Immature dendritic cell-derived exosomes can mediate HIV-1 trans infection.

Immature dendritic cells (DCs) capture HIV type 1 (HIV-1) and can transmit captured virus particles to T cells. In this report, we show that HIV-1 particles captured by DCs can be transmitted to T cells by exocytosis without de novo infection. Captured HIV-1 particles were rapidly endocytosed to tetraspan protein (CD9, CD63)-positive endocytic compartments that were reminiscent of multivesicular endosomal bodies. Furthermore, some of the endocytosed virus particles were constitutively released into the extracellular milieu in association with HLA-DR1(+), CD1b(+), CD9(+), and CD63(+) vesicles (exosomes) and could initiate productive infections of CD4(+) target cells. Surprisingly, the exocytosed vesicle-associated HIV-1 particles from DCs were 10-fold more infectious on a perparticle basis than cell-free virus particles. These studies describe a previously undescribed mechanism of DC-mediated HIV-1 transmission and suggest that virus particle trafficking to multivesicular endosomal bodies and subsequent exocytosis can provide HIV-1 particles captured by DCs an avenue for immune escape.