Protective CD8+ T-cell immunity to human malaria induced by chimpanzee adenovirus-MVA immunisation
Induction of antigen-specific CD8+ T cells offers the prospect of immunization against many infectious diseases, but no subunit vaccine has induced CD8+ T cells that correlate with efficacy in humans. Here we demonstrate that a replication-deficient chimpanzee adenovirus vector followed by a modified vaccinia virus Ankara booster induces exceptionally high fre- quency T-cell responses (median 42400 SFC/106 peripheral blood mononuclear cells) to the liver-stage Plasmodium falciparum malaria antigen ME-TRAP. It induces sterile protective efficacy against heterologous strain sporozoites in three vaccinees (3/14, 21%), and delays time to patency through substantial reduction of liver-stage parasite burden in five more (5/14, 36%), P1⁄40.008 compared with controls. The frequency of monofunctional inter- feron-g-producing CD8+ T cells, but not antibodies, correlates with sterile protection and delay in time to patency (Pcorrected 1⁄4 0.005). Vaccine-induced CD8+ T cells provide protection against human malaria, suggesting that a major limitation of previous vaccination approaches has been the insufficient magnitude of induced T cells.
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