No abstract

Previous studies have demonstrated that sickle cell disease (SCD) can be corrected in mouse models by transduction of hematopoietic stem cells with lentiviral vectors containing antisickling globin genes followed by transplantation of these cells into syngeneic recipients.

When transgenic mice that expressed human sickle hemoglobin were mated with mice having knockout mutations of the mouse alpha- and beta-globin genes, animals were produced that synthesized only human hemoglobin in adult red blood cells. Similar to many human patients with sickle cell disease, the mice developed a severe hemolytic anemia and extensive organ pathology. Numerous sickled erythrocytes were observed in peripheral blood. Although chronically anemic, most animals survived for 2 to 9 months and were fertile. Drug and genetic therapies can now be tested in this mouse model of sickle cell disease.

Previous studies demonstrated correct tissue-and temporal-specific expression of human 7-and ~-globin genes in transgenic mice; however, expression was extremely low. When the erythroid-specific DNase I superhypersensitive (HS) sites that are normally located upstream of the human 13-globin locus were fused individually to 7" or 13-globin genes, expression increased to endogenous mouse globin levels but temporal specificity was lost. In contrast, when the HS sequences were combined with fragments containing both 7" and 13-globin genes, correct developmental regulation was restored. We suggest that human 7" to 13-globin gene switching during development results from competition of individual globin gene family members for interaction with the HS sequences and that factors influencing these competitive interactions determine temporal specificity.