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Abstract: Stable protective immunity can be achieved against malaria by the injection of radiation-attenuated sporozoites (γ-spz) and is mediated by IFN-γ producing CD8+ T cells targeting the pre-erythrocytic stages. An efficient malaria vaccine should mimic this immunity. We compared the immune response specific for the circumsporozoite protein (CSP) of Plasmodium berghei (P. berghei), an important target of this protective response, elicited in mice immunized with the long synthetic polypeptide (LSP) PbCS 242–310, representing the C-terminus of the CSP of P. berghei, with the adjuvant QS-21 or injected with γ-spz. The ex vivo evaluation of the CD8+ T cell response by IFN-γ ELISPOT assay revealed that the injection of LSP with QS-21 induced, compared to γ-spz, a similar frequency of peptide-specific lymphocytes in the spleen but a eight-fold increase in the draining lymph-nodes. A very high frequency of CD8+ T cells, specific for the sequence PbCS 245–253, a H-2Kd-restricted CTL epitope, was obtained in the liver and spleen of mice immunized with the two regimens. Even though the frequency of H-2Kd PbCS 245–253 multimer+, CD8+ T cells was higher in γ-spz immunized mice, the frequency of IFN-γ producing CD8+ T cells was comparable. The phenotype of the CD8+ T cell responses was characterized with the help H-2Kd PbCS 245–253 multimer and most of the CSP-specific CD8+ T cells represented an intermediate subset between effector and central memory with CD44high, CD45RBhigh, CD62Llow and CD122high. The number of memory CD8+ T cells decreased after the last LSP immunization but could be boosted to higher level with live spz. The unique combination of LSP PbCS 242–310 and the adjuvant QS-21 induced an immune response that was comparable in terms of quality to the one generated with γ-spz. This confirmed the potential of LSP as malaria vaccine candidates as well as for the study of the repertoire of targets of protective immunity in the γ-spz vaccine model. [Copyright &y& Elsevier]

The present work describes the recognition of three synthetic polypeptides encompassing the N- and C-terminal regions of the transmembrane Exp-1 protein of the parasite Plasmodium falciparum by plasma and peripheral blood mononuclear cells from naturally exposed individuals living in African endemic areas. The three polypeptides comprise the sequences 23-105, 73-162 and 101-162, and overlap at the transmembrane domain (73-105). Thus, they permitted characterization of the immune response specific to the N- and C-terminal domains in an independent fashion. Two different populations were evaluated, one in the village of Safo in Mall and the other in the villages of Somnaway, Kabortenga and Toussouktenga in Burkina Faso. Antibodies to the sequence 73-162 of Pf Exp-1 were found in 70% of adult Mali donors and in all of the donors tested from Burkina Faso. Strikingly, the N-terminal fragment Pf Exp-1 23-105 was only weakly recognized by a few donors. Evaluation of the T-cell response indicated that the peptide Pf Exp-1 23-105 was more potent than Pf Exp-1 73-162 in inducing a proliferative response. A correlation between peptide-specific interferon-γ and interleukin-6 production and proliferation to peptide Pf Exp-1 23-105 was observed. Further studies are needed to evaluate this molecule as a vaccine candidate. [ABSTRACT FROM AUTHOR]