Why do organ transplant patients need anti-rejection medication? (A) To minimise infection (B) To prevent T-lymphocyte growth (C) To stimulate the interaction of B- and T-lymphocytes (D) To prevent the recipient’s blood type changing and adopting the immune system of the donor - HSC - SSCE Biology - Question 13 - 2009 - Paper 1

Organ transplant patients require anti-rejection medication primarily to suppress the immune response and prevent the proliferation of T-lymphocytes that can recognize the transplanted organ as foreign. This suppression is critical because T-lymphocytes play a key role in mediating rejection of the graft. Without such medication, the recipient's immune system may attack and damage the transplanted organ.