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

Carly M Bliss,Shahid M Khan,Adrian Vs Hill,Chris J Janse,Rhea J Longley,Katie J Ewer,Ahmed M Salman

doi:10.1186/1475-2875-13-s1-p14

Carly M Bliss, Shahid M Khan + Show 5 more

Open Access

https://doi.org/10.1186/1475-2875-13-s1-p14

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Abstract

Background Vaccination against liver stage malaria antigens can induce T cell-mediated immunity to the disease [1]. A viral vector vaccination regime undergoing Phase 2b clinical testing uses chimpanzee adenovirus 63 (ChAd63) and Modified Vaccinia virus Ankara (MVA) encoding liver stage antigen Thrombospondin-Related Adhesion Protein (TRAP) fused to a malaria multi-epitope string (ME). This regime induces high frequencies of antigen-specific T cells, providing 21% sterile protection and a delay to patent parasitaemia in a further 36% of vaccinees, following controlled human Plasmodium falciparum malaria infection (CHMI). Monofunctional IFNg-producing CD8 T cells correlate with vaccine-induced protection but the associated protective mechanisms remain unidentified [2]. Developing standardized immunological and functional assays is a research-specific aim of the WHO’s Malaria Vaccine Technology Roadmap, with emphasis on novel immunoassays for investigation of cellular products reflecting cellmediated malaria immunity [3]. Development of an in vitro parasite killing assay is underway, which quantifies cell-mediated killing of Plasmodium-infected human hepatocytes and investigates the underlying functional mechanisms. Additionally, the assay aims to compliment in vivo CHMI studies.

Highlights

Vaccination against liver stage malaria antigens can induce T cell-mediated immunity to the disease [1]
Thrombospondin-Related Adhesion Protein (TRAP)-specific killing was calculated by subtraction of non-specific killing in wild type P. berghei-infected hepatocytes
Transgenic P. berghei sporozoites with full replacement of wild type TRAP infect human hepatoma cells at >1% frequency

Summary

Background

Vaccination against liver stage malaria antigens can induce T cell-mediated immunity to the disease [1]. A viral vector vaccination regime undergoing Phase 2b clinical testing uses chimpanzee adenovirus 63 (ChAd63) and Modified Vaccinia virus Ankara (MVA) encoding liver stage antigen Thrombospondin-Related Adhesion Protein (TRAP) fused to a malaria multi-epitope string (ME). This regime induces high frequencies of antigen-specific T cells, providing 21% sterile protection and a delay to patent parasitaemia in a further 36% of vaccinees, following controlled human Plasmodium falciparum malaria infection (CHMI). Development of an in vitro parasite killing assay is underway, which quantifies cell-mediated killing of Plasmodium-infected human hepatocytes and investigates the underlying functional mechanisms. TRAP-specific killing was calculated by subtraction of non-specific killing in wild type P. berghei-infected hepatocytes

Results

Conclusions

Materials and methods