Hand transplants and the mandate for tolerance

The Impact of Alloantibodies on Clinical VCA Outcomes and the Need for Immune Tolerance

The functional outcomes and restoration of form after vascularized composite allotransplantation (VCA) have exceeded the results that could be achieved with current autologous surgical techniques. However, the longevity of VCA grafts has been limited due to the development of donor-specific antibodies (DSAs), and chronic rejection and graft failure occur despite long-term immunotherapy. Furthermore, despite widespread consensus that these non-life-saving transplants are beneficial for select patients, the application of VCA is limited by the need for lifelong immunosuppression. Therefore, attempts to achieve drug-free tolerance through safe and effective therapies are critical. This review highlights recent publications regarding alloantibody-mediated rejection (AMR) in various VCAs with a focus on the critical need for novel tolerance-inducing strategies. The development and implementation of effective methods of inducing tolerance, such as the use of anti-CD3 immunotoxins, could drastically improve VCA graft outcomes and recipient quality of life.

Donor bone-marrow CXCR4+ Foxp3+ T-regulatory cells are essential for costimulation blockade-induced long-term survival of murine limb transplants

Vascularized composite allotransplantation (VCA) allows tissue replacement after devastating loss but is currently limited in application and may be more widely performed if maintenance immunosuppression was not essential for graft acceptance. We tested whether peri-transplant costimulation blockade could prolong VCA survival and required donor bone-marrow cells, given that bone-marrow might promote graft immunogenicity or graft-versus-host disease. Peritransplant CD154 mAb/rapamycin (RPM) induced long-term orthotopic hindlimb VCA survival (BALB/c->C57BL/6), as did CTLA4Ig/RPM. Surprisingly, success of either protocol required a bone-marrow-associated, radiation-sensitive cell population, since long-bone removal or pre-transplant donor irradiation prevented long-term engraftment. Rejection also occurred if Rag1−/− donors were used, or if donors were treated with a CXCR4 inhibitor to mobilize donor BM cells pre-transplant. Donor bone-marrow contained a large population of Foxp3+ T-regulatory (Treg) cells, and donor Foxp3+ Treg depletion, by diphtheria toxin administration to DEREG donor mice whose Foxp3+ Treg cells expressed diphtheria toxin receptor, restored rejection with either protocol. Rejection also occurred if CXCR4 was deleted from donor Tregs pre-transplant. Hence, long-term VCA survival is possible across a full MHC disparity using peritransplant costimulation blockade-based approaches, but unexpectedly, the efficacy of costimulation blockade requires the presence of a radiation-sensitive, CXCR4+ Foxp3+ Treg population resident within donor BM.

The Ethics of Hand Transplantation: A Systematic Review

PURPOSE

We conducted a systematic review to document ethical concerns regarding human upper extremity (UE) allotransplantation and how these concerns have changed over time.

METHODS

We performed a systematic review of 5 databases to find manuscripts addressing ethical concerns related to UE allotransplantation. Inclusion criteria were papers that were on the topic of UE allotransplantation, and related ethical concerns, written in English. We extracted and categorized ethical themes under the 4 principles of bioethics: Autonomy, Beneficence, Nonmaleficence, and Justice. We assessed theme frequency by publication year using Joinpoint regression, analyzing temporal trends, and estimating annual percent change.

RESULTS

We identified 474 citations; 49 articles were included in the final analysis. Publication years were 1998 to 2015 (mean, 3 publications/y; range, 0-7 publications/y). Nonmaleficence was most often addressed (46 of 49 papers; 94%) followed by autonomy (36 of 49; 74%), beneficence (35 of 49; 71%), and justice (31 of 49; 63%). Of the 14 most common themes, only "Need for More Research/Data" (nonmaleficence) demonstrated a significant increase from 1998 to 2002.

CONCLUSIONS

Upper extremity transplantation is an appealing reconstructive option for patients and physicians. Its life-enhancing (vs life-saving) nature and requirement for long-term immunosuppression have generated much ethical debate. Availability of human data has influenced ethical concerns over time. Our results indicate that discussion of ethical issues in the literature increased following publication of UE transplants and outcomes as well as after meetings of national societies and policy decisions by regulatory agencies.

CLINICAL RELEVANCE

Because UE transplantation is not a life-saving procedure, much ethical debate has accompanied its evolution. It is important for UE surgeons considering referring patients for evaluation to be aware of this discussion to fully educate patients and help them make informed treatment decisions.

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.