Editors' ChoiceBlood Diseases

Ramping Up a Cell’s Chemical Weapon

See allHide authors and affiliations

Science Translational Medicine  08 Jun 2011:
Vol. 3, Issue 86, pp. 86ec85
DOI: 10.1126/scitranslmed.3002719

Oxygen free radicals produced by enzymes such as the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase are an important chemical species used by cells of our immune system such as neutrophils to kill invading microorganisms. A defect in NADPH oxidase, such as that found in X-linked chronic granulomatous disease (X-CGD), prevents neutrophils from killing microbes, resulting in life-threatening infections. Allogeneic hematopoietic stem cell transplantation is a potential curative option for X-CGD patients but is not always available and carries risks. Another option would be to correct the genetic defect in autologous hematopoietic stem cells from the patient ex vivo and then return the corrected cells to the patient, but there are several difficulties with this approach, too.

In a new study, Zou et al. explore the feasibility of a different strategy, in which induced pluripotent stem cells (iPSCs) derived from a patient with X-CGD would be genetically corrected and then would be returned to the patient, where they could differentiate into fully functional neutrophils. As a first step in demonstrating the feasibility of this approach, Zou et al. generated iPSCs from bone marrow mesenchymal stem cells from an X-CGD patient. They established that these iPSCs were pluripotent by demonstrating that they differentiated into cells of the hematopoietic system including neutrophils. They confirmed that the iPSC-derived neutrophils were unable to generate oxygen free radicals and hence retained the X-CGD phenotype. The next step for the investigators was to use genetic engineering to fix the mutant gene in the X-CGD iPSCs. The authors knew that the mutation causing the disease was in the CYBB gene, which encodes a component of NADPH oxidase called gp91phox. Using a gene insertion method exploiting zinc finger nucleases instead of a viral vector, they introduced the correct version of the gene encoding gp91phox into the patient-derived iPSCs. Their method enabled gene insertion through homologous recombination at only one site, the AAVS1 (safe harbor) locus, avoiding the usual route of insertional mutagenesis that may lead to malignancies such as myelodysplasia. Lastly, the researchers demonstrated that their gene insertion method had worked by showing that the neutrophils derived from the genetically corrected iPSCs exhibited normal NADPH oxidase activity and were able to generate oxygen free radicals.

Although preliminary, this study underscores the potential of iPSCs for clinical application. Furthermore, the authors’ targeted gene insertion method appears, at least in vitro, to circumvent the risks associated with insertional mutagenesis. Although there is still much more work to be done, genetically correcting patient-derived iPSCs may be a treatment strategy for at least some blood cell diseases for which, like X-CGD, the genetic mutation is known.

J. Zou et al., Oxidase-deficient neutrophils from X-linked chronic granulomatous disease iPS cells: Functional correction by zinc finger nuclease-mediated safe harbor targeting. Blood 16 March 2011 (10.1182/blood-2010-12-328161). [Abstract]

Navigate This Article