The need for inducing tolerance in vascularized composite allotransplantation

Immunogenicity and tolerance induction in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is the transplantation of multiple tissues such as skin, muscle, bone, nerve, and vessels, as a functional unit (i.e., hand or face) to patients suffering from major tissue trauma and functional deficits. Though the surgical feasibility has been optimized, issues regarding graft rejection remains. VCA rejection involves a diverse population of cells but is primarily driven by both donor and recipient lymphocytes, antigen-presenting cells, macrophages, and other immune as well as donor-derived cells. In addition, it is commonly understood that different tissues within VCA, such as the skin, elicits a stronger rejection response. Currently, VCA recipients are required to follow potent and lifelong immunosuppressing regimens to maximize graft survival. This puts patients at risk for malignancies, opportunistic infections, and cancers, thereby posing a need for less perilous methods of inducing graft tolerance. This review will provide an overview of cell populations and mechanisms, specific tissue involved in VCA rejection, as well as an updated scope of current methods of tolerance induction.

Tolerance Induction in Vascularized Composite Allotransplantation-A Brief Review of Preclinical Models

Pre-clinical studies are an obligatory tool to develop and translate novel therapeutic strategies into clinical practice. Acute and chronic rejection mediated by the recipient's immune system remains an important limiting factor for the (long-term) survival of vascularized composite allografts (VCA). Furthermore, high intensity immunosuppressive (IS) protocols are needed to mitigate the immediate and long-term effects of rejection. These IS regiments can have significant side-effects such as predisposing transplant recipients to infections, organ dysfunction and malignancies. To overcome these problems, tolerance induction has been proposed as one strategy to reduce the intensity of IS protocols and to thereby mitigate long-term effects of allograft rejection. In this review article, we provide an overview about animal models and strategies that have been used to induce tolerance. The induction of donor-specific tolerance was achieved in preclinical animal models and clinical translation may help improve short and long-term outcomes in VCAs in the future.

Tacrolimus before CTLA4Ig and rapamycin promotes vascularized composite allograft survival in MGH miniature swine

BACKGROUND

We evaluated the outcome of vertical rectus abdominus myocutaneous flap (VRAM) allotransplantation in a mini-pig model, using a combined co-stimulation blockade (Co-SB) and mechanistic target of rapamycin inhibition (mTORi)-based regimen, with or without preceding calcineurin inhibition (CNI).

MATERIALS AND METHODS

VRAM allotransplants were performed between SLA-mismatched MGH miniature swine. Group A (n = 2) was treated continuously with the mTOR inhibitor rapamycin from day -1 in combination with the Co-SB agent cytotoxic T lymphocyte antigen 4-Ig (CTLA4-Ig) from post-operative day (POD) 0. In group B (n = 3), animals received tacrolimus daily from POD 0 to POD 13, followed by rapamycin daily from POD 7 and CTLA4-Ig weekly from POD 7-28. Graft rejection was determined by Banff criteria and host cellular and humoral immunity monitored.

RESULTS

In group A, allografts developed grade-I acute rejection by POD 2 and POD 7, and reached grade-IV by POD 17 and POD 20, respectively. By contrast, in group B, two allografts demonstrated grade-I rejection on POD 30 and grade-IV on POD 74, while the third exhibited grade-I rejection starting on POD 50, though this animal had to be euthanized on POD 58 due to Pneumocystis jirovecii infection. Time-to-event incidence of grade-I rejection was significantly lower in group A compared to group B. During the first 3 weeks post-transplant, no significant differences in anti-donor immunity were observed between the groups.

CONCLUSION

A short course of CNI, followed by combined Co-SB and mTORi significantly delays acute rejection of VRAM allografts in SLA-mismatched miniature swine.

Preclinical Animal Models in Facial Transplantation

The technical feasibility and clinical applicability of facial transplantation (FT) have been demonstrated, yet animal models with different technical nuances and allograft compositions continue to be developed. We sought to provide a comprehensive appraisal of the current scope and value of animal models in FT.

Social, economic, and policy implications of organ preservation advances

PURPOSE OF REVIEW

Despite over 60 years of progress in the field of since the first organ transplant, insufficient organ preservation capabilities still place profound constraints on transplantation. These constraints play multiple and compounding roles in the predominant limitations of the field: the severe shortages of transplant organs, short-term and long-term posttransplant outcomes and complications, the unmet global need for development of transplant infrastructures, and economic burdens that limit patient access to transplantation and contribute to increasing global healthcare costs. This review surveys ways that advancing preservation technologies can play a role in each of these areas, ultimately benefiting thousands if not millions of patients worldwide.

RECENT FINDINGS

Preservation advances can create a wide range of benefits across many facets of organ transplantation, as well as related areas of transplant research. As these technologies mature, so will the policies around their use to maximize the benefits offered by organ preservation.

SUMMARY

Organ preservation advances stand to increase local and global access to transplantation, improve transplant outcomes, and accelerate progress in related areas such as immune tolerance induction and xenotransplantation. This area holds the potential to save the healthcare system many billions of dollars and reduce costs across many aspects of transplantation. Novel preservation technologies, along with other technologies facilitated by preservation advances, could potentially save millions of lives in the coming years.

