The Philadelphia chromosome, widely implicated in human leukaemia, is the result of a reciprocal translocation t(9;22) (q34;q11) in which the abl oncogene located at 9q34 is translocated to chromosome 22q11, where it is fused head-to-tail with 5' exons of the bcr gene. In acute lymphoblastic leukaemia, some patients have a breakpoint within the major breakpoint cluster region of the bcr gene, whereas others have the break within its first intron. This second type of translocation results in the transcription of a 7.0-kilobase chimaeric bcr/abl messenger RNA translated into a bcr/abl fusion protein, p190, which has an abnormal tyrosine kinase activity and is strongly autophosphorylated in vitro. We have generated mice transgenic for a bcr/abl p190 DNA construct and find that progeny are either moribund with, or die of acute leukaemia (myeloid or lymphoid) 10-58 days after birth. This finding is evidence for a causal relationship between the Philadelphia chromosome and human leukaemia.

Cells of the hemopoietic system arise by proliferation and differentiation of progenitor cells. This process begins with multipotential stem ceUls which can self-renew and also undergo progressive differentiation to progenitor cells committed to particular lineages, ultimately yielding mature blood cells (D. Metcalf and M. A. S. Moore, Haematopoietic Cells, 1971). Early commitment of lymphoid progenitors is generally believed to separate the lymphoid lineage from the myeloid and erythroid lineages, whose progenitors are separated late in differentiation (Metcalf and Moore, 1971). We recently developed a derivative of Moloney murine leukemia virus (M-MuLV) in which the enhancer sequences from simian virus 40 were substituted into the M-MuLV long terminal repeat. This recombinant virus (AMo+SV M-MuLV) induces pre-B and B lymphoid leukemia with long latency after inoculation of 2-day-old NIH Swiss mice (R. Hanecak, P. K. Pattengale, and H. Fan, J. Virol. 62:2427Virol. 62: -2436Virol. 62: , 1988 (Fig. 1B) demonstrated lymphoblastic lymphoma with small-to-intermediate lymphoid cells with monomorphic nuclei, scant cytoplasm, and primitive, dispersed nuclear chromatin. Positive immunoperoxidase staining of tumor tissue sections with the monoclonal antibody RA3-6B2 specific for the B220 antigen (a B-celllineage-specific marker [14]) indicated that the lymphoid tumor was B cell derived (data not shown). In addition, molecular analyses of high-molecular-weight DNA prepared from the tumor showed both immunoglobulin heavy-and light-chain gene rearrangements (8).The AMo+SV M-MuLV-induced lymphoblastic lymphoma described above was established in culture by finely mincing the leukemic cervical lymph node and plating the tissue in Dulbecco modified Eagle medium supplemented with 15% fetal calf serum, 4.0 mM L-glutamine, nonessential amino acids (GIBCO), and 5 x 10' M 2-mercaptoethanol. induced lymphoma (Fig. 1B), the 85-2M cells exhibited a morphology typical of macrophages on cytocentrifuge preparations (Fig. 1A). The cells demonstrated conspicuous vacuolated cytoplasm with eccentric nuclei and were irregular in shape.The 85-2M cells were also tested for the presence of surface antigens found associated with lymphoid cells or myeloid cells. 85-2M cell suspensions (1.5 x 106 cells) were incubated separately at 4°C with antibodies directed against Thyl.2 or B220 (T-and B-cell surface markers, respectively [5,12]) and also with antibodies against Mac-i or Mac-2, surface markers characteristic of myeloid cells and not generally found associated with lymphoid cells (9, 16). Monoclonal antibodies directed against B220, Mac-i, and Mac-2 antigens were not directly conjugated to fluorescein isothiocyanate and therefore were indirectly labeled by a second reaction with goat anti-rat fluorescein isothiocyanate-conjugated second antibody. Unstained 85-2M cells and 85-2M cells incubated with the second antibody alone were used to control for nonspecific fluorescence. The results of flow cytometry are shown in Fig. 2. The 85-2M cells, whil...

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Cells of the hemopoietic system arise by proliferation and differentiation of progenitor cells. This process begins with multipotential stem cells which can self-renew and also undergo progressive differentiation to progenitor cells committed to particular lineages, ultimately yielding mature blood cells (D. Metcalf and M. A. S. Moore, Haematopoietic Cells, 1971). Early commitment of lymphoid progenitors is generally believed to separate the lymphoid lineage from the myeloid and erythroid lineages, whose progenitors are separated late in differentiation (Metcalf and Moore, 1971). We recently developed a derivative of Moloney murine leukemia virus (M-MuLV) in which the enhancer sequences from simian virus 40 were substituted into the M-MuLV long terminal repeat. This recombinant virus (delta Mo + SV M-MuLV) induces pre-B and B lymphoid leukemia with long latency after inoculation of 2-day-old NIH Swiss mice (R. Hanecak, P. K. Pattengale, and H. Fan, J. Virol. 62:2427-2436, 1988). In this report, we describe the derivation of a permanent, virus-producing cell line with the phenotypic characteristics of mature macrophages from a B-cell-derived lymphoblastic lymphoma induced by delta Mo + SV M-MuLV. Comparison studies of immunoglobulin heavy-chain gene rearrangements and also delta Mo + SV M-MuLV proviral integration sites confirmed that the macrophage cell line was derived from the original B-lymphoblastic lymphoma. Moreover, inoculation of the macrophage cell line into animals resulted in histiocytic sarcomas of the macrophage type, thus reflecting stable conversion of B-lymphoid tumor cells to the macrophage phenotype. These results suggest a closer relationship between lymphoid and myeloid cells than previously believed.