A two-color flow cytometry assay for detection of hairy cells using monoclonal antibodies

We have developed a simple two-color immunofluorescence assay equally suited for microscopy and flow cytometry detecting hairy cells (HCs) in single cell suspensions, based on the concomitant reactivities with the B cell-specific monoclonal antibody B1 (CD20) and the monocyte/HC-associated antibody SHCL-3 (CD11c). Thus, HCs can be demonstrated in peripheral blood, bone marrow, and spleen specimens from hairy cell leukemia (HCL) patients even when they constitute less than 1% of the cell suspension. Likewise, admixture experiments with normal mononuclear cells and the MOLT-4 T-acute lymphocytic leukemia (ALL) cell line demonstrated that HCs could be detected in amounts as low as 1%. The validity of this assay has been ascertained by the lack of double marker positivity in cell suspensions from B-chronic lymphocytic leukemia (CLL) and acute myelogenous leukemia (AML) patients that only expressed B1 or SHCL-3, respectively. Furthermore, other malignant blood diseases, including malignant lymphomas, acute leukemias, and chronic leukemias disclosed no double marker positive cells. In a clinical setting, this assay was used for purifying HCs (by flow cytometry) from the peripheral blood from patients with no apparent morphological evidence of circulating HC infiltration and for monitoring the effect of interferon therapy. In conclusion, this assay should be of value for both diagnosis and monitoring patients with HCL.