Correction of uroporphyrinogen decarboxylase deficiency (hepatoerythropoietic porphyria) in Epstein-Barr virus-transformed B-cell lines by retrovirus-mediated gene transfer: Fluorescence-based selection of transduced cells

Hepatoerythropoietic porphyria (HEP) is an inherited metabolic disorder cha racterized by the accumulation of porphyrins resulting from a deficiency in uroporphyrinogen decarboxylase (UROD), This autosomal recessive disorder i s severe, starting early in infancy with no specific treatment. Gene therap y would represent a great therapeutic improvement. Because hematopoietic ce lls are the target for somatic gene therapy in this porphyria, Epstein-Barr virus-transformed B-cell lines from patients with HEP provide a model syst em for the disease. Thus, retrovirus-mediated expression of UROD was used t o restore enzymatic activity in B-cell lines from 3 HEP patients. The poten tial of gene therapy for the metabolic correction of the disease was demons trated by a reduction of porphyrin accumulation to the normal level in defi cient transduced cells. Mixed culture experiments demonstrated that there i s no metabolic cross-correction of deficient cells by normal cells, However , the observation of cellular expansion in vitro and in vivo in immunodefic ient mice suggested that genetically corrected cells have a competitive adv antage. Finally, to facilitate future human gene therapy trials, we have de veloped a selection system based on the expression of the therapeutic gene. Genetically corrected cells are easily separated from deficient ones by th e absence of fluorescence when illuminated under UV light. (C) 1999 by The American Society of Hematology.