Long-term composite tissue allograft survival in a porcine model with cyclosporine/mycophenolate mofetil therapy

Whole-eye transplantation: Current challenges and future perspectives

Whole-eye transplantation emerges as a frontier in ophthalmology, promising a transformative approach to irreversible blindness. Despite advancements, formidable challenges persist. Preservation of donor eye viability post-enucleation necessitates meticulous surgical techniques to optimize retinal integrity and ganglion cell survival. Overcoming the inhibitory milieu of the central nervous system for successful optic nerve regeneration remains elusive, prompting the exploration of neurotrophic support and immunomodulatory interventions. Immunological tolerance, paramount for graft acceptance, confronts the distinctive immunogenicity of ocular tissues, driving research into targeted immunosuppression strategies. Ethical and legal considerations underscore the necessity for stringent standards and ethical frameworks. Interdisciplinary collaboration and ongoing research endeavors are imperative to navigate these complexities. Biomaterials, stem cell therapies, and precision immunomodulation represent promising avenues in this pursuit. Ultimately, the aim of this review is to critically assess the current landscape of whole-eye transplantation, elucidating the challenges and advancements while delineating future directions for research and clinical practice. Through concerted efforts, whole-eye transplantation stands to revolutionize ophthalmic care, offering hope for restored vision and enhanced quality of life for those afflicted with blindness.

Orthotopic forelimb transplantation in a Yucatan minipig model: Anatomic and in vivo study

INTRODUCTION

Above elbow transplants represent 19% of the upper extremity transplants. Previous large-animal models have been too distal or heterotopic, did not use immunosuppression and had short survival. We hypothesize that an orthotopic forelimb transplant model, under standard immunosuppression, is feasible and can be used to address questions on peri-transplant ischemia reperfusion injury, and post-transplantation vascular, immunologic, infectious, and functional outcomes.

MATERIALS AND METHODS

Four forelimbs were used for anatomical studies. Four mock transplants were performed to establish technique/level of muscle/tendon repairs. Four donor and four recipient female Yucatan minipigs were utilized for in-vivo transplants (endpoint 90-days). Forelimbs were amputated at the midarm and preserved through ex vivo normothermic perfusion (EVNP) utilizing an RBC-based perfusate. Hourly perfusate fluid-dynamics, gases, electrolytes were recorded. Contractility during EVNLP was graded hourly using the Medical Research Council scale. EVNP termination criteria included systolic arterial pressure ≥115 mmHg, compartment pressure ≥30 mmHg (at EVNP endpoint), oxygen saturation reduction of 20%, and weight change ≥2%. Indocyanine green (ICG) angiography was performed after revascularization. Limb rejection was evaluated clinically (rash, edema, temperature), and histologically (BANFF classification) collecting per cause and protocol biopsies (POD 1, 7, 30, 60 and endpoint). Systemic infections were assessed by blood culture and tissue histology. CT scan was used to confirm bone bridging at endpoint.

RESULTS

Animals 2, 4 reached endpoint with grade 0-I rejection. Limbs 1, 3 presented grade III rejection on days 6, 61. CsA troughs averaged 461 ± 189 ng/mL. EVNLP averaged 4.3 ± 0.52 h. Perfusate lactate, PO2 , and pH were 5.6 ± 0.9 mmol/L, 557 ± 72 mmHg and 7.5 ± 0.1, respectively. Muscle contractions were 4 [1] during EVNLP. Transplants 2, 3, 4 showed bone bridging on CT.

CONCLUSION

We present preliminary evidence supporting the feasibility of an orthotopic, mid-humeral forelimb allotransplantation model under standard immunosuppression regimen. Further research should validate the immunological, infectious, and functional outcomes of this model.

Porcine-human glioma xenograft model. Immunosuppression and model reproducibility

BACKGROUND

Glioblastoma is the most common primary malignant and treatment-resistant human brain tumor. Rodent models have played an important role in understanding brain cancer biology and treatment. However, due to their small cranium and tumor volume mismatch, relative to human disease, they have been less useful for translational studies. Therefore, development of a consistent and simple large animal glioma xenograft model would have significant translational benefits.

