In a phase I/II trial we wish to determine the toxicity and provide preliminary clinical response information following the administration of humanized MiK-beta-1 (Hu MiK-Beta1), a monoclonal antibody directed toward IL-2/IL-15R Beta (CD122), in patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). This antibody blocks the action of IL-15, a cytokine involved in the pathogenesis of HTLV-I associated diseases and autoimmune disorders such as rheumatoid arthritis and multiple sclerosis.