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Summary Engineered CRISPR/Cas9-based transcriptional activators can potently and specifically activate endogenous fate-determining genes to direct differentiation of pluripotent stem cells. Here, we demonstrate that endogenous activation of the PAX7 transcription factor results in stable epigenetic remodeling and differentiates human pluripotent stem cells into skeletal myogenic progenitor cells. Compared with exogenous overexpression of PAX7 cDNA, we find that endogenous activation results in the generation of more proliferative myogenic progenitors that can maintain PAX7 expression over multiple passages in serum-free conditions while preserving the capacity for terminal myogenic differentiation. Transplantation of human myogenic progenitors derived from endogenous activation of PAX7 into immunodeficient mice resulted in a greater number of human dystrophin+ myofibers compared with exogenous PAX7 overexpression. RNA-sequencing analysis also revealed transcriptome-wide differences between myogenic progenitors generated via CRISPR-based endogenous activation of PAX7 and exogenous PAX7 cDNA overexpression. These studies demonstrate the utility of CRISPR/Cas9-based transcriptional activators for controlling cell-fate decisions., Graphical Abstract, Highlights • CRISPR activation generates myogenic progenitors from human iPSCs/ESCs • Activation of endogenous PAX7 leads to autonomously maintained gene expression • Endogenous activation outperforms cDNA expression in generating a stable phenotype • CRISPRa myogenic progenitors engraft and regenerate muscle fibers in vivo in mice, In this article, Gersbach and colleagues use a CRISPR/Cas9-based transcriptional activator to differentiate hPSCs into myogenic progenitor cells that can differentiate in vitro and participate in regeneration in vivo. They demonstrate stable epigenetic remodeling of the PAX7 locus and uncover transcriptome-wide differences that result from endogenous versus exogenous PAX7 expression.

Summary Chronic inflammatory diseases such as arthritis are characterized by dysregulated responses to pro-inflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor α (TNF-α). Pharmacologic anti-cytokine therapies are often effective at diminishing this inflammatory response but have significant side effects and are used at high, constant doses that do not reflect the dynamic nature of disease activity. Using the CRISPR/Cas9 genome-engineering system, we created stem cells that antagonize IL-1- or TNF-α-mediated inflammation in an autoregulated, feedback-controlled manner. Our results show that genome engineering can be used successfully to rewire endogenous cell circuits to allow for prescribed input/output relationships between inflammatory mediators and their antagonists, providing a foundation for cell-based drug delivery or cell-based vaccines via a rapidly responsive, autoregulated system. The customization of intrinsic cellular signaling pathways in stem cells, as demonstrated here, opens innovative possibilities for safer and more effective therapeutic approaches for a wide variety of diseases., Highlights • Stem cells were rewired via genome engineering to combat inflammation • Cells were used to engineer tissues that self-regulate biologic drug production • Autoregulated therapy protected tissues from cytokines that drive chronic diseases • This approach can form the basis of a cellular vaccine for inflammatory diseases, Exploiting genome-engineering technology, Guilak, Gersbach, and colleagues propose an approach to treating chronic diseases with “smart” stem cell-based therapies that provide dynamic, user-defined responses to environmental signals and provide feedback-controlled production of anti-inflammatory drugs. This approach can form the basis for engineered tissues that self-regulate biologic drug production or cell-based vaccines for autoimmune or inflammatory diseases such as arthritis.