METHODS

Immunosuppression was induced in twelve standard Yucatan minipigs. 3 pigs received cyclosporine only, while 9 pigs received a combined regimen including cyclosporine (55 mg/kg q12 h), prednisone (25 mg, q24 h) and mycophenolate (500 mg q24 h). U87 cells (2 × 106) were stereotactically implanted into the left frontal cortex. The implanted brains were imaged by MRI for monitoring. In a separate study, tumors were grown in 5 additional pigs using the combined regimen, and pigs underwent tumor resection with intra-operative image updating to determine if the xenograft model could accurately capture the spatial tumor resection challenges seen in humans.

RESULTS

Tumors were successfully implanted and grown in 11 pigs. One animal in cyclosporine only group failed to show clinical tumor growth. Clinical tumor growth, assessed by MRI, progressed slowly over the first 10 days, then rapidly over the next 10 days. The average tumor growth latency period was 20 days. Animals were monitored twice daily and detailed records were kept throughout the experimental period. Pigs were sacrificed humanely when the tumor reached 1 - 2 cm. Some pigs experienced decreased appetite and activity, however none required premature euthanasia. In the image updating study, all five pigs demonstrated brain shift after craniotomy, consistent with what is observed in humans. Intraoperative image updating was able to accurately capture and correct for this shift in all five pigs.

CONCLUSION

This report demonstrates the development and use of a human intracranial glioma model in an immunosuppressed, but nongenetically modified pig. While the immunosuppression of the model may limit its utility in certain studies, the model does overcome several limitations of small animal or genetically modified models. For instance, we demonstrate use of this model for guiding surgical resection with intraoperative image-updating technologies. We further report use of a surrogate extracranial tumor that indicates growth of the intracranial tumor, allowing for relative growth assessment without radiological imaging.

A systematic review of immunomodulatory strategies used in skin-containing preclinical vascularized composite allotransplant models

BACKGROUND

Acute rejection remains a vexing problem in vascularized composite allotransplantation (VCA). Available immunosuppressive regimens are successful at minimizing alloimmune response and allowing VCA in humans. However, repeated rejection episodes are common, and systemic side effects of the current standard regimen (Tacrolimus, MMF, Prednisone) are dose limiting. Novel immunomodulatory approaches to improve allograft acceptance and minimize systemic toxicity are continuously explored in preclinical models. We aimed to systematically summarize past and current approaches to help guide future research in this complex field.

METHODS

We conducted a systematic review of manuscripts listed in the MEDLINE and PubMed databases. For inclusion, articles had to primarily investigate the effect of a therapeutic approach on prolonging the survival of a skin-containing preclinical VCA model. Non-VCA studies, human trials, anatomical and feasibility studies, and articles written in a language other than English were excluded. We followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines.

RESULTS

The search retrieved 980 articles of which 112 articles were ultimately included. The majority of investigations used a rat model. An orthotopic hind limb VCA model was used in 53% of the studies. Cell and drug-based approaches were investigated 58 and 52 times, respectively. We provide a comprehensive review of immunomodulatory strategies used in VCA preclinical research over a timeframe of 44 years.

CONCLUSION

We identify a transition from anatomically non-specific to anatomical models mimicking clinical needs. As limb transplants have been most frequently performed, preclinical research focused on using the hind limb model. We also identify a transition from drug-based suppression therapies to cell-based immunomodulation strategies.

Subcutaneous transplantation of engineered islet/adipose-derived mesenchymal stem cell sheets in diabetic pigs with total pancreatectomy

Introduction

Intraportal islet transplantation is a promising therapeutic approach for patients with type 1 diabetes mellitus (T1DM). However, despite being minimally invasive, the method has some limitations, such as short-term graft loss, portal venous thrombosis, and difficulty in collecting adequate amounts of islets. Subcutaneous islet transplantation on adipose-derived mesenchymal stem cell (ADSC) sheets has been suggested to overcome these limitations, and in this study, we have examined its feasibility in T1DM pigs.

