Improving Immunosuppressive Therapy in Heart Transplantation

Cardiac allograft rejection (CAR) occurs in 30% to 40% of transplant recipients within the first year post-transplant, and carries an increased risk of both acute graft failure and reduced graft longevity. Because of the high morbidity of CAR when diagnosed after symptoms develop, surveillance endomyocardial biopsy (EMB) has been included in heart transplantation guidelines since 1990. Although EMB is the established gold standard for the diagnosis of CAR, the clinical utility of EMB using standard hematoxylin and eosin (H\&E) histologic analysis is limited by marked inter-observer variability and significant discordance between the histologic grade and clinical impression of CAR severity. On the other hand, Tacrolimus (TAC), one of the most important immunosuppressant drug and widely used for the prevention of rejection after solid organ transplantation (SOT), is considered a critical dose drug: too low exposure to TAC may result in under-immunosuppression and acute rejection, whereas overexposure puts patients at risk for toxicity. Tac concentrations, in whole-blood, are considered therapeutic when maintained in the range 5 and 20 ng/mL. In addition to being highly variable inter-individually, TAC pharmacokinetics can also be variable within individual patients. Although in recent years significant decrease of rejection post SOT has been observed, there is space for further modulation of immunosuppressive therapy, in order to reduce the most common adverse side effects (nephrotoxicity, diabetes, osteoporosis, cardiovascular disease, infections and malignancies), to improve the patients quality of life and to better individualize their therapies. Tac. Unfortunately, a clear correlation between TAC whole blood concentration and acute rejection risk has not yet been defined.