Summary Antibodies capable of neutralizing HIV-1 often target variable regions 1 and 2 (V1V2) of the HIV-1 envelope, but the mechanism of their elicitation has been unclear. Here we define the developmental pathway by which such antibodies are generated and acquire the requisite molecular characteristics for neutralization. Twelve somatically related neutralizing antibodies (CAP256-VRC26.01-12) were isolated from CAPRISA-donor CAP256; each antibody contained the protruding tyrosine-sulfated, anionic antigen-binding loop (CDR H3) characteristic of this category of antibodies. Their unmutated ancestor emerged between weeks 30–38 post-infection with a 35-residue CDR H3, and neutralized the virus that superinfected this individual 15 weeks after initial infection. Improved neutralization breadth occurred by week 59 with modest affinity maturation, and was preceded by extensive diversification of the virus population. HIV-1 V1V2-directed neutralizing antibodies can thus develop relatively rapidly through initial selection of B cells with a long CDR H3, and limited subsequent somatic hypermutation, an important vaccine insight.

The HIV-1-envelope (Env) trimer is covered by a glycan shield of ~90 N-linked oligosaccharides, which comprises roughly half its mass and is a key component of HIV evasion from humoral immunity. To understand how antibodies can overcome the barriers imposed by the glycan shield, we crystallized fully glycosylated Env trimers from clades A, B and G, visualizing the shield at 3.4-3.7 Å resolution. These structures reveal the HIV-1-glycan shield to comprise a network of interlocking oligosaccharides, substantially ordered by glycan crowding, which encase the protein component of Env and enable HIV-1 to avoid most antibody-mediated neutralization. The revealed features delineate a taxonomy of N-linked glycan-glycan interactions. Crowded and dispersed glycans are differently ordered, conserved, processed and recognized by antibody. The structures, along with glycan-array binding and molecular dynamics, reveal a diversity in oligosaccharide affinity and a requirement for accommodating glycans amongst known broadly neutralizing antibodies that target the glycan-shielded trimer.

SUMMARY Antibodies with ontogenies from VH1-2 or VH1-46-germline genes dominate the broadly neutralizing response against the CD4-binding site (CD4bs) on HIV-1. Here we define with longitudinal sampling from time-of-infection the development of a VH1-46-derived antibody lineage that matured to neutralize 90% of HIV-1 isolates. Structures of lineage antibodies CH235 (week 41 from time-of-infection, 18% breadth), CH235.9 (week 152, 77%) and CH235.12 (week 323, 90%) demonstrated the maturing epitope to focus on the conformationally invariant portion of the CD4bs. Similarities between CH235 lineage and five unrelated CD4bs lineages in epitope focusing, length-of-time to develop breadth, and extraordinary levels of somatic hypermutation suggested commonalities in maturation among all CD4bs antibodies. Fortunately, the required CH235-lineage hypermutation appeared substantially guided by the intrinsic mutability of the VH1-46 gene, which closely resembled VH1-2. We integrated our CH235-lineage findings with a second broadly neutralizing lineage and HIV-1 co-evolution to suggest a vaccination strategy for inducing both lineages.