Durable mixed chimerism may permit subsequent immunosuppression-free intestinal transplantation—A proof-of-principle study

Intestinal transplantation (ITx) is the definitive treatment for intestinal failure but has the highest rejection rate among solid organ transplants, requiring high doses of immunosuppressive medication, which is associated with high rates of infection, graft-versus-host disease, and malignancy. Transplant tolerance would overcome the need for long-term immunosuppression (ISP). Using nonmyeloablative conditioning, our laboratory has developed a novel swine model of hematopoietic stem cell transplantation (HSCT) that produces durable mixed chimerism (MC) and immune tolerance without toxicity. We investigated whether durable MC would promote tolerance of subsequently transplanted donor-matched intestinal allografts without ISP. Using miniature swine with a defined major histocompatibility complex (MHC), we performed HSCT across an MHC-class-I haplotype mismatch. Immunosuppressive therapy was stopped by day 45. MC was evaluated using flow cytometry, and mixed lymphocyte reaction assays were used to evaluate cellular responses. Subsequently, orthotopic ITx was performed without ISP using a donor that was MHC-matched to the HSCT donor. The recipients were observed for 4 weeks and euthanized for tissue collection and mechanistic assays. After HSCT, the recipients developed durable multilineage MC and apparent deletional tolerance. After ITx, recipients showed no clinical or histologic signs of rejection, and chimerism was unchanged. These results demonstrate the potential value of generating durable MC to achieve transplant tolerance.