Evolution of protective human antibodies against Plasmodium falciparum circumsporozoite protein repeat motifs

Abstract

Circumsporozoite protein of the human malaria parasite Plasmodium falciparum (PfCSP) is the main target of antibodies that prevent the infection and disease. Protective antibodies recognize the central PfCSP domain, but our understanding of how parasite inhibition is associated with recognition of this domain and with the evolution of potent antibodies remains scattered. Here, we characterized the epitope specificity of 200 human monoclonal PfCSP antibodies. We show that the majority of PfCSP antibodies bind to NANP and NANP-like motifs with different preferences and define the molecular basis for recognition. Epitope cross-reactivity evolved with increasing antibody affinity around a conserved (N/D)P-NANP-N(V/A) core. High affinity to this motif, but not binding to NANP-like motifs, was associated with parasite inhibition and protection. Thus, NANP drives the development of potent PfCSP antibodies independently of their cross-reactivity profile, a finding with direct implications for the design of a second-generation PfCSP-based malaria vaccine. KEYWORDS Plasmodium falciparum, malaria vaccine, circumsporozoite protein, human antibodies, crystal structures, clonal selection, affinity maturation HIGHLIGHTS • The majority of human PfCSP antibodies recognize multiple epitopes • NANP affinity maturation drives the evolution of cross-reactive PfCSP antibodies • Preferential PfCSP antibody binding to a conserved core motif • High affinity not epitope specificity is associated with PfCSP antibody potency

Structural ordering of thePlasmodium bergheicircumsporozoite protein repeats by inhibitory antibody 3D11

“…Our data suggest that somatic mutations of residues that partake in Fab-Fab contacts enhance homotypic interactions and indirectly improve the binding affinity of the mAb to PbCSP. In this aspect, mAb 3D11 binding to PbCSP resembles binding of some neutralizing human mAbs to PfCSP (37, 40, 41). Taken together, these findings indicate that homotypic interactions are a feature by which the mammalian immune system can robustly engage repetitive Plasmodium antigens with high affinity.…”

“…Biophysical studies of the PfCSP central NANP repeat have shown that this region possesses low secondary structure propensities (45, 47–49), and AFM studies on live Pf sporozoites suggest a range of conformations for PfCSP (50, 51). Recent studies have uncovered that some of the most potent antibodies at inhibiting sporozoites are crossreactive with the PfCSP N-junction region that harbors KQPA, NPDP and NVDP motifs interspersed with NANP motifs (39, 40, 43). Our MD simulations of different sub-regions of the PfCSP central repeat including the N-junction provided detailed descriptions of their conformational ensemble and revealed that all sequences possess similar low structural propensity.…”

“…Binding of the PfCSP repeat by inhibitory antibodies has been shown to induce various conformations in this intrinsically disordered region (37, 39, 40, 42–44, 59, 60). Here, we show that the PbCSP repeat adopts an extended and bent conformation when recognized by inhibitory mAb 3D11.…”

“…Our structural and biophysical data demonstrated that mAb 3D11 is cross-reactive and binds the different repeat motifs of PbCSP in nearly identical conformations. Such cross-reactivity is also exhibited by inhibitory human antibodies encoded by a variety of Ig-gene combinations when binding repeat motifs of subtle differences in PfCSP (39, 40, 43, 44, 62). Moreover, it was previously reported that human anti-PfCSP antibody affinity is often directly associated with epitope cross-reactivity (40).…”

“…Such cross-reactivity is also exhibited by inhibitory human antibodies encoded by a variety of Ig-gene combinations when binding repeat motifs of subtle differences in PfCSP (39, 40, 43, 44, 62). Moreover, it was previously reported that human anti-PfCSP antibody affinity is often directly associated with epitope cross-reactivity (40). Given the high inhibitory potency of mAb 3D11, our findings suggest that favorable selection of cross-reactive clones during B cell maturation may have evolved as a common mechanism of the immune response in mammals against Plasmodium CSP.…”