Management of acute rejection 2 years after allogeneic vascularized knee joint transplantation

Autogenous Arteriovenous Bundle Implantation Maintains Viability Without Increased Immune Response in Large Porcine Bone Allotransplants

BACKGROUND

Transplantation of living allogeneic bone segments may permit reconstruction of large defects, particularly if viability is maintained without immunosuppression. Development of a new autogenous osseous blood supply accomplishes this goal in rodent experimental models. This study evaluates potential systemic and local inflammatory responses to this angiogenesis in a large-animal model.

METHODS

Vascularized allogeneic tibia segments were transplanted orthotopically into matched tibial defects in Yucatan minipigs. Microvascular anastomoses of bone nutrient artery and vein were supplemented by intramedullary placement of an autogenous arteriovenous (AV) bundle in group 1. Group 2 served as a no-angiogenesis control. A 3-drug immunosuppression regimen was withdrawn after 2 weeks. During the 20-week survival period, periodic leukocyte counts and inflammatory cytokine levels were measured. Thereafter, osteocyte survival was quantified and transplant rejection graded by histologic examination and quantitative real-time polymerase chain reaction of immunologic markers.

RESULTS

Both groups developed an initial systemic response, which resolved after 4 to 6 weeks. No differences were seen in blood cytokine levels. Interleukin 2 expression was diminished in group 1 tibiae. As expected, nutrient pedicles had thrombosed without sustained immunosuppression, occluded by intimal hyperplasia. In group 1, angiogenesis from the autogenous AV bundle resulted in significantly less osteonecrosis (P = .04) and fibrosis (P = .02) than group 2 allotransplants.

CONCLUSIONS

Systemic immune responses to large-bone allotransplants were not increased by generation of an autogenous osseous blood supply within porcine tibial bone allotransplants. Implanted AV bundles diminished inflammation and fibrosis and improved bone viability when compared to no-angiogenesis controls.

A Flow Dynamic Rationale for Accelerated Vascularized Composite Allotransplant Rejection

BACKGROUND

From 1996 to 2000, Diefenbeck et al. carried out six knee vascularized composite allotransplants. The allotransplants were composed of bone, soft tissue, and femoral vascular pedicle (25 to 40 cm). All rejected between 14 and 56 months. Failures were attributed to chronic rejection. In 2008, the Louisville team lost their fourth patient's hand transplant at 8 months. During the rejection workup, intraoperative findings noted a thickened arterial pedicle attributed to intimal hyperplasia with significant fibrotic perivascular tissue and a near "no-flow phenomenon." No cutaneous rejection was appreciated and failure was attributed to chronic rejection.

METHODS

Data were collected from two teams, one in Germany and the other in Louisville, Kentucky. The population under study consisted of the six knee and one hand transplants. The factor of interest was the long donor arterial pedicle. The outcome measurements were transplant survival time and histopathologic results.

RESULTS

There are only seven published vascularized composite allotransplant cases where a donor artery longer than 25 cm was used. This cohort represents a 100 percent accelerated failure rate. The cause of these losses remains unexplained. The donor arteries suffered from T-cell-mediated rejection and ischemia-induced media/adventitial necrosis.

CONCLUSIONS

We hypothesize that the donor artery rejected at an accelerated rate because of ischemia caused by disruption of the external vasa vasorum in conjunction with intimal hyperplasia induced by T-cell-mediated rejection that led to disruption of the Windkessel effect. Loss of this effect presented as intimal hyperplasia accelerated by ischemia causing an expedited transplant failure.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.

Could Sentinel Skin Transplants Have Some Utility in Solid Organ Transplantation?

Accurate diagnosis of allograft rejection can be hazardous and challenging. A strategy that has emerged from experience with vascularized composite allografts (VCAs) is the use of sentinel skin transplants (SSTs)-portions of donor skin transplanted synchronously to an allograft. Work in nonhuman animal models and experience with VCAs suggest concordance between rejection occurring in the primary allograft and the SST, and that appearance of rejection in the SST may precede rejection in the primary allograft, permitting early therapeutic intervention that may improve outcomes with lower rates of chronic rejection. The encouraging findings reported in VCA transplantation raise the possibility that SST may also be useful in solid organ transplantation. Some evidence is provided by experience with abdominal wall transplantation in some intestinal and multivisceral transplant recipients. Results from those reports raise the possibility that rejection may manifest in the skin component before emergence in the intestinal allograft, providing a "lead time" during which treatment of rejection of the abdominal wall could prevent the emergence of intestinal rejection. It is plausible that these findings may be extrapolated to other solid organ allografts, especially those for which obtaining an accurate diagnosis of acute rejection can be hazardous and challenging, such as the lung or pancreas. However, more data are required to support widespread adoption of this technique.

