Abstract 9366: Generation of Human Embryonic Stem Cell-Derived Cardiac Progenitors: Is the Risk of Teratoma Still A Clinically Relevant Roadblock ?

Abstract

Background: The risk of teratoma is a major limitation to a safe clinical use of human embryonic stem cells (ESC) for heart repair.We developed a straightforward and clinically usable method for generating ESC-derived cardiac progenitors and assessed its safety in vitro and in animal models. Methods: Human ESC (I6 line) were treated for 4 days by bone morphogenetic protein (BMP)-2 in an insulin-free medium. Taking CD15 as a marker for cell differentiation, the lineage-directed population was immunomagnetically sorted and assessed for purity (flow cytometry), genetic stability (caryotype, FISH focused on chromosomes 12, 17, and 20 and 105K oligonucleotide-based array CGH) and phenotype (transcriptome). For in vivo testing, 58 nude rats underwent a myocardial infarction and, 4-6 weeks later, received a CD15 + -loaded fibrin patch overlaying the infarct area (n=26), a cell-free fibrin patch (controls; n=16) or were sham-operated (n=16). In addition, 54 immunodeficient RAG2-/- γc-/- C5-/- mice were subcutaneously injected with CD15 + cells, undifferentiated ESC, CD15 + cells spiked with different ratios of undifferentiated ESC or 100% CD15-negative cells. Results: The mean ± SD purity rate of the sorted CD15 + population was 96.2 ± 1.8% (average of 25 preclinical runs). These cells were genetically stable with gene polymorphisms considered usual in the human species and expressed cardiac markers, predominantly Isl-1. After 3 months of follow-up, none of the nude rats treated with the CD15 + -loaded fibrin patch had developed a teratoma and monthly echocardiograms showed that they yielded the highest values of LVEF ( p <0.003 vs baseline) and the smallest degree of remodeling compared to control or sham-operated rats. Likewise, while mice receiving undifferentiated ESC developed teratomas within 6 months post-injections, none of those (n=12) injected with the CD15 + cells presented a teratoma or an extra-cardiac tumor (maximal follow-up: 7 months). The CD15-negative population was not tumorigenic either (0/8). Conclusion: This CD15 + progenitor cell population had an overall reassuring safety profile, suggesting that our process of lineage commitment and purification may represent an efficient translational step towards a safe clinical use of these cells.