A clathrin–dynamin-dependent endocytic pathway for the uptake of HIV-1 by direct T cell–T cell transmission

Cellular contacts between HIV-1-infected cells and target primary T CD4+ lymphocytes trigger the formation of a structure known as the virological synapse. As a consequence, viral production in HIV-1-infected cells is polarized towards the virological synapse and nascent viral particles are directly transferred to target T CD4+ lymphocytes. In this study, we performed short time cocultures of target primary T CD4+ lymphocytes with effector T cells infected by either HIV-1 NL4-3 or BaL. Using flow cytometry and immuno-confocal analyses, we investigated the transfer of HIV-1 virion antigens. We found that after 3 h of coculture, unstimulated T CD4+ lymphocytes captured complete HIV-1 virions from infected T cells during cell–cell contacts. Virus transfer occurred through a dynamin-dependent pathway and could be inhibited by chlorpromazine, an inhibitor of clathrin-dependent endocytosis. Transferred HIV-1 virions were located in compartments close to the surface of the target cell in a polarized manner. These compartments were positive for clathrin and the early endosomal marker EEA1 but were negative for caveolin-1. Furthermore, the great majority of internalized HIV-1 particles did not colocalize with Lamp1, a well-known marker for the lysosomal-degradative pathway. Similar results were observed when stimulated primary T CD4+ lymphocytes were the target cells. Our results suggest a mechanism of cell to cell HIV-1 transfer through a clathrin- and dynamin-dependent early endocytic pathway where internalized HIV-1 particles would not reach Lamp1 positive compartments, suggesting that during HIV-1 transfer by cell–cell contacts, virions can be taken up by endocytosis but not be degraded in lysosomes.