Multifunctional IgG/IgM antibodies and cellular cytotoxicity are elicited by the full-length MSP1 SumayaVac-1 malaria vaccine

Radical control of malaria likely requires a vaccine that targets both the asymptomatic liver stages and the disease-causing blood stages of the human malaria parasite Plasmodium falciparum. While substantial progress has been made towards liver stage vaccines, the development of a blood stage vaccine is lagging behind. We have recently conducted a first-in-human clinical trial to evaluate the safety and immunogenicity of the recombinant, full-length merozoite surface protein 1 (MSP1(FL)) formulated with GLA-SE as adjuvant. Here, we show that the vaccine, termed SumayaVac-1, elicited both a humoral and cellular immune response as well as a recall T cell memory. The induced IgG and IgM antibodies were able to stimulate various Fc-mediated effector mechanisms associated with protection against malaria, including phagocytosis, release of reactive oxygen species, production of IFN-& gamma; as well as complement activation and fixation. The multifunctional activity of the humoral immune response remained for at least 6 months after vaccination and was comparable to that of naturally acquired anti-MSP1 antibodies from semi-immune adults from Kenya. We further present evidence of SumayaVac-1 eliciting a recallable cellular cytotoxicity by IFN-& gamma; producing CD8+ T cells. Our study revitalizes MSP1(FL) as a relevant blood stage vaccine candidate and warrants further evaluation of SumayaVac-1 in a phase II efficacy trial.

Automated summary

Effective control of malaria requires a vaccine that targets both the liver stages and blood stages of the parasite Plasmodium falciparum. While progress has been made in liver stage vaccines, development of a blood stage vaccine is lagging. A new vaccine called SumayaVac-1 has been shown to elicit a strong immune response, including antibodies and T cell memory, and demonstrate multifunctional activity against malaria. Further evaluation in efficacy trials is warranted.