Analysis of monoclonal antibodies against the malaria invasion complex protein RIPR reveals the structural basis for synergistic antibody protection.
Williams BG., Barrett JR., Scott JB., Rigby CA., Cagiada M., Quinkert D., McHugh K., Huhn A., Burnap SA., Gourjault C., Byrne F., Raghavan SSR., Rodrigues A., Bergamaschi L., Balzarotti B., Watson S., Miller N., King LDW., Donnellan FR., Gladstone CA., Paterson J., Scalabrino S., Silk SE., Salkeld J., Minassian AM., Skinner K., Struwe WB., Deane CM., Reece ST., Ward AB., Draper SJ.
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 (RIPREGF (6-8)), but not RIPREGF (9-10) or the C-terminal domain (RIPRCTD), synergized to constrain the RIPR-tail conformation. The same antibodies dissociated PTRAMP-CSS from RIPR, thereby enabling anti-RIPREGF (9-10)-CTD mAbs or anti-CSS single-domain Abs to bind and potentiate anti-RIPREGF (6-8) IgG. Addition of these mAbs to IgG from humans immunized with the R78C (RIPREGF (7-8)-CyRPA) candidate vaccine enhanced malaria growth inhibition. These data provide a framework to guide next-generation blood-stage malaria vaccine design.