Knee joint transplantation combined with surgical angiogenesis in rabbits--a new experimental model

PURPOSE

We have previously described a means to maintain bone allotransplant viability, without long-term immune modulation, replacing allogenic bone vasculature with autogenous vessels. A rabbit model for whole knee joint transplantation was developed and tested using the same methodology, initially as an autotransplant.

MATERIALS/METHODS

Knee joints of eight New Zealand White rabbits were elevated on a popliteal vessel pedicle to evaluate limb viability in a nonsurvival study. Ten additional joints were elevated and replaced orthotopically in a fashion identical to allotransplantation, obviating only microsurgical repairs and immunosuppression. A superficial inferior epigastric facial (SIEF) flap and a saphenous arteriovenous (AV) bundle were introduced into the femur and tibia respectively, generating a neoangiogenic bone circulation. In allogenic transplantation, this step maintains viability after cessation of immunosuppression. Sixteen weeks later, X-rays, microangiography, histology, histomorphometry, and biomechanical analysis were performed.

RESULTS

Limb viability was preserved in the initial eight animals. Both soft tissue and bone healing occurred in 10 orthotopic transplants. Surgical angiogenesis from the SIEF flap and AV bundle was always present. Bone and joint viability was maintained, with demonstrable new bone formation. Bone strength was less than the opposite side. Arthrosis and joint contractures were frequent.

CONCLUSION

We have developed a rabbit knee joint model and evaluation methods suitable for subsequent studies of whole joint allotransplantation.

A modified vascularized whole knee joint allotransplantation model in the rat

Previous papers have shown surgical neoangiogenesis to allow long-term bone allotransplant survival without immunosuppression. Whole joint composite tissue allotransplants (CTA) might be treated similarly. A novel rat knee CTA model is described for further study of the roles of neoangiogensis in joint allotransplant survival and adjustment of immunosuppression. Microvascular knee CTA was performed in nine rats across a major histocompatibility barrier with both pedicle repair and implantation of host-derived arteriovenous ("a/v") bundles. In the control group (N = 3), the pedicle was ligated. Immunosuppression was given daily. Joint mobility, weight-bearing, pedicle patency, bone blood flow, and sprouting from a/v bundles were assessed at 3 weeks. All but the nonrevascularized control knees had full passive motion and full weight bearing. One nutrient pedicle thrombosed prematurely. Blood flow was measurable in transplants with patent nutrient pedicles. Implanted a/v bundles produced new vascular networks on angiography. This new rat microsurgical model permits further study of joint allotransplantation. Patency of both pedicles and implanted a/v bundles was maintained, laying a foundation for future studies.

The history of human composite tissue allotransplantation

Restoration of amputations and disfigurement are represented in ancient mythology, but the modern history of composite tissue allotransplantation begins with World War II injuries that generated seminal immunologic experiments by Medawar and co-workers. These studies led to the first successful human allografts in the 1950s by Peacock with composite tissue and Murray and co-workers with solid organs. Pharmacologic immunosuppression brought rapid growth of solid organ transplantation over the next 50 years, but composite tissue transplantation virtually disappeared. This evolution was judged to be a consequence of the greater antigenicity of skin, which that was insurmountable by the available immunosuppression. In the mid-1990s, progress in immunosupression allowed skin-bearing grafts, led by successful hand transplants, which produced a renaissance in composite tissue allotransplantation. Since then, graft types have expanded to over 10, and graft numbers to over 150, with success rates that equal or exceed solid organs. The field has emerged as one of the most exciting in contemporary medicine, although accompanied by substantial challenges and controversy. This paper reviews the origins and progress of this field, assessing its potential for future evolution.

