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

Project Overview

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 AS01 (Mosquirix) which induces high titre antibodies to block malaria parasite infection of the liver cells (Rts, 2015), and heterologous vaccination with viral vectors ChAd63 and MVA expressing ME-TRAP which induces high numbers of effector CD8+ T cells which locate and kill the infected liver cells (Ewer et al., 2013).

The two leading clinical vaccine candidates, however, are based on malaria antigens (CS and TRAP) that were identified over 20 years ago. Recent work from our group showed better efficacy of two new liver-stage antigens when compared to CS and TRAP in an in vivo challenge model (Longley et al., 2015), suggesting that even better liver-stage antigens could still be found.

While one limitation in the selection of candidate liver-stage antigens continues to be the lack of proteomic data for the liver-stage of malaria. With the recent advances in mass spectrometry techniques, experiments are underway to identify peptide-MHC complexes from malaria infected liver cells, in the hope of identifying new liver stage malaria antigens. Despite this progress, one major gap in our knowledge is identifying the characteristic of malaria proteins that make then good vaccine candidate antigens, ie cellular location and duration of expression. While cellular location of the protein during blood-stage malaria can affect induction of T cell responses (Lin et al., 2014), protein location and its affect on CD8+ T cell activation during a liver-stage infection is not known.

This project aims to initially investigate the kinetics of protein expression and antigen presentation during the liver-stage of malaria and the subsequent knock on effect in protection from malaria challenge. By identifying “protective characteristics” of liver-stage malaria proteins we will be able to choose new candidate malaria antigens from proteomic data, generate new viral vectored vaccines and test their protective capacity in pre-clinical malaria models, with the ultimate goal of translating new vaccines to the clinic.

This DPhil project will make use of transgenic P.berghei and P.falciparum technology and sophisticated immunological techniques and thus provide training in immunology, parasitology, molecular biology and intra-vital imaging. In addition this project will combine the major steps for the development of a new generation of malaria vaccines; antigen identification, vaccine design and pre-clinical validation.

Training Opportunities

Both subject specific and generic training in research skills will be provided. Specific training will be available a large variety of immunoassays, cell biology, immune-histochemistry, flow cytometry, intra-vital imaging, vector construction, molecular biology, immunization techniques, parasitology, statistical analysis of data and experimental design. The research group is large and includes students, post-docs, clinical fellows, research nurses, clinical triallists, project managers, field researchers, and biomanufacturing experts, spanning activities in vaccinology and human genetics, thereby providing exposure to a broad range of research and development activities in the biomedical sciences. The Jenner Institute has performed more than 20 clinical trials and has accumulated unparalleled depth and breadth of experience in vaccinology, combining all the technologies required for the effective development of new vaccines, from vaccine design and production to pre-clinical studies and clinical trials.

Theme

Immunology & Infectious Disease and Tropical Medicine & Global Health

Admissions

Project reference number: 865

Funding and admissions information

Supervisors

Name Department Institution Country Email
Dr Alexandra J Spencer Jenner Institute Oxford University, Old Road Campus Research Building GBR alex.spencer@ndm.ox.ac.uk
Professor Adrian VS Hill Jenner Institute Oxford University, Old Road Campus Research Building GBR adrian.hill@ndm.ox.ac.uk

Spencer AJ, Longley RJ, Gola A, Ulaszewska M, Lambe T, Hill AV. 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. Read 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 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. Hide abstract