Gene therapy approaches to prevent corneal graft rejection: where do we stand?

Cornea transplantation (penetrating keratoplasty) is the most frequently performed transplant procedure in humans. Despite advances in microsurgery and immunosuppressive treatment protocols, a significant number of corneal grafts still undergo immune-mediated allograft rejection. Topical treatment with corticosteroids is currently the gold standard and while this treatment is effective in many corneal transplant patients, it is much less effective in 'high-risk' patients with previous episodes of neovascularisation or graft rejection. Therefore, alternative approaches such as genetic modification of donor corneas are needed to prevent corneal transplant rejection. Cornea transplantation holds the unique advantage in that gene therapy can be used to modify allografts ex vivo prior to transplantation. Many preclinical studies using local (and systemic) gene transfer have been performed to date and many different gene transfer vehicles (gene therapy vectors) and therapeutic strategies (immunomodulatory or graft-protective) have been investigated to prevent corneal allograft rejection. The most recent gene therapy applications to prevent corneal allograft rejection will be reviewed in this article. Moreover, it will be discussed why the development of clinical trials for the genetic modification of corneal grafts prior to transplantation is lagging behind of those for the treatment of inherited retinal diseases.