STEM-CELL GENE-THERAPY, POSITION EFFECTS AND CHROMATIN INSULATORS

Low efficiency of gene transfer is the main obstacle for a clinically effective gene therapy at the level of the pluripotent hematopoietic s tem cell. Another important aspect of stem cell gene therapy, the actu al expression of the transduced genes, has only been investigated adeq uately in very few studies, mainly for globin genes, Transcriptional s ilencing and position effects due to negative effects of surrounding c hromatin on the expression of randomly integrated vector sequences may seriously jeopardize the success of current gene therapy strategies, even if transduction efficiency can be significantly improved. We prop ose the incorporation of chromatin insulators in the design of gene th erapy vectors to overcome the problem of position effects. Chromatin i nsulators are protein-binding DNA elements that lack intrinsic promote r/enhancer activity but shelter genes from transcriptional influence o f surrounding chromatin. The best characterized insulators are from Dr osophila. We hypothesize that the important cellular function of chrom atin organization is evolutionarily conserved and that human homologs to Drosophila insulator binding proteins such as the suppressor of Hai ry-wing exist and can be cloned, Using these putative proteins, it sho uld be possible to identify corresponding minimal binding sites with i nsulator activity. The design and incorporation of effective chromatin insulator sequences in the next generation of gene therapy vectors sh ould lead to improved and more predictable expression of therapeutic t ransgenes and constitute an important step toward clinically effective gene therapy.