Is there a direct differentiation‐inducing effect of human recombinant interferon on hairy cell leukemia in vitro ?

We used a panel of monoclonal antibodies (moAb) to label splenic hairy cells from eight patients to determine the membrane phenotypes, the presence of cytoplasmic immunoglobulin (cIg), and the expression of maturation‐associated antigens. All eight patients had responded clinically to splenectomy either alone or in combination with α‐2b‐interferon (α‐IFN) therapy. For each sample, cytofluorimetric analysis showed distinct, and in six cases multiple, heavy chain isotypes. After short‐term culture in the presence of α‐IFN or γ‐interferon (γ‐IFN), samples from four patients displayed characteristic changes in surface immunoglobulin (sIg) expression. When compared with untreated cells, cells co‐cultured with α‐IFN or γ‐IFN showed in four and three patients, respectively, changes that were consistent with a shift to the more mature stage in B‐cell ontogeny. However, in parallel with the changes in the sIg isotypes, treatment with IFN did not induce the appearance of cIg nor did the staining patterns for moAb to CD5, CD19, CD20, and CD22 antigens indicate the induction of terminal maturation. These data suggest that hairy cell leukemia (HCL), a neoplasm of “mature” B‐cells, is potentially susceptible to maturation stimuli. Based on these findings, it might be of interest to examine whether co‐factors, which have proved to play a role in HCL ( e.g. , B‐cell growth factor [BCGF]), are capable of further enhancing IFN‐induced differentiation.