A Multistage Formulation Based on Full-Length CSP and AMA-1 Ectodomain of Plasmodium vivax Induces High Antibody Titers and T-cells and Partially Protects Mice Challenged with a Transgenic Plasmodium berghei Parasite

Abstract

Infections with Plasmodium vivax are predominant in the Americas, representing 75% of malaria cases. Previously perceived as benign, malaria vivax is, in fact, a highly debilitating and economically important disease. Considering the high complexity of the malaria parasite life cycle, it has been hypothesized that an effective vaccine formulation against Plasmodium should contain multiple antigens expressed in different parasite stages. Based on that, we analyzed a recombinant P. vivax vaccine formulation mixing the apical membrane antigen 1 ectodomain (PvAMA-1) and a full-length circumsporozoite protein (PvCSP-AllFL) previously studied by our group, which elicits a potent antibody response in mice. Genetically distinct strains of mice (C57BL/6 and BALB/c) were immunized with the proteins, alone or in combination, in the presence of poly(I:C) adjuvant, a TLR3 agonist. In C57BL/6, high-antibody titers were induced against PvAMA-1 and the three PvCSP variants (VK210, VK247, and P. vivax-like). Meanwhile, mixing PvAMA-1 with PvCSP-AllFL had no impact on total IgG antibody titers, which were long-lasting. Moreover, antibodies from immunized mice recognized VK210 sporozoites and blood-stage parasites by immunofluorescence assay. However, in the BALB/c model, the antibody response against PvCSP-AllFL was relatively low. PvAMA-1-specific CD3+CD4+ and CD3+CD8+ T-cell responses were observed in C57BL/6 mice, and the cellular response was impaired by PvCSP-AllFL combination. More relevant, the multistage vaccine formulation provided partial protection in mice challenged with a transgenic Plasmodium berghei sporozoite expressing the homologous PvCSP protein.

Immune System Modulation by the Adjuvants Poly (I:C) and Montanide ISA 720

“…Particularly, broad and balanced responses would be optimal for a vaccine against malaria, although it is known that strong antibody responses against specific antigens play a crucial role. For this reason, Poly (I:C) is an attractive adjuvant choice for malaria vaccine approaches, as it can induce high and long-lasting antibody titers against P. vivax antigens ( 7 ), as well as partial protection in immunized mice ( 6 , 8 , 9 , 14 ).…”

“…The percent of cytokine-producing cells was calculated after subtraction of the percent of cytokine-producing cells in the non-pulsed wells. CD4 + and CD8 + T cells were gated from CD3 + T lymphocyte population, as described elsewhere ( 14 ). Results were analyzed using the FlowJo program (Tree Star, Ashland, OR).…”

Evaluation of two sexual-stage antigens as bivalent transmission-blocking vaccines in rodent malaria

“…Subsequently, the mice were immunized by two boosters at 2-week intervals with 25 μg of Pbg37, 25 μg of PSOP25, mixed (25 μg Pbg37+25 μg PSOP25), or 25 μg Pbg37-PSOP25 chimeric recombinant proteins, emulsified with incomplete Freund’s adjuvant. For antisera, blood was collected 10 days after the third immunization and allowed to clot at room temperature [ 23 , 28 ]. Immunization with the recombinant Trx-His was used as a control.…”

Plasmodium vivax vaccine: What is the best way to go?

“…( 250 ) analysed the immunogenicity of vaccine formulations composed of yPvCSP-All FL (PEV candidate) and PvAMA-1 (BV candidate), alone or in combination, with Poly (I:C) as an adjuvant in BALB/c and C57BL/6 mice. The BALB/c antibody response was relatively low against PvCSP, while PvAMA-1 and the mixed vaccine were higher, which could be related to an immunodominance of the epitopes of PvAMA-1 ( 250 ). In contrast, the C57BL/6 antibody response was higher and long-lasting against both immunizations, and no difference was observed in the mixed vaccine ( 250 ).…”