Corneal Transplantation: Why Tissue Typing Is Unnecessary

Corneal transplantation (keratoplasty) uniquely does not require HLA matching or systemic immunosuppression, unlike solid organ transplants.

Immune Privilege of the Cornea

• Avascular: No blood vessels → no direct lymphocyte access; nutrients from tears/aqueous.
• Low MHC expression: Corneal endothelial cells express minimal HLA class II; epithelium lacks HLA-DR.
• Immunomodulatory factors: TGF-β, IL-10, α-MSH, Fas ligand, PD-L1 in aqueous humor suppress immune activation.
• Anterior chamber-associated immune deviation (ACAID): Antigen presentation in eye induces regulatory T cells, not effector response.
• Blood-aqueous barrier: Tight junctions limit immune cell entry.

Rejection Rates and Risk Factors

Keratoplasty Type	1-Year Rejection	5-Year Rejection
Penetrating (PKP)	5-10%	15-20%
Endothelial (DSEK/DMEK)	1-2%	5-8%
Anterior lamellar (DALK)	<1%	<5%

Risk factors: Vascularization, inflammation, regraft, herpes simplex, atopy, young age, large graft.

Management Without Systemic Immunosuppression

• Topical corticosteroids: Prednisolone acetate 1% q1-2h taper over 6-12 months (mainstay).
• Rejection episode: Hourly prednisolone + subconjunctival dexamethasone; systemic steroids rarely needed.
• High-risk cases: Prophylactic systemic immunosuppression (tacrolimus, MMF) sometimes used for regrafts/vascularized beds.

When Matching Matters

• Repeat grafts (especially >2 prior failures).
• Highly vascularized recipient beds (chemical burns, Stevens-Johnson, aniridia).
• Pediatric patients (more robust immune response).

Corneal immune privilege enables the highest success rate of any transplant (>90% at 1 year for low-risk PKP) without lifelong immunosuppression.