Breadth Of Human Monoclonal Antibodies Isolated From Rts, S/As01 Vaccinees Binding To Plasmodium Falciparum Circumsporozoite Protein Antigens

Recently, the structural basis of epitope recognition by vaccine-elicited human monoclonal antibodies (mAbs) specific for the Plasmodium falciparum (Pf) circumsporozoite protein (CSP) repeat region (containing NANP repeats interspersed with NVDP repeats) and the preceding N-terminal junction was detailed. Here we examined the interactions of mAbs isolated from RTS,S/AS01 (RTS,S) vaccinees with CSP antigens using Biolayer Interferometry and Surface Plasmon Resonance. Optimal epitope recognition of mAbs was examined for the NANP repeats, NANP and NVDP residues containing heterologous repeats, and the N-terminal junction peptide (N-JP) dual specificity, which was reported previously for a potent protective antibody against malaria. Here we show that mAbs that avidly (10-50 nM apparent Kd [AppKd]) bound to 1-1.5 NANP repeat containing peptide (NPNA2) also bound to all the other repeat peptides tested. In contrast, mAbs that bound weakly (AppKd ≥ 1μM) to NPNA2, required two NANP repeats (NPNA3) for avid binding. For 3 out of the 4 mAbs tested, the heterologous repeat peptide binding was similar to that of homologous NANP repeat peptide NPNA3, if NVDP residues were upstream of the NANP residues, but was drastically decreased (>100 fold higher AppKd) when the order was reversed. Remarkably, although the N-JP was not included in the RTS,S vaccine, the mAbs tested recognized this peptide (1-150 nM apparent Kd ). These data are partly consistent with the ability of previously reported RTS,S vaccine-induced mAbs to recognize NVDP repeat-containing epitopes. Most importantly, our results reveal the additional specificity of some of the RTS,S-elicited mAbs to the N-JP that was previously observed for the potent protective mAbs isolated from attenuated Pf sporozoite vaccinees. Selection of CSP-specific mAbs optimal in epitope targeting and affinity will advance preventative and therapeutic antibody development and immunogen design.