RAD, a new immunosuppressive macrolide in murine corneal transplantation

Abstract.

Background: RAD is a novel macrolide immunosuppressant with effects on growth factor signalling. We investigated the potency of RAD in inhibiting allograft rejection in the rat model of orthotopic allogeneic penetrating keratoplasty. Methods: Fifty-four allogeneic orthotopic penetrating keratoplasties were performed using Fisher rats as donors and Lewis rats as recipients. The animals were divided into five groups: syngeneic control, allogeneic control, RAD 1.5 mg/kg bw per day, RAD 2.5 mg/kg bw per day, cyclosporin A (CSA) 10 mg/kg bw per day. Medication started on the day of operation and continued daily for the duration of 18 days. Each animal was examined by slit-lamp microscopy every 3rd day. For immunohistological evaluation rats were killed on day 14. Immunohistology was performed using monoclonal mouse anti-rat antibodies against CD4, CD8, CD25, CD45 and CD54. Results: The average transplant survival time in the allogeneic combination was 12.3 days (±0.3). Therapy with RAD 1.5 mg/kg and 2.5 mg/kg led to a statistically significant prolongation of transplant survival to 32.3 days (±11.3, P<0.05) and 37.7 days (±12.5), respectively. This efficacy was similar to that of CSA 10 mg/kg (39.7±12.5 days). There was a statistically significant reduction in the number of CD4⁺, CD8⁺ as well as CD45⁺ cells in both the RAD- and the CSA-treated animals compared with the allogeneic control. Conclusions: The results show that oral immunosuppression with RAD significantly prolongs corneal allograft survival. Further investigation of RAD in preclinical and clinical high-risk keratoplasty is warranted.