Xenografts face the highest rejection rates due to maximum antigenic disparity, followed by allografts, while isografts have minimal rejection. Option (D) Xenograft > Allograft > Isograft is correct.

Graft Types Defined

• Autograft: Self-tissue (no rejection)

• Isograft: Identical twin/genetically identical donor (minimal rejection)

• Allograft: Same species, different individual (moderate rejection)

• Xenograft: Different species (hyperacute rejection)

Rejection Rate Hierarchy

Xenografts trigger hyperacute rejection within minutes-hours via pre-existing antibodies against foreign antigens (α-Gal in pigs), complement activation, and thrombosis.
Allografts undergo first-set rejection (10-14 days) via T-cell mediated response to MHC differences, accelerated in second exposures.​
Isografts succeed permanently due to genetic identity eliminating alloantigens.​

Correct Answer: Xenograft > Allograft > Isograft

Option (D) follows immunological distance: xenogeneic > allogeneic > syngeneic antigens determine rejection vigor.
Clinical data shows xenograft survival <24 hours untreated, allografts 7-14 days acute rejection, isografts >95% long-term success.​

Options Analysis Table

Clinical Implications

Immunosuppression (cyclosporine, steroids) controls allograft rejection but fails against xenograft hyperacute response requiring genetic modification.​
Pig-to-human xenotransplants use CRISPR knockouts (α-Gal, GGTA1) to reduce rejection barriers.​

Exam Strategy

NEET/AIIMS tests this MHC/antigen recognition sequence. Remember: species difference > MHC mismatch > genetic identity governs rejection speed.​