A 55-year-old man undergoes orthotopic cardiac transplantation. One month later, an endomyocardial biopsy specimenshows focal myocardial cell death with scattered lymphocytes and plasma cells. Which of the following pathologic processes best accounts for the biopsy findings? (A) Autoimmunity (B) Is chemia (C) Infection (D) Rejection (E) Autophagy