and sporozoites, we demonstrate that achieving protection toward liver-stage malaria is reliant on CD8+ T cells being able to locate infected hepatocytes, resulting in a protection threshold dependent on a fine balance between the number of infected hepatocytes and CD8+ T cells present in the liver. With such a fine balance determining protection, achieving a high number of CD8+ T cells will be critical to the success of a cell-mediated vaccine against liver-stage malaria.

Hodgson SH, Llewellyn D, Silk SE, Milne KH, Elias SC, Miura K, Kamuyu G, Juma EA, Magiri C, Muia A et al. 2016. Changes in Serological Immunology Measures in UK and Kenyan Adults Post-controlled Human Malaria Infection. Front Microbiol, 7 (OCT), pp. 1604. | Show Abstract | Read more

Background: The timing of infection is closely determined in controlled human malaria infection (CHMI) studies, and as such they provide a unique opportunity to dissect changes in immunological responses before and after a single infection. The first Kenyan Challenge Study (KCS) (Pan African Clinical Trial Registry: PACTR20121100033272) was performed in 2013 with the aim of establishing the CHMI model in Kenya. This study used aseptic, cryopreserved, attenuated Plasmodium falciparum sporozoites administered by needle and syringe (PfSPZ Challenge) and was the first to evaluate parasite dynamics post-CHMI in individuals with varying degrees of prior exposure to malaria. Methods: We describe detailed serological and functional immunological responses pre- and post-CHMI for participants in the KCS and compare these with those from malaria-naïve UK volunteers who also underwent CHMI (VAC049) (ClinicalTrials.gov NCT01465048) using PfSPZ Challenge. We assessed antibody responses to three key blood-stage merozoite antigens [merozoite surface protein 1 (MSP1), apical membrane protein 1 (AMA1), and reticulocyte-binding protein homolog 5 (RH5)] and functional activity using two candidate measures of anti-merozoite immunity; the growth inhibition activity (GIA) assay and the antibody-dependent respiratory burst activity (ADRB) assay. Results:Clear serological differences were observed pre- and post-CHMI by ELISA between malaria-naïve UK volunteers in VAC049, and Kenyan volunteers who had prior malaria exposure. Antibodies to AMA1 and schizont extract correlated with parasite multiplication rate (PMR) post-CHMI in KCS. Serum from volunteer 110 in KCS, who demonstrated a dramatically reduced PMR in vivo, had no in vitro GIA prior to CHMI but the highest level of ADRB activity. A significant difference in ADRB activity was seen between KCS volunteers with minimal and definite prior exposure to malaria and significant increases were seen in ADRB activity post-CHMI in Kenyan volunteers. Quinine and atovaquone/proguanil, previously assumed to be removed by IgG purification, were identified as likely giving rise to aberrantly high in vitro GIA results. Conclusions: The ADRB activity assay is a promising functional assay that warrants further investigation as a measure of prior exposure to malaria and predictor of control of parasite growth. The CHMI model can be used to evaluate potential measures of naturally-acquired immunity to malaria.

Morris SJ, Sebastian S, Spencer AJ, Gilbert SC. 2016. Simian adenoviruses as vaccine vectors. Future Virol, 11 (9), pp. 649-659. | Show Abstract | Read more

Replication incompetent human adenovirus serotype 5 (HAdV-C5) has been extensively used as a delivery vehicle for gene therapy proteins and infectious disease antigens. These vectors infect replicating and nonreplicating cells, have a broad tissue tropism, elicit high immune responses and are easily purified to high titers. However, the utility of HAdV-C5 vectors as potential vaccines is limited due to pre-existing immunity within the human population that significantly reduces the immunogenicity of HAdV-C5 vaccines. In recent years, adenovirus vaccine development has focused on simian-derived adenoviral vectors, which have the desirable vector characteristics of HAdV-C5 but with negligible seroprevalence in the human population. Here, we discuss recent advances in simian adenovirus vaccine vector development and evaluate current research specifically focusing on clinical trial data.

Ewer KJ, Lambe T, Rollier CS, Spencer AJ, Hill AV, Dorrell L. 2016. Viral vectors as vaccine platforms: from immunogenicity to impact. Curr Opin Immunol, 41 pp. 47-54. | Show Abstract | Read more

Viral vectors are the vaccine platform of choice for many pathogens that have thwarted efforts towards control using conventional vaccine approaches. Although the STEP trial encumbered development of recombinant human adenovirus vectors only a few years ago, replication-deficient simian adenoviruses have since emerged as a crucial component of clinically effective prime-boost regimens. The vectors discussed here elicit functionally relevant cellular and humoral immune responses, at extremes of age and in diverse populations. The recent Ebola virus outbreak highlighted the utility of viral vectored vaccines in facilitating a rapid response to public health emergencies. Meanwhile, technological advances in manufacturing to support scale-up of viral vectored vaccines have helped to consolidate their position as a leading approach to tackling 'old' and emerging infections.

Alharbi NK, Spencer AJ, Salman AM, Tully CM, Chinnakannan SK, Lambe T, Yamaguchi Y, Morris SJ, Orubu T, Draper SJ et al. 2016. Enhancing cellular immunogenicity of MVA-vectored vaccines by utilizing the F11L endogenous promoter. Vaccine, 34 (1), pp. 49-55. | Show Abstract | Read more

Modified vaccinia virus Ankara (MVA)-vectored vaccines against malaria, influenza, tuberculosis and recently Ebola virus are in clinical development. Although this vector is safe and immunogenic in humans, efforts remain on-going to enhance immunogenicity through various approaches such as using stronger promoters to boost transgene expression. We previously reported that endogenous MVA promoters such as pB8 and pF11 increased transgene expression and immunogenicity, as compared to the conventional p7.5 promoter. Here, we show that both promoters also rivalled the mH5 promoter in enhancing MVA immunogenicity. We investigated the mechanisms behind this improved immunogenicity and show that it was a result of strong early transgene expression in vivo, rather than in vitro as would normally be assessed. Moreover, keeping the TK gene intact resulted in a modest improvement in immunogenicity. Utilizing pB8 or pF11 as ectopic promoters at the TK locus instead of their natural loci also increased transgene expression and immunogenicity. In addition to a reporter antigen, the pF11 promoter was tested with the expression of two vaccine antigens for which cellular immunogenicity was significantly increased as compared to the p7.5 promoter. Our data support the use of the pF11 and pB8 promoters for improved immunogenicity in future MVA-vectored candidate vaccines.

Longley RJ, Halbroth BR, Ewer KJ, Hill AVS, Spencer AJ. 2015. Identification of Immunodominant Responses to the Plasmodium falciparum Antigens PfUIS3, PfLSA1 and PfLSAP2 in Multiple Strains of Mice. PLoS One, 10 (12), pp. e0144515. | Show Abstract | Read more

Malaria, caused by the Plasmodium parasite, remains a serious global public health concern. A vaccine could have a substantial impact on eliminating this disease, alongside other preventative measures. We recently described the development of three novel, viral vectored vaccines expressing either of the antigens PfUIS3, PfLSA1 and PfLSAP2. Each vaccination regimen provided high levels of protection against chimeric parasite challenge in a mouse model, largely dependent on CD8+ T cells. In this study we aimed to further characterize the induced cellular immune response to these vaccines. We utilized both the IFNγ enzyme-linked immunosorbent spot assay and intracellular cytokine staining to achieve this aim. We identified immunodominant peptide responses for CD4+ and CD8+ T cells for each of the antigens in BALB/c, C57BL/6 and HLA-A2 transgenic mice, creating a useful tool for researchers for subsequent study of these antigens. We also compared these immunodominant peptides with those generated from epitope prediction software, and found that only a small proportion of the large number of epitopes predicted by the software were identifiable experimentally. Furthermore, we characterized the polyfunctionality of the induced CD8+ T cell responses. These findings contribute to our understanding of the immunological mechanisms underlying these protective vaccines, and provide a useful basis for the assessment of these and related vaccines as clinical constructs.

Dicks MDJ, Spencer AJ, Coughlan L, Bauza K, Gilbert SC, Hill AVS, Cottingham MG. 2015. Differential immunogenicity between HAdV-5 and chimpanzee adenovirus vector ChAdOx1 is independent of fiber and penton RGD loop sequences in mice. Sci Rep, 5 (1), pp. 16756. | Show Abstract | Read more

Replication defective adenoviruses are promising vectors for the delivery of vaccine antigens. However, the potential of a vector to elicit transgene-specific adaptive immune responses is largely dependent on the viral serotype used. HAdV-5 (Human adenovirus C) vectors are more immunogenic than chimpanzee adenovirus vectors from species Human adenovirus E (ChAdOx1 and AdC68) in mice, though the mechanisms responsible for these differences in immunogenicity remain poorly understood. In this study, superior immunogenicity was associated with markedly higher levels of transgene expression in vivo, particularly within draining lymph nodes. To investigate the viral factors contributing to these phenotypes, we generated recombinant ChAdOx1 vectors by exchanging components of the viral capsid reported to be principally involved in cell entry with the corresponding sequences from HAdV-5. Remarkably, pseudotyping with the HAdV-5 fiber and/or penton RGD loop had little to no effect on in vivo transgene expression or transgene-specific adaptive immune responses despite considerable species-specific sequence heterogeneity in these components. Our results suggest that mechanisms governing vector transduction after intramuscular administration in mice may be different from those described in vitro.

