INDUCTION OF PROTECTIVE CTL RESPONSES AGAINST THE PLASMODIUM-YOELII CIRCUMSPOROZOITE PROTEIN BY IMMUNIZATION WITH PEPTIDES

To determine the optimum combination, concentration, and formulation o f synthetic peptides and adjuvants to induce protective CTL responses against the Plasmodium yoelii circumsporozoite protein (PyCSP), BALB/c mice were immunized with linear and multiple antigen peptides (MAP) i ncluding PyCSP CTL and Th epitopes in Montanide's ISA51, Lipofectin, a nd Lipofectamine, An H-2K(d)-restricted PyCSP CTL epitope, SYVPSAEQI ( amino acids (aa) 280-288), recognized by protective CTL clones, was in cluded in the following peptides: a 9-aa linear peptide (SYVPSAEQI; Py CSP9), a 20-aa linear peptide (aa 280-299; SYVPSAEQILEFVKQISSL; PyCSP2 0), a MAP containing four blanches of PyCSP20 (MAP(280-299)), and a li near peptide and a MAP(MAP(280-299)p2p30) in which PyCSP20 was colinea rly synthesized with two universal Th epitopes from tetanus toxin (p2p 30). A MAP containing the PyCSP Th epitope (aa 57-70; KIYNRNIVNRLLGD) was included in some experiments. The highest specific lytic activity against peptide-pulsed target cells was obtained with splenocytes from mite immunized with three doses at 3-wk intervals of MAP(280-299)p2p3 0 in Lipofectin or Lipofectamine. forty percent of the mice immunized with MAP(280-299)p2p30 and Lipofectin were protected against sporozoit e challenge, Immunization with CTL and Th epitopes co-linearly synthes ized in a MAP induced significantly better CTL than did immunization w ith the same sequence as a linear peptide, or immunization with a mixt ure of two individual MAPs, one with the CTL epitope and the second wi th the Th epitope.