Dysregulation of HOX11 by chromosome translocations in T-cell acute lymphoblastic leukemia: a paradigm for homeobox gene involvement in human cancer.

The translocation t(10;14)(q24;q11) is observed in the course of routine cancer cytogenetic studies in 5-10% of patients with T-cell acute lymphoblastic leukemia (ALL). Recent molecular dissections of t(10;14) translocations support the hypothesis that these relatively gross chromosomal mutations represent key genetic steps in neoplastic transformation. The genes consistently involved are the T-cell receptor (TCR) delta-chain gene in 14q11 and a human homeobox-containing gene in 10q24, HOX11, initially identified through cloning of t(10;14) translocations. Like other homeoproteins, HOX11 binds DNA with sequence specificity and is likely to be a transcription factor, controlling the expression of developmentally important genes. The t(10;14) translocations arise as a result of aberrant physiological recombinational events that occur at early stages of T-cell development, probably during failed attempts at TCR gene rearrangement. The net result of the aberrant genetic recombinations is inappropriate expression of HOX11 in individual T-cells that acquire the mutation. Tlx-1, the murine homolog of HOX11, is expressed embryologically in the developing spleen and in structures derived from cranial neural crest cells and migratory paraxial mesoderm. Mice homozygously deleted for Tlx-1 are asplenic. Thus, HOX11 may be one of the first examples in mammals of a "master gene" acting as a regulatory switch controlling a downstream program of organ-specific cell growth and proliferation. Preliminary tumorigenicity assays suggest that HOX11 expression in hematopoietic cells most likely plays an immortalization role in neoplastic transformation.(ABSTRACT TRUNCATED AT 250 WORDS)

Gene transfer into hematopoietic stem cells: long-term maintenance of in vitro activated progenitors without marrow ablation.

Adoptive transfer of genetically modified somatic cells will play an increasingly important role in the management of a wide spectrum of human diseases. Among the most appealing somatic cells as potential gene transfer vehicles are hematopoietic cells, because of their wide distribution and their well-characterized capacities for proliferation, differentiation, and self-renewal. Genes can be readily transferred into short-lived and lineage-restricted hematopoietic cells, but there remains a need to develop reliable methods for gene transfer into hematopoietic stem cells in large animals. In this work, we used a gene transfer approach in which hematopoietic cells in long-term marrow cultures were exposed to the replication-defective retrovirus N2, bearing the reporter gene neo, on multiple occasions during 21 days of culture. Genetically marked cultured autologous cells were infused into 18 canine recipients in the absence of marrow-ablative conditioning. neo was detected by Southern blotting and/or the polymerase chain reaction in the marrow, blood, marrow-derived granulocyte/macrophage and erythroid progenitors, and cultured T cells in dogs after infusion. In most dogs, the proportion of long-term marrow culture cells contributing to hematopoiesis rose during the first 3 months after infusion and peaked within the first 6. The maximal levels attained were between 10% and 30% G418-resistant (neo-positive) granulocyte/macrophage progenitors. At 12 months, five dogs maintained greater than 10% G418-resistant progenitors, and for two of them this level exceeded 20%. Two dogs had greater than 5% G418-resistant hematopoietic progenitors at 24 months after infusion. Our data suggest that very primitive hematopoietic progenitors are maintained in long-term marrow cultures, where they can be triggered into entering the cell cycle. In vivo, these activated cells likely continue normal programs of proliferation, differentiation, and self-renewal. Their progeny can be maintained at clinically relevant levels for up to 2 years without the requirement that endogenous hematopoiesis be suppressed through chemo- or radiotherapy prior to adoptive transfer. Long-term marrow culture cells may thus be ideal targets for gene therapy involving adoptive transfer of transduced hematopoietic cells.