Selection of a panel of monoclonal antibodies for monitoring residual disease in peripheral blood and bone marrow of interferon‐treated hairy cell leukaemia patients

Summary A panel of monoclonal antibodies (mAbs) directed against B‐cell and hairy cell leukaemia (HCL)‐associated antigens was used to identify residual hairy cells in the peripheral blood and/or bone marrow samples from 20 patients with HCL. following treatment with interferon‐alpha (IFN‐alpha) or interferon‐beta (IFN‐beta). In all cases, hairy cells retained their characteristic phenotype, e.g. positivity for CD22, CD11c, CD25, CD32, and the HCL‐associated trimeric protein (t‐GP) recognized by the mAbs HML‐1, B‐ly7, LF61 and Ber‐Act8. The most specific marker for identifying a small percentage of hairy cells in peripheral blood cytospins. was t‐GP. In alkaline phosphatase/anti alkaline phosphatase (APAAP) stained preparations, t‐GP+ hairy cells (provided with large cytoplasm and hairy surface) could be usually distinguished from t‐GP+ normal lymphocytes (small‐sized cells with smooth surface). In doubtful cases the percentage of residual hairy cells could exactly be estimated by double immunofluorescence staining for CD22 (B‐cell marker) and t‐GP. The rationale of the test is based on the finding that the small percentage (about 1%) of t‐GP + lymphocytes circulating in the peripheral blood of normal individuals are T‐cells of the CD8 subset and not B‐cells. The best markers for identifying residual hairy cells in routine bone marrow biopsies were CD45RA (mAb 4KB5) and CD20 (mAb L26). Immunohistological labelling was superior to morphological examination in picking up scattered hairy cells in bone marrow biopsies showing either severe hypoplasia or exuberant hyperplasia of normal haemopoietic series.