Vascularized composite allograft transplant survival in miniature swine: is MHC tolerance sufficient for acceptance of epidermis?

An innovative ear transplantation for vascularized composite allotransplantation research in porcine model

Vascularized composite allotransplantation (VCA) represents a clinical challenge for transplant therapy, as it involves different tissues with unique immunogenicity. Even when receiving immunosuppressive therapy, they are more vulnerable to severe hypoxia, microvascular damage, and ultimately the rejection or chronic graft dysfunction after transplantation. This study aimed to develop a surgical protocol for VCA of the ear in a porcine biomodel in the absence of immunosuppression, maintaining the in vitro co-culture of the allograft and assessing their relationship with allograft survival. We employed four crossbred pigs and four outbred mini pig biomodels (Sus scrofa), as donors and recipients, to perform four VCAs. Blood samples were taken from each biomodel for crossmatch testing and SLA haplotype identification. Bone marrow samples were taken from each recipient for subsequent co-culture. In vitro culture and co-culture conditions were maintained and assessed. Histological analysis using hematoxylin and eosin staining was performed on the allograft that lasted the longest time showing the smallest macroscopic signs of rejection. A surgical protocol for Vascularized Composite Allograft (VCA) ear transplantation in a porcine biomodel was developed, including the skin. The presence of SLA-DRB1*01:02 and SLA-DRB1*06:01 haplotypes in the recipient and donor, respectively, showed concordance with positive crossmatch tests. In the allograft with the highest survival time, no histological signs of hyperacute rejection were found ten days after transplantation in the anastomosis area. The results obtained from this protocol can provide valuable recommendations for translational applications in face transplantation and regenerative medicine.

Combination of a CD26 Inhibitor, G-CSF, and Short-term Immunosuppressants Modulates Allotransplant Survival and Immunoregulation in a Rodent Hindlimb Allotransplant Model

BACKGROUND

Recent studies have demonstrated that inhibition of CD26 potentiates stromal cell-derived factor-1α (SDF-1α), promotes tissue regeneration, and suppresses the rejection of organ transplants. This study investigated whether the combination of a CD26 inhibitor (CD26i) with granulocyte colony-stimulating factor (G-CSF) and short-term immunosuppressants modulates vascularized composite tissue allotransplant survival in a rodent orthotopic hindlimb allotransplant model.

METHODS

The hindlimb allotransplantation from Brown-Norway to Lewis rats was divided into 4 groups. Group 1 (controls) did not receive any treatment. Group 2 was treated with short-term antilymphocyte serum (ALS) and cyclosporine-A (CsA). Group 3 was administrated CD26i and G-CSF. Group 4 received a combination of CD26i/G-CSF/ALS/CsA. Each subgroup comprised 10 rats. Peripheral blood and sampling of transplanted tissues were collected for immunological and histological analysis.

RESULTS

The results revealed that allotransplant survival was found to be significantly prolonged in group 4 with CD26i/G-CSF/ALS/CsA treatment compared with those in the other groups. The interleukin-10 and transforming growth factor-βl levels, the percentage of CD4+/CD25+/FoxP3+ T cells, as well as the levels of SDF-1α expressions were significantly increased in group 4 compared with those in the other groups. Group 4 revealed a statistical increase in the percentage of donor cells (RT1n) expression in the recipient peripheral blood, and the mixed lymphocyte reaction showed hyporesponsiveness of the T cells to donor alloantigens.

CONCLUSION

The combination of CD26i/G-CSF and short-term immunosuppressants prolongs allotransplant survival by inducing immunoregulatory effects and enhancing the percentage of SDF-1α expression. This immunomodulatory approach has great potential as a strategy to increase vascularized composite allotransplantation survival.

Importance of the Major Histocompatibility Complex (Swine Leukocyte Antigen) in Swine Health and Biomedical Research

In pigs, the major histocompatibility complex (MHC), or swine leukocyte antigen (SLA) complex, maps to Sus scrofa chromosome 7. It consists of three regions, the class I and class III regions mapping to 7p1.1 and the class II region mapping to 7q1.1. The swine MHC is divided by the centromere, which is unique among mammals studied to date. The SLA complexspans between 2.4 and 2.7 Mb, depending on haplotype, and encodes approximately 150 loci, with at least 120 genes predicted to be functional. Here we update the whole SLA complex based on the Sscrofa11.1 build and annotate the organization for all recognized SLA genes and their allelic sequences. We present SLA nomenclature and typing methods and discuss the expression of SLA proteins, as well as their role in antigen presentation and immune, disease, and vaccine responses. Finally, we explore the role of SLA genes in transplantation and xenotransplantation and their importance in swine biomedical models.

Vascularized Thymosternal Composite Tissue Allo- and Xenotransplantation in Nonhuman Primates: Initial Experience

Background:

Vascularized composite allotransplantation is constrained by complications associated with standard immunosuppressive strategies. Vascularized thymus and bone marrow have been shown to promote prolonged graft survival in composite organ and soft-tissue vascularized composite allotransplantation models. We report development of a nonhuman primate vascularized thymosternal composite tissue transplant model as a platform to address donor-specific immune tolerance induction strategies.

Methods:

Vascularized thymosternal allograft (skin, muscle, thymus, sternal bone) was transplanted between MHC-mismatched rhesus monkeys (feasibility studies) and baboons (long-term survival studies), with end-to-side anastomoses of the donor aorta and SVC to the recipient common femoral vessels. A male allograft was transplanted to a female’s lower abdominal wall, and clinically applicable immunosuppression was given. Skin biopsies and immunological assays were completed at regular intervals, and chimerism was quantified using polymerase chain reaction specific for baboon Y chromosome.

