The Role of Human T Cell Lymphotropic Virus Type I Tax in the Development of Cutaneous T Cell Lymphoma
Although it has been well established that the human T cell lymphotropic virus type I (HTLV-I) causes adult T cell leukemia/lymphoma (ATLL) in regions of the world where this virus is endemic, its role in the pathogenesis of cutaneous T cell lymphoma (CTCL) in the Western world has been less well established. Most patients with CTCL are negative for antibodies to the structural proteins of HTLV-I, and thus a causative role for this virus is usually dismissed. However, the Tax sequence of HTLV-I has been found in the peripheral blood mononuclear cells of practically all patients with CTCL. Such patients express Tax mRNA and have antibodies to p40Tax, the protein encoded by this sequence. Sequence analysis of a 159-bp region of Tax extracted from CTCL cells proved to be homologous with the same region prepared from a cell line infected with prototypic HTLV-I. By in situ PCR, Tax has been demonstrated in the lymphocytes infiltrating the skin as well as in the keratinocytes of such patients. Apart from the pathophysiologic and clinical interest of these studies, these observations may have therapeutic implications. In vitro, the proliferation of HTLV-I-transformed cells can be inhibited by antisense to HTLV-I Tax. Since Tax has not been identified in the normal human genome, antisense to Tax deserves serious consideration as a treatment modality for patients whose cells have been demonstrated to harbor Tax.
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