Chromosomal rearrangements are initiating events in acute lymphoblastic leukaemia (ALL). Here using RNA sequencing of 560 ALL cases, we identify rearrangements between MEF2D (myocyte enhancer factor 2D) and five genes (BCL9, CSF1R, DAZAP1, HNRNPUL1 and SS18) in 22 B progenitor ALL (B-ALL) cases with a distinct gene expression profile, the most common of which is MEF2D-BCL9. Examination of an extended cohort of 1,164 B-ALL cases identified 30 cases with MEF2D rearrangements, which include an additional fusion partner, FOXJ2; thus, MEF2D-rearranged cases comprise 5.3% of cases lacking recurring alterations. MEF2D-rearranged ALL is characterized by a distinct immunophenotype, DNA copy number alterations at the rearrangement sites, older diagnosis age and poor outcome. The rearrangements result in enhanced MEF2D transcriptional activity, lymphoid transformation, activation of HDAC9 expression and sensitive to histone deacetylase inhibitor treatment. Thus, MEF2D-rearranged ALL represents a distinct form of high-risk leukaemia, for which new therapeutic approaches should be considered.

No abstract

Gene transfer vectors based on adeno-associated virus (AAV) appear promising because of their high transduction frequencies regardless of cell cycle status and ability to integrate into chromosomal DNA. We tested AAV-mediated gene transfer into a panel of human bone marrow or umbilical cord-derived CD34+ hematopoietic progenitor cells, using vectors encoding several transgenes under the control of viral and cellular promoters. Gene transfer was evaluated by (1) chromosomal integration of vector sequences and (2) analysis of transgene expression. Southern hybridization and fluorescence in situ hybridization analysis of transduced CD34 genomic DNA showed the presence of integrated vector sequences in chromosomal DNA in a portion of transduced cells and showed that integrated vector sequences were replicated along with cellular DNA during mitosis. Transgene expression in transduced CD34 cells in suspension cultures and in myeloid colonies differentiating in vitro from transduced CD34 cells approximated that predicted by the multiplicity of transduction. This was true in CD34 cells from different donors, regardless of the transgene or selective pressure. Comparisons of CD34 cell transduction either before or after cytokine stimulation showed similar gene transfer frequencies. Our findings suggest that AAV transduction of CD34+ hematopoietic progenitor cells is efficient, can lead to stable integration in a population of transduced cells, and may therefore provide the basis for safe and efficient ex vivo gene therapy of the hematopoietic system.

Twenty-nine of 172 patients (17%) who received an allogeneic bone marrow transplant (BMT) from histocompatible sibling donors for hematologic malignancies were mixed hematopoietic chimeras; ie, they had a mixture of donor and host hematopoietic or lymphohematopoietic cells at greater than or equal to 14 days after transplantation. Twenty- four of the 29 mixed chimeras (83%) have remained in continuous complete remission for up to 116 months (greater than 9 years) following BMT. Four of the 29 patients (14%) have had recurrent leukemia, and 7 of the 29 (24%) have had moderate or severe graft-v- host disease (GVHD). Twelve of these 29 patients have persisted as stable mixed chimeras for greater than or equal to 2 years after BMT, whereas other patients converted to all donor-type hematopoiesis. The incidence of mixed chimerism was independent of the pretransplant regimen, the donor or recipient age (less than 20 v greater than 20 years), remission status (first complete remission of acute leukemia and first chronic phase of chronic myelocytic leukemia v later stages of disease), and type of leukemia. Our data indicate that mixed hematopoietic chimerism is not rare after BMT for hematologic malignancies and that its presence is compatible with long-term disease- free survival. Prospective studies of mixed chimerism after BMT are warranted to achieve better understanding of its biologic importance.

We treated 109 patients with adult acute lymphoblastic leukemia (ALL) diagnosed by histochemical and immunologic techniques. Patients were excluded only for age greater than 50 years and Burkitt's leukemia. Treatment included a four-drug remission induction phase followed by alternating cycles of noncrossresistant chemotherapy and prolonged oral maintenance therapy. Eighty-eight percent of patients entered complete remission. With a median follow-up of 77 months (range, 48 to 111 months), 42% +/- 6% (SEM) of patients achieving remission are projected to remain disease-free at 5 years, and disease-free survival for all patients entered on study is 35% +/- 5%. Failure to achieve remission within the first 4 weeks of therapy and the presence of the Philadelphia chromosome are associated with a 100% risk of relapse. Remission patients with neither of these adverse features have a 48% +/- 6% probability of remaining in continuous remission for 5 years. Patients with T-cell phenotype have a favorable prognosis with 59% +/- 13% of patients achieving remission remaining disease-free compared with 31% +/- 7% of CALLA-positive patients. Intensive chemotherapy may produce prolonged disease-free survival in a sizable fraction of adults with ALL. Improved therapy is needed, especially for patients with adverse prognostic features.