Retrovirus infection of mDCs promotes expansion of Treg cells. (A) Uninfected antigen-presenting cells (APC) experiencing a brief interaction (“kiss and run”) between CD4⁺CD25⁻ T cells results in full activation of effector T-cell phenotype. (B) Friend retroviral infection of mDCs impairs APC costimulation mol-ecule expression, resulting in more prolonged DC–T-cell interaction (“pillow talk”), which results in expansion of Treg cells from CD4⁺CD25⁻ T cells. Emergence of Treg cells provides a novel pathway for immune escape from retroviral infection.