Differential effects of iron and iron carrier on hematopoietic cells differentiation and human ADA gene transfer.

The role of iron and heme was examined in bone marrow cells from iron-deficient and chronically iron-overloaded rats. Erythroid colony cultures (CFU-E) demonstrated that iron-overloaded bone marrow cells were poor hemin (iron carrier) and CFU-E responders in vitro, whereas iron-deficient marrows grew exuberant numbers of CFU-E and responded to hemin. Results support the concept that iron, or associated factors, plays an important role in the manipulation of HO activity which modulates the hemopoietic potential of the organism. Using cultures of erythroid (CFU-E, BFU-E) and myeloid (CFU-GM), results demonstrated that exogenous hemin (iron carrier) has a specific beneficial effect on human bone marrow progenitor cells, which is not seen with iron (10(-4)M) or other metalloporphyrins. Higher concentrations of iron (10(-3)M) and ZnPP were in fact inhibitory to bone marrow growth. This inhibition was not reversed with higher concentrations of Epo or GM-CSF. The beneficial effect of iron may be best realized in the bound form such as heme. In addition, the effect of bound and nonbound iron was tested for its effect on gene transfer. By using a murine adherent cell layer (ACL) in a prestimulation phase, followed by human gene transfer of ADA into mouse bone marrow cells and Southern blot analysis, successful gene transfer was accomplished. ADA integration patterns were detected in CFU-S from stem cells of mice 5-11 months after transfer. When 10 microM ferric chloride was included in the ACL prestimulation phase, there was a marked depression in ADA integration into stem cells as compared to heme or non-heme controls. Furthermore, heme-bound iron had no effect and deferoxamine included with iron was able to reverse the inhibitory effect of iron on the gene transfer process. Thus, iron must be non-bound to exert its suppressive effect, and chelation of excess iron under clinical conditions of iron overload may be essential for successive gene transfer.