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The Relationship and Biology of Human Retroviruses

Human retroviruses share structural features with other animal retroviruses, including long terminal repeat, group-specific polymerase, envelope, and transactivation genes. Human retroviruses discovered to date have been associated with lymphoproliferative or cytopathic disease states. Hutnan lmmunodeficiency virus (HIV) shares genomic sequence, structural features, replicative mechanisms, and cytopathic features with other animal len-tiviruses. Lentiviruses, such as HIV, share the common biological features of inducing fusion and death of infected host cells. Restricted transcription of viral gene products (in concert with host factors) and antigenic vari-ation (primarily in the envelope gene) allow these viruses to escape elimination by the immune system. Transmission of HIV is primarily via sexual routes and intravenous injection of blood or blood products. Epidemiology and virology data have associated human T cell tymphotropic virus I (HTLV-I) with adult T cell lymphomaileukemia (ATLL) and a unique spastic paraparesis syndrome in HTLV-I endemic regions. Transmission of HTLV-I is through cell-associated transfer of HTLV-I infected cells by sexual or transfusion routes. In addition, H~I’LV-I infection has been associated with breast feeding of chil-dren by HTLV-I-infected mothers. Mechanisms of leuke-mogenesis induced by HTLV-I have not been defined, but are believed to be determined by the ability of the virus to transactivate cellular genes. Animal models of human retrovirus infection and disease can provide data to further understand the pathogenesis of retrovirus-induced disease and support the development of effective therapies or vaccines. 355