George Herbert Hitchings (1905-1998) was awarded one-third of the 1988 Nobel Prize in Physiology or Medicine for his development of drugs that proved useful in the treatment of several major diseases. Working with fellow Nobel Laureate Gertrude B. Elion, Hitchings designed a variety of new drugs that interfered with the replication or other vital functions of certain pathogens. They developed thioguanine and 6-mercaptopurine (6MP), which became important drugs for the treatment of leukemia. By altering the structure of 6MP, Hitchings and Elion produced azathioprine, which has been used to treat autoimmune disorders and suppress the body's rejection of transplanted organs. Other drugs developed by Hitchings and Elion include allopurinol for gout, pyrimethamine for malaria, trimethoprim for urinary-tract infection and other bacterial infections, acyclovir for viral herpes, and azidothymidine (AZT) for AIDS.