DEVELOPMENT OF 2 MONOCLONAL-ANTIBODIES AGAINST PLASMODIUM-FALCIPARUM SPOROZOITE SURFACE PROTEIN-2 AND MAPPING OF B-CELL EPITOPES

The Plasmodium yoelii sporozoite surface protein 2 (PySSP2) is the tar get of protective cellular immunity, Cytotoxic T cells specific for th e Plasmodium falciparum analog PfSSP2, also known as thrombospondin-re lated anonymous protein (TRAP), are induced in human volunteers immuni zed with irradiated sporozoites, PfSSP2 is an important candidate anti gen for a multicomponent malaria vaccine, We generated and characteriz ed three monoclonal antibodies (MAbs) specific for PfSSP2/TRAP. The MA bs PfSSP2.1 (immunoglobulin G1 [IgG1]), PfSSP2.2 (IgC2a), and PfSSP2.3 (IgM) were species specific and identified three distinct B-cell epit opes containing sequences DRYI, CHPSDGKC, and TRPHGR, respectively, Pf SSP2.1 partially inhibited P. falciparum liver-stage parasite developm ent in human hepatocyte cultures (42 and 86% in two experiments at 100 mu g/ml). Mice immunized with vaccinia virus expressing full-length P fSSP2 protein produced antibodies to (DRYIPYSP)(3), and humans living in malaria-endemic areas (Indonesia and Kenya), who have lifelong expo sure and partial clinical immunity to malaria, had antibodies to both (DRYIPYSP)(3) and (CHPSDGKCN)(2). Mice immunized with multiple antigen peptides MAP4 (DRYIPYSP)(3)P2P30 and MAP4 (CHPSDGKCN)(3)P2P30 in Tite rMax developed antibodies to sporozoites that partially inhibited spor ozoite invasion of human hepatoma cells (39 to 71% at a serum dilution of 1:50 in three different experiments). The modest inhibitory activi ties of the MAbs and the polyclonal antibodies to PfSSP2/TRAP epitopes do not suggest that a single-component vaccine designed to induce ant ibodies against PfSSP2/TRAP will be protective, Nonetheless, the MAbs directed against PfSSP2, and the peptides recognized by these MAbs, wi ll be essential reagents in the development of PfSSP2/TRAP as a compon ent of a multivalent P. falciparum human malaria vaccine.