Common Tolerance Mechanisms, but Distinct Cross-Reactivities Associated with gp41 and Lipids, Limit Production of HIV-1 Broad Neutralizing Antibodies 2F5 and 4E10

Abstract

Developing an HIV-1 vaccine has been hampered by the inability of immunogens to induce broadly neutralizing antibodies (bnAbs) that protect against infection. Previously, we used knockin (KI) mice expressing a prototypical gp41-specific bnAb, 2F5, to demonstrate that immunological tolerance triggered by self-reactivity of the 2F5 H chain, impedes bnAb induction. Here, we generate KI models expressing H chains from two other HIV-1 Abs: 4E10 (another self-/polyreactive, α-gp41 bnAb) and 48d (an α-CD4 inducible, non-polyreactive Ab), and find a similar developmental blockade consistent with central B-cell deletion in 4E10, but not in 48d VH KI mice. Furthermore, in KI strains expressing the complete 2F5 and 4E10 Abs as BCRs, we find that residual splenic B-cells arrest at distinct developmental stages, yet exhibit uniformly low surface Ig densities, elevated basal activation, profoundly muted responses to BCR ligation, and when captured as hybridoma mAb lines, maintain their dual (gp41/lipid) affinities and capacities to neutralize HIV-1, establishing a key role for anergy in suppressing residual 2F5 or 4E10-expressing B-cells. Importantly, serum IgGs from naïve 2F5 and 4E10 KI strains selectively eliminate gp41 and lipid binding, respectively, suggesting B-cells expressing 2F5 or 4E10 as BCRs exhibit specificity for a distinct spectrum of host antigens, including selective interactions by 2F5 BCR+ B-cells (i.e., and not 4E10 BCR+ B-cells) with residues in self-antigen(s) that mimic its gp41 neutralization epitope.

Redemption of autoantibodies on anergic B cells by variable-region glycosylation and mutation away from self-reactivity

“…Glycosylated BCRs may also be recognized by lectins on follicular dendritic cells or macrophages in the germinal center to deliver a survival advantage (26). A need for some preimmune antibodies to mutate away from self-reactivity provides an alternative explanation for the phenomenon of repertoire shift during the maturation of antibody responses, when certain antibody specificities that ultimately dominate responses to haptens (52)(53)(54)(55)(56)(57) or RhD alloantigens (16,20) or bind conserved neutralizing epitopes of viruses (58)(59)(60)(61)(62) are minimally represented in the primary wave of plasma cells but gradually emerge after repetitive stimulation by foreign antigen. Inherited defects that prevent hypermutation away from self-reactivity by antimicrobial antibodies may explain the surprising prevalence of autoantibodies in human AICDA deficiency, where GCs are formed but hypermutation is crippled (63).…”

“…Inherited defects that prevent hypermutation away from self-reactivity by antimicrobial antibodies may explain the surprising prevalence of autoantibodies in human AICDA deficiency, where GCs are formed but hypermutation is crippled (63). Structural constraints that make it difficult for mutations to remove selfbinding without also losing binding to the eliciting foreign antigen, as has been shown for VH4-34 antibodies against RhD (13) and for the 2F5 broadly neutralizing antibody against HIV (61), may explain the difficulty eliciting high titers of certain broadly neutralizing antibodies against viruses (60)(61)(62).…”

Structure of an HIV-1–neutralizing antibody target, the lipid-bound gp41 envelope membrane proximal region trimer

“…In animal models, many of these vaccine designs have elicited antibodies that recognize epitopes in the MPER (19,22,23). However, none of the induced plasma antibodies strongly neutralize HIV-1 (19,20,23,24), either because the trial vaccines do not present the epitope residues in a native conformation or in the presence of the correct molecular environment, or because of the limitation of induction of MPER antibodies by host tolerance mechanisms (25)(26)(27)(28).…”

Anti-MPER Antibodies with Heterogeneous Neutralization Capacity Are Detectable in Most Untreated HIV Infected Individuals

“…This is the case of the different bnAbs isolated [7,15]. Furthermore, the hydrophobic CDRH3 regions recognize lipids [7,15] and at least 2F5 and 4E10 bnAbs are also cross reactive with human proteins, thus suggesting that tolerance may limit anti-MPER responses [25,26]. All these limitations seem to favor the diversion of humoral immune responses towards other gp41 regions, in particular the external loop, which has been described as an immunodominant nonneutralizing region [27].…”