Enhanced Host Defense After Gene Transfer in the Murine p47phox-Deficient Model of Chronic Granulomatous Disease

Abstract

Abstract The p47phox−/− mouse exhibits a phenotype similar to that of human chronic granulomatous disease (CGD) and, thus, is an excellent model for the study of gene transfer technology. Using the Moloney murine leukemia virus–based retroviral vector MFG-S encoding the human form of p47phox, we performed ex vivo gene transfer into Sca-1+ p47phox−/− marrow progenitor cells without conditioning of donors with 5-fluorouracil. Transduced progenitors were transplanted into moderately irradiated (500 cGy), G-CSF preconditioned sibling p47phox−/− mice. Using the fluorescent probe dihydrorhodamine 123 (DHR), in vivo biochemical correction of the superoxide-generating NADPH oxidase system was detected by flow cytometry in 12.3% ± 0.9% of phorbol myristate acetate–stimulated peripheral blood neutrophils at 4 weeks and 2.6% ± 1.0% at 14 weeks after transplantation. Following gene therapy, mice were challenged with the CGD pathogen Burkholderia (formerly Pseudomonas) cepacia and bacteremia levels were assessed at 24 hours and 7 days after inoculation. At both time points, bacteremia levels in gene corrected p47phox−/− mice were significantly lower than untreated p47phox−/− mice (0.89 ± 0.30 colonies v 237.7 ± 83.6 colonies at 24 hours, P < .02; 4.0 ± 2.0 colonies v 110.2 ± 26.5 colonies at 7 days, P < .0014). More importantly, Kaplan-Meier survival analysis showed a significant survival advantage of gene corrected versus untreated p47phox−/− mice (P < .001). Thus, stem-cell–directed ex vivo gene therapy is capable of restoring phagocyte oxidant-dependent host-defense function in this mouse model of a human immune-system disorder.