Host-derived neoangiogenesis with short-term immunosuppression allows incorporation and remodeling of vascularized diaphyseal allogeneic rabbit femur transplants

The purpose of this study was to demonstrate that living bone allotransplants can incorporate, remodel, and maintain mechanical properties without long-term immunosuppression in a fashion comparable to living autotransplants. For this, viability is maintained by repair of nutrient vessels and neovascularization from implanted host-derived vasculature. Microsurgically revascularized femoral diaphysis allotransplants were transferred from young male New-Zealand-White (NZW) into 4 groups of male Dutch-Belted (DB) rabbits. Short-term immunosuppression by tacrolimus (IS, groups 4 and 5) and host-derived neovascularization (NV) from implanted fascial flaps was used to maintain viability (groups 3 and 5) as independent variables. Group 2 received neither IS nor NV. Vascularized pedicled autotransplants were orthotopically transplanted in group 1. After 16 weeks, transplants were evaluated using radiologic, histologic, biomechanical, and histomorphometric parameters. Vascularized bone allotransplants treated with both short-term IS and host-derived NV (group 5) healed in a fashion similar to pedicled autotransplants (group 1). Their radiographic scores were higher than other groups. Groups with patent fascial flaps (3 and 5) showed significantly greater neoangiogenesis than ligated controls (2 and 4). Tacrolimus administration did not affect neoangiogenesis. Elastic modulus and ultimate stress were significantly greater in autogenous bone than in allotransplanted femora. Biomechanical properties were not significantly different among allotransplants. Bone turnover was decreased with IS, but increased with NV by the implanted fascial flaps. Living allogeneic femoral allotransplants treated with short-term IS and host-derived neoangiogenesis can lead to stable transplant incorporation in this rabbit model. The combination of both factors optimizes bone healing. Transplant mineralization is improved with neoangiogenesis but diminished with IS.

[Healing of free vascularized bone allotransplants: optimizing by short-term immunosuppression and host-derived neovascularization]

BACKGROUND

Living bone allotransplants (ATs) currently require long-term immunosuppression (IS), but this is impractical for extremity-preserving procedures. An alternative method to maintain viability of the transplant uses host-derived neoangiogeneic vessels combined with short-term IS.

MATERIALS AND METHODS

Diaphyseal femoral defects in Dutch-Belted rabbits were reconstructed with a free microvascular AT from New Zealand White rabbits. Additionally, a host-derived intramedullary pedicled fascial flap was placed and short-term IS administered to two of four groups. Neovascularization and bone healing were quantified by microangiography and a custom radiographic score.

RESULTS

Bone ATs with perfused fascial flaps achieved bone healing equivalent to autotransplant controls, even when they received IS only until host-derived neoangiogenesis replaced the original perfusion. Vascularized ATs without this combination achieved significantly inferior results.

SUMMARY

This rabbit model demonstrated that increased bone turnover allows good healing but may temporarily weaken the allotransplant. However, by the more intense replacement of the graft with host-derived cells, this process may, in the long-term, ultimately result in a better transplant than an avascular graft.

Outcome of allogeneic vascularized knee transplants

Transplantation of vascularized knee joints is a novel approach in Composite Tissue Allotransplantation (CTA). In 1996 our group started a clinical knee transplantation project and six transplantations have been performed since. Key problems identified early were the monitoring of acute rejection and choice of an immunosuppressive regime. One graft was lost due to postoperative infection and one due to of noncompliance where the patient discontinued the immunosuppressant regime. In three cases late rejection lead to necrosis and graft dysfunction after 15, 16 and 24 months, respectively. Exit-strategies were arthrodesis in one patient and Above Knee Amputation in two cases. With retrospective analysis after initial five cases the treatment protocol was improved. The immunosuppressive drug regime was altered, femoral diaphysis and knee joint grafting was combined and a vascularized block of donor skin and subcutaneous tissue was harvested with the graft (sentinel skin graft). The sentinel skin graft enabled us to monitor acute rejection by clinical and histological examination and avoid late rejection by rapid treatment with high dose steroids. In summary, over a four-year period, one of six allogeneic vascularized knee transplants has survived, one was lost from a surgical site infection, one by noncompliance and three by late rejection. Analysis of our data leads us to suggest that knee transplantation should be limited to a combined injury consisting of extensive loss of cartilage and bone, deficient extensor mechanism and soft tissue and skin defects without any signs of infection. Transplantation should only be taken into consideration as last option before Above Knee Amputation in an otherwise healthy patient under 35 years of age.

Vascularized bone allotransplantation: current state and implications for future reconstructive surgery

This article focuses on current advances in musculoskeletal tissue allotransplantation, including strategies for maintaining tissue viability in the face of histocompatibility mismatch and resulting acute and chronic rejection responses. In particular, it introduces a novel concept developed in the authors' laboratory and currently under evaluation that may obviate the problem of chronic rejection. The authors have used therapeutic angiogenesis to develop a host-derived neoangiogenic circulation that maintains blood flow regardless of rejection. The replacement of the allogeneic vessels together with bone remodeling from host-derived cells eventually may largely replace the allogeneic osteocytes and bone with native bone.