Organ Transplantation: Process, Challenges, and Future Prospects

Posted on Nov 23, 2024 in Biology

Transplants

When a person is declared legally dead but their organs are still viable, they may become an organ donor. After a short preservation period, most tissues and organs can be transplanted into another person. The viability window varies by organ; kidneys can last over 48 hours, while the pancreas has a 24-hour limit. Before transplantation, doctors perform compatibility tests to minimize the risk of immune system rejection.

Once compatibility is confirmed, the recipient undergoes surgery. Post-surgery, immunosuppressants are administered to reduce the risk of organ rejection, although these drugs have side effects, necessitating the lowest effective dose. The demand for organs far exceeds availability, leading to research into xenotransplantation (using animal donors, ideally pigs, due to their rapid growth and genetic manipulability) and autologous stem cells (which could potentially grow entire organs, eliminating rejection and availability issues).

Historical Context

Alexis Carrel is considered the father of transplantation, having conducted early experiments on dogs, demonstrating that blood vessels could be successfully reconnected. He posited that surgical aspects were resolved by 1914, but a “biological force” hindered inter-individual transplants. Human transplants became a reality in the latter half of the 20th century.

Medawar’s work with skin grafts revealed that graft rejection is an immune-based phenomenon. The body’s ability to distinguish self from non-self is central to immunology. This ability develops during fetal development and continues for a few months after birth. Cell surfaces have unique proteins, histocompatibility antigens (H antigens), determined by genes, which regulate immune responses. George Snell’s concept of H antigens was crucial for successful transplants, explaining why the body responds to infections and sometimes rejects cancer cells or tumors.

Immunosuppression and Rejection

Since 1962, immunosuppressants have been used to prevent organ rejection. Each cell has a unique “key” indicating its species, organ/tissue, and individual identity. Rejection is managed with immunosuppressive drugs, but excessive use increases the risk of opportunistic infections.

Organ Harvesting and Brain Death

Doctors adhere to the “Harvard criteria,” where a flat electroencephalogram signifies irreversible brain death. Organ removal is linked to brain death, as waiting for heartbeat or breathing cessation renders many organs non-transplantable. Transplantable organs and tissues include:

  • Cornea
  • Kidney
  • Skin (essential for severe burns)
  • Liver
  • Heart
  • Lung
  • Pancreas
  • Bone marrow (for treating blood disorders like leukemia)