The repeat B cell epitopes of the malaria circumsporozoite (CS) protein have formed the basis of synthetic peptide vaccines aimed at eliciting high levels of humoral immunity to block the invasion of the host hepatocytes by the infectious sporozoite. A synthetic peptide vaccine, containing repeat B cell epitopes (T1 B) combined with a universal T cell epitope (T*) of the P. falciparum CS protein, has been constructed using oxime bond ligation technology. The branched template core of the tri-epitope polyoxime vaccine contains the built-in synthetic lipopeptide adjuvant tripalmitoyl-S-glyceryl cysteine (P3C). A small-scale phase I trial to test the safety and immunogenicity of the (T1BT*)4-P3C polyoxime malaria vaccine has recently been carried out at the University of Geneva. The multicomponent polyoxime malaria vaccine was found to elicit anti-peptide antibody responses in 10/10 volunteers of diverse HLA haplotypes, without requiring the addition of exogenous adjuvant. The current grant application proposes to analyze the T cell and B cell responses of the polyoxime immunized volunteers and to assay the genetic restriction and effector functions of T cell lines and clones derived from these volunteers. These studies will provide the first immunological analysis of the human response to a polyoxime vaccine, as well as the first opportunity to investigate the function of a malaria universal T cell epitope in individuals of defined class II haplotypes. The preliminary serological results also demonstrate that, while anti-peptide antibodies were elicited in all the vaccinees, the magnitude of the antibody response was variable, reaching high antibody titers (greater than 5120) in 5/10 of the volunteers. To optimize humoral immunity, polyoximes containing varying T and B cell ratios and configurations would be tested in combination with different adjuvant formulations acceptable for human use. Immunogneicity would be assayed in inbred strains of mice, as well as HLA class II transgenic mice and in Aotus monkeys. The protective efficacy of polyoxime vaccines designed to elicit high levels of humoral, as well as cellular, immunity would be studied in the P. yoelii rodent malaria model. The analysis of the T and B cell responses of the (T1BT*)4-P3C immunized volunteers, the optimization of polyoxime vaccine formulation and the efficacy studies in the rodent malaria model will provide the experimental basis for the development of highly immunogenic synthetic peptide malaria vaccines as well as the preclinical data to support additional Phase I testing of polyoxime vaccines in human volunteers.
