Immunophenotype of hairy-cell leukemia

15 cases of HCL were studied with a panel of monoclonal antibodies against different leukocyte antigens. A B-cell phenotype different from that of B-CLL was observed (CD10-, CD19+, CD20+, CD21-, CD22+, CD37+, CD38-, FMC7+, LN1+, PCA-1+, BLy7+ and CD5-). As expected, CD11c and CD25 were positive and, in addition, a My7 and My9 positivity in varying degree was noted. 3 weeks of in vitro incubation did not significantly alter the phenotype. We conclude that HCL exhibits a unique phenotype among chronic B-cell leukemias, which is closer to the plasma cell stage of differentiation than that of B-CLL. The BLy7 monoclonal antibody seems to be a promising marker for HCL.