Inhibitory effects of 5-azapyrimidine nucleosides on cellular immunity.

The effect of 5-azacytidine (5-AzCR) and 5-aza-deoxycytidine (5-AzCdR) on the survival of skin grafts in mice and rats, the action of these drugs on regional GVH reaction, as well as the formation of haemopoietic colonies (CFU-5) in the spleen were studied. Both drugs prolonged the life span of skin grafts when administered 24 hr before transplantation, or on the 4th post-transplantation day. However, they were little effective when injected 24 hr after skin grafting, or after induction of the regional GVHR. Following intraperitoneal administration, they inhibited CFU-5 formation. Two-hour incubation in vitro of cells with 5-AzCR significantly reduced their GVH reactivity and capacity to form CFU-5; 5-AzCdR under the same conditions was ineffective.