Background: Blockade of CD28-mediated T cell costimulation by a modified cytotoxic T lymphocyte-associated antigen 4 (CTLA4-Ig), belatacept, is a clinically effective immunosuppressive therapy for the prevention of renal allograft rejection. Use of belatacept-based calcineurin inhibitor-free immunosuppression, however, has demonstrated an increased frequency of cellular rejection episodes and immunosuppression-related safety issues relative to conventional regimens. Furthermore, belatacept typically requires infusion for its administration chronically, which may present an inconvenience to patients. To address these issues, a novel CTLA4-Ig variant, ASP2409, with improved CD86 binding selectivity and affinity relative to belatacept was created using DNA shuffling directed evolution methods.
Methods: We evaluated the immunosuppressive effect of ASP2409 on in vitro alloimmune T cell responses, in vivo tetanus toxoid (TTx)-induced immunological responses and renal transplantation in cynomolgus monkeys.
Results: ASP2409 had 6.1-fold higher and 2.1-fold lower binding affinity to monkey CD86 and CD80 relative to belatacept, respectively. ASP2409 was 18-fold more potent in suppressing in vitro alloimmune T cell responses relative to belatacept. In a cynomolgus monkey TTx immunization model, ASP2409 inhibited anti-TTx immune responses at a 10-fold lower dose level than belatacept. In a cynomolgus monkey renal transplantation model, subcutaneous injection of 1 mg/kg ASP2409 prevented allograft rejection through complete CD86 and partial CD80 receptor occupancies and dramatically prolonged renal allograft survival in combination with tacrolimus or mycophenolate mofetil/methylprednisolone.
Conclusions: These results support the potential of ASP2409 as an improved CTLA4-Ig for maintenance immunosuppression in organ transplantation.