[Defective proviruses of the human T-cell leukemia virus: structure and classification]

Peripheral blood mononuclear cells of 24-70% individuals infected with HTLV-1 contain defective proviruses (dp) in addition to the full size ones. Most of them remain silent lacking regions sufficient for viral genes transcription except those activated under cell promoter or retaining viral open reading frames (orfs). It is still unclear whether these proviruses are associated with the development of T-cell leukemia in adults, tropic spastic paresis, or myelopathy. Classification of previously reported dp is presented, their origin and possible function in human HTLV-1 associated diseases are discussed.