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H 2 O 2 acts as a second messenger in key signaling circuits, transiently modulating tyrosine phosphatases and kinases. We investigated its origin, membrane transport, and functional role during B cell activation and differentiation. Our data identified NADPH-oxidase 2 as the main source of H 2 O 2 and aquaporin 8 as a transport facilitator across the plasma membrane. On aquaporin 8 silencing, inducible B lymphoma cells responded poorly to TLR and BCR stimulation. Their differentiation was severely impaired, as demonstrated by retarded onset of IgM polymerization, low amounts of IgM secretion, and prolonged BCR expression on the cell surface. A silencing-resistant aquaporin 8 rescued responsiveness, confirming that the import of H 2 O 2 across the membrane is essential for B cell activation. The addition of exogenous catalase to primary B splenocytes severely impaired the tyrosine phosphorylation induced by BCR cross-linking, as did the absence of NOX2 in a murine model of chronic granulomatous disease. Importantly, re-expression of gp91 phox through gene therapy restored the specific B cell signaling deficiency in NOX2 -/- cells. Thus, efficient induction of B cell activation and differentiation requires intact H 2 O 2 fluxes across the plasma membrane for signal amplification., (© Society for Leukocyte Biology.)

Chronic granulomatous disease (CGD) is a primary immunodeficiency due to a deficiency in one of the subunits of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. CGD patients are characterized by an increased susceptibility to bacterial and fungal infections, and to granuloma formation due to the excessive inflammatory responses. Several gene therapy approaches with lentiviral vectors have been proposed but there is a lack of in vivo data on the ability to control infections and inflammation. We set up a mouse model of acute infection that closely mimic the airway infection in CGD patients. It involved an intratracheal injection of a methicillin-sensitive reference strain of S. aureus. Gene therapy, with hematopoietic stem cells transduced with regulated lentiviral vectors, restored the functional activity of NADPH oxidase complex (with 20-98% of dihydrorhodamine positive granulocytes and monocytes) and saved mice from death caused by S. aureus, significantly reducing the bacterial load and lung damage, similarly to WT mice even at low vector copy number. When challenged, gene therapy-treated XCGD mice showed correction of proinflammatory cytokines and chemokine imbalance at levels that were comparable to WT. Examined together, our results support the clinical development of gene therapy protocols using lentiviral vectors for the protection against infections and inflammation.

Regulated transgene expression may improve the safety and efficacy of hematopoietic stem cell (HSC) gene therapy. Clinical trials for X-linked chronic granulomatous disease (X-CGD) employing gammaretroviral vectors were limited by insertional oncogenesis or lack of persistent engraftment. Our novel strategy, based on regulated lentiviral vectors (LV), targets gp91(phox) expression to the differentiated myeloid compartment while sparing HSC, to reduce the risk of genotoxicity and potential perturbation of reactive oxygen species levels. Targeting was obtained by a myeloid-specific promoter (MSP) and posttranscriptional, microRNA-mediated regulation. We optimized both components in human bone marrow (BM) HSC and their differentiated progeny in vitro and in a xenotransplantation model, and generated therapeutic gp91(phox) expressing LVs for CGD gene therapy. All vectors restored gp91(phox) expression and function in human X-CGD myeloid cell lines, primary monocytes, and differentiated myeloid cells. While unregulated LVs ectopically expressed gp91(phox) in CD34(+) cells, transcriptionally and posttranscriptionally regulated LVs substantially reduced this off-target expression. X-CGD mice transplanted with transduced HSC restored gp91(phox) expression, and MSP-driven vectors maintained regulation during BM development. Combining transcriptional (SP146.gp91-driven) and posttranscriptional (miR-126-restricted) targeting, we achieved high levels of myeloid-specific transgene expression, entirely sparing the CD34(+) HSC compartment. This dual-targeted LV construct represents a promising candidate for further clinical development.