A subdominant CD8(+) cytotoxic T lymphocyte (CTL) epitope from the Plasmodium yoelii circumsporozoite protein induces CTLs that eliminate infected hepatocytes from culture

Previous studies indicated that the Plasmodium yoelii circumsporozoite prot ein (PyCSP) 57-70 region elicits T cells capable of eliminating infected he patocytes in vitro. Herein, we report that the PyCSP58-67 sequence contains an H-2(d) binding motif; which binds purified K-d molecules in vitro with low affinity (3,267 nM) and encodes an H-2(d)-restricted cytotoxic T lympho cyte (CTL) epitope. Immunization of BALB/c mice with three doses of a multi ple antigen peptide (MAP) construct containing four branches of amino acids 57 to 70 linked to a lysine-glycine core [MAP4(PyCSP57-70)] and Lipofectin as the adjuvant induced both T-cell proliferation and a peptide-specific C TL response that was PyCSP59-67 specific, H-2(d) restricted, and CD8(+) T c ell dependent. Immunization with either DNA encoding the PyCSP or irradiate d sporozoites demonstrated that this CTL epitope is subdominant since it is not recognized in the context of whole CSP immunization. The biological re levance of this CTL response was underlined by the demonstration that it co uld mediate genetically restricted, CD8(+)- and nitric-oxide-dependent elim ination of infected hepatocytes in vitro, as well as partial protection of BALB/c mice against sporozoite challenge. These findings indicate that subd ominant epitopes with low major histocompatibility complex affinity can be used to engineer epitope-based vaccines and have implications for the selec tion of epitopes for subunit-based vaccines.