MAdCAM costimulation through Integrin-α

Human gut associated lymphoid tissues (GALT) play a key role in the acute phase of HIV infection. The propensity of HIV to replicate in these tissues however, is not fully understood. Access and migration of naïve and memory CD4+ T cells to these sites is mediated by interactions between integrin α4β7, expressed on CD4+ T cells, and MAdCAM, expressed on high endothelial venules. We report here that MAdCAM delivers a potent costimulatory signal to naïve and memory CD4+ T cells following ligation with α4β7. Such costimulation promotes high-levels of HIV replication. An anti-α4β7 mAb that prevents mucosal transmission of SIV blocks MAdCAM signaling through α4β7 and MAdCAM-dependent viral replication. MAdCAM costimulation of memory CD4+ T cells is sufficient to drive cellular proliferation and the up-regulation of CCR5, while naïve CD4+ T cells require both MAdCAM and retinoic acid to achieve the same response. The pairing of MAdCAM and retinoic acid is unique to the GALT, leading us to propose that HIV replication in these sites is facilitated by MAdCAM-α4β7 interactions. Moreover, complete inhibition of MAdCAM signaling by an anti-α4β7 mAb, an analogue of a clinically approved therapeutic (vedolizumab), highlights the potential of such agents to control acute HIV infection.