The number of clinical manifestations associated with human T-cell lymphotrophic virus type 1 infection continues to expand, as does the number of regulatory genes that human T-cell lymphotrophic virus 1 either transactivates or binds to directly. The relationship with the immunogenetics of the host is becoming more crucial with specific human leukocyte antigen types determining the risk of developing tropical spastic paraparesis/human T-cell lymphotrophic virus 1 associated myelopathy or adult T-cell leukaemia and lymphoma. Perhaps surprisingly, given the complexity of the virus-host interaction and the poor response to treatment of human T-cell lymphotrophic virus 1 associated conditions so far, a really remarkable response to azathioprine and alpha-interferon is reported for patients with adult T-cell leukaemia. Other reverse transcriptase inhibitors may also be effective in adult T-cell leukaemia and lymphoma and tropical spastic paraparesis/human T-cell lymphotrophic virus 1 associated myelopathy, although the fact that adult T-cell leukaemia is a monoclonal expansion disease that no longer requires virus replication per se, raises the question as to whether or not azathioprine is acting as an anti-cancer agent, which was its original role before the anti-HIV screening programme.
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