Azacytidine is a cytidine analog that is incorporated into DNA, inhibiting DNA methyltransferase (DNMT) activity and preventing DNA repair. This demethylating agent is clinically used to treat myelodysplastic syndromes and potentiates the effects of other chemotherapeutics, such as cisplatin. Azacytidine exhibits anticancer chemotherapeutic, immunomodulatory, and antiviral activities. In vitro, azacytidine increases levels of Bax and Bcl-2 in astrocytoma cells, and induces differentiation of mesenchymal stem cells into cardiomyocytes. In vivo, azacytidine increases glial differentiation and decreases cell proliferation, inhibiting tumor growth of glioma xenografts. Additionally, azacytidine decreases cell growth and inhibits tumor xenografts of myelodysplastic cells. In leukoblasts, this compound upregulates the expression of tumor antigens, and in vivo, it increases the number of Treg and CD8+ T cells. Azacytidine also inhibits replication of HIV in cellular models without displaying cytotoxicity.