Immunogenicity and immune privilege of corneal allografts

Corneal allografts enjoy a remarkable success rate when compared to all other forms of organ transplants. In routine keratoplasties, HLA matching and systemic immunosuppressive drugs are not employed, yet 90% of the uncomplicated transplants survive. The success of corneal allografts was recognized over half a century ago and led to the term 'immune privilege'. The original explanation for the immune privilege of corneal allografts attributed the escape of immune rejection to the avascular and alymphatic nature of the corneal graft bed, which sequestered the corneal allograft from the immune apparatus. In the past 20 years, the widespread use of animal models of keratoplasty has shed light on the mechanisms of corneal immune privilege and has revealed that the success of corneal allografts is due to a combination of properties of the corneal graft bed and the cornea itself.