Methods

Inguinal subcutaneous fat was harvested from young pigs and then isolated and cultured adequate ADSCs to prepare sheets. Islets were isolated from the pancreases of mature pigs and seeded on the ADSC sheets. T1DM pigs were generated by total pancreatectomy, and ADSC sheets with transplanted islets were administered subcutaneously to the waist (n = 2). The effects of the islets on the ADSC sheets and on blood glucose levels were evaluated. Insulin secretion was measured by insulin stimulation index.

Results

Islet viability was higher on ADSCs compared to islets alone (91.8 ± 4.3 vs. 81.7 ± 4.1%). The insulin stimulation index revealed higher glucose sensitivity of islets on ADSC sheets compared to islets alone (2.8 ± 2.0 vs. 0.8 ± 0.3). After transplantation, the blood glucose levels of two pigs were within the normal range, and sensitive insulin secretion was confirmed by intravenous glucose tolerance tests. After graftectomy, decreased insulin secretion and hyperglycemia were observed.

Conclusions

Subcutaneous islet transplantation using ADSC sheets can regulate the blood glucose levels of T1DM pigs.

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The adipose-derived mesenchymal stem cell sheet is useful to protect the islets.

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Subcutaneous islet transplantation on sheet normalized blood glucose in diabetic pig.

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Subcutaneous islet transplantation on sheet can be a useful tool.

The intragraft vascularized bone marrow component plays a critical role in tolerance induction after reconstructive transplantation

The role of the vascularized bone marrow component as a continuous source of donor-derived hematopoietic stem cells that facilitate tolerance induction of vascularized composite allografts is not completely understood. In this study, vascularized composite tissue allograft transplantation outcomes between recipients receiving either conventional bone marrow transplantation (CBMT) or vascularized bone marrow (VBM) transplantation from Balb/c (H2d) to C57BL/6 (H2b) mice were compared. Either high- or low-dose CBMT (1.5 × 10⁸ or 3 × 10⁷ bone marrow cells, respectively) was applied. In addition, recipients were treated with costimulation blockade (1 mg anti-CD154 and 0.5 mg CTLA4Ig on postoperative days 0 and 2, respectively) and short-term rapamycin (3 mg/kg/day for the first posttransplant week and then every other day for another 3 weeks). Similar to high-dose conventional bone marrow transplantation, 5/6 animals in the vascularized bone marrow group demonstrated long-term allograft survival (>120 days). In contrast, significantly shorter median survival was noted in the low-dose CBMT group (~64 days). Consistently high chimerism levels were observed in the VBM transplantation group. Notably, low levels of circulating CD4⁺ and CD8⁺ T cells and a higher ratio of Treg to Teff cells were maintained in VBM transplantation and high-dose CBMT recipients (>30 days) but not in low-dose VBM transplant recipients. Donor-specific hyporesponsiveness was shown in tolerant recipients in vitro. Removal of the vascularized bone marrow component after secondary donor-specific skin transplantation did not affect either primary allograft or secondary skin graft survival.

Immunosuppression for in vivo research: state-of-the-art protocols and experimental approaches

Almost every experimental treatment strategy using non-autologous cell, tissue or organ transplantation is tested in small and large animal models before clinical translation. Because these strategies require immunosuppression in most cases, immunosuppressive protocols are a key element in transplantation experiments. However, standard immunosuppressive protocols are often applied without detailed knowledge regarding their efficacy within the particular experimental setting and in the chosen model species. Optimization of such protocols is pertinent to the translation of experimental results to human patients and thus warrants further investigation. This review summarizes current knowledge regarding immunosuppressive drug classes as well as their dosages and application regimens with consideration of species-specific drug metabolization and side effects. It also summarizes contemporary knowledge of novel immunomodulatory strategies, such as the use of mesenchymal stem cells or antibodies. Thus, this review is intended to serve as a state-of-the-art compendium for researchers to refine applied experimental immunosuppression and immunomodulation strategies to enhance the predictive value of preclinical transplantation studies.

