Progress towards xenogenic tolerance

Anterior retroperitoneal approach in constructing thymokidney organs in swine for xenotransplantation

Introduction

Thymokidneys (TK) have been constructed to transplant life-supporting kidney grafts containing donor thymic tissue to induce transplant tolerance. Historically, TKs were constructed by inserting pieces of thymus tissue under the kidney capsule using an intra-abdominal or posterior retroperitoneal (lateral/flank) approach. The intra-abdominal approach is technically easier but causes intra-abdominal adhesions and makes kidney procurement more challenging. The posterior retroperitoneal approach causes fewer complications, but thymus tissue implantation is technically demanding due to limited visibility and exposure of the kidney. We herein describe the anterior retroperitoneal approach that overcomes these challenges.

Methods

8-week-old GalTKO-swine (n = 2) were sedated, intubated, and draped. Cervical thymus lobes were isolated and excised. Via a small midline abdominal incision, the peritoneum was dissected bilaterally from the abdominal muscles, identifying both kidneys without entering the peritoneal cavity. Multiple thymus pieces were inserted under the kidney capsule. After 8 weeks, TKs were recovered for flow cytometric and histopathological analysis.

Results

In all kidneys, we successfully constructed TKs with functional thymus tissue under the kidney capsule, verified by histopathology and flow cytometry. No surgical complications were observed, and no adhesions were observed intra-abdominally nor around the kidney, as the peritoneum covered the implanted tissue.

Conclusion

The anterior retroperitoneal approach to constructing thymokidneys is easy to perform, offers excellent kidney exposure, allows a larger volume of thymus tissue to be implanted, and decreases the risk of intra-abdominal adhesions. Such constructed TKs are easy to procure with minimal risk of injury to the vascularized thymus as the prerenal peritoneum covers it.

Functional Reconstruction of Denervated Muscle by Xenotransplantation of Neural Cells from Porcine to Rat

Neural cell transplantation targeting peripheral nerves is a potential treatment regime for denervated muscle atrophy. This study aimed to develop a new therapeutic technique for intractable muscle atrophy by the xenotransplantation of neural stem cells derived from pig fetuses into peripheral nerves. In this study, we created a denervation model using neurotomy in nude rats and transplanted pig-fetus-derived neural stem cells into the cut nerve stump. Three months after transplantation, the survival of neural cells, the number and area of regenerated axons, and the degree of functional recovery by electrical stimulation of peripheral nerves were compared among the gestational ages (E 22, E 27, E 45) of the pigs. Transplanted neural cells were engrafted at all ages. Functional recovery by electric stimulation was observed at age E 22 and E 27. This study shows that the xenotransplantation of fetal porcine neural stem cells can restore denervated muscle function. When combined with medical engineering, this technology can help in developing a new therapy for paralysis.

Inhibition of miR-let-7i Induces DC Immature Cells and Improves Skin Graft Tolerance

Dendritic cells (DC) initiate the immune response in the body. They can stimulate T cell activation, proliferation, and differentiation and ultimately participate in the immune response and the immune tolerance response. The purpose of this study was to coculture DCs and T cells and subcutaneously inject DCs transfected with miR-let-7i into rhesus monkey transplantations to verify the role of miR-let-7i in allograft immune tolerance. In vitro studies found that the expression of miR-let-7i was upregulated after inducing the maturation of DCs. The low expression of miR-let-7i inhibited the maturation of DCs, promoted the differentiation of T cells into T helper T cells 2 (Th2), and inhibited T helper T cell 1- (Th1-) driven rejection. In vivo studies also obtained similar results, and subcutaneous injection of DCs transfected with miR-let-7i inhibitor prolonged the survival time of allogeneic skin transplantation. Therefore, we conclude that inhibition of miR-let-7i inhibits DC maturation and improves the tolerance of grafted skin.