Multi-functional antibodies are induced by the RTS,S malaria vaccine and associated with protection in a phase I/IIa trial

Abstract

BackgroundRTS,S is the leading malaria vaccine candidate, but only confers partial efficacy against malaria in children. RTS,S is based on the major Plasmodium falciparum sporozoite surface antigen, circumsporozoite protein (CSP). The induction of anti-CSP antibodies is important for protection, however, it is unclear how protective antibodies function. MethodsWe quantified the induction of functional anti-CSP antibody responses in healthy malaria-naive adults (N=45) vaccinated with RTS,S/AS01. This included the ability to mediate effector functions via the fragment crystallizable (Fc) region, such as interacting with human complement proteins and Fc{gamma}-receptors (Fc{gamma}Rs) that are expressed on immune cells, which promote various immunological functions. ResultsOur major findings were i) RTS,S-induced antibodies mediate Fc-dependent effector functions, ii) functional antibodies were generally highest after the second vaccine dose; iii) functional antibodies targeted multiple regions of CSP, iv) participants with higher levels of functional antibodies had a reduced probability of developing parasitemia following homologous challenge (p<0.05); v) non-protected subjects had higher levels of anti-CSP IgM. ConclusionsOur data suggests a role for Fc-dependent antibody effector functions in RTS,S-induced immunity. Enhancing the induction of these functional activities may be a strategy to improve the protective efficacy of RTS,S or other malaria vaccines.