M. F. Greaves

Immunoglobulin gene organisation and expression in haemopoietic stem cell leukaemia.

We have analysed the organisation and expression of mu genes in the granulocytic phase and in the lymphoid and myeloid blast crises of Philadelphia chromosome (Ph1) chronic granulocytic leukaemia (CGL), a leukaemia which is known to arise in multipotential stem cells. We find that mu chain gene rearrangement occurs exclusively in lymphoid blast crisis leading in some, but not all, cases to the synthesis of small amounts of cytoplasmic mu chains characteristic of early pre‐B lymphocytes. In Southern blots, only one or two rearranged mu chain genes are seen, suggesting that a clonal event leading to blast crisis can occur in a committed B cell precursor rather than in the multipotential stem cell precursor, in which the Ph1 chromosome originated. The pattern of mu gene rearrangement observed in Ph1 CGL blast crisis is compared with that in normal B cells, other B lineage malignancies, myeloid leukaemias and T cell leukaemias.

Rearrangement of immunoglobulin heavy chain genes in human T leukaemic cells shows preferential utilization of the D segment (DQ52) nearest to the J region.

The DNA rearrangements leading to the assembly of genes coding for the immunoglobulin heavy chain (IgH) in B cells and the T cell receptor for antigen in T cells are not completely lineage specific. This probably reflects the use of a common recombinase by IgH and the T cell receptor. This paper describes novel observations on the nature of these cross‐lineage rearrangements. A high proportion (though not all) IgH rearrangements in human T leukaemic cells involve the D segment nearest to the J region (DQ52). This same D segment is not involved in B cell IgH rearrangements with one important exception, namely a proportion of B cell leukaemic clones with the most primitive B cell precursor phenotype. These observations have potentially important implications for early lymphoid cell differentiation and in particular support the idea that the 3′ D plus J region might lie within a limited window of accessibility of the IgH gene in precursor lymphocytes.

IS SPONTANEOUS MUTATION THE MAJOR ‘CAUSE’ OF CHILDHOOD ACUTE LYMPHOBLASTIC LEUKAEMIA?

Acute lymphoblastic leukaemia (ALL) in children has an annual incidence rate of around two to three cases per lo5 age-matched population in Europe and the U.S.A. (Breslow & Langholz, 1983; Davies, 1973). Although it is rare compared with the common cancers of adults, ALL is the major paediatric cancer in developed societies. Despite substantial advances in the treatment of ALL and understanding of its biology (reviewed in Murphy & Gilbert, 1983) the aetiology of this disease remains enigmatic. Doubtless the very rarity of childhood leukaemia has been a major impediment to epidemiological studies which might provide clues to causality. Nevertheless, a substantial number of environmental, genetic (inherited) or immunological factors are reported to be associated with the occurrence of ALL (reviewed in Magrath et al, 1984; Linet. 1985; Greaves et al, 1985; Pendergrass, 1985). Most of these correlates are, however, rather weak, controversial or as yet unsubstantiated. A few that are more striking and potentially important are discussed below.

Expression of HPCA‐1 and HLA‐DR antigens on growth factor‐ and stroma‐dependent colony forming cells

The expression of HLA‐DR and HPCA‐1 antigens (recognized by the L243 and BL3C5 antibodies respectively) on adult human bone marrow cells was examined by fluorescence activated cell sorting and colony assays. Nearly all the (day 14) lineage restricted and multipotential colony forming cells analysed in methylcellulose cultures in the presence of added growth factors express HLA‐DR and HPCA‐1 determinants. Two colour cell sorting reveals that the lineage restricted HLA‐DR positive progenitors express variable levels of BI.3C5 positivity whereas most of the multipotential progenitors, the multi‐CFC or CFU‐GEMM, are highly BI.3C5 positive. The isolated HLA‐DR and BI.3C5 positive populations also contain haemopoietic precursors which adhere to and form colonies on pre‐formed stromal layers. Thus, haemopoietic progenitors assayed in both types of culture system can be analysed and enriched by simultaneous two‐colour sorting using anti‐HLA‐DR and BI.3C5 monoclonal antibodies. Similarities in the antigenic phenotype of such cells, however, precludes the use of these reagents for segregating growth factor‐dependent from stroma‐dependent progenitors.

