We describe a patient with acute nonlymphocytic leukaemia (ANLL) derived from myelodysplastic syndrome in whom the Philadelphia chromosome (Ph1) first emerged at the late stage of ANLL transformation. Cytogenetically, the Ph1 chromosome was not detected until the late stage of ANLL transformation, 14 months after the transformation following a 3-month history of refractory anaemia with excess of blasts. The cells with and without the Ph1 chromosome had a common abnormal chromosome, t(3;3) (q21;q26). The reverse transcription-polymerase chain reaction analysis showed no bcr/abl message at diagnosis. However, the mRNA encoding P210bcr/abl was detected in the early stage of ANLL transformation. Furthermore, the mRNAs encoding both P210bcr/abl and P190bcr/abl were detected in the late stage of ANLL transformation when the Ph1 chromosome was detected by cytogenetic analysis. These evidences support a multistep pathogenesis of leukaemias, and the products of bcr/abl fusion gene may influence the course of disease.

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Summary. Acute promyelocytic leukaemia (APL) associated with a t(15:17) translocation generates a PML/KARa chimaeric gene which is transcribed as a fusion PML/RARα mRNA. To clarify the pathophysiologic role of PML/RARα in APL patients, we examined the expression of PML/RAKα in haemopoietic colonies in five patients with APIA by reverse transcriptase polymerase chain reaction (RT‐PCR) analysis. By the two‐step RT‐PCR method, we demonstrated that PML/ RARα positive clones were present in progenitor cells including both CFU‐GM'and BFU‐E in two cases. This result suggests that the translocation of PML/RARα occurred in a pluripotent stem cell in some APL patients. In four patients we detected two amplified cDNA fragments of 780 and 640 bp which presumably arose by alternative splicing of the PML gene. Interestingly of CFU‐GM and BFU‐E colonies examined in four patients, there were three different types of colonies: those expressing only the 780 bp fragment, those expressing only the 640 bp fragment, and those expressing both fragments. This suggests that alternative splicing was clonally determined in each colony. We describe a useful RT‐PCR technique for the study of gene expression in a limited number of haemopoietic precursor cells.

Bone marrow-derived fibroblastoid colony-forming cells (CFU-F) and granulocyte/macrophage precursor cells (CFU-GM) were studied in patients with acute leukemia. The numbers of CFU-F and CFU-GM were significantly lower in patients with acute myelogenous leukemia (AML) and acute lymphocytic leukemia (ALL) at diagnosis than in normal subjects, although patients with AML had a very wide range of CFU-F colony-forming efficiency. However, a suppressive effect of leukemic cells on normal CFU-F colony formation was not observed. CFU-F and CFU-GM in patients with acute leukemia recovered to normal levels when complete remission (CR) was achieved and decreased again at relapse. Serial studies showed that the increase in CFU-F preceded the recovery of CFU-GM. In AML, furthermore, patients who achieved CR had a higher number of CFU-F than patients without CR, suggesting that the CFU-F level at diagnosis may contribute to the prediction of the likelihood of remission induction in patients with AML.

The number of bone marrow-derived fibroblastoid colony-forming cells (CFU-F) and the production of colony-stimulating activity (CSA) by bone marrow stromal cells were studied in 71 patients with myeloproliferative disorders (MPD). The numbers of CFU-F in chronic-phase chronic myelogenous leukemia (CML), polycythemia vera (PV) and essential thrombocythemia (ET) were not different from those in normal subjects. However, the number of CFU-F in acute-phase CML was markedly decreased. Bone marrow adipocyte colony-forming capacity (adipo-CFC), which was previously shown to reflect both the number of pre-adipocytes and the stromal cell function in vivo, was increased in patients with chronic-phase CML, PV and ET, but was absent in acute-phase CML patients. The production of CSA by marrow stromal cells of MPD patients, however, was not different from that of normal subjects. These results suggest that the characteristics of marrow stromal and its precursor cells of chronic-phase MPD patients were not different from those of normal subjects, however, they became changed in acute-phase CML patients.