Induction of humoral immune response against Plasmodium falciparum sporozoites by immunization with a synthetic peptide mimotope whose sequence was derived from screening a filamentous phage epitope library

The mouse monoclonal antibody 2A10 (immunoglobulin G), which recognizes the (NANP)(n) repeat of Plasmodium falciparum circumsporozoite surface protein, was used to screen a filamentous phage epitope library expressing random amino acid hexamers. The sequences obtained were TNRNPQ, SNRNPQ, NNDNPQ, SNYNPQ, and QNDNPQ (single-letter amino acid designation). These peptides showed 50% homology with the native epitope (PNANPN) and therefore were considered to mimic its structure (mimotopes). Two of these mimotopes (TNRNPQ and NNDNPQ) inhibited the binding of monoclonal antibody 2A10 to the recombinant protein R32LR, which contains the amino acid sequence [(NANP)₁₅NVDP]₂. Immunization of mice and rabbits using the peptide (TNRNPQ)₄ induced a humoral response that recognized R32LR by an enzyme- linked immunosorbent assay and P. falciparum sporozoites by an immunofluorescence assay. These results suggest that phage epitope libraries can be exploited to screen for mimotopes in the design of subunit vaccines against infectious agents.