In this single center, open label trial, four subjects with HAM/TSP will receive 0.5 mg/kg Hu MiK-beta1 dosed every three weeks for a total of five doses, and two subjects with HAM/TSP will receive placebo (normal saline) under the same dosing schedule. In addition, following the completion of the 0.5 mg/kg dose administration in four subjects with HAM/TSP, a dose escalation study will be performed with three subjects with HAM/TSP receiving 1.0 mg/kg of Hu MiK-beta1 at three week intervals for a total of five doses per subject, and three subjects with HAM/TSP receiving 1.5 mg/kg of Hu MiK-beta1 at three week intervals for a total of five doses per subject A Total of 10 subjects will receive study drug/placebo. We anticipate consenting up to eighteen subjects to allow for up to eight dropouts. Participants who withdraw voluntarily (not due to toxicity) after initiation of the study are considered dropouts. If this occurs prior to receiving three doses of the study medication the subjects can be replaced and should have three follow-up evaluations at four-week intervals following the last dose of the study drug. Patients who voluntarily drop out after receiving at least 3 doses of the study drug will remain in the study and continue the protocol-specific evaluations. Toxicity will be assessed using standard criteria. The clinical response will be evaluated using standardized scales including expanded disability status scale, Scripps neurologic rating scale and ambulation index. In addition, viral and immunologic outcome measures will include assays of spontaneous lymphoproliferation analysis of HTLV-I tax tetramer specific CD8+ cells, HTLV-I proviral load determination and T-cell phenotype analysis.