Exosomes from human immunodeficiency virus type 1 (HIV-1)-infected cells license quiescent CD4+ T lymphocytes to replicate HIV-1 through a Nef- and ADAM17-dependent mechanism.

Resting CD4(+) T lymphocytes resist human immunodeficiency virus (HIV) infection. Here, we provide evidence that exosomes from HIV-1-infected cells render resting human primary CD4(+) T lymphocytes permissive to HIV-1 replication. These results were obtained with transwell cocultures of HIV-1-infected cells with quiescent CD4(+) T lymphocytes in the presence of inhibitors of exosome release and were confirmed using exosomes purified from supernatants of HIV-1-infected primary CD4(+) T lymphocytes. We found that the expression of HIV-1 Nef in exosome-producing cells is both necessary and sufficient for cell activation as well as HIV-1 replication in target CD4(+) T lymphocytes. We also identified a Nef domain important for the effects we observed, i.e., the (EEEE65)-E-62 acidic cluster domain. In addition, we observed that ADAM17, i.e., a disintegrin and metalloprotease converting pro-tumor necrosis factor alpha (TNF-alpha) in its mature form, associates with exosomes from HIV-1-infected cells, and plays a key role in the HIV-1 replication in quiescent CD4(+) T lymphocytes. Treatment with an inhibitor of ADAM17 abolished both activation and HIV-1 replication in resting CD4(+) T lymphocytes. TNF-alpha is the downstream effector of ADAM17 since the treatment of resting lymphocytes with anti-TNF-alpha antibodies blocked the HIV-1 replication. The data presented here are consistent with a model where Nef induces intercellular communication through exosomes to activate bystander quiescent CD4(+) T lymphocytes, thus stimulating viral spread.