Phase I trial of anti-B4-blocked ricin in pediatric patients with leukemiaand lymphoma

Monoclonal antibodies, specific for antigens expressed on lymphoid malignan cies, which have been conjugated to toxins such as ricin, hold promise in t he therapy of childhood leukemia and lymphoma. Anti-B4-blocked ricin (anti- B4-bR) is such an agent, and a phase I study of this agent was conducted in children with relapsed or refractory B-lineage leukemia and lymphoma. Anti -B4-bR was given as two 7-day continuous infusions separated by 7 days. Twe nty patients were enrolled and 19 received the drug. Two dosage levels (30 and 40 mug/kg per day) were evaluated. Forty micrograms per kilogram per da y was the maximally tolerated dose. Dose-limiting toxicity was capillary le ak syndrome. Grade 3 reversible elevation in transaminases was also encount ered. Human antimouse antibodies or human antiricin antibodies were detecte d in five patients. No complete remissions or partial remissions were seen.