Broadly neutralizing HIV antibodies (bNAbs) can recognize carbohydrate-dependent epitopes on gp120. In contrast to previously characterized glycan-dependent bNAbs that recognize high-mannose N -glycans, PGT121 binds complex-type N -glycans in glycan microarrays. We isolated the B-cell clone encoding PGT121, which segregates into PGT121-like and 10-1074–like groups distinguished by sequence, binding affinity, carbohydrate recognition, and neutralizing activity. Group 10-1074 exhibits remarkable potency and breadth but no detectable binding to protein-free glycans. Crystal structures of unliganded PGT121, 10-1074, and their likely germ-line precursor reveal that differential carbohydrate recognition maps to a cleft between complementarity determining region (CDR)H2 and CDRH3. This cleft was occupied by a complex-type N -glycan in a “liganded” PGT121 structure. Swapping glycan contact residues between PGT121 and 10-1074 confirmed their importance for neutralization. Although PGT121 binds complex-type N -glycans, PGT121 recognized high-mannose-only HIV envelopes in isolation and on virions. As HIV envelopes exhibit varying proportions of high-mannose- and complex-type N -glycans, these results suggest promiscuous carbohydrate interactions, an advantageous adaptation ensuring neutralization of all viruses within a given strain.

Janssen Vaccines & Prevention BV, National Institutes of Health, Ragon Institute of MGH, MIT and Harvard, Henry M Jackson Foundation for the Advancement of Military Medicine, US Department of Defense, and International AIDS Vaccine Initiative.

Broadly reactive neutralizing antibodies are the focus of human immunodeficiency virus (HIV) type 1 vaccine design. However, only little is known about their role in acquired immunodeficiency syndrome (AIDS) pathogenesis and the factors associated with their development. Here we used a multisubtype panel of 23 HIV-1 variants to determine the prevalence of cross-reactive neutralizing activity in serum samples obtained approximately 35 months after seroconversion from 82 HIV-1 subtype B-infected participants from the Amsterdam Cohort Studies on HIV Infection and AIDS. Of these patients, 33%, 48%, and 20%, respectively, had strong, moderate, or absent cross-reactive neutralizing activity in serum. Viral RNA load at set point and AIDS-free survival were similar for the 3 patient groups. However, higher cross-reactive neutralizing activity was significantly associated with lower CD4(+) T cell counts before and soon after infection. Our findings underscore the importance of vaccine-elicited immunity in protecting from infection. The association between CD4(+) T cell counts and neutralizing humoral immunity may provide new clues as to how to achieve this goal.

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Overall, we here demonstrate a relatively high prevalence of cross-reactive neutralizing serum activity in HIV-1-infected patients, which increased with duration of infection. These data may imply that immunogenicity of the native envelope spike of HIV-1 for eliciting cross-reactive humoral immune responses may be better than previously anticipated.

By comparing HIV-1 variants from people who became infected at the beginning of the epidemic and from people who have recently contracted the virus, we observed an enhanced resistance of the virus to antibody neutralization over time, accompanied by an increase in the length of the variable loops and in the number of potential N-linked glycosylation sites on the HIV-1 envelope gp120 subunit. The enhanced neutralization resistance of HIV-1 in contemporary seroconverters coincided with the poorer elicitation of neutralizing antibody responses, which may have implications for vaccine design.

The broadly neutralizing HIV monoclonal antibodies (bnMAbs) PG9, PG16, PGT151, and PGT152 have been shown earlier to occasionally display an unusual virus neutralization profile with a non-sigmoidal slope and a plateau at <100% neutralization. In the current study, we were interested in determining the extent of non-sigmoidal slopes and plateaus at <100% for HIV bnMAbs more generally. Using both a 278 panel of pseudoviruses in a CD4 T-cell (U87.CCR5.CXCR4) assay and a panel of 117 viruses in the TZM-bl assay, we found that bnMAbs targeting many neutralizing epitopes of the spike had neutralization profiles for at least one virus that plateaued at <90%. Across both panels the bnMAbs targeting the V2 apex of Env and gp41 were most likely to show neutralization curves that plateaued <100%. Conversely, bnMAbs targeting the high-mannose patch epitopes were less likely to show such behavior. Two CD4 binding site (CD4bs) Abs also showed this behavior relatively infrequently. The phenomenon of incomplete neutralization was also observed in a large peripheral blood mononuclear cells (PBMC)-grown molecular virus clone panel derived from patient viral swarms. In addition, five bnMAbs were compared against an 18-virus panel of molecular clones produced in 293T cells and PBMCs and assayed in TZM-bl cells. Examples of plateaus <90% were seen with both types of virus production with no consistent patterns observed. In conclusion, incomplete neutralization and non-sigmoidal neutralization curves are possible for all HIV bnMAbs against a wide range of viruses produced and assayed in both cell lines and primary cells with implications for the use of antibodies in therapy and as tools for vaccine design.

We previously established that at 3 years postseroconversion, ϳ30% of HIV-infected individuals have cross-reactive neutralizing activity (CrNA) in their sera. Here we studied the kinetics with which CrNA develops and how these relate to the development of autologous neutralizing activity as well as viral escape and diversification. For this purpose, sera from five individuals with CrNA and one elite neutralizer that were obtained at three monthly intervals in the first year after seroconversion and at multiple intervals over the disease course were tested for neutralizing activity against an established multiclade panel of six viruses. The same serum samples, as well as sera from three individuals who lacked CrNA, were tested for their neutralizing activities against autologous clonal HIV-1 variants from multiple time points covering the disease course from seroconversion onward. The elite neutralizer already had CrNA at 9.8 months postseroconversion, in contrast with the findings for the other five patients, in whom CrNA was first detected at 20 to 35 months postseroconversion and peaked around 35 months postseroconversion. In all patients, CrNA coincided with neutralizing activity against autologous viruses that were isolated <12 months postseroconversion, while viruses from later time points had already escaped autologous neutralizing activity. Also, the peak in gp160 sequence diversity coincided with the peak of CrNA titers. Individuals who lacked CrNA had lower peak autologous neutralizing titers, viral escape, and sequence diversity than individuals with CrNA. A better understanding of the underlying factors that determine the presence of CrNA or even an elite neutralizer phenotype may aid in the design of an HIV-1 vaccine.