Longer transplanted heart allograft survival in rats without immunosuppressants after intrathymic myocardial cell inoculation in the neonatal period.

In order to induce immunological tolerance, intrathymic inoculation of incompatible donor myocardial cells in rats was performed in the neonatal period. Isolated myocardial cells harvested from donor rat hearts were inoculated into the thymus of incompatible neonatal recipient rats without administration of immunosuppressive agents. Ten weeks later, the hearts from the donors were transplanted heterotopically to these pretreated rats. The animals were sacrificed on the 7th day of heterotopic transplantation and were examined histopathologically. The results showed no early rejection in the group in which intrathymic myocardial cell inoculation had been performed in the neonatal period. Immunohistochemical staining for myoglobin of the thymus from the inoculated recipient revealed that the donor myocardial cells continued to survive. The longest proven graft survival in this series, thus far, was 60 days, while it was only 7 days in the control group.