Hairy cell leukemia: a model for studying the B cell family of diseases

Nineteen patients with hairy cell leukemia (HCL) were treated with recombinant interferon alpha-2a/Roche (Roferon) given by daily intramuscular injection of 3 X 10(6) for 6 months followed by three injections per week. Pretreatment and follow-up marker studies were performed on 14 of 16 evaluable patients. Peripheral blood and bone marrow mononuclear cells were analyzed by flow cytometry for reactivity with monoclonal antibodies to B cell associated surface antigens (B1, B2, B4, BL1, BL3, and BL7) and two hairy cell (HC) antibodies, anti-HCL1 and HCL3. B cell monoclonality was determined by clonal excess calculation of immunoglobulin light chains. Right angle scatter analysis showed that HCs are scattered between lymphocytes and monocytes. Nine of the 14 patients achieved a partial remission, three patients achieved a minimal response, and two patients failed therapy. Phenotypically, ten patients had kappa clonal excess and four had lambda clonal excess. These cases expressed a mature B cell phenotype, ie, BL1-, BL7+, BL3+, B1+, B2-, B4+, HCL1+, HCL3+. All 12 responders became nonreactive with monoclonal antibodies 4 to 8 weeks after therapy; in five of these cases, reactivity with monoclonal antibodies was again detected at the time of maximum clinical response (2 to 8 months), without affecting clinical response status. In four of 12 responders, clonal excess disappeared 4 to 8 weeks after therapy; in three more patients, clonal excess disappeared at the time of maximum clinical response (2 to 4 months); in three patients, clonal excess disappeared from the peripheral blood, but not from the bone marrow at the time of maximum clinical response (3 to 5 months); two patients had persistent clonal excess. In the two failures, there was persistence of clonal excess and reactivity with monoclonal antibodies. This study shows that phenotypic analysis is a sensitive and objective method of assessing response of HCL to alpha interferon. This system could be used as a model for the study of other B cell neoplasms.