The role of estrogen in cardiac transplantation: mechanistic insights and effects on clinical outcomes.

Sex hormones profoundly shape immune responses and influence outcomes after heart transplantation. Estrogen enhances allosensitization and is associated with a higher incidence of acute rejection in female recipients. Beyond its immunological effects, estrogen also modulates the pharmacokinetics and pharmacodynamics of calcineurin inhibitors-particularly cyclosporine A-thereby influencing immunosuppressive efficacy and early graft performance. Donor-recipient sex mismatch further modulates transplant outcomes. Female-to-male transplants in particular exhibit the poorest short- and long-term survival and show increased rates of primary graft failure and cardiac allograft vasculopathy. Mechanistic and experimental data provide a biological basis for these observations: estrogen protects the myocardium against ischemia-reperfusion injury and preserves vascular integrity through both nuclear estrogen receptors and GPER-mediated signaling. Abrupt withdrawal of this estrogen-mediated protection in male recipients of female donor hearts may therefore increase susceptibility to early graft dysfunction and chronic vasculopathy. Integrating sex and hormonal status into transplant medicine-through hormonal profiling, receptor-specific mechanistic studies, and sex-adapted immunosuppressive strategies-may pave the way toward more individualized and effective therapeutic approaches in heart transplantation.