Head Transplantation in Mouse Model

AIMS

The mouse model of allo-head and body reconstruction (AHBR) has recently been established to further the clinical development of this strategy for patients who are suffering from mortal bodily trauma or disease, yet whose mind remains healthy. Animal model studies are indispensable for developing such novel surgical practices. The goal of this work was to establish head transplant mouse model, then the next step through the feasible biological model to investigate immune rejection and brain function in next step, thereby promoting the goal of translation of AHBR to the clinic in the future.

METHODS AND RESULTS

Our approach involves retaining adequate blood perfusion in the transplanted head throughout the surgical procedure by establishing donor-to-recipient cross-circulation by cannulating and anastomosing the carotid artery on one side of the body and the jugular vein on the other side. Neurological function was preserved by this strategy as indicated by electroencephalogram and intact cranial nerve reflexes.

CONCLUSIONS

The results of this study support the feasibility of this method for avoiding brain ischemia during transplantation, thereby allowing for the possibility of long-term studies of head transplantation.

Short-term pharmacokinetic study of mycophenolate mofetil in neonatal swine

BACKGROUND

Mycophenolate mofetil (MMF) is an effective immunosuppressive agent that has been frequently used in laboratory animals including swine; however, the pharmacokinetic properties of MMF in swine have not been studied. This short-term study was designed to evaluate the feasibility and the pharmacokinetic profiles of MMF therapy in neonatal swine.

MATERIALS AND METHODS

Twelve neonatal pigs were randomized into four groups including one control and three treated groups with oral MMF administered at 0.5, 1, and 2 g/m(2)/d for 4 days, divided by 2 half-doses at 9:00 and 17:00 (except day 4 during which MMF was not administered at 17:00). Blood samples were collected at 9:00 on days 0, 2, 3 and 4 for complete blood count and hepatic/renal function examination; the trough concentration of plasma mycophenolic acid (MPA) was also determined. On days 2 and 4, blood was collected to determine the area under the curve (AUC) of plasma MPA concentration. Animal body-weight growth and manifestations of MMF side-effects such as anorexia, vomiting, and diarrhea were also observed.

RESULTS

MMF has no acute hepatic/renal toxicity in newborn pigs; however, less body-weight growth was observed in treated groups. In the control group, a spontaneous increase of lymphocyte count was observed; in contrast, MMF therapy with doses of 1 and 2 g/m(2)/d reduced both lymphocyte and monocyte counts of piglets. Oral MMF had high bioavailability in neonatal swine. MPA-AUC0-12h of doses 0.5, 1, and 2 g/m(2)/d was 22.00 ± 3.32, 57.57 ± 34.30, and 140.00 ± 19.70 μg × h/mL, respectively. Neither MPA trough concentration (MPA-C0), nor MPA maximum concentration (MPA-Cmax) or MPA-AUC0-6h had high correlation with MMF-dose. For surveillance of MPA exposure, MPA-C0 had significant correlation with MPA-AUC0-12h (Spearman's ρ = 0.933, AUC0-12h = 17.882 × C0 + 14.479, r(2) = 0.966).

CONCLUSION

To reach adequate drug exposure and to reduce dose-dependent side effects, an MMF dose of 1 g/m(2)/d is recommended to be used as an initial dose for immunosuppressive therapy in piglets, and MPA-C0 monitoring is the most practical strategy for experimental transplantation study.

Allogeneic head and body reconstruction: mouse model

AIMS

There is still no effective way to save a surviving healthy mind when there is critical organ failure in the body. The next frontier in CTA is allo-head and body reconstruction (AHBR), and just as animal models were key in the development of CTA, they will be crucial in establishing the procedures of AHBR for clinical translation.

METHODS AND RESULTS

Our approach, pioneered in mice, involves retaining the donor brain stem and transplanting the recipient head. Our preliminary data in mice support that this allows for retention of breathing and circulatory function. Critical aspects of the current protocol include avoiding cerebral ischemia through cross-circulation (donor to recipient) and retaining the donor brain stem. Successful clinical translation of AHBR will become a milestone of medical history and potentially could save millions of people.

