Effects of Lung Cotransplantation on Cardiac Allograft Tolerance Across a Full Major Histocompatibility Complex Barrier in Miniature Swine

A 12‐day course of high‐dose tacrolimus induces tolerance of major histocompatibility complex–mismatched lung allografts in miniature swine but does not induce tolerance of heart allografts unless a kidney is cotransplanted. To determine whether lungs share with kidneys the ability to induce cardiac allograft tolerance, we investigated heart–lung cotransplantation using the same induction protocol. Hearts (n = 3), heart–kidneys (n = 3), lungs (n = 6), and hearts–lungs (n = 3) were transplanted into fully major histocompatibility complex–mismatched recipients treated with high‐dose tacrolimus for 12 days. Serial biopsy samples were used to evaluate rejection, and in vitroassays were used to detect donor responsiveness. All heart–kidney recipients and five of six lung recipients demonstrated long‐term graft survival for longer than 272 days, while all heart recipients rejected their allografts within 35 days. Tolerant recipients remained free of alloantibody and showed persistent donor‐specific unresponsiveness by cell‐mediated lympholysis/mixed‐lymphocyte reaction. In contrast, heart–lung recipients demonstrated rejection of both allografts (days 47, 55, and 202) and antidonor responsiveness in vitro. In contrast to kidneys, lung cotransplantation leads to rejection of both heart and lung allografts, indicating that lungs do not have the same tolerogenic capacity as kidneys. We conclude that cells or cell products present in kidney, but not heart or lung allografts, have a unique capacity to confer unresponsiveness on cotransplanted organs, most likely by amplifying host regulatory mechanisms. Lungs, unlike kidneys, do not induce cardiac allograft tolerance, suggesting that a cell or cell product unique to the kidney confers unresponsiveness upon cotransplanted organs.