Heterotopic heart transplantations were performed as previously described [31 (link)] by grafting BALB/c hearts from 6-8 week old donors onto the aorta and inferior vena cava in the peritoneal cavity of 8-12 week old C57BL/6 recipients. 500 μg of CTLA4-Ig (abatacept; Bristol-Myers Squibb) per mouse, intraperitoneally, starting on day −2, 0 and 2 or on days 6, 8, 10, and then twice per week until the end of the experiment.