Longley RJ, Hill AVS, Spencer AJ. 2015. Malaria vaccines: identifying Plasmodium falciparum liver-stage targets. Front Microbiol, 6 (SEP), pp. 965. | Show Abstract | Read more

The development of a highly efficacious and durable vaccine for malaria remains a top priority for global health researchers. Despite the huge rise in recognition of malaria as a global health problem and the concurrent rise in funding over the past 10-15 years, malaria continues to remain a widespread burden. The evidence of increasing resistance to anti-malarial drugs and insecticides is a growing concern. Hence, an efficacious and durable preventative vaccine for malaria is urgently needed. Vaccines are one of the most cost-effective tools and have successfully been used in the prevention and control of many diseases, however, the development of a vaccine for the Plasmodium parasite has proved difficult. Given the early success of whole sporozoite mosquito-bite delivered vaccination strategies, we know that a vaccine for malaria is an achievable goal, with sub-unit vaccines holding great promise as they are simple and cheap to both manufacture and deploy. However a major difficulty in development of sub-unit vaccines lies within choosing the appropriate antigenic target from the 5000 or so genes expressed by the parasite. Given the liver-stage of malaria represents a bottle-neck in the parasite's life cycle, there is widespread agreement that a multi-component sub-unit malaria vaccine should preferably contain a liver-stage target. In this article we review progress in identifying and screening Plasmodium falciparum liver-stage targets for use in a malaria vaccine.

Dicks MDJ, Guzman E, Spencer AJ, Gilbert SC, Charleston B, Hill AVS, Cottingham MG. 2015. The relative magnitude of transgene-specific adaptive immune responses induced by human and chimpanzee adenovirus vectors differs between laboratory animals and a target species. Vaccine, 33 (9), pp. 1121-1128. | Show Abstract | Read more

Adenovirus vaccine vectors generated from new viral serotypes are routinely screened in pre-clinical laboratory animal models to identify the most immunogenic and efficacious candidates for further evaluation in clinical human and veterinary settings. Here, we show that studies in a laboratory species do not necessarily predict the hierarchy of vector performance in other mammals. In mice, after intramuscular immunization, HAdV-5 (Human adenovirus C) based vectors elicited cellular and humoral adaptive responses of higher magnitudes compared to the chimpanzee adenovirus vectors ChAdOx1 and AdC68 from species Human adenovirus E. After HAdV-5 vaccination, transgene specific IFN-γ(+) CD8(+) T cell responses reached peak magnitude later than after ChAdOx1 and AdC68 vaccination, and exhibited a slower contraction to a memory phenotype. In cattle, cellular and humoral immune responses were at least equivalent, if not higher, in magnitude after ChAdOx1 vaccination compared to HAdV-5. Though we have not tested protective efficacy in a disease model, these findings have important implications for the selection of candidate vectors for further evaluation. We propose that vaccines based on ChAdOx1 or other Human adenovirus E serotypes could be at least as immunogenic as current licensed bovine vaccines based on HAdV-5.

Douglas AD, Baldeviano GC, Lucas CM, Lugo-Roman LA, Crosnier C, Bartholdson SJ, Diouf A, Miura K, Lambert LE, Ventocilla JA et al. 2015. A PfRH5-based vaccine is efficacious against heterologous strain blood-stage Plasmodium falciparum infection in aotus monkeys. Cell Host Microbe, 17 (1), pp. 130-139. | Show Abstract | Read more

Antigenic diversity has posed a critical barrier to vaccine development against the pathogenic blood-stage infection of the human malaria parasite Plasmodium falciparum. To date, only strain-specific protection has been reported by trials of such vaccines in nonhuman primates. We recently showed that P. falciparum reticulocyte binding protein homolog 5 (PfRH5), a merozoite adhesin required for erythrocyte invasion, is highly susceptible to vaccine-inducible strain-transcending parasite-neutralizing antibody. In vivo efficacy of PfRH5-based vaccines has not previously been evaluated. Here, we demonstrate that PfRH5-based vaccines can protect Aotus monkeys against a virulent vaccine-heterologous P. falciparum challenge and show that such protection can be achieved by a human-compatible vaccine formulation. Protection was associated with anti-PfRH5 antibody concentration and in vitro parasite-neutralizing activity, supporting the use of this in vitro assay to predict the in vivo efficacy of future vaccine candidates. These data suggest that PfRH5-based vaccines have potential to achieve strain-transcending efficacy in humans.

Longley RJ, Bauza K, Ewer KJ, Hill AVS, Spencer AJ. 2015. Development of an in vitro assay and demonstration of Plasmodium berghei liver-stage inhibition by TRAP-specific CD8+ T cells. PLoS One, 10 (3), pp. e0119880. | Show Abstract | Read more

The development of an efficacious vaccine against the Plasmodium parasite remains a top priority. Previous research has demonstrated the ability of a prime-boost virally vectored sub-unit vaccination regimen, delivering the liver-stage expressed malaria antigen TRAP, to produce high levels of antigen-specific T cells. The liver-stage of malaria is the main target of T cell-mediated immunity, yet a major challenge in assessing new T cell inducing vaccines has been the lack of a suitable pre-clinical assay. We have developed a flow-cytometry based in vitro T cell killing assay using a mouse hepatoma cell line, Hepa1-6, and Plasmodium berghei GFP expressing sporozoites. Using this assay, P. berghei TRAP-specific CD8+ T cell enriched splenocytes were shown to inhibit liver-stage parasites in an effector-to-target ratio dependent manner. Further development of this assay using human hepatocytes and P. falciparum would provide a new method to pre-clinically screen vaccine candidates and to elucidate mechanisms of protection in vitro.

Alharbi NK, Spencer AJ, Hill AVS, Gilbert SC. 2015. Deletion of Fifteen Open Reading Frames from Modified Vaccinia Virus Ankara Fails to Improve Immunogenicity. PLoS One, 10 (6), pp. e0128626. | Show Abstract | Read more

Modified vaccinia virus Ankara (MVA) is a highly attenuated strain of vaccinia virus, which has been used as a recombinant vaccine vector in many vaccine development programmes. The loss of many immunosuppressive and host-range genes resulted in a safe and immunogenic vaccine vector. However it still retains some immunomodulatory genes that may reduce MVA immunogenicity. Earlier reports demonstrated that the deletion of the A41L, B15R, C6L, or C12L open reading frames (ORFs) enhanced cellular immune responses in recombinant MVA (rMVA) by up to 2-fold. However, previously, we showed that deletion of the C12L, A44L, A46R, B7R, or B15R ORFs from rMVA, using MVA-BAC recombineering technology, did not enhance rMVA immunogenicity at either peak or memory cellular immune responses. Here, we extend our previous study to examine the effect of deleting clusters of genes on rMVA cellular immunogenicity. Two clusters of fifteen genes were deleted in one rMVA mutant that encodes either the 85A antigen of Mycobacterium tuberculosis or an immunodominant H2-Kd-restricted murine malaria epitope (pb9). The deletion mutants were tested in prime only or prime and boost vaccination regimens. The responses showed no improved peak or memory CD8+ T cell frequencies. Our results suggest that the reported small increases in MVA deletion mutants could not be replicated with different antigens, or epitopes. Therefore, the gene deletion strategy may not be taken as a generic approach for improving the immunogenicity of MVA-based vaccines, and should be carefully assessed for every individual recombinant antigen.

Longley RJ, Salman AM, Cottingham MG, Ewer K, Janse CJ, Khan SM, Spencer AJ, Hill AVS. 2015. Comparative assessment of vaccine vectors encoding ten malaria antigens identifies two protective liver-stage candidates. Sci Rep, 5 (1), pp. 11820. | Show Abstract | Read more

The development of an efficacious Plasmodium falciparum malaria vaccine remains a top priority for global health. Vaccination with irradiated sporozoites is able to provide complete sterile protection through the action of CD8(+) T cells at the liver-stage of infection. However, this method is currently unsuitable for large-scale deployment and focus has instead turned to the development of sub-unit vaccines. Sub-unit vaccine efforts have traditionally focused on two well-known pre-erythrocytic antigens, CSP and TRAP, yet thousands of genes are expressed in the liver-stage. We sought to assess the ability of eight alternative P. falciparum pre-erythrocytic antigens to induce a high proportion of CD8(+) T cells. We show that all antigens, when expressed individually in the non-replicating viral vectors ChAd63 and MVA, are capable of inducing an immune response in mice. Furthermore, we also developed chimeric P. berghei parasites expressing the cognate P. falciparum antigen to enable assessment of efficacy in mice. Our preliminary results indicate that vectors encoding either PfLSA1 or PfLSAP2 are capable of inducing sterile protection dependent on the presence of CD8(+) T cells. This work has identified two promising P. falciparum liver-stage candidate antigens that will now undergo further testing in humans.

Bliss CM, Spencer AJ, Salman AM, Longley RJ, Galan AR, Khan SM, Janse CJ, O'Shea MK, Hill AV, Ewer KJ. 2014. Development of an in vitro Plasmodium parasite killing assay for the evaluation of cell-mediated immune responses following vaccination with pre-erythrocytic malaria vaccine candidates IMMUNOLOGY, 143 pp. 74-75.

