Autologous IgG antibodies block outgrowth of a substantial but variable fraction of viruses in the latent reservoir for HIV-1

In untreated HIV-1 infection, rapid viral evolution allows escape from immune responses. Viral replication can be blocked by antiretroviral therapy. However, HIV-1 persists in a latent reservoir in resting CD4+ T cells, and rebound viremia occurs following treatment interruption. The reservoir, which is maintained in part by clonal expansion, can be measured using quantitative viral outgrowth assays (QVOAs) in which latency is reversed with T cell activation to allow viral outgrowth. Recent studies have shown that viruses detected in QVOAs prior to treatment interruption often differ from rebound viruses. We hypothesized that autologous neutralizing antibodies directed at the HIV-1 envelope (Env) protein might block outgrowth of some reservoir viruses. We modified the QVOA to reflect pressure from low concentrations of autologous antibodies and showed that outgrowth of a substantial but variable fraction of reservoir viruses is blocked by autologous contemporaneous immunoglobulin G (IgG). A reduction in outgrowth of >80% was seen in 6 of 15 individuals. This effect was due to direct neutralization. We established a phylogenetic relationship between rebound viruses and viruses growing out in vitro in the presence of autologous antibodies. Some large infected cell clones detected by QVOA carried neutralization-sensitive viruses, providing a cogent explanation for differences between rebound virus and viruses detected in standard QVOAs. Measurement of the frequency of reservoir viruses capable of outgrowth in the presence of autologous IgG might allow more accurate prediction of time to viral rebound. Ultimately, therapeutic immunization targeting the subset of variants resistant to autologous IgG might contribute to a functional cure.

Competitive exclusion by autologous antibodies can prevent broad HIV-1 antibodies from arising

The past decade has seen the discovery of numerous broad and potent monoclonal antibodies against HIV type 1 (HIV-1). Eliciting these antibodies via vaccination appears to be remarkably difficult, not least because they arise late in infection and are highly mutated relative to germline antibody sequences. Here, using a computational model, we show that broad antibodies could in fact emerge earlier and be less mutated, but that they may be prevented from doing so as a result of competitive exclusion by the autologous antibody response. We further find that this competitive exclusion is weaker in infections founded by multiple distinct strains, with broadly neutralizing antibodies emerging earlier than in infections founded by a single strain. Our computational model simulates coevolving multitype virus and antibody populations. Broadly neutralizing antibodies may therefore be easier for the adaptive immune system to generate than previously thought. If less mutated broad antibodies exist, it may be possible to elicit them with a vaccine containing a mixture of diverse virus strains.

Characterization of the autologous antibodies that opsonize erythrocytes with clustered integral membrane proteins

In earlier studies we presented evidence that the clustering of the integral membrane protein, band 3, can serve as a signal for immune recognition and clearance of senescent or abnormal erythrocytes from circulation. In this study, we have exploited the capacity of 1 mmol/L Zn+2 to mildly and reversibly cluster band 3 in situ to characterize the nature of the autologous antibodies specific for the clustered state. We report that the autologous IgG elute almost exclusively in a high molecular weight complex with other proteins when C12E8 detergent extracts of Zn clustered membranes are chromatographed on Sepharose CL- 6B. The complex was also seen to contain complement component C3, hemoglobin, and a cross-linked oligomer of band 3. Autologous IgG and complement were virtually absent from all other fractions. When the band 3 clusters were disaggregated by removal of the Zn+2, the autologous IgG eluted from the erythrocyte surface. Collection of this IgG and use of the antibody in immunoblots of erythrocyte membranes showed that the band 3 monomer, dimer, and oligomers were the major antigenic species. Except for a minor unidentified band at approximately 78,000 d, no other proteins were significantly stained. Curiously, band 3 showed an uneven staining pattern, with oligomers and the leading edge of the monomers appearing more intensely than expected from their abundances in the Coomassie blue-stained gels. Typing of the same autologous IgG with monoclonal antibodies specific for the different subclasses of IgG showed the presence of only subtypes 2 and 3. Taken together, these data suggest that a specific population of autologous IgG recognizes sites of integral membrane protein clustering (a common lesion in senescent and abnormal red blood cells) and that the antigen within these clusters involves an aggregated state of band 3.