Cutaneous leukocyte lineages in tolerant large animal and immunosuppressed clinical vascularized composite allograft recipients

Challenges and opportunities in vascularized composite allotransplantation of joints: a systematic literature review

Background

Joint allotransplantation (JA) within the field of vascularized composite allotransplantation (VCA) holds great potential for functional and non-prosthetic reconstruction of severely damaged joints. However, clinical use of JA remains limited due to the immune rejection associated with all forms of allotransplantation. In this study, we aim to provide a comprehensive overview of the current state of JA through a systematic review of clinical, animal, and immunological studies on this topic.

Methods

We conducted a systematic literature review in accordance with the PRISMA guidelines to identify relevant articles in PubMed, Cochrane Library, and Web of Science databases. The results were analyzed, and potential future prospects were discussed in detail.

Results

Our review included 14 articles describing relevant developments in JA. Currently, most JA-related research is being performed in small animal models, demonstrating graft survival and functional restoration with short-term immunosuppression. In human patients, only six knee allotransplantations have been performed to date, with all grafts ultimately failing and a maximum graft survival of 56 months.

Conclusion

Research on joint allotransplantation has been limited over the last 20 years due to the rarity of clinical applications, the complex nature of surgical procedures, and uncertain outcomes stemming from immune rejection. However, the key to overcoming these challenges lies in extending graft survival and minimizing immunosuppressive side effects. With the emergence of new immunosuppressive strategies, the feasibility and clinical potential of vascularized joint allotransplantation warrants further investigation.

Cellular activation pathways and interaction networks in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is an evolving field of reconstructive surgery that has revolutionized the treatment of patients with devastating injuries, including those with limb losses or facial disfigurement. The transplanted units are typically comprised of different tissue types, including skin, mucosa, blood and lymphatic vasculature, muscle, and bone. It is widely accepted that the antigenicity of some VCA components, such as skin, is particularly potent in eliciting a strong recipient rejection response following transplantation. The fine line between tolerance and rejection of the graft is orchestrated by different cell types, including both donor and recipient-derived lymphocytes, macrophages, and other immune and donor-derived tissue cells (e.g., endothelium). Here, we delineate the role of different cell and tissue types during VCA rejection. Rejection of VCA grafts and the necessity of life-long multidrug immunosuppression remains one of the major challenges in this field. This review sheds light on recent developments in decoding the cellular signature of graft rejection in VCA and how these may, ultimately, influence the clinical management of VCA patients by way of novel therapies that target specific cellular processes.

Hand transplantation: can we balance the risks and benefits?

Asking 'can we balance the risks and benefits?' implies that a quantification of both risk and benefit in hand transplantation (here the terms hand transplant and hand transplantation refer to allotransplantation of the human hand or hand and part or all of the upper limb or limbs) is possible. Despite all we have learned in recent years about hand transplantation, much remains unknown. Even if reliable methods for quantification of risk and benefit were available, fundamental issues relating to effective communication across the gulf of lived experience between the (presumably) handed surgeon and the handless patient remain. Inherent complexities mean some consider hand transplantation an unsolved problem, but we believe the medical and technical considerations fall within the ambit of a competent multidisciplinary team, and that psychosocial and ethical challenges are open to management through robust frameworks for assessment and decision making, underpinned by an extended period of assessment and dialogue, with candid acknowledgement where uncertainty remains. This respects the patient's autonomy while addressing the need for a prolonged period of informing consent.Level of evidence: V.

Skin Immunology and Rejection in VCA and Organ Transplantation

Purpose of Review

Skin provides a window into the health of an individual. Using transplanted skin as a monitor can provide a powerful tool for surveillance of rejection in a transplant. The purpose of this review is to provide relevant background to the role of skin in vascularized transplantation medicine.

Recent Findings

Discrete populations of T memory cells provide distributed immune protection in skin, and cycle between skin, lymph nodes, and blood. Skin-resident TREGcells proliferate in response to inflammation and contribute to long-term VCA survival in small animal models. Early clinical studies show sentinel flap rejection to correlate well with facial VCA skin rejection, and abdominal wall rejection demonstrates concordance with visceral rejection, but further studies are required.

Summary

This review focuses on the immunology of skin, skin rejection in vascularized composite allografts, and the recent advances in monitoring the health of transplanted tissues using distant “sentinel” flaps.