No FDA-approved anti-CD40/CD40L agents for xenotransplant use

The most promising immunosuppressive strategy for xenotransplantation is co-stimulation blockade targeting the CD40-CD40L pathway, which has shown far superior results in preclinical primate models compared to traditional calcineurin inhibitor-based regimens like tacrolimus. With CD40-CD40L blockade, pig heart survival in baboons reached months instead of days. But there is no FDA-approved anti-CD40 or anti-CD40L monoclonal antibody available for clinical use in xenotransplantation. The agents used in preclinical studies are experimental, and clinical teams performing compassionate-use xenotransplants have had to fall back on conventional immunosuppression regimens designed for human-to-human transplants, which are known to be inadequate for the stronger xenogeneic immune response. This means every xenotransplant performed on a living human so far has used a suboptimal immunosuppression strategy. The reason this persists is that pharmaceutical companies see the xenotransplant market as too small and too uncertain to justify the cost of bringing an anti-CD40L drug through Phase III trials and FDA approval, and the FDA has no accelerated pathway specifically for xenotransplantation-enabling drugs.