HIV-1 dissemination from the genital mucosal tract to the lymphoid organs is the first critical step towards systemic infection. HIV-1 can disseminate either as free-virus, or it can be transported to lymphoid tissues by migratory cells. Our previous studies strongly argued that the trafficking of cell-associated HIV-1 from the genital mucosa to lymphoid organs played a dominant role in viral spread early after sexual transmission in humanized mice. Here, we further extend these observations by addressing the role of migratory DCs in the capture, retention and transfer of HIV-1 to susceptible T cells through trans-infection, a route of viral transmission that occurs through cell-cell contact.
To characterize the molecular and cellular aspects of DC:T trans-infection, we modeled the dynamics of DC:HIV and DC:T cell interactions within a 3D collagen matrix that recapitulates the stromal networks of the lymph node. Two-photon microscopy was performed to visualize (1) the cellular dynamic of HIV capture and retention by DCs, and (2) the interaction between HIV-bearing DCs and T cells. We used blocking antibodies to dissect the molecular underpinnings of HIV capture by DCs, and the role of adhesion molecules ICAM-1 and LFA-1 in stabilizing DC:T cell contacts during trans-infection. To determine the role chemoattractant receptor-mediated DCs such as S1PR1 and CCR7 play in spreading HIV, we employed transwell chemotaxis assays and live-cell imaging studies of in situ DC migration within explanted mouse ear slices.
Mature DCs captured HIV-1 on the cell surface, mediated by Siglec-1, and that captured virus rapidly formed dense clusters near the uropodia of migrating DCs. The chemotactic responses of HIV-1 bearing DCs towards lymph node homing chemokines CCL19/21 and S1P were preserved. HIV-bearing DCs engaged in progressively stable contacts with T cells in 3D collagen, which was a pre-requisite for rapid HIV transmission at the contact site. Consistent with this, HIV-bearing DCs transmitted virus was five-fold more efficient at infected T cells compared to cell-free virus, and that LFA-1:ICAM-1 adhesive contacts played a critical role in this process.
DCs retain their ability to migrate into lymph nodes following virus capture, and are able to engage T cells and form stable DC:T cell interactions. This suggests that blocking the movement of HIV+DCs out of the genital mucosa may be a novel approach to restrain virus dissemination and limit systemic viremia.