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How do T lymphocytes contribute to organ transplant rejection?

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Kidney transplant — transplant British surgeon Andrew Ready flushing a donated kidney during a transplant at Queen Elizabeth Hospital, Birmingham, England, 2006.

In the context of transplant surgery, T lymphocytes (or T cells) are the primary drivers of organ rejection through a process known as cell-mediated immunity.1

These cells possess the ability to distinguish "self" from "nonself" by recognizing foreign antigens on the surface of transplanted tissue. Once they identify the graft as foreign, T cells latch onto these antigens and initiate a complex immune response that leads to the infiltration and destruction of the transplanted organ. This type of rejection typically develops over a period of days or months.1

Because T cells are central to this destructive process, many immunosuppressant drugs are specifically designed to inhibit their activation, signaling, or proliferation. By suppressing these cell-mediated reactions, medical professionals aim to prevent the immune system from attacking the graft, thereby increasing the chances of transplant success.21