Use of interferon alfa-2a to treat hematologic relapse of chronic myelogenous leukemia after bone marrow transplantation.

The use of recombinant human alpha interferon (IFN) to treat relapse of chronic myelogenous leukemia (CML) in chronic phase after bone marrow transplantation (BMT) was studied in a prospective trial. Relapse was defined as > 90% metaphases containing the Philadelphia chromosome (Ph) and hematologic abnormalities consistent with chronic phase CML. In the initial 18 patients, all received allogeneic marrow, 17 from a related donor, 1 from an unrelated donor. Only 1 patient received T-depleted marrow initially. Three patients had relapsed after second BMT. IFN was started at 3 x 10(6) IU/m2/day and escalated to the maximum tolerated dose or to a maximum of 6 x 10(6) IU/m2/day. Elevated white blood counts and platelet counts were controlled in 14 of 16 and 6 of 6 patients, respectively. Six patients (33%) have had a complete disappearance of the Ph (cytogenetic complete response) and 2 have had a partial response (cytogenetic partial response < 35% Ph+ metaphases but > 0%) on at least one sample. Six patients had no significant response after 9-12 months and 4 patients developed clinical accelerated phase or blast crisis after 3-6 months. IFN controlled the blood counts in 75% of patients. Of 4 patients with a sex marker, the Ph- population was of donor origin in 3 and of host origin in 1. Clonal cytogenetic abnormalities other than the Ph were present in 13 patients and did not predict for lack of response to IFN. IFN effectively produces hematologic control in the majority of patients and suppresses the Ph clone in up to one third. A trial of IFN treatment in an earlier stage of relapse is indicated.