CRISPR-Cas9-based gene editing of human mesenchymal stromal cells to improve the outcome of cell therapy

Abstract Background The environment of the failing and infarcted myocardium drives resident and transplanted mesenchymal stromal cells (MSCs) toward a pro-inflammatory phenotype, thus restricting their survival and their reparative effects in a mechanism mediated by toll-like receptor 4 (TLR4). Hence, new approaches are needed to improve the efficacy of cell therapy for heart failure. CRISPR is a promising tool for genome editing, which raises the hope for therapeutic genome editing in the clinic. Purpose We aimed to provide a new strategy to enhance MSC-based cell therapy to improve cardiac remodeling and function. We hypothesized that ex vivo knockout (KO) of the human TLR4 gene by CRISPR would switch human-cardiac MSCs (hMSCs) to an anti-inflammatory, reparative phenotype that could prevent remodeling of the left ventricle after myocardial infarction (Fig. 1A). Methods and results We achieved up to 68% (out of 4x105 cells, R2=0.93) success rate in editing the genome of primary cardiac hMSCs taken from patients with ischemic heart disease. The deletion of TLR4 in hMSCs significantly reduced the secretion of inflammatory and extracellular-matrix (ECM) proteins, compared with unedited hMSCs, by protein mass spectrometry (Fig. 1B) and by multiplex ELISA (Fig. 1C). Additionally, edited cells secreted significantly more extracellular vesicles (EVs) than unedited hMScs (Fig. 1D, p<0.001). These EVs from edited hMSCs stimulated faster migration of hMSCs in a “wound healing” assay (p<0.001). Conclusions We show, for the first time, that CRISPR-based deletion of the TLR4 gene in hMSCs inhibits inflammatory and ECM protein secretion and facilitates a reparative response by hMSCs in vitro. This precise and efficient ex vivo gene editing could provide a newly engineered cell line to improve the outcome of hMSC-based cell therapy. Figure 1 Funding Acknowledgement Type of funding source: Public hospital(s). Main funding source(s): The Foundation in Memory of Seymour Fefer, Sheba Medical Center