Kimani D, Jagne YJ, Cox M, Kimani E, Bliss CM, Gitau E, Ogwang C, Afolabi MO, Bowyer G, Collins KA et al. 2014. Translating the immunogenicity of prime-boost immunization with ChAd63 and MVA ME-TRAP from malaria naive to malaria-endemic populations. Mol Ther, 22 (11), pp. 1992-2003. | Show Abstract | Read more

To induce a deployable level of efficacy, a successful malaria vaccine would likely benefit from both potent cellular and humoral immunity. These requirements are met by a heterologous prime-boost immunization strategy employing a chimpanzee adenovirus vector followed by modified vaccinia Ankara (MVA), both encoding the pre-erythrocytic malaria antigen ME-thrombospondin-related adhesive protein (TRAP), with high immunogenicity and significant efficacy in UK adults. We undertook two phase 1b open-label studies in adults in Kenya and The Gambia in areas of similar seasonal malaria transmission dynamics and have previously reported safety and basic immunogenicity data. We now report flow cytometry and additional interferon (IFN)-γ enzyme-linked immunospot (ELISPOT) data characterizing pre-existing and induced cellular immunity as well as anti-TRAP IgG responses. T-cell responses induced by vaccination averaged 1,254 spot-forming cells (SFC) per million peripheral blood mononuclear cells (PBMC) across both trials and flow cytometry revealed cytokine production from both CD4(+) and CD8(+) T cells with the frequency of CD8(+) IFN-γ-secreting monofunctional T cells (previously shown to associate with vaccine efficacy) particularly high in Kenyan adults. Immunization with ChAd63 and MVA ME-TRAP induced strong cellular and humoral immune responses in adults living in two malaria-endemic regions of Africa. This prime-boost approach targeting the pre-erythrocytic stage of the malaria life-cycle is now being assessed for efficacy in a target population.

Spencer AJ, Cottingham MG, Jenks JA, Longley RJ, Capone S, Colloca S, Folgori A, Cortese R, Nicosia A, Bregu M, Hill AVS. 2014. Enhanced vaccine-induced CD8+ T cell responses to malaria antigen ME-TRAP by fusion to MHC class ii invariant chain. PLoS One, 9 (6), pp. e100538. | Show Abstract | Read more

The orthodox role of the invariant chain (CD74; Ii) is in antigen presentation to CD4+ T cells, but enhanced CD8+ T cells responses have been reported after vaccination with vectored viral vaccines encoding a fusion of Ii to the antigen of interest. In this study we assessed whether fusion of the malarial antigen, ME-TRAP, to Ii could increase the vaccine-induced CD8+ T cell response. Following single or heterologous prime-boost vaccination of mice with a recombinant chimpanzee adenovirus vector, ChAd63, or recombinant modified vaccinia virus Ankara (MVA), higher frequencies of antigen-specific CD4+ and CD8+ T cells were observed, with the largest increases observed following a ChAd63-MVA heterologous prime-boost regimen. Studies in non-human primates confirmed the ability of Ii-fusion to augment the T cell response, where a 4-fold increase was maintained up to 11 weeks after the MVA boost. Of the numerous different approaches explored to increase vectored vaccine induced immunogenicity over the years, fusion to the invariant chain showed a consistent enhancement in CD8+ T cell responses across different animal species and may therefore find application in the development of vaccines against human malaria and other diseases where high levels of cell-mediated immunity are required.

Spencer AJ, Furze J, Honeycutt JD, Calvert A, Saurya S, Colloca S, Wyllie DH, Gilbert SC, Bregu M, Cottingham MG, Hill AVS. 2014. 4-1BBL enhances CD8+ T cell responses induced by vectored vaccines in mice but fails to improve immunogenicity in rhesus macaques. PLoS One, 9 (8), pp. e105520. | Show Abstract | Read more

T cells play a central role in the immune response to many of the world's major infectious diseases. In this study we investigated the tumour necrosis factor receptor superfamily costimulatory molecule, 4-1BBL (CD137L, TNFSF9), for its ability to increase T cell immunogenicity induced by a variety of recombinant vectored vaccines. To efficiently test this hypothesis, we assessed a number of promoters and developed a stable bi-cistronic vector expressing both the antigen and adjuvant. Co-expression of 4-1BBL, together with our model antigen TIP, was shown to increase the frequency of murine antigen-specific IFN-γ secreting CD8(+) T cells in three vector platforms examined. Enhancement of the response was not limited by co-expression with the antigen, as an increase in CD8(+) immunogenicity was also observed by co-administration of two vectors each expressing only the antigen or adjuvant. However, when this regimen was tested in non-human primates using a clinical malaria vaccine candidate, no adjuvant effect of 4-1BBL was observed limiting its potential use as a single adjuvant for translation into a clinical vaccine.

Warimwe GM, Lorenzo G, Lopez-Gil E, Reyes-Sandoval A, Cottingham MG, Spencer AJ, Collins KA, Dicks MDJ, Milicic A, Lall A et al. 2013. Immunogenicity and efficacy of a chimpanzee adenovirus-vectored Rift Valley fever vaccine in mice. Virol J, 10 (1), pp. 349. | Show Abstract | Read more

BACKGROUND: Rift Valley Fever (RVF) is a viral zoonosis that historically affects livestock production and human health in sub-Saharan Africa, though epizootics have also occurred in the Arabian Peninsula. Whilst an effective live-attenuated vaccine is available for livestock, there is currently no licensed human RVF vaccine. Replication-deficient chimpanzee adenovirus (ChAd) vectors are an ideal platform for development of a human RVF vaccine, given the low prevalence of neutralizing antibodies against them in the human population, and their excellent safety and immunogenicity profile in human clinical trials of vaccines against a wide range of pathogens. METHODS: Here, in BALB/c mice, we evaluated the immunogenicity and efficacy of a replication-deficient chimpanzee adenovirus vector, ChAdOx1, encoding the RVF virus envelope glycoproteins, Gn and Gc, which are targets of virus neutralizing antibodies. The ChAdOx1-GnGc vaccine was assessed in comparison to a replication-deficient human adenovirus type 5 vector encoding Gn and Gc (HAdV5-GnGc), a strategy previously shown to confer protective immunity against RVF in mice. RESULTS: A single immunization with either of the vaccines conferred protection against RVF virus challenge eight weeks post-immunization. Both vaccines elicited RVF virus neutralizing antibody and a robust CD8+ T cell response. CONCLUSIONS: Together the results support further development of RVF vaccines based on replication-deficient adenovirus vectors, with ChAdOx1-GnGc being a potential candidate for use in future human clinical trials.

Sheehy SH, Spencer AJ, Douglas AD, Sim BKL, Longley RJ, Edwards NJ, Poulton ID, Kimani D, Williams AR, Anagnostou NA et al. 2013. Optimising Controlled Human Malaria Infection Studies Using Cryopreserved P. falciparum Parasites Administered by Needle and Syringe. PLoS One, 8 (6), pp. e65960. | Show Abstract | Read more

BACKGROUND: Controlled human malaria infection (CHMI) studies have become a routine tool to evaluate efficacy of candidate anti-malarial drugs and vaccines. To date, CHMI trials have mostly been conducted using the bite of infected mosquitoes, restricting the number of trial sites that can perform CHMI studies. Aseptic, cryopreserved P. falciparum sporozoites (PfSPZ Challenge) provide a potentially more accurate, reproducible and practical alternative, allowing a known number of sporozoites to be administered simply by injection. METHODOLOGY: We sought to assess the infectivity of PfSPZ Challenge administered in different dosing regimens to malaria-naive healthy adults (n = 18). Six participants received 2,500 sporozoites intradermally (ID), six received 2,500 sporozoites intramuscularly (IM) and six received 25,000 sporozoites IM. FINDINGS: Five out of six participants receiving 2,500 sporozoites ID, 3/6 participants receiving 2,500 sporozoites IM and 6/6 participants receiving 25,000 sporozoites IM were successfully infected. The median time to diagnosis was 13.2, 17.8 and 12.7 days for 2,500 sporozoites ID, 2,500 sporozoites IM and 25,000 sporozoites IM respectively (Kaplan Meier method; p = 0.024 log rank test). CONCLUSIONS: 2,500 sporozoites ID and 25,000 sporozoites IM have similar infectivities. Given the dose response in infectivity seen with IM administration, further work should evaluate increasing doses of PfSPZ Challenge IM to identify a dosing regimen that reliably infects 100% of participants. TRIAL REGISTRATION: ClinicalTrials.gov NCT01465048.

