Abstract
A well-characterized mechanism by which anti-HLA class I monoclonal antibodies (MAb) inhibit human immunodeficiency virus type 1 (HIV-1) propagation in in vitro cell cultures is the neutralization of the virus through interactions with HLA molecules associated with the virion envelope. Yet, the possibility that another mechanism of inhibition might affect a postbinding stage of the virus life cycle has been strongly suggested by our previous investigations. To demonstrate that the interaction of MAb B1-1G6 with the light chain of cell surface-expressed HLA class I molecules inhibits a postbinding step of the HIV-1 life cycle, peripheral blood mononuclear cells (PBMCs) were exposed to viruses grown in HLA class I-negative, CD4-positive cells (these viruses, which did not carry HLA class I molecules, cannot be neutralized by anti-HLA MAb during the first round of infection), and PCR was used at various times postexposure to search for the different forms of HIV-1 DNA and RNA in virus-exposed PBMCs cultured in either the presence or [correction of] absence of MAb B1-1G6. Although viral DNA was found in MAb B1-1G6-treated cells, spliced HIV-1 mRNA could not be detected in those cells. In contrast, HIV-1 gene expression was found in HIV-1-infected PBMCs treated with B9-12-1, another HLA class I-specific MAb which prevents infection of cells by cell-free viruses but which fails to inhibit cell-to-cell transmission of HIV-1. These results highlight a second antiviral mechanism by which anti-HLA MAb inhibit in vitro HIV-1 propagation.