However, the investigators also observed progressive
clonal expansion of myeloid cells with common insertional mutagenesis events, as well as progressive gene silencing. Most importantly, the gene therapy was associated with eventual emergence of myelodysplasia with chromosome 7 abnormalities consequent to EVI1 oncogene activation [38]. These findings raise concerns about leukemogenesis, such as that observed in the French gene therapy trials for severe combined immunodeficiency [39]. The clinical relevance of ROS was first demonstrated in phagocytes of patients with CGD that have defective microbicidal activity 5-Fluoracil ic50 resulting from deficient superoxide production because of mutations affecting NADPH oxidase components [40, 41]. In addition, Odell and Segal [42] have shown that phagocyte oxidase function Venetoclax supplier also influences phagosomal pH, which may affect granule-mediated killing of pathogens and help explain the microbial spectrum of infections in CGD, when killing depends on non-oxidative mechanisms alone. For example, S. aureus, S. marcescens, N. asteroids and A. fumigatus require neutral pH for effective non-oxidative killing and are resistant at the acid pH found in the phagosomes of CGD neutrophils; whereas C. albicans may be an uncommon pathogen in CGD
because it is susceptible to non-oxidative killing at the acid pH found in the CGD neutrophil phagosome. Moreover, Reeves et al. [43] have shown that phagocyte production of ROS leads to microbial killing through
the activation of certain primary granule proteins inside the phagocytic vacuole. This paradigm for NADPH oxidase–mediated killing suggests that ROS also act as intracellular signalling molecules, leading to the activation of other non-oxidative pathways. One implication is that, in the absence of NADPH oxidase activity, phagocyte enzymes are present but hypofunctional. This model suggests that phagocytes are capable of a spectrum of microbicidal activity that can be regulated to varying degrees, rather than encompassing distinct oxidative and non-oxidative mechanisms [22]. Mutations in all of the five structural genes of the NADPH oxidase Leukotriene-A4 hydrolase have been found to cause CGD. Mutations in gp91phox account for about 65% of cases, mutations in p47phox about 25%, and the remainder is divided between p67phox and p22phox; there are no autosomal dominant cases of CGD [23, 44]. To date, no patients with CGD have been reported with defects in Rap1A, Rac1 or GDI components. A single patient with a defect in p40phox has been reported, with mild disease limited to granulomatous colitis [45]. The two reported cases of Rac2 deficiency demonstrated a very severe phenotype combining clinical and biochemical features of both CGD and leucocyte adhesion deficiency [46].