Lambe T, Carey JB, Li Y, Spencer AJ, van Laarhoven A, Mullarkey CE, Vrdoljak A, Moore AC, Gilbert SC. 2013. Immunity against heterosubtypic influenza virus induced by adenovirus and MVA expressing nucleoprotein and matrix protein-1. Sci Rep, 3 (1), pp. 1443. | Show Abstract | Read more

Alternate prime/boost vaccination regimens employing recombinant replication-deficient adenovirus or MVA, expressing Influenza A virus nucleoprotein and matrix protein 1, induced antigen-specific T cell responses in intradermally (ID) vaccinated mice; with the strongest responses resulting from Ad/MVA immunization. In BALB/C mice the immunodominant response was shifted from the previously identified immunodominant epitope to a novel epitope when the antigen was derived from A/Panama/2007/1999 rather than A/PR/8. Alternate immunization routes did not affect the magnitude of antigen-specific systemic IFN-γ response, but higher CD8(+) T-cell IFN-γ immune responses were seen in the bronchoalveolar lavage following intransal (IN) boosting after intramuscular (IM) priming, whilst higher splenic antigen-specific CD8(+) T cell IFN-γ was seen following IM boosting. Partial protection against heterologous influenza virus challenge was achieved following either IM/IM or IM/IN but not ID/ID immunization. These data may be of relevance for the design of optimal immunization regimens for human influenza vaccines, especially for influenza-naïve infants.

Ogwang C, Afolabi M, Kimani D, Jagne YJ, Sheehy SH, Bliss CM, Duncan CJA, Collins KA, Garcia Knight MA, Kimani E et al. 2013. Safety and immunogenicity of heterologous prime-boost immunisation with Plasmodium falciparum malaria candidate vaccines, ChAd63 ME-TRAP and MVA ME-TRAP, in healthy Gambian and Kenyan adults. PLoS One, 8 (3), pp. e57726. | Show Abstract | Read more

BACKGROUND: Heterologous prime boost immunization with chimpanzee adenovirus 63 (ChAd63) and Modified vaccinia Virus Ankara (MVA) vectored vaccines is a strategy recently shown to be capable of inducing strong cell mediated responses against several antigens from the malaria parasite. ChAd63-MVA expressing the Plasmodium falciparum pre-erythrocytic antigen ME-TRAP (multiple epitope string with thrombospondin-related adhesion protein) is a leading malaria vaccine candidate, capable of inducing sterile protection in malaria naïve adults following controlled human malaria infection (CHMI). METHODOLOGY: We conducted two Phase Ib dose escalation clinical trials assessing the safety and immunogenicity of ChAd63-MVA ME-TRAP in 46 healthy malaria exposed adults in two African countries with similar malaria transmission patterns. RESULTS: ChAd63-MVA ME-TRAP was shown to be safe and immunogenic, inducing high-level T cell responses (median >1300 SFU/million PBMC). CONCLUSIONS: ChAd63-MVA ME-TRAP is a safe and highly immunogenic vaccine regimen in adults with prior exposure to malaria. Further clinical trials to assess safety and immunogenicity in children and infants and protective efficacy in the field are now warranted. TRIAL REGISTRATION: Pactr.org PACTR2010020001771828 Pactr.org PACTR201008000221638 ClinicalTrials.gov NCT01373879 NCT01373879 ClinicalTrials.gov NCT01379430 NCT01379430.

Biswas S, Spencer AJ, Forbes EK, Gilbert SC, Holder AA, Hill AVS, Draper SJ. 2012. Recombinant viral-vectored vaccines expressing Plasmodium chabaudi AS apical membrane antigen 1: mechanisms of vaccine-induced blood-stage protection. J Immunol, 188 (10), pp. 5041-5053. | Show Abstract | Read more

Apical membrane Ag 1 (AMA1) is one of the leading candidate Ags for inclusion in a subunit vaccine against blood-stage malaria. However, the efficacy of Ab-inducing recombinant AMA1 protein vaccines in phase IIa/b clinical trials remains disappointing. In this article, we describe the development of recombinant human adenovirus serotype 5 and modified vaccinia virus Ankara vectors encoding AMA1 from the Plasmodium chabaudi chabaudi strain AS. These vectors, when used in a heterologous prime-boost regimen in BALB/c mice, are capable of inducing strong transgene-specific humoral and cellular immune responses. We show that this vaccination regimen is protective against a nonlethal P. chabaudi chabaudi strain AS blood-stage challenge, resulting in reduced peak parasitemias. The role of vaccine-induced, AMA1-specific Abs and T cells in mediating the antiparasite effect was investigated by in vivo depletion of CD4(+) T cells and adoptive-transfer studies into naive and immunodeficient mice. Depletion of CD4(+) T cells led to a loss of vaccine-induced protection. Adoptive-transfer studies confirmed that efficacy is mediated by both CD4(+) T cells and Abs functioning in the context of an intact immune system. Unlike previous studies, these results confirm that Ag-specific CD4(+) T cells, induced by a clinically relevant vaccine-delivery platform, can make a significant contribution to vaccine blood-stage efficacy in the P. chabaudi model. Given that cell-mediated immunity may also contribute to parasite control in human malaria, these data support the clinical development of viral-vectored vaccines that induce both T cell and Abs against Plasmodium falciparum blood-stage malaria Ags like AMA1.

Lambe T, Spencer AJ, Mullarkey CE, Antrobus RD, Yu L-M, de Whalley P, Thompson BAV, Jones C, Chalk J, Kerridge S et al. 2012. T-cell responses in children to internal influenza antigens, 1 year after immunization with pandemic H1N1 influenza vaccine, and response to revaccination with seasonal trivalent-inactivated influenza vaccine. Pediatr Infect Dis J, 31 (6), pp. e86-e91. | Show Abstract | Read more

BACKGROUND: During seasonal influenza epidemics, 5-15% of the population are affected with an illness having a nontrivial mortality, morbidity and economic burden. Inactivated influenza vaccines are routinely used to prevent influenza infection, primarily by inducing humoral immunity. In addition, trivalent-inactivated influenza vaccines have previously been shown to boost influenza-specific T-cell responses in a small percentage of adults. We investigate here the influenza-specific T-cell response, in children, 1 year after pandemic H1N1 vaccination and the ability to boost the T-cell response with trivalent-inactivated influenza immunization. METHODS: Peripheral blood mononuclear cells (PBMCs) were isolated from children previously vaccinated with pandemic H1N1 vaccine, pre- and postseasonal 2010-2011 trivalent influenza vaccine (TIV) vaccination. Samples were analyzed by interferon-gamma enzyme-linked immunosorbent spot for reactogenicity toward internal influenza antigens (nucleoprotein, matrix protein 1 and nonstructural protein 1). RESULTS: Basal ex vivo T-cell responses to nucleoprotein, matrix protein 1 and nonstructural protein 1 measured by interferon-gamma enzyme-linked immunosorbent spot assay were significantly higher in those children who had previously received an AS03B-adjuvanted split virion pandemic vaccine 12 months earlier rather than a nonadjuvanted whole virion vaccine. Boosting of these responses, 21 days after 2010/2011 seasonal TIV vaccination was observed regardless of age or prior pandemic vaccination regime, although boosting was greater in those groups with the lowest initial response. CONCLUSIONS: We show here that children previously vaccinated with the 2009 pandemic H1N1 vaccine have measurable T-cell responses 1 year after vaccination. The magnitudes of these responses are dependent on both age of vaccine and type of pandemic H1N1 vaccine used. After 2010/2011 seasonal TIV vaccination, these T-cell responses undergo a small but significant boost.

Lillie PJ, Berthoud TK, Powell TJ, Lambe T, Mullarkey C, Spencer AJ, Hamill M, Peng Y, Blais M-E, Duncan CJA et al. 2012. Preliminary assessment of the efficacy of a T-cell-based influenza vaccine, MVA-NP+M1, in humans. Clin Infect Dis, 55 (1), pp. 19-25. | Show Abstract | Read more

BACKGROUND: The novel influenza vaccine MVA-NP+M1 is designed to boost cross-reactive T-cell responses to internal antigens of the influenza A virus that are conserved across all subtypes, providing protection against both influenza disease and virus shedding against all influenza A viruses. Following a phase 1 clinical study that demonstrated vaccine safety and immunogenicity, a phase 2a vaccination and influenza challenge study has been conducted in healthy adult volunteers. METHODS: Volunteers with no measurable serum antibodies to influenza A/Wisconsin/67/2005 received either a single vaccination with MVA-NP+M1 or no vaccination. T-cell responses to the vaccine antigens were measured at enrollment and again prior to virus challenge. All volunteers underwent intranasal administration of influenza A/Wisconsin/67/2005 while in a quarantine unit and were monitored for symptoms of influenza disease and virus shedding. RESULTS: Volunteers had a significantly increased T-cell response to the vaccine antigens following a single dose of the vaccine, with an increase in cytolytic effector molecules. Intranasal influenza challenge was undertaken without safety issues. Two of 11 vaccinees and 5 of 11 control subjects developed laboratory-confirmed influenza (symptoms plus virus shedding). Symptoms of influenza were less pronounced in the vaccinees and there was a significant reduction in the number of days of virus shedding in those vaccinees who developed influenza (mean, 1.09 days in controls, 0.45 days in vaccinees, P = .036). CONCLUSIONS: This study provides the first demonstration of clinical efficacy of a T-cell-based influenza vaccine and indicates that further clinical development should be undertaken. CLINICAL TRIALS REGISTRATION: NCT00993083.

