Immune Tolerance Negatively Regulates B Cells in Knock-In Mice Expressing Broadly Neutralizing HIV Antibody 4E10

Abstract

A major goal of HIV research is to develop vaccines reproducibly eliciting broadly neutralizing antibodies (bNAbs). This has proved to be challenging, however. One suggested explanation for this difficulty is that epitopes seen by bNAbs mimic self, leading to immune tolerance. We generated “knock-in” mice expressing bNAb 4E10, which recognizes the membrane proximal external region of gp41. Unlike b12 knock-in mice, described in the accompanying study, 4E10HL mice were found to undergo profound negative selection of B cells, indicating that 4E10 is, to a physiologically significant extent, autoreactive. Negative selection occurred by various mechanisms including receptor editing, clonal deletion and receptor downregulation. Despite significant deletion, small amounts of IgM and IgG anti-gp41 were found in the sera of 4E10HL mice. On a Rag1−/− background 4E10HL mice had virtually no serum immunoglobulins of any kind. These results are consistent with a model in which B cells with 4E10 specificity are counterselected, raising the question of how 4E10 was generated in the patient from whom it was isolated. This represents the second example of an MPER-directed bNAb that is apparently autoreactive in a physiological setting. The relative conservation in HIV of the 4E10 epitope might reflect the fact that it is under less intense immunological selection as a result of B cell self-tolerance. The safety and desirability of targeting this epitope by a vaccine is discussed in light of the newly-described bNAb 10E8.

Polyreactivity and Autoreactivity among HIV-1 Antibodies

“…The generation of the MPER bNAbs 2F5 and 4E10 is controlled by immunological tolerance (18)(19)(20)(21)46) and our identification of UBE3A as another self-antigen recognized by HIV-1 bNAbs provides a new example of host mimicry by HIV-1. Such mimicry conceals vulnerable neutralization sites by hiding in plain sight: immunological tolerance purges the primary immune response of those lymphocytes most suited for protective immunity.…”

“…Knock-in mice expressing the 4E10 V(D)J rearrangements exhibit impaired B-cell development (21,46). However, even if a higher PI threshold were chosen (e.g., 0.27, or 2.5-fold-stronger overall binding), the frequency of polyreactive bNAbs and nNAbs would not have changed (Fig.…”

“…3 and 4). The final measure of significant poly-and autoreactivity is the generation of V(D)J knock-in mice (19)(20)(21)(46)(47)(48), and additional knock-in strains will be necessary to determine the significance of off-target bNAb reactivities. However, if the 2F5 and 4E10 mice are reasonable guides, we expect that most, if not all, of the poly-and autoreactive bNAbs studied here will be subject to some degree of immunological control.…”

Antibody‐virus co‐evolution in HIV infection: paths for HIV vaccine development

“…Some bnAb types such as gp41 MPER bnAbs (2F5, 4E10, DH511 and 10E8) must have hydrophobic CDR H3s for binding to the virion membrane, and bnAb precursors with these characteristics are either deleted in bone marrow or became anergic in the periphery (98, 105–109). Other bnAb types such as CD4bs antibodies are either not deleted in bone marrow or less so than gp41 antibodies, but rather antibody poly-reactivity or auto-reactivity is acquired later in bnAb B cell lineage maturation (17).…”

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).…”