The correct answer is CD8+ T lymphocytes.
This process is known as graft rejection and it is defined as the immunological destruction of transplanted organs or tissues. The graft rejection may be based on both cell-mediated and antibody-mediated immunity against cells of the graft. When rejection occurs via cellular immunity, it is mediated by killer T cells (cytotoxic or CD8+ cells) which induce the apoptosis of target cells.