Structural and biophysical correlation of anti-NANP antibodies with in vivo protection against P. falciparum

Abstract

The most advanced P. falciparum circumsporozoite protein-based malaria vaccine, RTS,S/AS01 (RTS,S), confers partial protection but with antibody titers that wane relatively rapidly, highlighting the need to elicit more potent and durable antibody responses. Here, we elucidate crystal structures, binding affinities and kinetics, and in vivo protection of eight anti-NANP antibodies derived from an RTS,S phase 2a trial and encoded by three different heavy-chain germline genes. The structures reinforce the importance of homotypic Fab-Fab interactions in protective antibodies and the overwhelmingly dominant preference for a germline-encoded aromatic residue for recognition of the NANP motif. In this study, antibody apparent affinity correlates best with protection in an in vivo mouse model, with the more potent antibodies also recognizing epitopes with repeating secondary structural motifs of type I β- and Asn pseudo 310 turns; such insights can be incorporated into design of more effective immunogens and antibodies for passive immunization.

The P. falciparum CSP repeat region contains three distinct epitopes required for protection by antibodies in vivo

“…While CIS43, L9, and 317 preferentially bind JR, MR and CR epitopes, respectively, they do promiscuously bind all three epitopes in the repeat region ( S1 Table ). This extensive cross-reactivity has raised questions regarding the extent to which the in vivo protection mediated by these mAbs is strictly due to recognition of their preferred repeat epitopes or if it is influenced by binding to their non-preferred repeat epitopes [ 10 , 11 ].…”

Structural basis of Plasmodium vivax inhibition by antibodies binding to the circumsporozoite protein repeats

“…Our structural studies reveal how mAbs 2F2 and 2E10.E9 lock PvCSP repeat peptides in a predominant coiled conformation, with antibody germline-encoded aromatic residues contributing significantly to the antigen contacts. Moreover, we describe how mAb 2E10.E9 engages in head-to-head homotypic interactions when targeting PvCSP, in a similar manner as previously-described human mAbs against PfCSP (Imkeller et al, 2018;Oyen et al, 2018;Pholcharee et al, 2021) and a murine mAb against PbCSP (Kucharska et al, 2020).…”

“…The central region of CSP is immunodominant and antibodies targeting the repeats can inhibit sporozoite infection (Imkeller et al, 2018;Kisalu et al, 2018Kisalu et al, , 2018Mishra et al, 2012;Murugan et al, 2020;Oyen et al, 2017Oyen et al, , 2020Pholcharee et al, 2020Pholcharee et al, , 2021Potocnjak et al, 1980;Tan et al, 2018;Triller et al, 2017;Wang et al, 2020). The PfCSP central repeat is a major component of the most advanced malaria vaccine to date, RTS,S/AS01 (Adepoju, 2019;Draper et al, 2018), and PvCSP or PvCSP-derived peptides are present in various clinical vaccine candidates against Pv (Mueller et al, 2009(Mueller et al, , 2015.…”

RTS,S: the first malaria vaccine

“…Considerable advances have been achieved regarding the structure and fine specificity of anti-CSP protective antibodies. Recent biophysical studies have characterized the binding properties of protective antibodies, and crystallography studies have defined the precise conformation of the CSP epitopes recognized by these antibodies ( 13 ). Importantly, studies with protective human monoclonal antibodies obtained from individuals immunized with sporozoites have identified unique antigenic moieties within the repeat domain of the CSP, which are recognized by protective antibodies but are not included in the RTS,S vaccine ( 14 – 16 ).…”