Prime-Boost Immunization of Rabbits with HIV-1 gp120 Elicits Potent Neutralization Activity against a Primary Viral Isolate

Abstract

Development of a vaccine for HIV-1 requires a detailed understanding of the neutralizing antibody responses that can be experimentally elicited to difficult-to-neutralize primary isolates. Rabbits were immunized with the gp120 subunit of HIV-1 JR-CSF envelope (Env) using a DNA-prime protein-boost regimen. We analyzed five sera that showed potent autologous neutralizing activity (IC50s at ∼103 to 104 serum dilution) against pseudoviruses containing Env from the primary isolate JR-CSF but not from the related isolate JR-FL. Pseudoviruses were created by exchanging each variable and constant domain of JR-CSF gp120 with that of JR-FL or with mutations in putative N-glycosylation sites. The sera contained different neutralizing activities dependent on C3 and V5, C3 and V4, or V4 regions located on the glycan-rich outer domain of gp120. All sera showed enhanced neutralizing activity toward an Env variant that lacked a glycosylation site in V4. The JR-CSF gp120 epitopes recognized by the sera are generally distinct from those of several well characterized mAbs (targeting conserved sites on Env) or other type-specific responses (targeting V1, V2, or V3 variable regions). The activity of one serum requires specific glycans that are also important for 2G12 neutralization and this serum blocked the binding of 2G12 to gp120. Our findings show that different fine specificities can achieve potent neutralization of HIV-1, yet this strong activity does not result in improved breadth.

Holes in the Glycan Shield of the Native HIV Envelope Are a Target of Trimer-Elicited Neutralizing Antibodies

“…Most Env subunit immunizations have yielded non-nAbs or Abs that only neutralize highly susceptible (Tier 1) viruses (Chen et al, 2013; Narayan et al, 2013; Qin et al, 2015; Qin et al, 2014; Schiffner et al, 2013; Seaman et al, 2010; Vaine et al, 2008; Zhang et al, 2015). One system in which strong autologous Tier 2 serum nAb responses have been observed following Env immunization is that of rabbits immunized with B41 and BG505 SOSIP.664 and SOSIP.v4 trimers (de Taeye et al, 2015; Sanders et al, 2013; Sanders et al, 2015).…”

“…Despite these advances in the presentation of native-like HIV trimers and the reproducible induction of greater autologous neutralizing titers, little is understood about the epitopes targeted. In part, this is because the neutralization response to Env immunization in model systems has most commonly been assessed by serology alone (Narayan et al, 2013; Qin et al, 2014; Schiffner et al, 2013; Sundling et al, 2010; Zhang et al, 2015). Attempts to map serum neutralization following BG505 SOSIP.664 immunization have been limited to those epitopes easily dissected with the use of CD4-binding site mutants, peptides to linear epitopes, and alanine-scanning panels (Sanders et al, 2015).…”

Envelope Variants Circulating as Initial Neutralization Breadth Developed in Two HIV-Infected Subjects Stimulate Multiclade Neutralizing Antibodies in Rabbits

“…Thus, a high degree of research effort has been devoted to understanding the development of NAbs in HIV infection (8)(9)(10) in order to inform development of an Env-based vaccine to elicit a broad cross-clade neutralizing response in animal models (7,11). Unfortunately, NAbs elicited by vaccination so far have shown weak to moderate potency and a low degree of neutralization breadth, despite the use of diverse envelopes (Envs) in the vaccines tested (12)(13)(14)(15)(16)(17)(18)(19) and novel approaches to develop re-combinant Env proteins that mimic the native trimeric Env protein (20). In addition, Envs isolated from different human subjects have divergent antigenic and immunogenic properties (11), further complicating the selection criteria for candidate immunogens.…”

Human Immunodeficiency Virus Type 1 Cellular Entry and Exit in the T Lymphocytic and Monocytic Compartments

“…With respect to the production of HIV-1 gp120 V5 region neutralizing antibody during human infection, antibodies directed at the V5 region have not been reported within an HIV-1-infected hemophiliac cohort (Douglas et al, 1997). However, in a recent vaccine study, neutralizing activity against V5 was identified in sera from rabbits that were immunized with the HIV-1 gp120 subunit derived from the JR-CSF envelope (Narayan et al, 2013).…”