Structural basis for synergistic antibody protection against the essential malaria invasion complex protein RIPR

Abstract

SUMMARY Plasmodium falciparum RH5-interacting protein (RIPR) is central to the essential PTRAMP-CSS-RIPR-CyRPA-RH5 (PCRCR)-complex; a leading target of blood-stage malaria vaccines. However, mechanisms whereby anti-RIPR antibodies inhibit parasite invasion are poorly understood. Here, we characterise 83 human IgG mAbs from RIPR-vaccinated Kymouse platform mice. Single mAbs have minimal neutralising activity, however, high-level synergistic inhibition is observed with pools of mAbs targeting the RIPR-Tail region. Structural characterisation and molecular dynamics simulations of RIPR-Tail show that mAbs targeting EGF-like domains 6-8 (RIPR EGF (6-8) ), but not EGF-like domains 9-10 or the C-terminal domain (RIPR EGF (9-10)-CTD ), synergise to constrain the RIPR-Tail conformation. The same antibodies dissociate PTRAMP-CSS from RIPR, thereby enabling anti-RIPR EGF (9-10)-CTD mAbs or anti-CSS sdAbs to bind and potentiate anti-RIPR EGF (6-8) IgG. Addition of these mAbs to IgG from humans immunised with the R78C (RIPR EGF (7-8) -CyRPA) candidate vaccine enhances malaria growth inhibition. These data provide a framework to guide next-generation blood-stage malaria vaccine design.