Molecular characterization of the circulating anti-HIV-1 gp120-specific B cell repertoire using antibody phage display libraries generated from pre-selected HIV-1 gp120 binding PBLs

Human bone marrow is a major repository for maturated antibody-secreting plasma cells, which produce the majority of the antibodies found in serum, making it an attractive source for generating human immune antibody libraries. Unfortunately, bone marrow is not always readily available and, although human immune libraries can be generated from circulating B cells, the low frequency of antigen-specific B cells in the circulation yield few monoclonal antibodies of interest. We used a pre-selection strategy to enrich for antigen-specific B cells prior to library generation, and applied this approach to evaluate, at a molecular level, the nature of the human anti-HIV-1 gp120 repertoire encoded by circulating B cells. IgG antibody phage display libraries were generated from HIV-1 seropositive individuals using either affinity-selected anti-gp120 IgG-bearing circulating B cells, predominantly exhibiting memory/activated B cell phenotype, or unselected PBMCs. These libraries were selected against HIV-1 gp120, resulting in isolation of a panel of gp120-specific antibodies. Whereas only 2 gp120-specific antibodies were retrieved from the non-pre-selected HIV-1 library, 9 gp120-specific antibodies were retrieved from the 10-fold smaller library generated from the pre-selected B cells, demonstrating the feasibility of the approach. The anti-gp120 antibodies derived from the circulating B cells of HIV-1 donors generally resembles those from bone marrow plasma cells with respect to epitope specificity, affinity and neutralization ability. They exhibit high affinity for gp120, are directed against a variety of epitopes, but rarely exhibit the ability to neutralize HIV-1.