Temporal dynamics of human T‐lymphotropic virus type I tax mRNA and proviral DNA load in peripheral blood mononuclear cells of human T‐lymphotropic virus type I‐associated myelopathy patients

Human T‐cell lymphotropic virus type I (HTLV‐I) is the etiologic agent of HTLV‐I‐associated myelopathy/tropical spastic paraparesis (HAM/TSP). High HTLV‐I provirus load and tax mRNA level have been suggested as predictors of disease progression in patients with HAM/TSP, but little is known about the temporal variation in patients. To clarify the role of high proviral and tax mRNA loads and their fluctuations in the pathogenesis of HAM/TSP, we measured proviral load and tax mRNA in serially collected peripheral blood mononuclear cells (PBMCs) from nine patients with HAM/TSP during a long‐term follow‐up, by use of real‐time polymerase chain reaction using tax primers. The real‐time PCR quantitation revealed a wide range of variation of proviral loads (7.82–97.13 copies per 100 PBMCs) and tax mRNA (0.20–245.30 copies) among HAM/TSP patients. Patients showed three different patterns of HTLV‐I tax mRNA loads during the course of the disease. Tax mRNA load showed a separate evolution with respect to the disease. The dynamic patterns of proviral load and mRNA Tax expression suggest that only the permanent presence of a basal level of tax mRNA, rather than the tax mRNA load, is related to the development of HAM/TSP. To our knowledge, this is the first longitudinal study to determine tax mRNA expression at different clinical stages. J. Med. Virol. 79: 782–790, 2007. © 2007 Wiley‐Liss, Inc.