Engineered Heart Muscle from Human Embryonic Stem Cell-Derived Cardiomyocytes for Transmural Myocardial Repair

Background and Objective: Engineered heart muscle (EHM) of human origin has recently attracted attention in surgical heart failure repair. Here we investigated the applicability of human embryonic stem cell (hESC)-derived EHM for transmural repair in a rat model of severe left ventricular injury.

Methods: hESC-cardiomyocytes (hESC-CM) were generated by directed differentiation from a genetically modified HES2 line, expressing either red fluorescent protein (RFP) or firefly luciferase. EHM were created using 9 million hESC-CMs, 1 million human fibroblasts and certified bovine collagen type 1. Non-contractile control grafts (NCG) were generated from 1 million human fibroblasts. Graft survival in vivo was monitored by bioluminescence imaging (BLI, IVIS). We used the model of volume-loaded heterotopic rat heart transplantation (RNU rats) and established a transmural circular defect with a diameter of 6 mm in the left ventricle of the donor heart using a punch device. The defect was closed on the endocardial side with an aortic patch restoring the ventricle cavity and yet leaving a transmural wall defect where tissue xenografts (n = 14 EHM; n = 14 NCG) could be inserted. Subsequently, engrafted donor hearts were heterotopically implanted into male nude rats (n = 28). Echocardiography (ECHO) was used 1 and 4 weeks after transplantation to assess heart function and blood flow. After 4 weeks engrafted hearts were harvested and subjected to histological analysis.

Results: 69% of the graft recipients survived the procedure with 73% in the EHM and 64% in the NCG. BLI indicated survival of the EHM with a decline of signal in the first two weeks after implantation. After explantation RFP signal revealed human muscle tissue mainly on the edge of the transmural defect close to the recipient's myocardium. Histological and immunohistochemical staining (H&E, α-Actinin, CD31) confirmed the presence of human myocardium (cardiac Troponin T, human nuclear antigen) with strong vascularization. Echo demonstrated left ventricular wall stabilization with apparently no differences in wall kinetics and blood flow at 4 weeks after implantation of EHM and NCG.

Conclusion: Our study provides first evidence for hESC-EHM survival after implantation as transmural left ventricular wall replacement. This has important implications for the preclinical development of tissue engineered myocardial grafts for heart failure repair.