Background--Prolonged survival of xenografted neonatal cardiomyocytes was achieved by blocking the CD28/B7 costimulatory pathway via CTLA4-Ig gene transfer. We examined the long-term survival of xenografted neonatal cardiomyocytes by adenovirus-mediated CTLA4-Ig expression and transient CD40 blockade with anti-CD40L monoclonal antibody (MR1).

Methods and Results--Neonatal cardiomyocytes derived from Dark Agouti rats were infected with CTLA4-Ig-expressing adenovirus vectors and injected directly into the normal myocardium of C3H/He mice. Mice were also given an intraperitoneal injection of 500 µg MR1 (CTLA+MR group, n=30) or control immunoglobulin (CTLA group, n=30) 1 hour before and 1, 3, and 7 days after cardiomyocyte implantation. As a control, cells infected with -Gal-expressing adenovirus vector (RL group, n=15) and cells without infection (control group, n=15) were injected into additional mice. Mice from all groups were killed 2, 4, and 8 weeks after xenotransplantation, and mice from the CTLA+MR and CTLA groups were killed 4 and 6 months after xenotransplantation. Neonatal cardiomyocytes were successfully infected by adenovirus vectors. Immunohistochemical analysis showed that the xenografted cardiomyocytes survived and expressed CTLA4-Ig for 6 months in all mice from the CTLA+MR and CTLA groups. A gap junction between the xenografted and host cardiomyocytes was also confirmed. Conversely, neonatal cardiomyocytes did not survive for even 2 weeks after xenotransplantation in the mice from the RL and control groups.

Conclusions--Long-term survival of xenografted neonatal cardiomyocytes was achieved by adenovirus-mediated CTLA4-Ig expression and transient CD40 blockade.