Lambe T, Spencer AJ, Mullarkey CE, Antrobus RD, Yu LM, de Whalley P, Thompson BAV, Jones C, Chalk J, Kerridge S et al. 2012. T-Cell Responses in Children to Internal Influenza Antigens, 1 Year After Immunization with Pandemic H1N1 Influenza Vaccine, and Response to Revaccination with Seasonal Trivalent-inactivated Influenza Vaccine Pediatric Infectious Disease Journal, 31 (6), pp. e86-e91. | Read more

Sheehy SH, Duncan CJA, Elias SC, Biswas S, Collins KA, O'Hara GA, Halstead FD, Ewer KJ, Mahungu T, Spencer AJ et al. 2012. Phase Ia clinical evaluation of the safety and immunogenicity of the Plasmodium falciparum blood-stage antigen AMA1 in ChAd63 and MVA vaccine vectors. PLoS One, 7 (2), pp. e31208. | Show Abstract | Read more

BACKGROUND: Traditionally, vaccine development against the blood-stage of Plasmodium falciparum infection has focused on recombinant protein-adjuvant formulations in order to induce high-titer growth-inhibitory antibody responses. However, to date no such vaccine encoding a blood-stage antigen(s) alone has induced significant protective efficacy against erythrocytic-stage infection in a pre-specified primary endpoint of a Phase IIa/b clinical trial designed to assess vaccine efficacy. Cell-mediated responses, acting in conjunction with functional antibodies, may be necessary for immunity against blood-stage P. falciparum. The development of a vaccine that could induce both cell-mediated and humoral immune responses would enable important proof-of-concept efficacy studies to be undertaken to address this question. METHODOLOGY: We conducted a Phase Ia, non-randomized clinical trial in 16 healthy, malaria-naïve adults of the chimpanzee adenovirus 63 (ChAd63) and modified vaccinia virus Ankara (MVA) replication-deficient viral vectored vaccines encoding two alleles (3D7 and FVO) of the P. falciparum blood-stage malaria antigen; apical membrane antigen 1 (AMA1). ChAd63-MVA AMA1 administered in a heterologous prime-boost regime was shown to be safe and immunogenic, inducing high-level T cell responses to both alleles 3D7 (median 2036 SFU/million PBMC) and FVO (median 1539 SFU/million PBMC), with a mixed CD4(+)/CD8(+) phenotype, as well as substantial AMA1-specific serum IgG responses (medians of 49 µg/mL and 41 µg/mL for 3D7 and FVO AMA1 respectively) that demonstrated growth inhibitory activity in vitro. CONCLUSIONS: ChAd63-MVA is a safe and highly immunogenic delivery platform for both alleles of the AMA1 antigen in humans which warrants further efficacy testing. ChAd63-MVA is a promising heterologous prime-boost vaccine strategy that could be applied to numerous other diseases where strong cellular and humoral immune responses are required for protection. TRIAL REGISTRATION: ClinicalTrials.gov NCT01095055.

Spencer AJ, Hill F, Honeycutt JD, Cottingham MG, Bregu M, Rollier CS, Furze J, Draper SJ, Søgaard KC, Gilbert SC et al. 2012. Fusion of the Mycobacterium tuberculosis antigen 85A to an oligomerization domain enhances its immunogenicity in both mice and non-human primates. PLoS One, 7 (3), pp. e33555. | Show Abstract | Read more

To prevent important infectious diseases such as tuberculosis, malaria and HIV, vaccines inducing greater T cell responses are required. In this study, we investigated whether fusion of the M. tuberculosis antigen 85A to recently described adjuvant IMX313, a hybrid avian C4bp oligomerization domain, could increase T cell responses in pre-clinical vaccine model species. In mice, the fused antigen 85A showed consistent increases in CD4(+) and CD8(+) T cell responses after DNA and MVA vaccination. In rhesus macaques, higher IFN-γ responses were observed in animals vaccinated with MVA-Ag85A IMX313 after both primary and secondary immunizations. In both animal models, fusion to IMX313 induced a quantitative enhancement in the response without altering its quality: multifunctional cytokines were uniformly increased and differentiation into effector and memory T cell subsets was augmented rather than skewed. An extensive in vivo characterization suggests that IMX313 improves the initiation of immune responses as an increase in antigen 85A specific cells was observed as early as day 3 after vaccination. This report demonstrates that antigen multimerization using IMX313 is a simple and effective cross-species method to improve vaccine immunogenicity with potentially broad applicability.

Antrobus RD, Lillie PJ, Berthoud TK, Spencer AJ, McLaren JE, Ladell K, Lambe T, Milicic A, Price DA, Hill AVS, Gilbert SC. 2012. A T cell-inducing influenza vaccine for the elderly: safety and immunogenicity of MVA-NP+M1 in adults aged over 50 years. PLoS One, 7 (10), pp. e48322. | Show Abstract | Read more

BACKGROUND: Current influenza vaccines have reduced immunogenicity and are of uncertain efficacy in older adults. We assessed the safety and immunogenicity of MVA-NP+M1, a viral-vectored influenza vaccine designed to boost memory T cell responses, in a group of older adults. METHODS: Thirty volunteers (aged 50-85) received a single intramuscular injection of MVA-NP+M1 at a dose of 1·5×10(8) plaque forming units (pfu). Safety and immunogenicity were assessed over a period of one year. The frequency of T cells specific for nucleoprotein (NP) and matrix protein 1 (M1) was determined by interferon-gamma (IFN-γ) ELISpot, and their phenotypic and functional properties were characterized by polychromatic flow cytometry. In a subset of M1-specific CD8(+) T cells, T cell receptor (TCR) gene expression was evaluated using an unbiased molecular approach. RESULTS: Vaccination with MVA-NP+M1 was well tolerated. ELISpot responses were boosted significantly above baseline following vaccination. Increases were detected in both CD4(+) and CD8(+) T cell subsets. Clonality studies indicated that MVA-NP+M1 expanded pre-existing memory CD8(+) T cells, which displayed a predominant CD27(+)CD45RO(+)CD57(-)CCR7(-) phenotype both before and after vaccination. CONCLUSIONS: MVA-NP+M1 is safe and immunogenic in older adults. Unlike seasonal influenza vaccination, the immune responses generated by MVA-NP+M1 are similar between younger and older individuals. A T cell-inducing vaccine such as MVA-NP+M1 may therefore provide a way to circumvent the immunosenescence that impairs routine influenza vaccination. TRIAL REGISTRATION: ClinicalTrials.gov NCT00942071.

Dicks MDJ, Spencer AJ, Edwards NJ, Wadell G, Bojang K, Gilbert SC, Hill AVS, Cottingham MG. 2012. A novel chimpanzee adenovirus vector with low human seroprevalence: improved systems for vector derivation and comparative immunogenicity. PLoS One, 7 (7), pp. e40385. | Show Abstract | Read more

Recombinant adenoviruses are among the most promising tools for vaccine antigen delivery. Recently, the development of new vectors has focused on serotypes to which the human population is less exposed in order to circumvent pre-existing anti vector immunity. This study describes the derivation of a new vaccine vector based on a chimpanzee adenovirus, Y25, together with a comparative assessment of its potential to elicit transgene product specific immune responses in mice. The vector was constructed in a bacterial artificial chromosome to facilitate genetic manipulation of genomic clones. In order to conduct a fair head-to-head immunological comparison of multiple adenoviral vectors, we optimised a method for accurate determination of infectious titre, since this parameter exhibits profound natural variability and can confound immunogenicity studies when doses are based on viral particle estimation. Cellular immunogenicity of recombinant E1 E3-deleted vector ChAdY25 was comparable to that of other species E derived chimpanzee adenovirus vectors including ChAd63, the first simian adenovirus vector to enter clinical trials in humans. Furthermore, the prevalence of virus neutralizing antibodies (titre >1:200) against ChAdY25 in serum samples collected from two human populations in the UK and Gambia was particularly low compared to published data for other chimpanzee adenoviruses. These findings support the continued development of new chimpanzee adenovirus vectors, including ChAdY25, for clinical use.

Sheehy SH, Duncan CJA, Elias SC, Collins KA, Ewer KJ, Spencer AJ, Williams AR, Halstead FD, Moretz SE, Miura K et al. 2011. Phase Ia clinical evaluation of the Plasmodium falciparum blood-stage antigen MSP1 in ChAd63 and MVA vaccine vectors. Mol Ther, 19 (12), pp. 2269-2276. | Show Abstract | Read more

Efficacy trials of antibody-inducing protein-in-adjuvant vaccines targeting the blood-stage Plasmodium falciparum malaria parasite have so far shown disappointing results. The induction of cell-mediated responses in conjunction with antibody responses is thought to be one alternative strategy that could achieve protective efficacy in humans. Here, we prepared chimpanzee adenovirus 63 (ChAd63) and modified vaccinia virus Ankara (MVA) replication-deficient vectors encoding the well-studied P. falciparum blood-stage malaria antigen merozoite surface protein 1 (MSP1). A phase Ia clinical trial was conducted in healthy adults of a ChAd63-MVA MSP1 heterologous prime-boost immunization regime. The vaccine was safe and generally well tolerated. Fewer systemic adverse events (AEs) were observed following ChAd63 MSP1 than MVA MSP1 administration. Exceptionally strong T-cell responses were induced, and these displayed a mixed of CD4(+) and CD8(+) phenotype. Substantial MSP1-specific serum immunoglobulin G (IgG) antibody responses were also induced, which were capable of recognizing native parasite antigen, but these did not reach titers sufficient to neutralize P. falciparum parasites in vitro. This viral vectored vaccine regime is thus a leading approach for the induction of strong cellular and humoral immunogenicity against difficult disease targets in humans. Further studies are required to assess whether this strategy can achieve protective efficacy against blood-stage malaria infection.

