Immunogenicity and Structure of a Stabilized HIV -1 clade C Env from a Pediatric Elite neutralizer in Complex with an Autologous bnAb

Introduction: The envelope (Env) glycoproteins derived from circulating viruses in elite[ndash]neutralizers (ENs), who naturally develop potent broadly neutralizing antibody (bnAb) responses, serve as a potential template for HIV - vaccine design. Here, we investigated the immunogenicity and structure of a clade C HIV -1 Env trimer (330) derived from the pediatric elite -neutralizer AIIMS_330. Methods: The 330 Env was engineered as SOSIP.664, NFL.664, and multivalent ferritin -nanoparticle (NP) immunogens. Biophysical and antigenic properties were assessed using HIV -1 trimer-specific bnAbs and non-neutralizing antibodies. Immunogenicity was evaluated in rabbits immunized with Addavax-formulated SOSIP.664, NFL.664, or ferritin NP immunogens (n = 4), with an adjuvant only placebo group (n = 2). Structural characterization was performed by cryo[ndash]electron[ndash]microscopy (cryo -EM) using the autologous Env 330 SOSIP.664 trimer in complex with the bnAb 44m. Results: The 330 Env trimers exhibited native - like antigenic properties, high thermostability, strong binding to trimer - specific bnAbs, and limited reactivity with non[ndash]neutralizing antibodies. Immunization of rabbits elicited strong autologous neutralizing antibody responses together with modest heterologous Tier -1 neutralization. Autologous neutralizing responses were significantly higher for ferritin -NP (P = 0.019) and SOSIP.664 (P = 0.048) than for NFL.664, with no significant difference between ferritin -NP and SOSIP.664 (P = 0.681). A 5.1 [A] cryo -EM reconstruction of the autologous Env 330 SOSIP.664 -44m complex revealed native -like presentation of the N332 -V3 supersite. The structural analysis further suggested the interacting Env contacts E293, R32, K337, and K446, along with glycans N332, N326, N442, and N448 with the bnAb -44m. We identified R327 of the conserved GDIR -motif and the N332 glycan, within the V3 -loop, as neutralizing determinants on the 330 Env, with a fold reduction of 116, on testing the mutant 330 viruses with autologous bnAb 44m. Discussion: Pediatric elite-neutralizer AIIMS_330 derived Env trimers represent structurally and antigenically well characterized clade C immunogens with ability to elicit strong autologous neutralizing antibodies, with modest heterologous Tier-1 neutralization. Together, these findings advance our understanding of clade C Env antigenic variability. Further, the structural and immunological insights support the potential utility of AIIMS_330 derived Env as an antigenic probe and may inform future rational design of Clade C HIV-1 vaccines and structure-guided strategies for eliciting neutralizing antibodies.