STAT4 and Kaposi's sarcoma: In contrast, T cell-mediated control of KSHV is less well characterized, but immunodeficiencies affecting TCR signaling (STIM1, WASP), co-stimulation (OX40, XMEN) or T cell effector functions (STAT4, IFNɣR1) are also known to predispose for Kaposi sarcoma (KS) development, the most common malignancy associated with KSHV8.