CD277 reduces B cell Activation by HIV Env Immunogens

Abstract

Abstract CD277 is a human B7-like molecule. involved in activation of Vγ9Vδ2 T cells. Its counter-receptor is unknown and its role in B cell activation has not been described. B cell lines were stably transduced with the IgG isotype of the inferred germline B cell receptor (BCR) form of the broad and potent HIV-1 neutralizing antibody, VRC01, and stimulated with recombinant HIV Env in Ca2+-dependent activation assays. CD277 ectodomain proteins partially inhibited Ca2+ flux in response to heptameric and trimeric HIV Env. Similar observations were made with B cells expressing an anti-HA BCR, when stimulated with recombinant HA. We conclude that the reduction in B cell activation recorded in the presence of CD277 was not specific for the HIV Env. In contrast, CD277 completely abolished B cell activation that was induced by cross-linking the same BCRs with anti-Fab antibodies. To identify molecules that may serve as counter-receptors for CD277 binding, a fluorescently coupled CD277 ectodomain was utilized to conduct a FACs-based negative selection screen from a pooled lentiCRISPR-Cas9 knockout library (GeCKO). This strategy resulted in a significant reduction in library diversity with the overall sgRNA pool by the end of the screen restricted to a few, highly abundant sgRNAs. Specific binding assays among putative counter-receptors are ongoing. Once identified, CD277 counter-receptors could be targeted for inhibition in vaccination studies, to enhance B cell responses to antigen such as HIV Env. These data indicate an important physiological role for CD277 in inhibiting B cell activation and its role in influencing the B cell repertoire should be pursued.