CD4 and cancer: CD4+ T cells may also have direct cytolytic potential (CD4+ CTLs).10 Such class II-restricted CTLs have significance in the pathogenesis of autoimmune diseases11, 12 and in the control of chronic viral infections such as EBV,13 CMV,14 HIV,15 as well as malignancies.16, 17, 18 Two major cell-killing mechanisms have been reported.