Pentostatin is a ring-expanded nucleoside (REN) that potently inhibits adenosine deaminase inhibitor, which leads to lymphocyte toxicity. Pentostatin is used as anticancer agent to treat leukemia (hairy cell leukemia and chronic lymphocytic leukemia) and is investigated as an agent to treat graft-versus-host disease (GVHD) Pentostatin is a ring-expanded nucleoside (REN) that potently inhibits adenosine deaminase inhibitor, which leads to lymphocyte toxicity. Pentostatin is used as anticancer agent to treat leukemia (hairy cell leukemia and chronic lymphocytic leukemia) and is investigated as an agent to treat graft-versus-host disease (GVHD)