CONCLUSIONS

This experimental study has confirmed a method to avoid cerebral ischemia during the surgery and solved an important part of the problem of how to accomplish long-term survival after transplantation and preservation of the donor brain stem.

Current status of vascularized composite tissue allotransplantation

Vascularized composite tissue allotransplantation (VCA) offers treatment options of complex functional deficiencies that cannot be repaired with conventional reconstructive methods. VCAs consist of blocks of functional units comprising different tissue types such as skin, bone, muscle, nerves, blood vessels, tendons, ligaments and others, and are thus substantially different from the composition of organ transplants. The field of VCA has made fascinating progresses in the recent past. Among other VCAs, numerous successful hand, face and limb transplants have been performed in the world. At the same time, specific questions in regard to innate and adaptive immunity, consequences of ischemia/reperfusion injury, immunosuppression, preservation, and regenerative capacity remain. In spite of this, the field is poised to make significant advances in the near future.

Upper extremity transplantation: current concepts and challenges in an emerging field

Loss of an isolated upper limb is an emotionally and physically devastating event that results in significant impairment. Patients who lose both upper extremities experience profound disability that affects nearly every aspect of their lives. While prosthetics and surgery can eventually provide the single limb amputee with a suitable assisting hand, limited utility, minimal haptic feedback, weight, and discomfort are persistent problems with these techniques that contribute to high rates of prosthetic rejection. Moreover, despite ongoing advances in prosthetic technology, bilateral amputees continue to experience high levels of dependency, disability, and distress. Hand and upper extremity transplantation holds several advantages over prosthetic rehabilitation. The missing limb is replaced with one of similar skin color and size. Sensibility, voluntary motor control, and proprioception are restored to a greater degree, and afford better dexterity and function than prosthetics. The main shortcomings of transplantation include the hazards of immunosuppression, the complications of rejection and its treatment, and high cost. Hand and upper limb transplantation represents the most commonly performed surgery in the growing field of Vascularized Composite Allotransplantation (VCA). As upper limb transplantation and VCA have become more widespread, several important challenges and controversies have emerged. These include: refining indications for transplantation, optimizing immunosuppression, establishing reliable criteria for monitoring, diagnosing, and treating rejection, and standardizing outcome measures. This article will summarize the historical background of hand transplantation and review the current literature and concepts surrounding it.

A modified heterotopic swine hind limb transplant model for translational vascularized composite allotransplantation (VCA) research

Vascularized Composite Allotransplantation (VCA) such as hand and face transplants represent a viable treatment option for complex musculoskeletal trauma and devastating tissue loss. Despite favorable and highly encouraging early and intermediate functional outcomes, rejection of the highly immunogenic skin component of a VCA and potential adverse effects of chronic multi-drug immunosuppression continue to hamper widespread clinical application of VCA. Therefore, research in this novel field needs to focus on translational studies related to unique immunologic features of VCA and to develop novel immunomodulatory strategies for immunomodulation and tolerance induction following VCA without the need for long term immunosuppression. This article describes a reliable and reproducible translational large animal model of VCA that is comprised of an osteomyocutaneous flap in a MHC-defined swine heterotopic hind limb allotransplantation. Briefly, a well-vascularized skin paddle is identified in the anteromedial thigh region using near infrared laser angiography. The underlying muscles, knee joint, distal femur, and proximal tibia are harvested on a femoral vascular pedicle. This allograft can be considered both a VCA and a vascularized bone marrow transplant with its unique immune privileged features. The graft is transplanted to a subcutaneous abdominal pocket in the recipient animal with a skin component exteriorized to the dorsolateral region for immune monitoring. Three surgical teams work simultaneously in a well-coordinated manner to reduce anesthesia and ischemia times, thereby improving efficiency of this model and reducing potential confounders in experimental protocols. This model serves as the groundwork for future therapeutic strategies aimed at reducing and potentially eliminating the need for chronic multi-drug immunosuppression in VCA.