Cited:

107

Scopus

Sheehy SH, Duncan CJA, Elias SC, Collins KA, Ewer KJ, Spencer AJ, Williams AR, Halstead FD, Moretz SE, Miura K et al. 2011. Phase Ia clinical evaluation of the plasmodium falciparum blood-stage antigen MSP1 in ChAd63 and MVA vaccine vectors Molecular Therapy, 19 (12), pp. 2269-2276. | Show Abstract | Read more

Efficacy trials of antibody-inducing protein-in-adjuvant vaccines targeting the blood-stage Plasmodium falciparum malaria parasite have so far shown disappointing results. The induction of cell-mediated responses in conjunction with antibody responses is thought to be one alternative strategy that could achieve protective efficacy in humans. Here, we prepared chimpanzee adenovirus 63 (ChAd63) and modified vaccinia virus Ankara (MVA) replication-deficient vectors encoding the well-studied P. falciparum blood-stage malaria antigen merozoite surface protein 1 (MSP1). A phase Ia clinical trial was conducted in healthy adults of a ChAd63-MVA MSP1 heterologous prime-boost immunization regime. The vaccine was safe and generally well tolerated. Fewer systemic adverse events (AEs) were observed following ChAd63 MSP1 than MVA MSP1 administration. Exceptionally strong T-cell responses were induced, and these displayed a mixed of CD4 and CD8 phenotype. Substantial MSP1-specific serum immunoglobulin G (IgG) antibody responses were also induced, which were capable of recognizing native parasite antigen, but these did not reach titers sufficient to neutralize P. falciparum parasites in vitro. This viral vectored vaccine regime is thus a leading approach for the induction of strong cellular and humoral immunogenicity against difficult disease targets in humans. Further studies are required to assess whether this strategy can achieve protective efficacy against blood-stage malaria infection. © The American Society of Gene & Cell Therapy.

Draper SJ, Biswas S, Spencer AJ, Remarque EJ, Capone S, Naddeo M, Dicks MDJ, Faber BW, de Cassan SC, Folgori A et al. 2010. Enhancing blood-stage malaria subunit vaccine immunogenicity in rhesus macaques by combining adenovirus, poxvirus, and protein-in-adjuvant vaccines. J Immunol, 185 (12), pp. 7583-7595. | Show Abstract | Read more

Protein-in-adjuvant formulations and viral-vectored vaccines encoding blood-stage malaria Ags have shown efficacy in rodent malaria models and in vitro assays against Plasmodium falciparum. Abs and CD4(+) T cell responses are associated with protective efficacy against blood-stage malaria, whereas CD8(+) T cells against some classical blood-stage Ags can also have a protective effect against liver-stage parasites. No subunit vaccine strategy alone has generated demonstrable high-level efficacy against blood-stage infection in clinical trials. The induction of high-level Ab responses, as well as potent T and B cell effector and memory populations, is likely to be essential to achieve immediate and sustained protective efficacy in humans. This study describes in detail the immunogenicity of vaccines against P. falciparum apical membrane Ag 1 in rhesus macaques (Macaca mulatta), including the chimpanzee adenovirus 63 (AdCh63), the poxvirus modified vaccinia virus Ankara (MVA), and protein vaccines formulated in Alhydrogel or CoVaccine HT adjuvants. AdCh63-MVA heterologous prime-boost immunization induces strong and long-lasting multifunctional CD8(+) and CD4(+) T cell responses that exhibit a central memory-like phenotype. Three-shot (AdCh63-MVA-protein) or two-shot (AdCh63-protein) regimens induce memory B cells and high-titer functional IgG responses that inhibit the growth of two divergent strains of P. falciparum in vitro. Prior immunization with adenoviral vectors of alternative human or simian serotype does not affect the immunogenicity of the AdCh63 apical membrane Ag 1 vaccine. These data encourage the further clinical development and coadministration of protein and viral vector vaccine platforms in an attempt to induce broad cellular and humoral immune responses against blood-stage malaria Ags in humans.

Wong SH, Vannberg FO, Spencer AJ, van der Weyden L, Hill AVS, Wyllie DH. 2010. Comment on "CRTAM confers late-stage activation of CD8+ T cells to regulate retention within lymph node". J Immunol, 184 (8), pp. 4052-4053. | Read more

Alcock R, Cottingham MG, Rollier CS, Furze J, De Costa SD, Hanlon M, Spencer AJ, Honeycutt JD, Wyllie DH, Gilbert SC et al. 2010. Long-term thermostabilization of live poxviral and adenoviral vaccine vectors at supraphysiological temperatures in carbohydrate glass. Sci Transl Med, 2 (19), pp. 19ra12. | Show Abstract | Read more

Live recombinant viral vectors based on adenoviruses and poxviruses are among the most promising platforms for development of new vaccines against diseases such as malaria, tuberculosis, and HIV-AIDS. Vaccines based on live viruses must remain infectious to be effective, so therefore need continuous refrigeration to maintain stability and viability, a requirement that can be costly and difficult, especially in developing countries. The sugars sucrose and trehalose are commonly used as stabilizing agents and cryoprotectants for biological products. Here, we have exploited the ability of these sugars to vitrify on desiccation to develop a thermostabilization technique for live viral vaccine vectors. By slowly drying vaccines suspended in solutions of these disaccharide stabilizers onto a filter-like support membrane at ambient temperature, an ultrathin glass is deposited on the fibers of the inert matrix. Immobilization of two recombinant vaccine vectors-E1/E3-deleted human adenovirus type 5 and modified vaccinia virus Ankara-in this glass on the membranes enabled complete recovery of viral titer and immunogenicity after storage at up to 45 degrees C for 6 months and even longer with minimal losses. Furthermore, the membrane carrying the stabilized vaccine can be incorporated into a holder attached to a syringe for almost simultaneous reconstitution and injection at point of use. The technology may potentially be developed for the deployment of viral vector-based biopharmaceuticals in resource-poor settings.

Larsen KC, Spencer AJ, Goodman AL, Gilchrist A, Furze J, Rollier CS, Kiss-Toth E, Gilbert SC, Bregu M, Soilleux EJ et al. 2009. Expression of tak1 and tram induces synergistic pro-inflammatory signalling and adjuvants DNA vaccines. Vaccine, 27 (41), pp. 5589-5598. | Show Abstract | Read more

Improving vaccine immunogenicity remains a major challenge in the fight against developing country diseases like malaria and AIDS. We describe a novel strategy to identify new DNA vaccine adjuvants. We have screened components of the Toll-like receptor signalling pathways for their ability to activate pro-inflammatory target genes in transient transfection assays and assessed in vivo adjuvant activity by expressing the activators from the DNA backbone of vaccines. We find that a robust increase in the immune response necessitates co-expression of two activators. Accordingly, the combination of tak1 and tram elicits synergistic reporter activation in transient transfection assays. In a mouse model this combination, but not the individual molecules, induced approximately twofold increases in CD8+ T-cell immune responses. These results indicate that optimal immunogenicity may require activation of distinct innate immune signalling pathways. Thus this strategy offers a novel route to the discovery of a new generation of adjuvants.

Cottingham MG, Andersen RF, Spencer AJ, Saurya S, Furze J, Hill AVS, Gilbert SC. 2008. Recombination-mediated genetic engineering of a bacterial artificial chromosome clone of modified vaccinia virus Ankara (MVA). PLoS One, 3 (2), pp. e1638. | Show Abstract | Read more

The production, manipulation and rescue of a bacterial artificial chromosome clone of Vaccinia virus (VAC-BAC) in order to expedite construction of expression vectors and mutagenesis of the genome has been described (Domi & Moss, 2002, PNAS99 12415-20). The genomic BAC clone was 'rescued' back to infectious virus using a Fowlpox virus helper to supply transcriptional machinery. We apply here a similar approach to the attenuated strain Modified Vaccinia virus Ankara (MVA), now widely used as a safe non-replicating recombinant vaccine vector in mammals, including humans. Four apparently full-length, rescuable clones were obtained, which had indistinguishable immunogenicity in mice. One clone was shotgun sequenced and found to be identical to the parent. We employed GalK recombination-mediated genetic engineering (recombineering) of MVA-BAC to delete five selected viral genes. Deletion of C12L, A44L, A46R or B7R did not significantly affect CD8(+) T cell immunogenicity in BALB/c mice, but deletion of B15R enhanced specific CD8(+) T cell responses to one of two endogenous viral epitopes (from the E2 and F2 proteins), in accordance with published work (Staib et al., 2005, J. Gen. Virol.86, 1997-2006). In addition, we found a higher frequency of triple-positive IFN-gamma, TNF-alpha and IL-2 secreting E3-specific CD8+ T-cells 8 weeks after vaccination with MVA lacking B15R. Furthermore, a recombinant vaccine capable of inducing CD8(+) T cells against an epitope from Plasmodium berghei was created using GalK counterselection to insert an antigen expression cassette lacking a tandem marker gene into the traditional thymidine kinase locus of MVA-BAC. MVA continues to feature prominently in clinical trials of recombinant vaccines against diseases such as HIV-AIDS, malaria and tuberculosis. Here we demonstrate in proof-of-concept experiments that MVA-BAC recombineering is a viable route to more rapid and efficient generation of new candidate mutant and recombinant vaccines based on a clinically deployable viral vector.

