Pluripotent stem cell-derived cardiomyocyte grafts can remuscularize substantial amounts of infarcted myocardium and beat in synchrony with the heart, but in some settings cause ventricular arrhythmias. It is unknown whether human cardiomyocytes can restore cardiac function in a physiologically relevant large animal model. Here we show that transplantation of ∼750 million cryopreserved human embryonic stem cell-derived cardiomyocytes (hESC-CMs) enhances cardiac function in macaque monkeys with large myocardial infarctions. One month after hESC-CM transplantation, global left ventricular ejection fraction improved 10.6 ± 0.9% vs. 2.5 ± 0.8% in controls, and by 3 months there was an additional 12.4% improvement in treated vs. a 3.5% decline in controls. Grafts averaged 11.6% of infarct size, formed electromechanical junctions with the host heart, and by 3 months contained ∼99% ventricular myocytes. A subset of animals experienced graft-associated ventricular arrhythmias, shown by electrical mapping to originate from a point-source acting as an ectopic pacemaker. Our data demonstrate that remuscularization of the infarcted macaque heart with human myocardium provides durable improvement in left ventricular function.

The glutamate receptor ␦2 subunit (GluR␦2) is selectively expressed in cerebellar Purkinje neurons (PNs) and is involved in the long-term depression (LTD). However, little is known about the mechanism of its action. Acute expression of the wild-type GluR␦2 in the GluR␦2-deficient PN rescued the induction of LTD, suggesting the direct role of GluR␦2 in LTD. To identify the critical region of GluR␦2 necessary for LTD, we constructed and expressed various mutant GluR␦2 proteins in the GluR␦2-deficient PNs. The mutant GluR␦2 possessing the membrane-proximal 21 aa residues in the C-terminal cytoplasmic region rescued the induction of LTD, whereas the mutant with membrane-proximal 13 aa failed. In addition, overexpression of 865ϳ871 aa of GluR␦2 (corresponding to membrane-proximal 14 -20 aa) fused to EGFP (enhanced green fluorescent protein) suppressed LTD in a wild-type PN. These results suggest that 865ϳ871 aa of GluR␦2 play an essential role in LTD. We next identified protein interacting with C kinase 1 (PICK1) as a molecule interacting with the membrane-proximal C-terminal region of GluR␦2 by yeast two-hybrid screening. PICK1 plays an essential role in LTD. It colocalized with GluR␦2 at spines of PNs, and immunoprecipitation assays showed that GluR␦2 bound to PICK1 mainly through 865-871 aa. These results indicate that 865-871 aa of GluR␦2 are essential for both LTD and interaction with PICK1, and suggest that interaction between GluR␦2 and PICK1 might be critical for the induction of LTD.

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Summary Heart failure remains a significant cause of morbidity and mortality following myocardial infarction. Cardiac remuscularization with transplantation of human pluripotent stem cell-derived cardiomyocytes is a promising preclinical therapy to restore function. Recent large animal data, however, have revealed a significant risk of engraftment arrhythmia (EA). Although transient, the risk posed by EA presents a barrier to clinical translation. We hypothesized that clinically approved antiarrhythmic drugs can prevent EA-related mortality as well as suppress tachycardia and arrhythmia burden. This study uses a porcine model to provide proof-of-concept evidence that a combination of amiodarone and ivabradine can effectively suppress EA. None of the nine treated subjects experienced the primary endpoint of cardiac death, unstable EA, or heart failure compared with five out of eight (62.5%) in the control cohort (hazard ratio = 0.00; 95% confidence interval: 0–0.297; p = 0.002). Pharmacologic treatment of EA may be a viable strategy to improve safety and allow further clinical development of cardiac remuscularization therapy.