ImmunoGen Inc. has begun a clinical trial of its lead product,Oncolysin B, aimed at overcoming resistance by cancerous tumors toconventional chemotherapeutic drugs.The Phase I/II trial involving 12 to 20 patients with relapsed non-Hodgkin's lymphoma is the sixth indication in clinical studies forOncolysin B. The drug, an immunotoxin, is comprised of an anti-B4monoclonal antibody and a modified plant toxin called blocked ricin.Oncolysin B is directed to CD19+ cells and delivers the toxic portionof blocked ricin to cytoplasm to inhibit protein synthesis.Mark Ratner, director of external communications for the Cambridge,Mass.-based company, said the study is being conducted at the DanaFarber Cancer Institute in Boston and should be complete by next year.The trial is designed to test whether Oncolysin B has the potential to"sensitize" drug-resistant tumors to chemotherapy. Patients will betreated with Oncolysin B prior to receiving conventionalchemotherapeutic drugs.Results from ImmunoGen's preclinical studies showed that OncolysinB enhanced the response to chemotherapy in mice that were givendrug-resistant B cell tumors. Mice treated with a single dose ofOncolysin B followed by conventional anti-cancer drugs lived 200days. In two other test groups, mice receiving no chemotherapy lived25 days and those treated only with anti-cancer drugs survived 30 to 60days.Other clinical studies involving Oncolysin B in the treatment of non-Hodgkin's lymphoma and lymphocytic leukemia are: a Phase III trialfor preventing relapses of lymphoma after autologous bone marrowtransplants; a Phase II study for preventing relapses of lymphoma andleukemia after chemotherapy; two Phase I/II trials for treating AIDS-related lymphoma; a Phase I/II study for purging bone marrow duringtransplants for lymphoma; and Phase I/II trials for pediatric lymphomaand leukemia. _ Charles Craig

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