Immunohistochemical evaluation of bone marrow involvement in hairy cell leukemia during interferon therapy

Bone marrow biopsies from 7 patients afflicted with hairy cell leukemia were studied with a panel of monoclonal antibodies at different intervals during alpha recombinant interferon therapy. Monoclonal antibodies Dako-LC and F 8.11.13 were used because they are highly reactive with hairy cells, and 82H3 and LeuM 1 were also utilized to identify respectively the residual hemopoietic and myeloid tissue. All antibodies are reactive on sections of formalin-fixed, paraffin-embedded biopsy material. Before therapy a uniform hairy cell infiltrate was present and very little tissue was visible even after immunohistochemical staining. During therapy, identification of hairy cells in routine biopsies was difficult, since they were mixed with normal cells and the bone marrow was generally hypoplastic. Immunohistochemical stains seem to allow better identification of hairy cells and a more precise estimate of the degree of repopulation by normal bone marrow cells. It was evident, especially after immunocytochemical analysis, that interferon drastically reduced the extent of the infiltrate and allowed recovery of normal hemopoiesis, but did not produce complete remissions.