Results:

Four allo- and 2 xenotransplants were performed, demonstrating consistent technical feasibility. In 1 baboon thymosternal allograft recipient treated with anti-CD40–based immunosuppression, loss of peripheral blood microchimerism after day 5 was observed and anticipated graft rejection at 13 days. In the second allograft, when cutaneous erythema and ecchymosis with allograft swelling was treated with anti-thymocyte globulin starting on day 6, microchimerism persisted until immunosuppression was reduced after the first month, and the allograft survived to 87 days, 1 month after cessation of immunosuppression treatment.

Conclusions:

We established both allo- and xeno- composite vascularized thymosternal transplant preclinical models, which will be useful to investigate the role of primarily vascularized donor bone marrow and thymus.

Therapeutic application of T regulatory cells in composite tissue allotransplantation

With growing number of cases in recent years, composite tissue allotransplantation (CTA) has been improving the quality of life of patient who seeks reconstruction and repair of damaged tissues. Composite tissue allografts are heterogeneous. They are composed of a variety of tissue types, including skin, muscle, vessel, bone, bone marrow, lymph nodes, nerve, and tendon. As a primary target of CTA, skin has high antigenicity with a rich repertoire of resident cells that play pivotal roles in immune surveillance. In this regard, understanding the molecular mechanisms involved in immune rejection in the skin would be essential to achieve successful CTA. Although scientific evidence has proved the necessity of immunosuppressive drugs to prevent rejection of allotransplanted tissues, there remains a lingering dilemma due to the lack of specificity of targeted immunosuppression and risks of side effects. A cumulative body of evidence has demonstrated T regulatory (Treg) cells have critical roles in induction of immune tolerance and immune homeostasis in preclinical and clinical studies. Presently, controlling immune susceptible characteristics of CTA with adoptive transfer of Treg cells is being considered promising and it has drawn great interests. This updated review will focus on a dominant form of Treg cells expressing CD4+CD25+ surface molecules and a forkhead box P3 transcription factor with immune tolerant and immune homeostasis activities. For future application of Treg cells as therapeutics in CTA, molecular and cellular characteristics of CTA and immune rejection, Treg cell development and phenotypes, Treg cell plasticity and stability, immune tolerant functions of Treg cells in CTA in preclinical studies, and protocols for therapeutic application of Treg cells in clinical settings are addressed in this review. Collectively, Treg cell therapy in CTA seems feasible with promising perspectives. However, the extreme high immunogenicity of CTA warrants caution.

Immunomodulatory Strategies Directed Toward Tolerance of Vascularized Composite Allografts

BACKGROUND

Achieving tolerance of vascularized composite allografts (VCAs) would improve the risk-to-benefit ratio in patients who undergo this life-enhancing, though not lifesaving, transplant. Kidney cotransplantation along with a short course of high-dose immunosuppression enables tolerance of heart allografts across a full major histocompatibility complex (MHC) mismatch. In this study, we investigated whether tolerance of VCAs across full MHC disparities could be achieved in animals already tolerant of heart and kidney allografts.

METHODS

Miniature swine that were tolerant of heart and/or kidney allografts long term underwent transplantation of myocutaneous VCA across the same MHC barrier. Before VCA transplant, group 1 (n = 3) underwent class I-mismatched kidney transplantation; group 2 (n = 3) underwent 2 sequential class I-mismatched kidney transplantations; group 3 (n = 2) underwent haploidentical MHC-mismatched heart/kidney transplantation; and group 4 (n = 2) underwent full MHC-mismatched heart/kidney transplantation.

RESULTS

All 3 animals in group 1 and 2 of 3 animals in group 2 showed skin rejection within 85 days; 1 animal in group 2 showed prolonged skin survival longer than 200 days. Animals in groups 3 and 4 showed skin rejection within 30 days and regained in vitro evidence of donor responsiveness.

CONCLUSIONS

This is the first preclinical study in which hearts, kidneys, and VCAs have been transplanted into the same recipient. Despite VCA rejection, tolerance of heart and kidney allografts was maintained. These results suggest that regulatory tolerance of skin is possible but not generally achieved by the same level of immunomodulation that is capable of inducing tolerance of heart and kidney allografts. Achieving tolerance of skin may require additional immunomodulatory therapies.

The potential role for regulatory T-cell therapy in vascularized composite allograft transplantation

PURPOSE OF REVIEW

Vascularized composite allograft (VCA) transplantation restores defects to a degree not possible by conventional techniques. However, it is limited by the need for long-term immunosuppression and high rates of acute rejection directed against skin. There is therefore a need for a therapy that may shift the risk-benefit ratio in favour of VCA transplantation. Regulatory T cells (Tregs) are a subset of T cells with potent immunoregulatory properties and the potential to promote immunosuppression-free allograft survival. In this review, we consider the evidence for Treg therapy in VCA transplantation.

RECENT FINDINGS

CD4 Tregs are the best-studied immunoregulatory cell type, and a large amount of experimental and clinical data is emerging to endorse their use in VCA transplantation. Data from animal and humanized models are particularly encouraging and demonstrate the potent efficacy of Treg at preventing skin allograft rejection. Moreover, central tolerance induction techniques in VCA transplantation models are demonstrating a dependence on Tregs for graft survival.

SUMMARY

An improvement in outcomes after VCA transplantation has the potential to revolutionize the field. Several effective therapeutic strategies have demonstrated great promise experimentally, and there is now a need to assess their safety and efficacy in a clinical setting.