Vascularized composite tissue allotransplantation--state of the art

Vascularized composite tissue allotransplantation is a viable treatment option for injuries and defects that involve multiple layers of functional tissue. In the past 15 yr, more than 150 vascularized composite allotransplantation (VCA) surgeries have been reported for various anatomic locations including - but not limited to - trachea, larynx, abdominal wall, face, and upper and lower extremities. VCA can achieve a level of esthetic and functional restoration that is currently unattainable using conventional reconstructive techniques. Although the risks of lifelong immunosuppression continue to be an important factor when evaluating the benefits of VCA, reported short- and long-term outcomes have been excellent, thus far. Acute rejections are common in the early post-operative period, and immunosuppression-related side effects have been manageable. A multidisciplinary approach to the management of VCA has proven successful. Reports of long-term graft losses have been rare, while several factors may play a role in the pathophysiology of chronic graft deterioration in VCA. Alternative approaches to immunosuppression such as cellular therapies and immunomodulation hold promise, although their role is so far not defined. Experimental protocols for VCA are currently being explored. Moving forward, it will be exciting to see whether VCA-specific aspects of allorecognition and immune responses will be able to help facilitate tolerance induction.

The next frontier in composite tissue allotransplantation

Solid organ transplantations became a clinical option in the 1950s. The hand allograft was the pioneer of composite tissue allotransplantation (CTA), successfully started near the end of the last century despite arguments over the practicality and methods. Since then, CTA such as hand and face has continued to progress from the theoretical to clinical reality. The treatment principles, drug combinations, and mechanisms of the immunosuppression medications on which contemporary transplant surgeries have been based continue to develop as researchers and physicians gain more experience in the CTA field. It could be argued that the ethical issues associated with CTA have prevented evolution of the field rather than surgical or technical skill. This is particularly true for allo-head and body reconstruction (AHBR). How can leaders in the field of CTA develop a model that would satisfy ethical concerns? Bolstered by recent successes in the field, is it time to traverse the next frontier? Can AHBR ever be a feasible option in the clinical setting? The reader will be provided with a brief history of CTA from theory to research to clinical practice. A concise description of AHBR as it pertains to the critical procedure (i.e., surgery design) will also be discussed.

Bone flap perfusion assessment using near-infrared fluorescence imaging

BACKGROUND

Microsurgical vascularized bone flaps are a versatile technique for reconstructing large bone defects. However, the assessment of perfusion is challenging, because clinical examination is difficult intraoperatively and often not possible postoperatively. Therefore, it is important to develop techniques to assess the perfusion of vascularized bone flaps and potentially improve the surgical outcomes. Near-infrared (NIR) fluorescence imaging has previously been shown to provide real-time, intraoperative evaluation of vascular perfusion. The present pilot study investigated the ability of NIR imaging to assess the perfusion of vascularized bone flaps.

METHODS

Vascularized bone flaps were created in female Yorkshire pigs using well-established models for porcine forelimb osteomyocutaneous flap allotransplantation (n = 8) and hindlimb fibula flaps (n = 8). Imaging of the bone flaps was performed during harvest using the FLARE intraoperative fluorescence imaging system after systemic injection of indocyanine green. Perfusion was also assessed using the standard of care by clinical observation and Doppler ultrasonography. NIR fluorescence perfusion assessment was confirmed by intermittent clamping of the vascular pedicle.

RESULTS

NIR fluorescence imaging could identify bone perfusion at the cut end of the osteotomy site. When the vascular pedicle was clamped or ligated, NIR imaging demonstrated no fluorescence when injected with indocyanine green. With clamp removal, the osteotomy site emitted fluorescence, indicating bone perfusion. The results using fluorescence imaging showed 100% agreement with the clinical observation and Doppler findings.

CONCLUSIONS

Vascularized bone transfers have become an important tool in reconstructive surgery; however, no established techniques are available to adequately assess perfusion. The results of our pilot study have indicated that NIR imaging can provide real-time, intraoperative assessment of bone perfusion.

Biological therapy of bone defects: the immunology of bone allo-transplantation

IMPORTANCE OF THE FIELD

Bone is one of the most transplanted tissues worldwide. Autograft is the ideal bone graft but is not widely used because of donor site morbidity and restricted availability. Allograft is easily accessible but can transmit infections and elicit an immune response.

