Peldesine (also known as BCX-34) was developed as a purine nucleoside phosphorylase (PNP) inhibitor. It is known PNP inhibitors may be useful for treating a variety of T-cell related autoimmune diseases including psoriasis, rheumatoid arthritis, and Crohn s disease and T-cell cancers. Peldesine has undergone phase I trials for the treatment of human Immunodeficiency virus (HIV) infections. In addition, this drug participated in phase III clinical trial as a topical therapy for cutaneous T-cell lymphoma. This drug was also studied as a potential therapy for psoriasis, multiple sclerosis; rheumatoid arthritis; transplant rejection. However, all these indications were discontinued because of the lack of significant effects over placebo.