Use of a panel of monoclonal antibodies for the diagnosis of hairy cell leukaemia. An immunocytochemical study of 36 cases.

The phenotype of 36 cases of hairy cell leukaemia has been investigated using a panel of monoclonal antibodies reactive with normal human lymphoid cells and with hairy cells. Staining was performed on frozen sections and/or cell smears by the recently developed APAAP immuno-alkaline phosphatase procedure. In about 90% of cases, neoplastic cells reacted strongly with antibodies against HLA-DR, leucocyte common antigen, B-cells (antibodies B1 and To15), hairy-associated antigens (antibodies KB-90, S-HCL3, HC2) and activated T-lymphocytes (antibodies anti-Tac and Tü69). The phenotype of 10% of cases was clearly different in that the neoplastic cells were negative or only weakly positive for one or more of the antigens recognized by HC2, anti-Tac and Tü69. Antibody HC1 reacted with tumour cells of only 50% of the hairy cell leukaemia cases investigated. Monoclonal antibody Ki-67 (which selectively detects proliferating cells) stained only a low percentage of cells in all but three of the cases studied. The neoplastic cells in all cases were unreactive with monoclonal antibodies anti-Leu1, Tü1, Tü33 and a meshwork of follicular dendritic cells was consistently absent from tissues infiltrated by hairy cells. The immunological phenotype associated with hairy cell leukaemia was not observed in any case of non-Hodgkin's lymphoma, suggesting that it represents a unique type of B-cell neoplasm.