AREAS COVERED IN THIS REVIEW

This review identifies all in vitro and in vivo evidence of immune responses following bone transplantation and highlights methods of improving host tolerance to bone allotransplantation.

WHAT THE READER WILL GAIN

In humans, the presence of anti-HLA specific antibodies against freeze-dried and fresh-frozen bone allografts has been demonstrated. Fresh-frozen bone allograft can still generate immune reactions whilst freeze-dried bone allografts present with less immunogenicity but have less structural integrity. This immune response can have an adverse effect on the graft's incorporation and increase the incidence of rejection. Decreasing the immune reaction against the allograft by lowering the immunogenic load of the graft or lowering the host immune response, would result in improved bone incorporation.

TAKE HOME MESSAGE

It is essential that the complex biological processes related to bone immunogenicity are understood, since this may allow the development of safer and more successful ways of controlling the outcome of bone allografting.

Science of composite tissue allotransplantation

The science of composite tissue allotransplantation (CTA) is rooted in progressive thinking by surgeons, fueled by innovative solutions, and aided by understanding the immunology of tolerance and rejection. These three factors have allowed CTA to progress from science fiction to science fact. Research using preclinical animal models has allowed an understanding of the antigenicity of complex tissue transplants and mechanisms to promote graft acceptance. As a result, translation to the clinic has shown that CTA is a viable treatment option well on the way of becoming a standard of care for those who have lost extremities and suffered large tissue defects. The field of CTA has been progressing exponentially over the past decade. Transplantation of hands, larynx, vascularized knee, trachea, face, and abdominal wall has been performed. Several important observations have emerged from translation to the clinic. Although it was predicted that rejection would pose a major limitation, this has not proven true. In fact, steroid-sparing protocols for immunosuppression that have been successfully used in renal transplantation are sufficient to prevent rejection of limbs. Although skin is highly antigenic when transplanted alone in animal models, when part of a CTA, it has not proven to be. Chronic rejection has not been conclusively demonstrated in hand transplant recipients and is difficult to induce in rodent models of CTA. This review focuses on the science of CTA, provides a snapshot of where we are in the clinic, and discusses prospects for the future to make the procedures even more widely available.

Hand transplantation: the state-of-the-art

The feasibility of hand transplantation has been demonstrated, both surgically and immunologically. Levels of immunosuppression comparable to regimens used in solid organ transplantation are proving sufficient to prevent graft loss. Many patients have achieved discriminative sensibility and recovery of intrinsic muscle function. In addition to restoration of function, hand transplantation offers considerable psychological benefits. The recipient's pre-operative psychological status, his motivation and his compliance with the intense rehabilitation programme are key issues. While the induction of graft specific tolerance represents a hope for the future, immunosuppression currently remains necessary and carries significant risks. Hand transplantation should, therefore, only be considered a therapeutic option for a carefully selected group of patients.

Hand transplantation. A future clinical option?

Transplantation of a vascularized limb or its components is defined as composite tissue allotransplantation, and is one of the newest areas in surgery. To date, 24 hands have been transplanted onto 18 recipients. The initial results have been promising, and hand transplantation may become an important procedure for functional restoration of upper limbs. However, the ethical aspects of using chronic immunosuppression for a condition which is not life threatening have been the subject of debate. In this article, we review the field of composite tissue allotransplantation.

Functional results of the first human double-hand transplantation

OBJECTIVE

Objective of this study was to analyze fifteen months after surgery the sensorimotor recovery of the first human double hand transplantation.

SUMMARY BACKGROUND DATA

As for any organ transplantation the success of composite tissue allografts such as a double hand allograft depends on prevention of rejection and its functional recovery.

