Detection of HIV Env-mediated B cell receptor aggregation on engineered B cells by flow cytometry.

Abstract

Abstract Approximately 20% of individuals infected with HIV-1 produce broadly neutralizing antibodies (bNAbs) against the virus. Understanding how bNAb linked B cell receptors (BCRs) are initially stimulated by the HIV-1 envelope (Env) in the context of natural HIV infection is a major focus of HIV research. While germline-reverted BCR forms of bNAbs do not efficiently recognize Env, recombinant Env proteins have been recently designed to engage and activate some germline BCRs. To better understand how such modified Envs engage BCRs and to further optimize the activation of B cells, we (a) created a stable Ramos cell line that expresses the germline BCR form of a potent and broadly neutralizing antibody, VRC01 and (b) developed a fluorescence-based assay that allows for the monitoring of Env-mediated BCR aggregation. B cells were incubated with different multimeric forms of Env (valency ranging from 1–24) and determined the extent of BCR aggregation and compared it with the extent of B cell activation (measured by Ca2+flux assays). Significant increases in BCR aggregation and B cell-activation were detected in response to heptameric and 24-meric forms of Env. In contrast, lower valency multimeric forms of Env activated B cells inefficiently. No aggregation or calcium flux was detected in response to monomeric Env. A positive correlation was observed between the magnitudes of calcium flux and BCR aggregation. Thus, either BCR aggregation or Ca2+ flux assays can be used to monitor the activation of B cells by recombinant Env proteins that are being evaluated as possible immunogens to elicit bNAbs. Our results are relevant to optimizing the design and formulation of recombinant Env proteins for the elicitation of broadly neutralizing HIV-1 antibodies.