Immunogenicity and protective efficacy of Plasmodium falciparum liver‐stage Ag‐3 in Aotus lemurinus griseimembra monkeys

Abstract

Three recombinant proteins spanning the Plasmodium falciparum liver-stage Ag-3 (LSA-3) were used to immunize Aotus monkeys. The proteins were delivered subcutaneously without adjuvant, adsorbed onto polystyrene 0.5 ? m particles at a concentration of 2 ? g per immunization. Control animals received glutathione-S-transferase formulated similarly. Animals were challenged as late as 5 months after the last immunization, by intravenous inoculation of 100,000 P. falciparum sporozoites of a strain heterologous to the one from which the immunogens were derived. Sterile protection was achieved in three of the five immunized monkeys but in none of four controls. Antibodies were at low titer, but reacted with the native parasite protein and were boosted by parasite challenge. Ag-specific IFN-+ secretion was detectable in all LSA-3-immunized animals in response to the LSA-3-derived Ag. The protection was apparently associated with high levels of IFN-+ production in response to in vitro recall Ag. These results lend support to the vaccine potential of LSA-3 indicated by previous results obtained in chimpanzees, as well as the value of yet another Ag-delivery system. They also support the value of the Aotus model for the pre-clinical development of preerythrocytic-stage vaccines.

Protection against Plasmodium falciparum challenge induced in Aotus monkeys by liver‐stage antigen‐3‐derived long synthetic peptides

“…Therefore, further analysis of responses elicited by NRP in models and in humans may contribute to elucidation of these mechanisms. Although, the number of monkeys does not allow to reach statistical significance, these results are consistent with previous data obtained with P. falciparum LSA3-DG729 region [3,4], particularly with the protection induced by lipopeptide formulations of the peptides NRI and NRII contained in the NRP employed in the present work [3].It is noteworthy that the vaccination with LSA3-LSP induced immune responses that protected against a challenge with a strain heterologous to that used to design the vaccine. This is in agreement both with previous challenge data also performed using heterologous P. falciparum NF54 parasites [3] and with the high degree of LSA3-sequence conservation [3].…”

“…By analyzing the differential immune responses observed between protected and non-protected volunteers upon a viable sporozoite challenge, we selected within a subset of Plasmodium falciparum preerythrocytic antigens a protein that we named liver stage antigen-3 (LSA3), which was preferentially recognized by sera from protected humans [2,3]. This antigen is highly conserved, is expressed in sporozoite and liver stages, and its protective potential against challenge with P. falciparum sporozoites has been demonstrated in non-human primates using a large set of antigen-presentation systems [3,4]. …”

“…1) against a P. falciparum sporozoite challenge in chimpanzees and in Aotus monkeys [3,4]. Four formulations have been found able to induce protection: the LSA3-729 recombinant protein either adsorbed to microparticles without adjuvant or adjuvanted by ASO2, lipopeptides formulations of the NRI and NRII peptides with the non-lipid-tailed R peptide [3,4], and genetic immunization using the nearly full-length gene [7] (Daubersies et al, in preparation). Here, we perform a preliminary evaluation of the immunogenicity and protective efficacy in A. l. griseimembra of two LSP covering either the nonrepeat (100-222) or the repeat (501-596) sequences derived from the P. falciparum LSA3-729 protein (Fig.…”

“…Its role in protection has been observed in vitro in P. falciparum-infected human hepatocytes, at concentrations ranging from 1 to 10 I U [8] as well as in vivo in mice immunized by irradiated sporozoites [9] and is supported by studies in chimpanzees immunized either with irradiated sporozoites or with LSA3-derived antigens [2, 10], or in Aotus immunized with particulate formulations [4]. Because peptides NRP and RP contain epitopes, which are main targets of Th1 responses and the protection is associated with strong Th1 responses [4], analysis of T-cell responses in immunized Aotus was limited to the study of IFN-g production by specific T cells. PBMC from immunized monkeys produced substantial amounts of IFN-g as determined by ELISPOT upon stimulation with at least one of the short or long synthetic peptides, or in one animal in culture supernatants.…”

“…The chemical synthesis of LSP provides several practical advantages and has contributed to the evaluation of the antigenicity and immunogenicity of both P. falciparum and P. vivax proteins in animals and humans [6]. We selected two LSA3-LSP from the N-terminal non-repeated (100-222) and the repeat region R2 (501-596), which cover the sequence of the LSA3-729 subunit protein used in previous protective experiments [3,4] and which is a target of Th1 protective responses in primates. In order to determine the region of greatest importance for the induction of protective mechanisms, we immunized Aotus monkeys with either the non-repeat region peptide alone, or mixed with the repeat region peptide and evaluated the efficacy of the immune responses induced in this manner against challenge by P. falciparum sporozoites.…”