Pietro Presicce, Maria E. Moreno-Fernandez, Laura K. Rusie, Carl Fichtenbaum, Claire A. Chougnet

Myeloid dendritic cells (mDCs) are the antigen-presenting cells best capable of promoting peripheral induction of regulatory T cells (Tregs), and are among the first targets of HIV. It is thus important to understand whether HIV alters their capacity to promote Treg conversion. Monocyte-derived DCs (moDCs) from uninfected donors induced a Treg phenotype (CD25(+)FOXP3(+)) in autologous conventional T cells. These converted FOXP3(+) cells suppressed the proliferation of responder T cells similarly to circulating Tregs. In contrast, the capacity of moDCs to induce CD25 or FOXP3 was severely impaired by their in vitro infection with CCR5-utilizing virus. MoDC exposure to inactivated HIV was sufficient to impair FOXP3 induction. This DC defect was not dependent on IL-10, TGF-β or other soluble factors, but was due to preferential killing of Tregs by HIV-exposed/infected moDCs, through a caspase-dependent pathway. Importantly, similar results were obtained with circulating primary myeloid DCs. Upon infection in vitro, these mDCs also killed Treg through mechanisms at least partially caspase-dependent, leading to a significantly lower proportion of induced Tregs. Taken together, our data suggest that Treg induction may be defective when DCs are exposed to high levels of virus, such as during the acute phase of infection or in AIDS patients.