Technical, Immunological, and Ethical Similarities and Differences Between Vascularized Composite Allotransplantation and Solid Organ Transplantation in Current Practice

Solid organ transplantation (SOT) is a surgical method used as the gold standard in end-term organ failure. Following SOT, successful results have also been achieved in vascularized composite tissue transplantation, which improves the quality of life with the success of solid organ transplants and the development of modern immunosuppressive regimens. This review discusses the preoperative, operative, postoperative, and immunological differences between vascularized tissue transplantation and SOT.

Improved Cuff Technique and Intraoperative Detection of Vascular Complications for Hind Limb Transplantation in Mice

BACKGROUND

Vascularized composite tissue allotransplantation (VCA) from a cadaveric donor has now become a clinical reality and the treatment modality of choice for patients with devastating injuries, deformities, and complex tissue defects. However, many VCA patients experience severe toxicities due to the strong immunosuppression required secondary to high antigenicity of the grafts. To improve immunosuppressive protocols for VCA, feasible and reliable preclinical models are necessary. The purpose of this study was to introduce new techniques to an established preclinical VCA model to accelerate future investigations.

METHODS

C57BL/6 (H-2b) and BALB/c (H-2d) mice were used to perform VCA as recipients and donors, respectively. Surgery time, success rate, associated complications, and mortality were analyzed. Blood flow in grafts was interrogated with laser speckle image (LSI).

RESULTS

A nonsuture cuff technique was used with the abdominal aorta for end-to-end anastomosis. The cuff technique demonstrated efficiency for donor surgery (52 ± 10 minutes for donor vs. 45 ± 8 minutes for recipient surgery). Successful revascularization was achieved in 27 (90%) of 30 transplants. The majority of surgical complications occurred within 48 hours including artery occlusion, venous occlusion, cerebral stroke, and minor bleeding without mortality. LSI was useful in detecting intraoperative vascular complications with display patterns predictive of complication type.

CONCLUSIONS

The described techniques may facilitate a more efficient heterotopic hind limb transplantation mouse model of VCA.

The Macrophage-depleting Agent Clodronate Promotes Durable Hematopoietic Chimerism and Donor-specific Skin Allograft Tolerance in Mice

Hematopoietic chimerism is known to promote donor-specific organ allograft tolerance; however, clinical translation has been impeded by the requirement for toxic immunosuppression and large doses of donor bone marrow (BM) cells. Here, we investigated in mice whether durable chimerism might be enhanced by pre-treatment of the recipient with liposomal clodronate, a macrophage depleting agent, with the goal of vacating BM niches for preferential reoccupation by donor hematopoietic stem cells (HSC). We found that liposomal clodronate pretreatment of C57BL/6 mice permitted establishment of durable hematopoietic chimerism when the mice were given a low dose of donor BM cells and transient immunosuppression. Moreover, clodronate pre-treatment increased durable donor-specific BALB/c skin allograft tolerance. These results provide proof-of-principle that clodronate is effective at sparing the number of donor BM cells required to achieve durable hematopoietic chimerism and donor-specific skin allograft tolerance and justify further development of a tolerance protocol based on this principle.

Changing attitudes toward hand allotransplantation among North American hand surgeons

OBJECTIVES

Although more than 70 hand transplants have been performed worldwide, the appropriate clinical indications for this operation are still being determined. Cost and patient exposure to the challenges of lifelong immunosuppression for what is a quality of life-improving (but not life-saving) operation are the focus of the ongoing discussion. A study performed in 2007 showed that surgeons' opinions on the issue varied widely. Recently, more information has been made available regarding long-term patient outcomes, and significant improvements in immunotherapy protocols have been reported. In light of this, we sought to examine changing attitudes regarding hand allotransplantation and its indications by surveying hand surgeons.

METHODS

An email-based survey was sent to members of the American Society for Surgery of the Hand. Demographic information and practice profiles were identified, followed by their risk assessment of hand allotransplants and endorsement of performing the operation in different clinical scenarios. Additional questions focused on the appropriate indications for hand allotransplantation, as well as the procedure's associated ethical and financial implications.

RESULTS

A total of 385 surgeons responded to the survey (14% response rate). The majority (82%) considered hand transplantation to be a high-risk operation (as opposed to 27% in hand replantation), with 78% citing lifelong immunosuppression as the primary factor impacting their overall risk assessment. The most commonly accepted indication for hand vascularized composite allotransplantation was loss of bilateral hands (80% in favor). Dominant hand loss (with an intact contralateral hand) was a far less frequently accepted indication (36% in favor). Patient adherence to immunosuppressive regimens (51%) and expectations of functional/aesthetic outcome (38%) were the most frequently chosen top psychosocial issues that must be addressed by the surgical/medical teams involved in the operation.

CONCLUSIONS

Our study's results demonstrate increasing overall support for hand allotransplantation and increasing acceptance of today's immunosuppressive regimens compared to prior literature. Bilateral hand loss remains the primary agreed-upon indication for transplantation. Despite increasing acceptance in the surgical community, the dangers of chronic immunosuppression, cost and patient adherence continue to be the primary concerns hindering its broader acceptance.