Rodríguez-Galán A, Salman AM, Bowyer G, Collins KA, Longley RJ, Brod F, Ulaszewska M, Ewer KJ, Janse CJ, Khan SM et al. 2017. An in vitro assay to measure antibody-mediated inhibition of P. berghei sporozoite invasion against P. falciparum antigens. Sci Rep, 7 (1), pp. 17011. | Show Abstract | Read more

A large research effort is currently underway to find an effective and affordable malaria vaccine. Tools that enable the rapid evaluation of protective immune responses are essential to vaccine development as they can provide selection criteria to rank order vaccine candidates. In this study we have revisited the Inhibition of Sporozoite Invasion (ISI) assay to assess the ability of antibodies to inhibit sporozoite infection of hepatocytes. By using GFP expressing sporozoites of the rodent parasite P. berghei we are able to robustly quantify parasite infection of hepatocyte cell lines by flow cytometry. In conjunction with recently produced transgenic P. berghei parasites that express P. falciparum sporozoite antigens, we have been able to use this assay to measure antibody mediated inhibition of sporozoite invasion against one of the lead malaria antigens P. falciparum CSP. By combining chimeric rodent parasites expressing P. falciparum antigens and a flow cytometric readout of infection, we are able to robustly assess vaccine-induced antibodies, from mice, rhesus macaques and human clinical trials, for their functional ability to block sporozoite invasion of hepatocytes.

Ewer K, Sebastian S, Spencer AJ, Gilbert S, Hill AVS, Lambe T. 2017. Chimpanzee adenoviral vectors as vaccines for outbreak pathogens. Hum Vaccin Immunother, 13 (12), pp. 3020-3032. | Show Abstract | Read more

The 2014-15 Ebola outbreak in West Africa highlighted the potential for large disease outbreaks caused by emerging pathogens and has generated considerable focus on preparedness for future epidemics. Here we discuss drivers, strategies and practical considerations for developing vaccines against outbreak pathogens. Chimpanzee adenoviral (ChAd) vectors have been developed as vaccine candidates for multiple infectious diseases and prostate cancer. ChAd vectors are safe and induce antigen-specific cellular and humoral immunity in all age groups, as well as circumventing the problem of pre-existing immunity encountered with human Ad vectors. For these reasons, such viral vectors provide an attractive platform for stockpiling vaccines for emergency deployment in response to a threatened outbreak of an emerging pathogen. Work is already underway to develop vaccines against a number of other outbreak pathogens and we will also review progress on these approaches here, particularly for Lassa fever, Nipah and MERS.

Spencer AJ, Longley RJ, Gola A, Ulaszewska M, Lambe T, Hill AVS. 2017. The Threshold of Protection from Liver-Stage Malaria Relies on a Fine Balance between the Number of Infected Hepatocytes and Effector CD8+ T Cells Present in the Liver. J Immunol, 198 (5), pp. 2006-2016. | Show Abstract | Read more

Since the demonstration of sterile protection afforded by injection of irradiated sporozoites, CD8+ T cells have been shown to play a significant role in protection from liver-stage malaria. This is, however, dependent on the presence of an extremely high number of circulating effector cells, thought to be necessary to scan, locate, and kill infected hepatocytes in the short time that parasites are present in the liver. We used an adoptive transfer model to elucidate the kinetics of the effector CD8+ T cell response in the liver following Plasmodium berghei sporozoite challenge. Although effector CD8+ T cells require <24 h to find, locate, and kill infected hepatocytes, active migration of Ag-specific CD8+ T cells into the liver was not observed during the 2-d liver stage of infection, as divided cells were only detected from day 3 postchallenge. However, the percentage of donor cells recruited into division was shown to indicate the level of Ag presentation from infected hepatocytes. By titrating the number of transferred Ag-specific effector CD8+ T cells and sporozoites, we demonstrate that achieving protection toward liver-stage malaria is reliant on CD8+ T cells being able to locate infected hepatocytes, resulting in a protection threshold dependent on a fine balance between the number of infected hepatocytes and CD8+ T cells present in the liver. With such a fine balance determining protection, achieving a high number of CD8+ T cells will be critical to the success of a cell-mediated vaccine against liver-stage malaria.

Morris SJ, Sebastian S, Spencer AJ, Gilbert SC. 2016. Simian adenoviruses as vaccine vectors. Future Virol, 11 (9), pp. 649-659. | Show Abstract | Read more

Replication incompetent human adenovirus serotype 5 (HAdV-C5) has been extensively used as a delivery vehicle for gene therapy proteins and infectious disease antigens. These vectors infect replicating and nonreplicating cells, have a broad tissue tropism, elicit high immune responses and are easily purified to high titers. However, the utility of HAdV-C5 vectors as potential vaccines is limited due to pre-existing immunity within the human population that significantly reduces the immunogenicity of HAdV-C5 vaccines. In recent years, adenovirus vaccine development has focused on simian-derived adenoviral vectors, which have the desirable vector characteristics of HAdV-C5 but with negligible seroprevalence in the human population. Here, we discuss recent advances in simian adenovirus vaccine vector development and evaluate current research specifically focusing on clinical trial data.

Ewer KJ, Lambe T, Rollier CS, Spencer AJ, Hill AV, Dorrell L. 2016. Viral vectors as vaccine platforms: from immunogenicity to impact. Curr Opin Immunol, 41 pp. 47-54. | Show Abstract | Read more

Viral vectors are the vaccine platform of choice for many pathogens that have thwarted efforts towards control using conventional vaccine approaches. Although the STEP trial encumbered development of recombinant human adenovirus vectors only a few years ago, replication-deficient simian adenoviruses have since emerged as a crucial component of clinically effective prime-boost regimens. The vectors discussed here elicit functionally relevant cellular and humoral immune responses, at extremes of age and in diverse populations. The recent Ebola virus outbreak highlighted the utility of viral vectored vaccines in facilitating a rapid response to public health emergencies. Meanwhile, technological advances in manufacturing to support scale-up of viral vectored vaccines have helped to consolidate their position as a leading approach to tackling 'old' and emerging infections.

Longley RJ, Hill AVS, Spencer AJ. 2015. Malaria vaccines: identifying Plasmodium falciparum liver-stage targets. Front Microbiol, 6 (SEP), pp. 965. | Show Abstract | Read more

The development of a highly efficacious and durable vaccine for malaria remains a top priority for global health researchers. Despite the huge rise in recognition of malaria as a global health problem and the concurrent rise in funding over the past 10-15 years, malaria continues to remain a widespread burden. The evidence of increasing resistance to anti-malarial drugs and insecticides is a growing concern. Hence, an efficacious and durable preventative vaccine for malaria is urgently needed. Vaccines are one of the most cost-effective tools and have successfully been used in the prevention and control of many diseases, however, the development of a vaccine for the Plasmodium parasite has proved difficult. Given the early success of whole sporozoite mosquito-bite delivered vaccination strategies, we know that a vaccine for malaria is an achievable goal, with sub-unit vaccines holding great promise as they are simple and cheap to both manufacture and deploy. However a major difficulty in development of sub-unit vaccines lies within choosing the appropriate antigenic target from the 5000 or so genes expressed by the parasite. Given the liver-stage of malaria represents a bottle-neck in the parasite's life cycle, there is widespread agreement that a multi-component sub-unit malaria vaccine should preferably contain a liver-stage target. In this article we review progress in identifying and screening Plasmodium falciparum liver-stage targets for use in a malaria vaccine.

Longley RJ, Bauza K, Ewer KJ, Hill AVS, Spencer AJ. 2015. Development of an in vitro assay and demonstration of Plasmodium berghei liver-stage inhibition by TRAP-specific CD8+ T cells. PLoS One, 10 (3), pp. e0119880. | Show Abstract | Read more

The development of an efficacious vaccine against the Plasmodium parasite remains a top priority. Previous research has demonstrated the ability of a prime-boost virally vectored sub-unit vaccination regimen, delivering the liver-stage expressed malaria antigen TRAP, to produce high levels of antigen-specific T cells. The liver-stage of malaria is the main target of T cell-mediated immunity, yet a major challenge in assessing new T cell inducing vaccines has been the lack of a suitable pre-clinical assay. We have developed a flow-cytometry based in vitro T cell killing assay using a mouse hepatoma cell line, Hepa1-6, and Plasmodium berghei GFP expressing sporozoites. Using this assay, P. berghei TRAP-specific CD8+ T cell enriched splenocytes were shown to inhibit liver-stage parasites in an effector-to-target ratio dependent manner. Further development of this assay using human hepatocytes and P. falciparum would provide a new method to pre-clinically screen vaccine candidates and to elucidate mechanisms of protection in vitro.