METHODS

The recipient was a 33-year-old man with bilateral amputation. Surgery included procurement of the upper extremities from a multiorgan cadaveric donor, preparation of the graft and recipient's stumps; then, bone fixation, arterial and venous anastomoses, nerve sutures, joining of tendons and muscles and skin closure. Rehabilitation program included physiotherapy, electrostimulation and occupational therapy. Immunosuppressive protocol included tacrolimus, prednisone and mycophenolate mofetil and, for induction, antithymocyte globulins and then CD25 monoclonal antibody were added. Sensorimotor recovery tests and functional magnetic resonance imaging (fMRI) were performed to assess functional return and cortical reorganization. All the results were classified according to Ipsen's classification.

RESULTS

No surgical complications occurred. Two episodes of skin acute rejection characterized by maculopapular lesions were completely reversed increasing steroid dose within 10 days. By fifteen months the sensorimotor recovery was encouraging and the life quality improved. fMRI showed that cortical hand representation progressively shifted from lateral to medial region in the motor cortex.

CONCLUSION

Even though at present this double hand allograft, treated using a conventional immunosuppression, allowed to obtain results at least as good as those achieved in replanted upper extremities, longer follow-up will be necessary to demonstrate the final functional restoration.

Sequential histological and immunohistochemical study of the skin of the first human hand allograft

BACKGROUND

On September 1998, the first human hand allograft was successfully performed in Lyon.

METHODS

A 48-year-old white man who had suffered accidental amputation of the arm in 1984, received a forearm and hand allograft from a 42-year-old white male cadaveric heart-beating donor. Immunosuppressive therapy included prednisone, mycophenolate mofetil, FK506, and antithymocyte globulins. Sequential skin biopsies were taken from the grafted limb and examined (immuno)histologically to detect a possible graft rejection and to evaluate the structural integrity of the skin of the allograft.

RESULTS

The skin showed histologically a normal appearance, except on days 57 and 63, when a mononuclear perivascular cell infiltrate was observed in the dermis; this appeared concomitantly with erythematous lesions of the skin that developed after a slight decrease of the immunosuppressive treatment. These changes were considered as signs of graft rejection, and were reversed by an increase of the immunosuppressive treatment. No skin necrosis was seen at any time. Immunohistochemically, the main cell types of the skin were present throughout the study. From day 77 onward the epidermis of the grafted hand harbored some epidermal Langerhans cells of recipient's origin.

CONCLUSION

This study shows that the skin of the hand allograft maintains overall a normal histological structure and contains most essential cell types, including cells of recipient origin, such as Langerhans cells. Furthermore, it shows that in this system of composite tissue transplantation, skin biopsies may reveal a starting graft rejection, before the appearance of clinically obvious lesions.

Microneurovascular allotransplantation of the canine tongue

INTRODUCTION

Reconstruction of the tongue with existing methods of tissue transfer often leaves glossectomy patients with significant deficits in speech and swallowing. The critical role of the tongue is implied by its unique structure and function. This paper reports the development of an animal model of hemitongue allotransplantation and documents functional and anatomic outcomes of this procedure.

METHODS

Ten pairs of unmatched dogs underwent reciprocal exchange of the left hemitongue with microneurovascular replantation. The unoperated hemitongue acted as the control. Under cyclosporine immunosuppression, animals surviving long term underwent clinical observation, before electromyography, force transduction studies, and histological evaluation being euthanized.

RESULTS

Five animals survived between 6 and 13 months for long-term evaluation. The remaining group were euthanized because of or died of overwhelming infection or uncontrollable transplant rejection. The latter sometimes resulted from difficulty in the delivery of the cyclosporine. Clinical recovery of tongue function was observed, as well as resumption of motor unit potential activity on electromyography. Contractile force recovery of the transplanted tongue averaged 68% of control (range, 47%-97%), and histological study of the hypoglossal and lingual nerves demonstrated anatomic evidence of reinnervation. Preservation of muscle, mucosal, and stromal ultrastructure was seen with light microscopy of the transplanted tongue.

CONCLUSIONS

Allotransplantation of the hemitongue and associated neurovascular apparatus is possible in a large mammalian model, with long-term survival of tissue being accompanied by partial recovery of contractile properties. Anatomical and clinical evidence also points to sensory recovery. These data support the future possibility of employing a similar technique in glossectomy patients.