Background: Inhibiting the B7/CD28 co-stimulatory pathway of T-cell activation by blocking agents such as the CTLA4-Ig variant LEA29Y might alleviate cellular rejection mechanisms in xenotransplantation settings. Pigs that express LEA29Y systemically under the control of the ubiquitously active CAG promoter have been established and characterized and serve as recipients of human engineered heart tissue (EHT). These pigs show a significantly impaired immune system and present with a defect in T cell maturation processes and an almost complete absence of B cells and NK cells.

Methods: Fibrin-based EHTs containing induced pluripotent stem cell derived cardiomyocytes are cultured for 21 days before transplantation under continuous monitoring of their contractile activity. For transplantation, left lateral thoracotomy is performed in CAG-LEA29Y transgenic pigs and EHT patches are sutured to the epicardium of the left ventricle. Pigs are additionally immuno-suppressed by daily intravenous or oral application of corticosteroids, Mycophenolat-Mofetil and Tacrolimus throughout the 14 day follow up period.  On experimental day 14, the graft area is explanted, conserved and investigated for the presence of human cardiomyocytes, graft integrity and immune cell infiltration.

Results: Transplantation of EHTs to the epicardium of the left ventricle is successful. Surgical procedures and aftercare are performed adequately, including reliable application of immunosuppressive medication.  Upon recovery of the grafted ventricle area on day 14, histological analysis demonstrates the presence of human cell material in considerable quantities with moderate immune cell infiltration.

Conclusions and outlook: An experimental set up that allows for the investigation of xenogeneic graft implantation into an immunosuppressed transgenic pig model has been established. Analysis after 14 days shows survival of transplanted tissue to possibly facilitate regeneration of heart tissue. To determine long-term regenerative outcome, the follow up period will be increased and pigs will be additionally subjected to an impairment in heart function.