Hairy cell leukemia. Immunological study.

The study has been performed on peripheral blood and splenic malignant cells from 16 patients with hairy cell leukaemia (HCL). The cell surface markers were identified by rosette techniques and using monoclonal antibodies (m Ab). The surface markers' expression of the hairy cells (HC) varied. The E receptors, the T-cell antigens, the HLA-DR antigens and smIgG were either expressed or not according to the affected organ, the progress of illness, or the treatment. The surface pattern changed sometimes in the same patient during the progress of illness. These observations demonstrate that HCL is a unique disease with malignant cells characterized by a marked variability of the cell surface markers. To demonstrate the ability of hairy cells to bind labile smIgG, the cells were studied by affinity chromatography on SpA-Sepharose 6MB and by ES-rosette assay. The percent of cells bound on SpA-Sepharose varied between 6% and 66%, representing the hairy cells with labile-bound smIgG. With affinity chromatography it was also possible to separate the hairy cells with a special phenotype: T3+ T4+ T8+ T11+ surface membrane labile-bound IgG+ (11gG+) FcR+, HLA-DR+ EACD+ (Ripley rosette forming cells), resembling a normal subset of large granular lymphocytes (LGL). The percentage of these cells varied between 60% and 86% of the bound cells. These observations suggest that in HCL, the malignant transformation might involve a common progenitor for the B, T and LGL lineages, the hairy cell being a hybrid type of malignant cell. Its main immunological peculiarity is the marked mobility of the surface membrane structures and hence the lability (plasticity) of the surface markers' expression.