Therapeutic globin expression in thalassemia patient induced pluripotent stem cells from genomic safe harbors

The advent of human induced pluripotent stem (iPS) cells enables for the first time the derivation of unlimited numbers of patient-specific stem cells and holds great promise for regenerative medicine. However, realizing the full potential of iPS cells requires robust, precise and safe strategies for their genetic modification. Safe human iPS cell engineering is especially needed for therapeutic applications, as stem cell-based therapies that rely on randomly integrated transgenes pose oncogenic risks. Here we describe a strategy to genetically modify iPS cells from patients with beta-thalassemia in a potentially clinically relevant manner. Our approach is based on the identification and selection of safe harbor sites for transgene expression in the human genome. We show that thalassemia patient iPS cell clones harboring a transgene can be isolated and screened according to chromosomal position. We next demonstrate that iPS cell clones that meet our safe harbor criteria resist silencing and allow for therapeutic levels of beta-globin expression upon erythroid differentiation without perturbation of neighboring gene expression. Combined bioinformatics and functional analyses thus provide a robust and dependable approach for achieving desirable levels of transgene expression from selected chromosomal loci. This approach may be broadly applicable to introducing therapeutic or suicide genes into patient specific iPS cells for use in cell therapy.

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Papapetrou EP, Lee G, Malani N, Setty M, Riviere I, Tirunagari LM, Kadota K, Roth SL, Giardina P, Viale A, Leslie C, Bushman FD, Studer L, Sadelain M