Longley RJ, Salman AM, Cottingham MG, Ewer K, Janse CJ, Khan SM, Spencer AJ, Hill AVS. 2015. Comparative assessment of vaccine vectors encoding ten malaria antigens identifies two protective liver-stage candidates. Sci Rep, 5 (1), pp. 11820. | Show Abstract | Read more

The development of an efficacious Plasmodium falciparum malaria vaccine remains a top priority for global health. Vaccination with irradiated sporozoites is able to provide complete sterile protection through the action of CD8(+) T cells at the liver-stage of infection. However, this method is currently unsuitable for large-scale deployment and focus has instead turned to the development of sub-unit vaccines. Sub-unit vaccine efforts have traditionally focused on two well-known pre-erythrocytic antigens, CSP and TRAP, yet thousands of genes are expressed in the liver-stage. We sought to assess the ability of eight alternative P. falciparum pre-erythrocytic antigens to induce a high proportion of CD8(+) T cells. We show that all antigens, when expressed individually in the non-replicating viral vectors ChAd63 and MVA, are capable of inducing an immune response in mice. Furthermore, we also developed chimeric P. berghei parasites expressing the cognate P. falciparum antigen to enable assessment of efficacy in mice. Our preliminary results indicate that vectors encoding either PfLSA1 or PfLSAP2 are capable of inducing sterile protection dependent on the presence of CD8(+) T cells. This work has identified two promising P. falciparum liver-stage candidate antigens that will now undergo further testing in humans.

Spencer AJ, Cottingham MG, Jenks JA, Longley RJ, Capone S, Colloca S, Folgori A, Cortese R, Nicosia A, Bregu M, Hill AVS. 2014. Enhanced vaccine-induced CD8+ T cell responses to malaria antigen ME-TRAP by fusion to MHC class ii invariant chain. PLoS One, 9 (6), pp. e100538. | Show Abstract | Read more

The orthodox role of the invariant chain (CD74; Ii) is in antigen presentation to CD4+ T cells, but enhanced CD8+ T cells responses have been reported after vaccination with vectored viral vaccines encoding a fusion of Ii to the antigen of interest. In this study we assessed whether fusion of the malarial antigen, ME-TRAP, to Ii could increase the vaccine-induced CD8+ T cell response. Following single or heterologous prime-boost vaccination of mice with a recombinant chimpanzee adenovirus vector, ChAd63, or recombinant modified vaccinia virus Ankara (MVA), higher frequencies of antigen-specific CD4+ and CD8+ T cells were observed, with the largest increases observed following a ChAd63-MVA heterologous prime-boost regimen. Studies in non-human primates confirmed the ability of Ii-fusion to augment the T cell response, where a 4-fold increase was maintained up to 11 weeks after the MVA boost. Of the numerous different approaches explored to increase vectored vaccine induced immunogenicity over the years, fusion to the invariant chain showed a consistent enhancement in CD8+ T cell responses across different animal species and may therefore find application in the development of vaccines against human malaria and other diseases where high levels of cell-mediated immunity are required.

Spencer AJ, Furze J, Honeycutt JD, Calvert A, Saurya S, Colloca S, Wyllie DH, Gilbert SC, Bregu M, Cottingham MG, Hill AVS. 2014. 4-1BBL enhances CD8+ T cell responses induced by vectored vaccines in mice but fails to improve immunogenicity in rhesus macaques. PLoS One, 9 (8), pp. e105520. | Show Abstract | Read more

T cells play a central role in the immune response to many of the world's major infectious diseases. In this study we investigated the tumour necrosis factor receptor superfamily costimulatory molecule, 4-1BBL (CD137L, TNFSF9), for its ability to increase T cell immunogenicity induced by a variety of recombinant vectored vaccines. To efficiently test this hypothesis, we assessed a number of promoters and developed a stable bi-cistronic vector expressing both the antigen and adjuvant. Co-expression of 4-1BBL, together with our model antigen TIP, was shown to increase the frequency of murine antigen-specific IFN-γ secreting CD8(+) T cells in three vector platforms examined. Enhancement of the response was not limited by co-expression with the antigen, as an increase in CD8(+) immunogenicity was also observed by co-administration of two vectors each expressing only the antigen or adjuvant. However, when this regimen was tested in non-human primates using a clinical malaria vaccine candidate, no adjuvant effect of 4-1BBL was observed limiting its potential use as a single adjuvant for translation into a clinical vaccine.

Sheehy SH, Spencer AJ, Douglas AD, Sim BKL, Longley RJ, Edwards NJ, Poulton ID, Kimani D, Williams AR, Anagnostou NA et al. 2013. Optimising Controlled Human Malaria Infection Studies Using Cryopreserved P. falciparum Parasites Administered by Needle and Syringe. PLoS One, 8 (6), pp. e65960. | Show Abstract | Read more

BACKGROUND: Controlled human malaria infection (CHMI) studies have become a routine tool to evaluate efficacy of candidate anti-malarial drugs and vaccines. To date, CHMI trials have mostly been conducted using the bite of infected mosquitoes, restricting the number of trial sites that can perform CHMI studies. Aseptic, cryopreserved P. falciparum sporozoites (PfSPZ Challenge) provide a potentially more accurate, reproducible and practical alternative, allowing a known number of sporozoites to be administered simply by injection. METHODOLOGY: We sought to assess the infectivity of PfSPZ Challenge administered in different dosing regimens to malaria-naive healthy adults (n = 18). Six participants received 2,500 sporozoites intradermally (ID), six received 2,500 sporozoites intramuscularly (IM) and six received 25,000 sporozoites IM. FINDINGS: Five out of six participants receiving 2,500 sporozoites ID, 3/6 participants receiving 2,500 sporozoites IM and 6/6 participants receiving 25,000 sporozoites IM were successfully infected. The median time to diagnosis was 13.2, 17.8 and 12.7 days for 2,500 sporozoites ID, 2,500 sporozoites IM and 25,000 sporozoites IM respectively (Kaplan Meier method; p = 0.024 log rank test). CONCLUSIONS: 2,500 sporozoites ID and 25,000 sporozoites IM have similar infectivities. Given the dose response in infectivity seen with IM administration, further work should evaluate increasing doses of PfSPZ Challenge IM to identify a dosing regimen that reliably infects 100% of participants. TRIAL REGISTRATION: ClinicalTrials.gov NCT01465048.

Lambe T, Spencer AJ, Mullarkey CE, Antrobus RD, Yu L-M, de Whalley P, Thompson BAV, Jones C, Chalk J, Kerridge S et al. 2012. T-cell responses in children to internal influenza antigens, 1 year after immunization with pandemic H1N1 influenza vaccine, and response to revaccination with seasonal trivalent-inactivated influenza vaccine. Pediatr Infect Dis J, 31 (6), pp. e86-e91. | Show Abstract | Read more

BACKGROUND: During seasonal influenza epidemics, 5-15% of the population are affected with an illness having a nontrivial mortality, morbidity and economic burden. Inactivated influenza vaccines are routinely used to prevent influenza infection, primarily by inducing humoral immunity. In addition, trivalent-inactivated influenza vaccines have previously been shown to boost influenza-specific T-cell responses in a small percentage of adults. We investigate here the influenza-specific T-cell response, in children, 1 year after pandemic H1N1 vaccination and the ability to boost the T-cell response with trivalent-inactivated influenza immunization. METHODS: Peripheral blood mononuclear cells (PBMCs) were isolated from children previously vaccinated with pandemic H1N1 vaccine, pre- and postseasonal 2010-2011 trivalent influenza vaccine (TIV) vaccination. Samples were analyzed by interferon-gamma enzyme-linked immunosorbent spot for reactogenicity toward internal influenza antigens (nucleoprotein, matrix protein 1 and nonstructural protein 1). RESULTS: Basal ex vivo T-cell responses to nucleoprotein, matrix protein 1 and nonstructural protein 1 measured by interferon-gamma enzyme-linked immunosorbent spot assay were significantly higher in those children who had previously received an AS03B-adjuvanted split virion pandemic vaccine 12 months earlier rather than a nonadjuvanted whole virion vaccine. Boosting of these responses, 21 days after 2010/2011 seasonal TIV vaccination was observed regardless of age or prior pandemic vaccination regime, although boosting was greater in those groups with the lowest initial response. CONCLUSIONS: We show here that children previously vaccinated with the 2009 pandemic H1N1 vaccine have measurable T-cell responses 1 year after vaccination. The magnitudes of these responses are dependent on both age of vaccine and type of pandemic H1N1 vaccine used. After 2010/2011 seasonal TIV vaccination, these T-cell responses undergo a small but significant boost.

Antigen presentation from malaria infected liver cells – identifying better CD8+ T cell antigens

Despite global efforts, malaria continues to cause significant morbidity and mortality worldwide, particularly in developing countries with greater than 70% of childhood related deaths occurring in Sub-Saharian Africa are due to malaria. There is an urgent need for a durable and efficacious malaria vaccine, to date the most promising candidates are against the first stage of malaria infection in humans and have shown some degree of efficacy. The two lead clinical candidate vaccines are RTS,S in ...

View project

Development of a durable and efficacious pre-erythrocytic malaria vaccine

Despite global efforts, malaria continues to cause significant morbidity and mortality worldwide, particularly in developing countries with greater than 70% of childhood related deaths occurring in Sub-Saharian Africa due to malaria. A malaria infection in humans starts with the bite of an infected mosquito which injects P. falciparum sporozoites into the skin as it takes a blood meal. Sporozoites then migrate to the liver where they infect hepatocytes and undergo asexual replication, ...

View project

2728