The only way to solve the problem of donor cornea shortage is through xenograft cornea transplantation. However, full-thickness corneal transplantation has problems that need to be addressed, such as excessive use of immunosuppression. Partial corneal transplantation is being proposed as an alternative for rapid clinical use. We have done partial thickness xenografts to primates using the corneas of transgenic pigs. Minimal immunosuppression was used in the transplanted primates using steroids and sufficient graft survival was demonstrated. Therefore, we consider what conditions are necessary to initiate clinical trial with partial thickness corneal transplantation.

We have conducted 19 xenograft partial corneal transplant studies since 2016 with the corneas of transgenic pigs based on αGal-knockout(GTKO). Immunosuppression using steroids was administered in all. The transgenic pigs used for partial thickness corneal transplantation were KO only in 2 cases, 1 knock-in(KI) in 10 cases, and 2 KI in 7 cases. The criteria for partial thickness corneal transplantation to initiate clinical trials were set as 5 or more of the 8 recently performed corneal transplants showing survival of 6 months or more, or graft survival of 6 months or more in 5 or more consecutive corneal transplants.

There were a total of 8 cases with a long-term survival rate of more than 200 days. From these results, it is difficult to conclude that more transformation was helpful for survival. In the results of a recent corneal transplant study, 3 out of 8 cases survived for more than 6 months, but 3 out of the last 5 cases showed satisfactory results. Based on these results, it seemed likely that the conditions could be met if additional corneal transplantation was performed in the future. Out of 8 cases, 5 or more cases showed survival for more than 6 months once between 2 and 9 times, and among all cases, there were 5 cases with long-term survival of more than 1 year.

Our research team's partial corneal transplantation survival results showed a long-term survival rate of more than 6 months in half of the cases. Additionally, in partial thickness corneal transplantation using various transgenic pig corneas, it was confirmed that rejection was suppressed through the use of minimal immunosuppression and subconjunctival injection or systemic immunosuppression. For better results, 2~3 more genes need to be KO based on GTKO, and KI for CD46, TBM, and 1~2 more genes are needed. It is expected that this will enable clinical trials to show good results even with the current minimal immunosuppressive treatment. In addition, to these survival records, it is confirmed that the infection route has been blocked, it is expected that we will be able to discuss the possibility of clinical trials in earnest since minimal immunosuppression is already in place.