ESTABLISHMENT OF A HUMAN PRO-B CELL-LINE (JKB-1) AND ITS DIFFERENTIATION OF PREESTABLISHED BONE-MARROW STROMAL CELL LAYER

A human pro-B cell line, named JKB-1, was established from the bone ma rrow of a 16-year-old girl with acute lymphoblastic leukemia (ALL) in relapse. The origin of the JKB-1 cell line was indicated by its chromo somal and immunologic similarity to the patient's fresh leukemic cells . This cell line has been growing for more than 14 months in suspensio n culture medium and had a doubling time of about 24 hours. JKB-1 expr essed terminal deoxynucleotide transferase (TdT) and early antigens (H LA-DR, CD19, CD24) of B cells, with heavy chain gene rearrangement. Ho wever, it did not express late antigens (CD10, CD20, CD21, CD22, CD23) of B cells, light chain gene rearrangement, and cytoplasmic mu-chain. These results suggested that JKB-1 is at the stage of ''pro-B'' cell or early B-cell precursors. This cell line was induced to differentiat e after 7 days of co-incubation with irradiated bone marrow stromal ce lls because of the expression of pre-B cell antigens (CD10, CD20), cyt oplasmic mu-chain, light chain gene rearrangement, and disappearance o f TdT. JKB-1 cells adhered to a preestablished bone marrow stromal cel l layer with string-like processes under scanning electron microscope. When JKB-1 cells were separated from the stromal layer by a cyclopore membrane with 0.45 mu m pore size, they did not differentiate. Bone m arrow stromal cell conditioned medium could not induce differentiation either. Thus it was suspected that direct contact between JKB-1 cells and stromal cells was required for differentiation. In methylcellulos e semisolid medium, the colony size and number of JKB-1 cells were inc reased by stem cell factor (SCF), or interleukin (IL)-3, or IL-7, but they were decreased by IL-6. Moreover, SCF synergized with IL-3 or IL- 7 to stimulate the proliferation of JKB-1 cells. Because there are ver y few reproducible models for examing early stages of human B-cell dif ferentiation, the JKB-1 cell line would be useful for studying the rel ationship between human B-cell differentiation and bone marrow microen vironment, as well as leukemogenesis. (C) 1994 Wiley-Liss, Inc.