Study of Intravenous BCX-1777 in Relapsed or Refractory Aggressive T-Cell Leukemias or Lymphomas

Inclusion Criteria: * Previously treated, relapsed or refractory aggressive T-cell malignancies (leukemias and lymphomas) histologically proven with measurable disease. * Capable of only limited self-care, confined to bed or chair more than 50% of waking hours. * All ages are eligible. Pediatric patients (\<15 years of age) are eligible to be treated at a dose level previously tested in adults. * Adequate liver and renal function. * Patients with prior history of stem cell transplant if they meet all other eligibility requirements. * Negative pregnancy test within 72 hours of study treatment in females of childbearing potential. * Life expectancy of at least 2 months. Exclusion: * Active serious infection not controlled by oral or intravenous antibiotics. * Treatment with any investigational antileukemic agents or chemotherapy agents in the last 7 days before study entry, unless full recovery from side-effects has occurred or patient has rapidly progressive disease judged to be life-threatening by the investigator. * Concurrent treatment with other anti-cancer agents. * Known CNS leukemia or lymphoma requiring intrathecal or craniospinal radiation therapy. Lumbar puncture not required in asymptomatic patients. * Pregnant and/or lactating women; or fertile men or women not willing to use contraception.