A.V. Hoffbrand

“Pre-B” phenotypes in blast crisis of Ph1 positive CML: Evidence for a pluripotential stem cell “target”

Abstract Twenty six cases of Ph1 positive acute leukaemia, either CML in blast crisis (20 patients) presenting with acute leukaemia (6 patients) were tested with a panel of membrane markers, enzyme assays and for cytoplasmic IgM, the latter being a marker of the earliest detectable cells in the B cell lineage (—“pre-B” cells). Nineteen cases are described with the same same “lymphoid” phenotype as Ph1 negative common ALL, and three of these, all CML in blast crisis, had leukaemic cells with a pre-B phenotype. In two further cases a minority population of leukaemic cells had a similar pre-B phenotype. Two of the former cases are described in detail. These data provide evidence for Ph1 chromosome expression in the B cell lineage in patients with CML; this is suggested to reflect the existence of a common progenitor of lymphoid and myeloid lineages in humans, providing a “target” cell for the Ph1 chromosomal alteration and leukaemia.

Human thymus/leukaemia-associated antigen (a low-molecular weight form of adenosine deaminase) and the phenotype of leukaemic cells

Abstract A water soluble human thymus/leukaemia-associated antigen (HThy-L) was recently identified as a low-molecular-weight form of adenosine deaminase (ADA). In the present study levels of the enzyme in normal and leukaemic cells and plasma have been assessed by an enzymatic method and/or radioimmunoassay (RIA) for HThy-L. In addition, the relationship between the levels of enzyme and the phenotype of leukaemic cells was evaluated. The findings can be summarised as follows: 1. There is a good correlation between levels of ADA detected by the RIA and the enzymatic method in normal and leukaemic cells but a poor correlation between levels in cells versus plasma in leukaemic patients. 2. All patients with T-cell acute lymphoblastic leukaemia (ALL) tested had high quantities of ADA in plasma and blast cells compared with normal blood or marrow cells. 3. Approximately 50% of patients with common ALL had increased quantities of ADA in leukaemic cells. 4. Patients with chronic myeloid leukaemia both in the stable phase of disease and in blast crisis generally had low quantities of ADA in leukaemic cells although some cases of blast crises (both ‘lymphoid’ and ‘myeloid’) had raised plasma levels. These data further support the view that ADA activity is highest in the early stages of T-lymphocyte maturation and in corresponding leukaemias.

DNA strand breakage and ADP-ribosyl transferase mediated DNA ligation during stimulation of human bone marrow cells by granulocyte-macrophage colony stimulating activity

ADP-ribosyl transferase (ADP-RT) is a chromatin-bound nuclear enzyme catalysing the transfer of ADP-ribose from NAD+ to chromatin proteins. The enzyme is activated by DNA strand breaks and has been suggested to have roles in both DNA repair (via its effect on DNA ligase II) and in differentiation. We recently demonstrated that specific inhibitors of ADP-RT preferentially inhibit differentiation of human granulocyte-macrophage progenitor cells to the macrophage lineage and that the specific proliferation/differentiation stimulus granulocyte-macrophage colony stimulating activity (GM-CSA) activates ADP-RT in human marrow cells within 3 h of exposure. The purpose of this study was to investigate the role of ADP-RT in monocyte-macrophage differentiation. By altering the time of addition of ADP-RT inhibitor it was demonstrated that maximal inhibition of macrophage differentiation only occurs when the inhibitor is added within the first 24 h of culture. This suggests that it is an early event during the induced differentiation of granulocyte-macrophage progenitor cells which requires ADP-RT. Fluorometric assay of the level of DNA strand breaks showed that GM-CSA induces DNA strand breaks which are rapidly ligated only if ADP-RT is available. These data and those of our earlier studies suggest that DNA rearrangement may be involved in differentiation of granulocyte-macrophage progenitors to the monocyte-macrophage pathway. Such a DNA rearrangement could provide a molecular basis for commitment of multipotent progenitors to a single lineage.