Monoclonal IgG plasma antibodies elicited by R21/Matrix-M vaccine provide sterile protection in mice. (A) Binding of mAbs to either WT 3D7 Pf (WT Pf) or transgenic Pb expressing PfCSP (Tg Pb) measured by indirect IFA. (B) Relationship between either IFA or ISI and NANP-binding EC₅₀. (C and D) C57BL/6J mice (n = 6 per group) were injected i.p. with 400 µg of mAb on day −1. The following day, mice were challenged with 5,000 Pb-PfCSP Pb sporozoites administered by s.c. injection at the base of the tail. From 5 days after sporozoite injection, mice were monitored by thin blood film for the development of blood-stage malaria. Parasitemia was calculated daily, and linear regression was used to determine the time mice reached a threshold of 1% parasitemia. Sterile protection was defined as any animal that remained parasite-free until day 9 after sporozoite administration. C and D are replicate experiments. (E) Summary of sterile protection for each mAb (grey bars represent the percent survival for each group over the two experiments).