Leucemia linfoma T del adulto en Chile.: Estudio clínico-patológico y molecular de 26 pacientes

Background: Adult T cell leukemia lymphoma is a lymphoproliferative syndrome etiologically associated to human T cell lymphotropic virus type I. Aim: To describe the clinical and laboratory features of 26 Caucasian Chilean patients, with HTLV-I positive adult T-cell leukemia lymphoma (ATLL). Material and methods: Diagnostic criteria included clinical features, cell morphology, immunophenotype, HTLV-I serology and/or DNA analysis by Southern blot or PCR. Results: According to the clinical presentation, 12 cases had the acute ATLL form, 6 had a lymphoma, 4 the chronic form and 4 had smoldering ATLL. The median presentation age was 50 years, younger than the Japanese patients, but significantly older than patients from other South American countries (eg Brasil, Jamaica, Colombia). The main clinical features: lymphadenopathy, skin lesions and hepatosplenomegaly, were similar in frequency to those of patients from other countries, except for the high incidence of associated neurological disease. Tropical Spastic Paraparesis (TSP) in our series of ATLL, was seen in one third of the patients (8/26). A T-cell immunophenotype was shown in all 26 cases and HTLV-I serology was positive in 25/26 patients. Molecular analysis on the seronegative patient showed clonal integration of proviral HTLV-I DNA into the lymphocytes DNA, and thus he may have been a poor responder to the retroviral infection. Proviral DNA integration was also demonstrated in 15/16 patients being clonal in 10, polyclonal in 3 (all smoldering cases) and oligoclonal in one. Conclusions: ATLL in Chile has similar clinical and laboratory features than the disease in other parts of the world, except for a younger age than Japanese patients but older than those from other Latin American countries and a high incidence of patients with associated TSP. Detailed morphological and immunophenotypic analysis of the abnormal circulating lymphocytes, together with the documentation of HTLV-I by serology and/or DNA analysis are key tests for the identification of this disease.

Cell Lineage Specificity of Chromatin Configuration and Gene Expression in Haemopoietic Progenitor Cells

Haemopoietic stem cells have the potential to activate up to eight distinct cell lineage specific genetic programmes [1]. The mechanisms of cell lineage choice or commitment are fundamental to developmental biology in general and are beginning to be unravelled at least in invertebrates (e.g., Drosophila, Nematodes, slime moulds). Transacting DNA binding proteins that directly or indirectly regulate gene transcription are central players in the game [2], as are inductive cellular interactions [3]. In haemopoietic differentiation, it is clear that selective progenitor-stromal cell interactions involving both adhesive and growth factor recognition [4–7] are playing a role in early decision-making but the basic mechanisms whereby uni-lineage adoption is made are still obscure.

Involvement of the D segment (DQ52) nearest to the JH region in immunoglobulin gene rearrangements of lymphoid-cell precursors.

The specific antigen recognition molecules expressed by B and T lymphocytes, the immunoglobulins (Ig) and the T-cell receptor for antigen (TCR) are coded for by genes which are assembled in an ordered series of somatic DNA recombination events during lymphocyte differentiation. In B lymphocytes the heavy chain gene of the Ig molecule (IgH) is the first to be assembled and this occurs by two successive DNA rearrangements in which first a diversity segment (D) and then a variable gene segment (V) are joined, usually by a process of intrachromosomal deletion, to a joining segment (J) to form a complete variable region sequence (for a review, see Alt et al. 1986). A similar sequence of DNA recombinations leads to the assembly of variable region sequences from V, D and J gene segments in the TCR genes (for a recent review, see Kronenberg et al. 1986).

Cloning of Human Thymic Subcapsular Cortex Epithelial Cells by SV40 ori− Transfection

Critical steps in the early differentiation of T lymphocytes occur within the thymus. Bone-marrow derived cells migrating into this organ undergo extensive proliferation, clonal rearrangement of antigen receptor genes and an associated immunological “education” involving tolerance to self-antigens and positive selection for antigen recognition in association with self-MHC (Zinkernagel 1978; Haynes 1984; Rothenberg and Lugo 1985; Lo and Sprent 1986). The control of this complex process of commitment, expansion, clonal diversification, selection and maturation is not understood, but almost certainly involves selective interactions with distinct elements of the thymic stromal environment and diffusable regulators, thymic “hormones” or growth factors.