Humoral immunogenicity of ChAd63_MVA ME-TRAP vaccination in African infants and children

Abstract

Background The only malaria vaccine to have been tested in Phase III clinical vaccine trials [1] induces protection which has been associated with high titres of antibodies against sporozoites. Efficacy against clinical malaria in infants of 5-17 months and 6-12 weeks was 55.8% and 31.3% respectively. A successful malaria vaccine will likely need to induce both cellular and humoral immunity in order to achieve a deployable level of efficacy in the target age groups. Prime-boost immunisation with viral vectors ChAd63 and MVA, both encoding ME-TRAP, has been shown to induce high T cell responses and modest antibody responses to the pre-erythrocytic malaria antigen TRAP. A Phase II study with this vaccine regime in malaria-naive adults showed significant efficacy, which correlated with frequency of monofunctional CD8+ T cells secreting IFNg. TRAP antibody titres were modest and did not correlate with protection [2]. In contrast to this, high titres of vaccine-induced anti-TRAP antibodies are measured in infants in malaria-endemic settings.