Multiple Antigen Peptide Vaccines againstPlasmodium falciparumMalaria

Abstract

The multiple antigen peptide (MAP) approach is an effective method to chemically synthesize and deliver multiple T-cell and B-cell epitopes as the constituents of a single immunogen. Here we report on the design, chemical synthesis, and immunogenicity of three Plasmodium falciparum MAP vaccines that incorporated antigenic epitopes from the sporozoite, liver, and blood stages of the life cycle. Antibody and cellular responses were determined in three inbred (C57BL/6, BALB/c, and A/J) strains, one congenic (HLA-A2 on the C57BL/6 background) strain, and one outbred strain (CD1) of mice. All three MAPs were immunogenic and induced both antibody and cellular responses, albeit in a somewhat genetically restricted manner. Antibodies against MAP-1, MAP-2, and MAP-3 had an antiparasite effect that was also dependent on the mouse major histocompatibility complex background. Anti-MAP-1 (CSP-based) antibodies blocked the invasion of HepG2 liver cells by P. falciparum sporozoites (highest, 95.16% in HLA-A2 C57BL/6; lowest, 11.21% in BALB/c). Vaccinations against several deadly infectious agents continue to save millions of lives annually and have improved the quality of life of tens of millions of individuals by significantly preventing or reducing the transmission of several pandemic and locally transmitted infectious diseases. Thus, there are reasons to believe that a successful malaria vaccine would not only significantly reduce malaria mortality and morbidity but also become an important tool in disease control efforts.The quest to develop a malaria vaccine began more than 6 decades ago with successful vaccination against malaria in birds (16). Since then, several decades of research in experimental models have demonstrated that both whole-parasiteand subunit (recombinant and synthetically produced)-based vaccines can induce protective immunity when delivered under optimal conditions. However, after hundreds of millions of dollars in investments and several dozen clinical trials, recombinant-protein-based candidate malaria vaccines have failed to induce the level of protection that would warrant production as licensed vaccines. The most successful recombinant vaccine, RTS,S, has undergone trials and, at its best, induced 53% protection against clinical malaria in a placebo-controlled clinical trial that involved 5-to 17-month-old children in Kenya and Tanzania (3). The limited success of recombinant vaccines has led to a surge in interest to produce and test whole attenuated parasite-based vaccines against malaria, most of which are based on live attenuated Plasmodium falciparum sporozoites (24, 59). Nonetheless, the whole-parasite-based vaccination approach presents unique challenges in terms of safety, residual virulence, and the potential for reversion in virulence, mode of delivery, and difficulties associated with sufficient production for en masse vaccination. Thus, given the limited amount of clinical immunity conferred by the recombinantprotein-based vaccines and the perceived hurdles with the whole-parasite-base...

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