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Geographically restricted heterogeneity of the Plasmodium falciparum circumsporozoite protein: relevance for vaccine development.

ABSTRACT: The design of a subunit vaccine against the malaria parasite relies on the epitopes recognized by T cells being identified and polymorphisms therein being defined. Here we present the analysis of a 354-bp fragment of the circumsporozoite (CS) protein encompassing defined proliferative and cytotoxic T-cell recognition regions. We reveal that the polymorphism of CS protein T-cell sites appears to be very limited among Plasmodium falciparum isolates prevalent in certain geographical regions, in particular Papua New Guinea. Furthermore, the more extensive polymorphism noted in other areas appears to be restricted. Although the extent of variation observed for the T-cell recognition domains suggests that any vaccine designed to stimulate this form of immunity will need to be polyvalent, this variation appears to be finite and the combination of peptides necessary for inclusion in a polyvalent vaccine may be small. If ways to increase immune responsiveness can be found, then a vaccine designed to stimulate CS protein-specific T-cell activity may prevent malaria.

SUBMITTER: Doolan DL

PROVIDER: S-EPMC257683 | biostudies-other | 1992 Feb

REPOSITORIES: biostudies-other

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Geographically restricted heterogeneity of the Plasmodium falciparum circumsporozoite protein: relevance for vaccine development.

Doolan D L DL Saul A J AJ Good M F MF

Infection and immunity 19920201 2

The design of a subunit vaccine against the malaria parasite relies on the epitopes recognized by T cells being identified and polymorphisms therein being defined. Here we present the analysis of a 354-bp fragment of the circumsporozoite (CS) protein encompassing defined proliferative and cytotoxic T-cell recognition regions. We reveal that the polymorphism of CS protein T-cell sites appears to be very limited among Plasmodium falciparum isolates prevalent in certain geographical regions, in par ...[more]

PMID: 1730503

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Project description:RTS,S is the most advanced malaria vaccine candidate, currently under phase-III clinical trials in Africa. This Plasmodium falciparum vaccine contains part of the central repeat region and the complete C-terminal T cell epitope region (Th2R and Th3R) of the circumsporozoite protein (CSP). Since naturally occurring polymorphisms at the vaccine candidate loci are critical determinants of the protective efficacy of the vaccines, it is imperative to investigate these polymorphisms in field isolates. In this study we have investigated the genetic diversity at the central repeat, C-terminal T cell epitope (Th2R and Th3R) and N-terminal T cell epitope regions of the CSP, in P. falciparum isolates from Madhya Pradesh state of India. These isolates were collected through a 5-year prospective study aimed to develop a well-characterized field-site for the future evaluation of malaria vaccine in India. Our results revealed that the central repeat (63 haplotypes, n?=?161) and C-terminal Th2R/Th3R epitope (24 haplotypes, n = 179) regions were highly polymorphic, whereas N-terminal non-repeat region was less polymorphic (5 haplotypes, n = 161) in this population. We did not find any evidence of the role of positive natural selection in maintaining the genetic diversity at the Th2R/Th3R regions of CSP. Comparative analysis of the Th2R/Th3R sequences from this study to the global isolates (n = 1160) retrieved from the GenBank database revealed two important points. First, the majority of the sequences (~61%, n = 179) from this study were identical to the Dd2/Indochina type, which is also the predominant Th2R/Th3R haplotype in Asia (~59%, n = 974). Second, the Th2R/Th3R sequences in Asia, South America and Africa are geographically distinct with little allele sharing between continents. In conclusion, this study provides an insight on the existing polymorphisms in the CSP in a parasite population from India that could potentially influence the efficacy of RTS,S vaccine in this region.

Project description:BackgroundPlasmodium falciparum circumsporozoite protein (CSP) is a leading malaria vaccine candidate antigen, known to elicit protective antibody responses in humans (RTS,S vaccine). Recently, a DNA prime / adenovirus (Ad) vector boost vaccine encoding CSP and a second P. falciparum antigen, apical membrane antigen-1, also elicited sterile protection, but in this case associated with interferon gamma ELISpot and CD8+ T cell but not antibody responses. The finding that CSP delivered by an appropriate vaccine platform likely elicits protective cell-mediated immunity provided a rationale for identifying class I-restricted epitopes within this leading vaccine candidate antigen.MethodsLimited samples of peripheral blood mononuclear cells from clinical trials of the Ad vaccine were used to identify CD8+ T cell epitopes within pools of overlapping 15mer peptides spanning portions of CSP that stimulated recall responses. Computerized algorithms (NetMHC) predicted 17 minimal class I-restricted 9-10mer epitopes within fifteen 15mers positive in ELISpot assay using PBMC from 10 HLA-matched study subjects. Four additional epitopes were subsequently predicted using NetMHC, matched to other study subjects without initial 15mer ELISpot screening. Nine of the putative epitopes were synthesized and tested by ELISpot assay, and six of these nine were further tested for CD8+ T cell responses by ELISpot CD4+ and CD8+ T cell-depletion and flow cytometry assays for evidence of CD8+ T cell dependence.ResultsEach of the nine putative epitopes, all sequence-conserved, recalled responses from HLA-matched CSP-immunized research subjects. Four shorter sequences contained within these sequences were identified using NetMHC predictions and may have contributed to recall responses. Five (9-10mer) epitopes were confirmed to be targets of CD8+ T cell responses using ELISpot depletion and ICS assays. Two 9mers among these nine epitopes were each restricted by two HLA supertypes (A01/B07; A01A24/A24) and one 9mer was restricted by three HLA supertypes (A01A24/A24/B27) indicating that some CSP class I-restricted epitopes, like DR epitopes, may be HLA-promiscuous.ConclusionsThis study identified nine and confirmed five novel class I epitopes restricted by six HLA supertypes, suggesting that an adenovirus-vectored CSP vaccine would be immunogenic and potentially protective in genetically diverse populations.

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Geographically restricted heterogeneity of the Plasmodium falciparum circumsporozoite protein: relevance for vaccine development.

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Geographically restricted heterogeneity of the Plasmodium falciparum circumsporozoite protein: relevance for vaccine development.

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