A JAX inhibitor (IC50s = 6.1, 12, and 8 nM for JAK1, JAK2, and JAK3, respectively); selective for JAK1-3 over ROCK-II and Lck (IC50s = 3,400 and 3,870 nM, respectively) as well as 28 additional kinases in enzyme assays (IC50s = >10,000 nM); inhibits IL-2-mediated phosphorylation of JAK3 and STAT5 (30 ng/ml); prevents rejection and prolongs survival in murine and cynomolgus monkey models of heterotopic heart and kidney transplantation