Recombinant vaccinia viruses for the characterization of Plasmodium falciparum-specific cytotoxic T lymphocytes: recognition of processed antigen despite limited re-stimulation efficacy.

Cytotoxic T lymphocytes (CTL) have been implicated in immunity to Plasmodium falciparum infection and disease. We have previously described the use of peptides to define malaria-specific CTL epitopes. To determine whether these peptide epitopes are processed intracellularly from the whole antigen we have developed recombinant vaccinia viruses (rVV) expressing three malaria antigens: thrombospondin-related adhesive protein (TRAP), Pfs16 and the C-terminal half of liver-stage antigen (LSA)-1. Target cells infected with recombinant viruses were lysed by malaria-specific CTL from semi-immune African donors. We also tested the ability of cells infected with these recombinant vaccinia viruses to re-stimulate malaria-specific CTL in peripheral blood lymphocytes from malaria immune adults. Two other pox virus recombinants, NYVAC, an attenuated vaccinia virus, and ALVAC, a canarypox virus, both expressing malaria antigens were also evaluated for their ability to stimulate malaria-specific CTL in contrast to peptide, none of these viruses successfully re-stimulated CTL from the peripheral blood lymphocytes of semi-immune donors. The ability of human CTL from naturally exposed individuals to recognize processed antigen supports the relevance of these cells in protective immunity to malaria.