Vascularised composite allotransplantation in solid organ transplant recipients: A systematic review

INTRODUCTION

A solid organ transplant (SOT) recipient, already taking immunosuppression, may represent the ideal candidate for vascularised composite allograft transplantation (VCA). However, concerns have been raised about the potential risk of SOT loss or the need for increased immunosuppression to sustain the VCA. This systematic review examines all published cases of SOT recipients who have received a VCA to establish associated morbidity and immunosuppression requirements.

METHODS

A systematic review was performed in accordance with the PRISMA guidelines. The PubMed, MEDLINE and EMBASE databases were searched for original articles published between January 1997 and May 2019. Only articles relating to patients who had received both a VCA and SOT with a reported follow up of greater than six months were included.

RESULTS

Fifteen articles were identified, including data from 39 VCAs in 37 patients. There was no increase in the number of SOT rejection episodes, complications such as post-transplant lymphoproliferative disorder or graft versus host disease, de novo donor specific HLA antibodies or short-term risks to the recipient when compared with SOT in isolation. One child required a sustained increase in their baseline immunosuppression following bilateral hand transplantation.

CONCLUSIONS

In this small heterogeneous cohort, the addition of a VCA to a SOT does not appear to increase the short-term risks to the SOT or the patient with comparable results to SOT in isolation. However, data are often poorly reported and longer-term follow up and uniform reporting of outcomes would be beneficial to more accurately assess the safety profile of combining VCA with SOT.

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.

Optimizing chimerism level through bone marrow transplantation and irradiation to induce long-term tolerance to composite tissue allotransplantation

BACKGROUND

Mixed chimerism with long-term composite tissue allotransplant (CTA) acceptance can be achieved through allogeneic bone marrow transplantation (BMT). The present study investigated the optimal chimerism level by giving different irradiation dosages to recipients to induce tolerance to CTA.

METHODS

Chimera were prepared using Brown-Norway and Lewis rats with strong major histocompatibility complex incompatibility. The Lewis rats received 5 mg antilymphocyte globulin (day -1 and 10) and 16 mg/kg cyclosporine (day 0-10) and were separated into groups 1, 2, 3, 4, and 5 according to the day -1 irradiation dosage: 0, 200, 400, 600, and 950 cGy, respectively. The Lewis rats were then reconstituted with 100 × 10(6) T-cell-depleted Brown-Norway bone marrow cells (day 0) and received vascularized Brown-Norway-CTA on day 28. Chimerism was assessed monthly by flow cytometry starting on day 28 after BMT. Graft-versus-host disease (GVHD) was assessed clinically and histologically.

RESULTS

Chimerism, 4 weeks after BMT, averaged 0.2%, 9.2%, 30.7%, 58%, and 99.3% in groups 1 to 5, respectively. GVHD occurred as follows: groups 1 and 2, none; group 3, 1 case of GVHD; group 4, 7 cases of GVHD (of which 3 died); and group 5, 10 cases of GVHD (of which 6 died). The percentage of long-term CTA acceptance was 0%, 0%, 90%, 70%, and 40% in groups 1 to 5, respectively. The percentage of regulatory T cells was significantly lower in high-chimerism (≥ 20%, n = 15) than in low-chimerism (<20%, n = 5) rats that accepted CTA long-term .

CONCLUSIONS

The chimerism level correlated positively with GVHD occurrence and long-term CTA acceptance but correlated negatively with regulatory T-cell levels. Optimal chimerism for CTA acceptance through pre-CTA BMT and irradiation occurs at 20-50% at day 28 after BMT in the rat model.

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.

Tacrolimus (FK506): Safety and Applications in Reconstructive Surgery

Tacrolimus (FK506) is a macrolide immunosuppressive drug that is approved for the prevention of allograft rejection. It is a standard component of immunosuppressive regimens currently in use for organ and reconstructive tissue transplants. The experimental literature has demonstrated potential efficacy in the management of other diseases for which transplantation does not play a role. The ability of tacrolimus to modulate the immune system and inhibit T cell activation provides a potential benefit for the treatment of disorders in which autoimmune phenomena are central to their pathogenesis such as rheumatoid arthritis and inflammatory bowel disease. Tacrolimus also has well-established neuroprotective and neuroregenerative properties through both similar and different mechanisms that have been extensively demonstrated in both small and large animal models. However, as a potent immunosuppressive agent, it can cause serious adverse effects, some of which are irreversible and potentially life threatening. This article reviews its safety under different therapeutic requirements and applications in both allogeneic and autogenous tissue reconstruction.

Clinical experience in allogeneic vascularized bone and joint allografting

The allotransplantation of vascularized femoral diaphyses and total knee joints is a novel approach in orthopedic surgery. Allogeneic femoral diaphyses were transplanted into three patients suffering from chondrosarcoma or posttraumatic defects. Total knee joints allografts were transplanted in five patients with large bone defects of the knee and loss of the extensor apparatus caused either by major trauma alone or infection after a major trauma. Bone segments and total joints were harvested from multi-organ donors, perfused with UW-solution and transplanted within cold ischemia times of 18-25 h. Patients were immunosuppressed postoperatively primarily with cyclosporine (Cyclosporin A) and azathioprine. Two allografts (1 femur, 1 knee) were lost due to infections. Seven of the eight patients are able to walk with full weight-bearing posttransplant. Two of the patients with transplanted joint allografts subsequently received total knee arthroplasty implantations. Vascularized bone and joint allotransplantation may serve as a last line of defense treatment before considering lower limb amputation.