Messmer, T. | Search bioRxiv

bioRxiv2019

HIV Envelope Trimer-Elicited Autologous Neutralizing Antibodies Bind a Region Overlapping the N332 Glycan Supersite

To date, immunization studies of rabbits with the BG505 SOSIP.664 HIV envelope glycoprotein trimers have revealed the 241/289 glycan hole as the dominant neutralizing antibody epitope. Here, we isolated monoclonal antibodies from a rabbit that did not exhibit glycan hole-dependent autologous serum neutralization. The antibodies did not compete with a previously isolated glycan hole-specific antibody but did compete with N332 glycan supersite broadly neutralizing antibodies. A high resolution cryoEM structure of one of the antibodies in complex with the BG505 SOSIP.664 trimer demonstrated that, while the epitope recognized overlapped with the N332 glycan supersite by contacting the GDIR motif at the base of V3, the primary contacts were located in the variable V1 loop. These data suggest that strain-specific responses to V1 may interfere with broadly neutralizing responses to the N332 glycan supersite and vaccine immunogens may require engineering to minimize these off-target responses or steer them toward a more desirable pathway.

immunology↗

bioRxiv2019

Neutralizing antibody responses to an HIV envelope glycan hole are not easily broadened

Extensive studies with subtype A BG505-derived HIV envelope glycoprotein (Env) SOSIP immunogens have revealed that the dominant autologous neutralizing site in rabbits is located in an exposed region of the heavily glycosylated trimer that lacks potential N-linked glycosylation sites at positions 230, 241, and 289. The Env derived from B41, a subtype B virus, shares a glycan hole centered on positions 230 and 289. BG505 and B41 SOSIP immunogens were combined to test whether immunization in rabbits could induce broader Tier 2 neutralizing responses to the common glycan hole shared between BG505 and B41. Here we isolated autologous neutralizing antibodies (nAbs) that were induced by immunization with B41 SOSIP alone, as well as B41 and BG505 co-immunization, and describe their structure in complex with the B41 SOSIP trimer. Our data suggest that distinct autologous nAb lineages are induced by BG505 and B41 immunogens, even when both immunogens were administered together. In contrast to previously described BG505 glycan hole antibodies, the B41-specific nAbs accommodate the highly conserved N241 glycan (>97% conserved), which is present in B41. Single particle cryo-electron microscopy (cryoEM) studies confirmed that B41 and BG505-specific nAbs bind to overlapping glycan hole epitopes. In an attempt to broaden the reactivity of a B41-specific nAb, mutations in the BG505 glycan hole epitope guided by our high-resolution data only recovered partial binding. Overall, designing prime-boost immunogens to increase the breath of nAb responses directed at glycan holes epitopes remains challenging even when the typically immunodominant glycan holes despite overlap with different Envs.\n\nIMPORTANCEA glycan hole is one of the most dominant autologous neutralizing epitopes targeted on BG505 and B41 SOSIP trimer immunized rabbits. Our high-resolution cryoEM studies of B41 in complex with a B41-specific antibody complex elucidate the molecular basis of this strain-specific glycan hole response. We conclude that eliciting cross-reactive responses to this region would likely require hybrid immunogens that bridge between BG505 and B41.

immunology↗