Analysis of monoclonal antibodies against the malaria invasion complex protein RIPR reveals the structural basis for synergistic antibody protection

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. We characterized 83 human IgG monoclonal antibodies (mAbs) from RIPR-vaccinated Kymouse platform mice. Single mAbs had minimal neutralizing activity; however, high-level synergistic inhibition was observed with pools of mAbs targeting the RIPR-tail region. Structural characterization and molecular dynamics simulations of RIPR-tail showed that mAbs targeting epidermal growth factor (EGF)-like domains 6–8 (RIPR EGF (6–8) ), but not RIPR EGF (9–10) or the C-terminal domain (RIPR CTD ), synergized to constrain the RIPR-tail conformation. The same antibodies dissociated PTRAMP-CSS from RIPR, thereby enabling anti-RIPR EGF (9–10)-CTD mAbs or anti-CSS single-domain Abs to bind and potentiate anti-RIPR EGF (6–8) IgG. Addition of these mAbs to IgG from humans immunized with the R78C (RIPR EGF (7–8) -CyRPA) candidate vaccine enhanced malaria growth inhibition. These data provide a framework to guide next-generation blood-stage malaria vaccine design.