Reactivity of the monoclonal antibody RFB1 in chronic B-cell leukaemias.

The monoclonal antibody RFB1, which reacts with early haemopoietic precursors in human bone marrow and peripheral T-lymphocytes, but not with pre-B cells and mature peripheral blood and marrow B lymphocytes, was tested in blood from 60 patients with chronic B cell leukaemias. All 37 cases of B chronic lymphocytic leukaemia (B-CLL) and 9 of hairy cell leukaemia (HCL) were positive. The antibody showed particularly strong reaction in HCL. On the other hand, RFB1 did not react with peripheral blood and B lymphocytes from 9 patients with non-Hodgkin lymphoma (NHL) in leukaemic phase and was negative or weakly expressed in 5 with prolymphocytic leukaemia (B-PLL). These findings may be significant for investigations on the cell origin of B-CLL and HCL. The reactivity of RFB1 was different from that of two anti-T1 monoclonal antibodies. The combined use of these reagents gave distinct patterns in B-CLL (RFB1+, T1+), HCL (RFB1++, T1-) and NHL and B-PLL (RFB1-/+/-, Tl-/+), suggesting they may be of value in the differential diagnosis of these B-lymphoproliferative disorders.