Autonomous proliferation of HTLV-CD4+ T cell clones derived from human T cell leukemia virus type I (HTLV-I)-associated myelopathy patients.

That HTLV-I infects CD4(+) T cells and enhances their cell growth has been shown as successful long-term in vitro proliferation in the presence of IL-2. It is known that T cells isolated from HAM patients possess strong ability for cell proliferation in vitro and mRNA of various cytokines are abundantly expressed in CNS tissues of HAM patients. Hence, the cytokine-induced proliferation could have an important role in pathogenesis and immune responses of HAM. In this study, we examined the relationship between cell proliferation and ability of in vitro cytokine production of CD4(+) T cell clones isolated from HAM patients. We started a culture from a single cell to isolate cell clones immediately after drawing blood from the patients using limiting dilution method, which could allow the cell to avoid in vitro HTLV-I infection after initiation of culture. Many cell clones were obtained and the rate of proliferation efficiency from a single cell was as high as 80%, especially in the 4 weeks' culture cells from HAM patients. These cells were classified as mainly Th0 phenotype that produce both IFN-gamma and IL-4 after CD3-stimulation. However, the frequency of proviral DNA in these cloned cells was significantly low. Our results indicate that the ability of cell proliferation in HAM patients is not restricted in HTLV-I-infected T cells. HTLV-Iuninfected CD4(+) T cells, mainly Th0 cells, also have a strong ability to respond to IL-2-stimulation, showing that unusual immune activation on T cells has been observed in HAM patients.