ReportsMalaria

Prime-boost vaccination with chimpanzee adenovirus and modified vaccinia Ankara encoding TRAP provides partial protection against Plasmodium falciparum infection in Kenyan adults

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Science Translational Medicine  06 May 2015:
Vol. 7, Issue 286, pp. 286re5
DOI: 10.1126/scitranslmed.aaa2373

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Setting a TRAP for the malaria parasite

Previous studies have shown that T cells induced by vaccines can clear liver-stage malaria parasites, but these vaccines have not been effective in field trials. In a new study, Bejon et al. randomly allocated 121 healthy adult male volunteers to receive either a T cell–inducing vaccine or rabies vaccine as a control. They gave antimalarials to clear malaria parasites from the subjects’ blood and then did frequent blood tests to identify new infections with the malaria parasite Plasmodium falciparum. They found that the volunteers receiving the T cell vaccine had a 67% reduction in the risk of malaria infection during 8 weeks of follow-up.

Abstract

Protective immunity to the liver stage of the malaria parasite can be conferred by vaccine-induced T cells, but no subunit vaccination approach based on cellular immunity has shown efficacy in field studies. We randomly allocated 121 healthy adult male volunteers in Kilifi, Kenya, to vaccination with the recombinant viral vectors chimpanzee adenovirus 63 (ChAd63) and modified vaccinia Ankara (MVA), both encoding the malaria peptide sequence ME-TRAP (the multiple epitope string and thrombospondin-related adhesion protein), or to vaccination with rabies vaccine as a control. We gave antimalarials to clear parasitemia and conducted PCR (polymerase chain reaction) analysis on blood samples three times a week to identify infection with the malaria parasite Plasmodium falciparum. On Cox regression, vaccination reduced the risk of infection by 67% [95% confidence interval (CI), 33 to 83%; P = 0.002] during 8 weeks of monitoring. T cell responses to TRAP peptides 21 to 30 were significantly associated with protection (hazard ratio, 0.24; 95% CI, 0.08 to 0.75; P = 0.016).

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