Correction of deficient CD34+ cells from peripheral blood after mobilization in a patient with congenital erythropoietic porphyria.

Congenital erythropoietic porphyria (CEP) is an inherited disease due to a deficiency in the uroporphyrinogen III synthase (UROS), the fourth enzyme of the heme pathway. It is characterized by accumulation of uroporphyrin I in the bone marrow, peripheral blood, and other organs. The onset of most cases occurs in infancy and the main symptoms are cutaneous photosensitivity and hemolysis. For severe transfusion-dependent cases, when allogeneic cell transplantation cannot be performed, autografting of genetically modified primitive/stem cells is the only alternative. In the present study, efficient mobilization of peripheral blood primitive CD34+ cells was performed on a young adult CEP patient. Retroviral transduction of this cell population with the therapeutic human UROS (hUS) gene resulted in both enzymatic and metabolic correction of CD34+-derived cells, as demonstrated by the increase in UROS activity and by a 53% drop in porphyrin accumulation. A 10–24% gene transfer efficiency was achieved in the most primitive cells, as demonstrated by the expression of enhanced green fluorescent protein (EGFP) in long-term culture-initiating cells (LTC-IC). Furthermore, gene expression remained stable during in vitro erythroid differentiation. Therefore, these results are promising for the future treatment of CEP patients by gene therapy.