The human T-cell leukemia virus family, adult T cell leukemia, and AIDS.

Human T cell leukemia virus (HTL V) is the name by which we have designated a family of related retroviruses from humans. HTLV type I (HTLV-I) is the name we gave the first human retrovirus isolate. HTLV-I is endemic at low rates in different parts of the world, including southern Japan, the Caribbean, South and Central America, the southeastern United States, and especially in Africa. Seroepidemiologic studies show that HTL V-I is the primary etiologic agent of an aggressive form of adult T cell leukemia/lymphoma (ATLL). Infection with HTLV-I in vivo occurs preferentially with OKT4+ T cells and results in immortalization of the infected cells as well as abrogation of various immune functions of the infected cells, in keeping with its role in the etiology of ATLL. A second related but distinct virus, HTL V type II (HTL V-II), was identified by us in collaboration with D. Golde and colleagues after type I, in material from a patient with hairy cell leukemia. HTLV-II shares many features with HTLV-I, including in vitro transforming activity, but it has been isolated only rarely and has not yet been associated with any disease. A third virus, HTLV type III (HTLV-III), has been isolated many times from individuals who have acquired im-