Human engineered heart tissue transplantation in a guinea pig chronic injury model

Myocardial injury leads to an irreversible loss of cardiomyocytes (CM). The implantation of human engineered heart tissue (EHT) has become a promising regenerative approach. Previous studies exhibited beneficial, dose-dependent effects of human induced pluripotent stem cell (hiPSC)-derived EHT patch transplantation in a guinea pig model in the subacute phase of myocardial injury. Yet, advanced heart failure often results from a chronic remodeling process. Therefore, from a clinical standpoint it is worthwhile to explore the ability to repair the chronically injured heart. In this study human EHT patches were generated from hiPSC-derived CM (15x10^6 cells) and implanted epicardially four weeks after injury in a guinea-pig cryo-injury model. Cardiac function was evaluated by echocardiography after a follow-up period of four weeks. Hearts revealed large transmural myocardial injuries amounting to 27% of the left ventricle. EHT recipient hearts demonstrated compact muscle islands of human origin in the scar region, as indicated by a positive staining for human Ku80 and dystrophin, remuscularizing 5% of the scar area. Echocardiographic analysis demonstrated no significant difference between animals that received EHT patches and animals in the control group. Thus, EHT patches engrafted in the chronically injured heart but in contrast to the subacute model, grafts were smaller and EHT patch transplantation did not improve left ventricular function, highlighting the difficulties for a regenerative approach.

Human Engineered Heart Tissue Patches Remuscularize the Injured Heart in a Dose-Dependent Manner

Background: Human engineered heart tissue (EHT) transplantation represents a potential regenerative strategy for heart failure patients and has been successful in preclinical models. Clinical application requires upscaling, adaptation to good manufacturing practices (GMP) and determination of the effective dose. Methods: Cardiomyocytes were differentiated from three different human induced pluripotent stem cell (hiPSC) lines including one reprogrammed under GMP conditions. Protocols for hiPSC expansion, cardiomyocyte differentiation and EHT generation were adapted to substances available in GMP quality. EHT geometry was modified to generate patches suitable for transplantation in a small animal model and perspectively humans. Repair efficacy was evaluated at 3 doses in a cryo-injury guinea pig model. Human-scale patches were epicardially transplanted onto healthy hearts in pigs to assess technical feasibility. Results: We created mesh structured tissue patches for transplantation in guinea pigs (1.5x2.5 cm, 9-15x10 6 cardiomyocytes) and pigs (5x7 cm, 450 x10 6 cardiomyocytes). EHT patches coherently beat in culture and developed high force (mean 4.6 mN). Cardiomyocytes matured, aligned along the force lines, and demonstrated advanced sarcomeric structure and action potential characteristics closely resembling human ventricular tissue. EHT patches containing ~4.5, 8.5, 12x10 6 or no cells were transplanted 7 days after cryo-injury (n=18-19 per group). EHT transplantation resulted in a dose-dependent remuscularization (graft size: 0-12% of the scar). Only high-dose patches improved left-ventricular function (+8% absolute, +24% relative increase). The grafts showed time-dependent cardiomyocyte proliferation. While standard EHT patches did not withstand transplantation in pigs, the human-scale patch enabled successful patch transplantation. Conclusions: EHT patch transplantation resulted in a partial remuscularization of the injured heart and improved left-ventricular function in a dose-dependent manner in a guinea pig injury model. Human scale patches were successfully transplanted in pigs in a proof-of-principle study.