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We have designed a pre-erythrocytic vaccine candidate based on the Plasmodium vivax circumsporozoite (CSV) protein, which includes its N- and C-terminal parts and a truncated region containing repeat sequences from both the VK210 and the VK247 P. vivax subtypes. Two versions of this vaccine candidate were made: a soluble recombinant protein expressed in Escherichia coli, designated VMP001 and a particulate antigen expressed in Saccharomyces cerevisiae, designated CSV-S,S. The latter is composed of CSV-S, a fusion protein between VMP001 and hepatitis B surface antigen (HBsAg), and free HBsAg co-expressed in yeast and self-assembling into mixed particles. Both antigen versions, adjuvanted with AS01, were shown to be immunogenic in rhesus monkeys. CSV-S,S/AS01 induced higher levels of VMP001-specific antibodies than did VMP001/AS01. Antibody responses against the N- and C-terminal regions of CSV and the VK210 repeat motif were of a similar magnitude following immunization with either the soluble or the particulate antigen. However, antibodies against the AGDR region, a potentially protective B cell epitope, were only detected after immunization with CSV-S,S. Analysis of the induced CD4(+) T cells highlighted different cytokine profiles depending on the antigen form. These results warrant further clinical evaluation of these two vaccine candidates to assess the added value of a particulate versus soluble form of CSV, in terms of both immunogenicity and protective efficacy., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Immunization of BALB/c mice with irradiated sporozoites (IrSp) of Plasmodium yoelii can lead to sterile immunity. The circumsporozoite protein (CSP) plays a dominant role in protection. Nevertheless after hyper-immunization with IrSp, complete protection is obtained in CSP-transgenic BALB/c mice that are T-cell tolerant to the CSP and cannot produce antibodies [CSP-Tg/JhT(-/-)]. This protection is mediated exclusively by CD8(+) T cells [1]. To identify the non-CSP protective T cell antigens, we studied the properties of 34 P. yoelii sporozoite antigens that are predicted to be secreted and to contain strong Kd-restricted CD8(+) T cell epitopes. The synthetic peptides corresponding to the epitopes were used to screen for the presence of peptide-specific CD8(+) T cells secreting interferon-γ (IFN-γ) in splenocytes from CSP-Tg/JhT(-/-) BALB/c mice hyper immunized with IrSp. However, the numbers of IFN-γ-secreting splenocytes specific for the non-CSP antigen-derived peptides were 20-100 times lower than those specific for the CSP-specific peptide. When mice were immunized with recombinant adenoviruses expressing selected non-CSP antigens, the animals were not protected against challenge with P. yoelii sporozoites although large numbers of CD8(+) specific T cells were generated., (Copyright © 2011 Elsevier Ltd. All rights reserved.)