Microglia are the resident inflammatory cells of the central nervous system (CNS) and have important roles in development, homeostasis and a variety of neurologic and psychiatric diseases. Difficulties in procuring human microglia have limited their study and hampered the clinical translation of microglia-based treatments shown to be effective in animal disease models. Here, we report the differentiation of human induced pluripotent stem cells (iPSC) into microglia-like cells by exposure to defined factors and co-culture with astrocytes. These iPSC-derived microglia (iPS-MG) have the phenotype, gene expression profile and functional properties of brain-isolated microglia. Murine iPS-MG generated using a similar protocol have equivalent efficacy to primary brain-isolated microglia in the treatment of murine syngeneic intracranial malignant gliomas. The ability to generate human microglia facilitates the further study of this important CNS cell type and raises the possibility of their use in personalized medicine applications.
We have developed induced pluripotent stem cells (iPSCs) from a patient with X-linked chronic granulomatous disease (X-CGD), a defect of neutrophil microbicidal reactive oxygen species (ROS) generation resulting from gp91phox deficiency. We demonstrated that mature neutrophils differentiated from X-CGD iPSCs lack ROS production, reproducing the pathognomonic CGD cellular phenotype. Targeted gene transfer into iPSCs, with subsequent selection and full characterization to ensure no off-target changes, holds promise for correction of monogenic diseases without the insertional mutagenesis caused by multisite integration of viral or plasmid vectors. Zinc finger nuclease–mediated gene targeting of a single-copy gp91phox therapeutic minigene into one allele of the “safe harbor” AAVS1 locus in X-CGD iPSCs without off-target inserts resulted in sustained expression of gp91phox and substantially restored neutrophil ROS production. Our findings demonstrate how precise gene targeting may be applied to correction of X-CGD using zinc finger nuclease and patient iPSCs.
Gene repair of CD34 hematopoietic stem and progenitor cells (HSPCs) may avoid problems associated with gene therapy, such as vector-related mutagenesis and dysregulated transgene expression. We used CRISPR (clustered regularly interspaced short palindromic repeat)/Cas9 (CRISPR-associated 9) to repair a mutation in the CYBB gene of CD34 HSPCs from patients with the immunodeficiency disorder X-linked chronic granulomatous disease (X-CGD). Sequence-confirmed repair of >20% of HSPCs from X-CGD patients restored the function of NADPH (nicotinamide adenine dinucleotide phosphate) oxidase and superoxide radical production in myeloid cells differentiated from these progenitor cells in vitro. Transplant of gene-repaired X-CGD HSPCs into NOD (nonobese diabetic) SCID (severe combined immunodeficient) γc mice resulted in efficient engraftment and production of functional mature human myeloid and lymphoid cells for up to 5 months. Whole-exome sequencing detected no indels outside of the CYBB gene after gene correction. CRISPR-mediated gene editing of HSPCs may be applicable to other CGD mutations and other monogenic disorders of the hematopoietic system.
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