Correct Answer: B. Allograft
An allograft is a tissue or organ transplant between two genetically non-identical individuals of the same species. In this case, the son (donor) and father (recipient) are both human beings but genetically distinct, making this a classic allograft scenario. The key discriminator is that allograft involves same-species, genetically different individuals. India has a robust organ transplant program under the Transplantation of Human Organs and Tissues Act (THOTA), 1994, and living-related liver transplants (LRLT) from biological relatives are among the most common transplants performed in Indian centers like AIIMS, CMC Vellore, and Apollo. The son donating a portion of his liver to his father represents a living-related allograft, which carries better outcomes than cadaveric allografts due to shorter cold ischemia time and better HLA matching potential. The immunological response to an allograft is managed through calcineurin inhibitors (tacrolimus, cyclosporine) and mycophenolate mofetil as per Indian transplant protocols, reflecting the need for lifelong immunosuppression in allograft recipients.
Why the other options are wrong
A. Xenograft — A xenograft involves transplantation between different species (e.g., pig heart to human). This question explicitly states the donor is the patient's biological son—both are humans. Xenografts trigger hyperacute rejection and are not routinely used in clinical practice in India; they remain experimental. The presence of a human donor rules out xenograft entirely. C. Xenograft — This is a duplicate of option A and carries the same error: xenografts are inter-species transplants. The question clearly specifies a biological son as donor, confirming same-species transplantation. This duplication in the question stem is likely a typographical error, but the correct classification remains allograft, not xenograft. D. Autograft — An autograft involves transplantation of tissue from one site to another within the same individual (e.g., skin graft from thigh to burn wound, or bone graft from iliac crest to femur). Here, the donor (son) and recipient (father) are two different people, making autograft impossible. Autografts have no immunological rejection risk because the tissue is genetically identical to the recipient.
High-Yield Facts
- Allograft = same species, genetically different individuals; requires lifelong immunosuppression (tacrolimus, mycophenolate mofetil per Indian protocols).
- Living-related liver transplant (LRLT) is the standard of care in India for end-stage liver disease; son-to-father donation is a common scenario in Indian transplant centers.
- Xenograft = different species (e.g., porcine valve, pig-to-human); triggers hyperacute rejection and remains experimental in India.
- Autograft = same individual, different anatomical sites; zero rejection risk (e.g., split-thickness skin graft, bone graft).
- Isograft = genetically identical individuals (monozygotic twins); rare in clinical practice but has minimal rejection.
Mnemonics
AAXA Rule Auto (same person), Allo (same species, different person), Xeno (different species), Allografts need immunosuppression. Use this to quickly classify any transplant question by asking: 'Is it same person? Same species? Same genetics?' Living-Related Liver Transplant (LRLT) in India Son/daughter donates partial liver to parent → Allograft (living-related). This is the most common scenario in Indian transplant practice because cadaveric organs are scarce. Remember: biological relationship ≠ genetic identity; still requires immunosuppression.
NBE Trap
NBE pairs "biological son" with students who conflate biological relationship with genetic identity, leading them to incorrectly choose autograft. The trap is that "biological" means "from a living relative," not "genetically identical"—only monozygotic twins are genetically identical, and the son is genetically distinct from his father.
Clinical Pearl
In Indian transplant practice, living-related liver transplants from adult children to parents are increasingly common due to organ scarcity. A 56-year-old with alcoholic cirrhosis receiving a partial liver from his son represents the most frequent LRLT scenario in Indian centers—and it is always an allograft requiring lifelong tacrolimus/mycophenolate therapy, not an autograft.
_Reference: Bailey & Love Ch. 4 (Transplantation); Robbins Ch. 4 (Immunopathology); Harrison Ch. 135 (Organ Transplantation)_