PU02.03
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Isolation of new CAP256-VRC26 lineage members reveals determinants of breadth and potency

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BACKGROUND: Broadly neutralizing antibodies (bNAbs) may be an important component of a future vaccine for HIV-1, and are being tested for prevention. Donor CAP256 of the CAPRISA cohort in South Africa developed the VRC26 lineage of V1V2-directed bNAbs, which have been studied extensively. The best of the 33 published VRC26 lineage members, CAP256-VRC26.25, is exceptionally potent, with 70% breadth for clade C but only 15% breadth against clade B. We sought to isolate additional lineage members with the aims of finding an antibody with greater breadth, and to further characterize the genetic determinants of neutralization.
METHODS: B cells from donor CAP256 were sorted with a native trimer probes generated from the autologous lineage-triggering Env, CAP256wk34c80, using the repair-and-stabilize approach. To identify V1V2-directed antibodies, we included a probe bearing a K169E mutation which abolishes binding by all previous VRC26 lineage members; and a BG505.SOSIP trimer with the V1V2 of clade B strain WITO, to look for broader antibodies. We sorted B cells from week 193 post infection, the same time point from which we previously isolated CAP256-VRC26.25.
RESULTS: Eight VRC26 heavy chain sequences were recovered, of which 6 were IgG and 2 were IgA. The VH genes showed a range of 7.3-18.1% mutation from germline, and CDRH3 lengths between 37 and 39 amino acids (IMGT numbering), consistent with other members of the lineage. Five had matched light chains, were expressed as IgG1, and were characterized for binding to Env via octet and TZM-bl neutralization assays. The best of these showed 64% breadth against clade C, and 40% breadth on a 46 virus multi-clade panel. Variations that reduced the probability of tyrosine sulfation correlated with reduced breadth and potency. One heavy chain lacked multiple conserved residues at the tip of the CDRH3 and the expressed antibody was non-neutralizing. Comparisons with CAP256-VRC26.25 and its cryo-EM structure in complex with trimer suggest the structural basis of these effects.
CONCLUSIONS: These data improve our understanding of critical residues in VRC26 antibodies. This can guide future efforts to improve the breadth of these highly potent antibodies.