Retroviruses—Human T-Cell Lymphotropic Virus

Abstract

Retroviruses comprise a class of enveloped RNA viruses that have been long postulated to be a cause of various human diseases based on numerous animal models. These animal retroviruses were described by Rous and colleagues in the first decade of this century as the cause of sarcomatous neoplasms in chickens. Subsequently, mammalian retroviruses were discovered first in mice by Gross and colleagues, and subsequently in many species including cats, ungulates, and nonhuman primates. The range of diseases observed in animals includes malignancies, particularly leukemias and lymphomas, but also sarcomas, brain tumors, and breast cancers, as well as diseases of the immunologic system.⁽²¹⁵⁾ Despite the many examples of retrovirus-associated disease in animals, intensive laboratory-based studies, particularly in the late 1950s through mid-1970s, failed to identify a candidate human retrovirus. By then, most investigators had abandoned the search and had focused their attention instead on the transforming genes, termed oncogenes, which were essentially transduced host genes incorporated in some acutely transforming retroviruses. However, with the report in 1980 by Poiesz in Gallo’s laboratory of the first human retrovirus—human T-cell lymphotropic virus type I (HTLV I), also known as T-cell leukemia/lymphoma virus type I—a major new chapter in human virology was opened.⁽²¹²⁾) A second HTLV (HTLV-II) was identified in 1982,⁽¹¹³⁾ and understanding of its epidemiology is slowly evolving. Understanding of the virology and immunology of both of these viruses has been substantially fostered by the explosion of research following the discovery of the human immunodeficiency virus (HIV).