Survival of Allogeneic Self-Assembled Cultured Skin

Immune tolerance of tissue-engineered skin produced with allogeneic or xenogeneic fibroblasts and syngeneic keratinocytes grafted on mice

Organs are needed for the long-term replacement of diseased or wounded tissues. Various technologies based on cells seeded in synthetic or biomaterial scaffolds, or scaffold-free methods have been developed in order to produce substitutes that mimic native organs and tissues. For cell-based approaches, the use of living allogeneic fibroblasts could potentially lead to the production of "off-the-shelf" bioengineered organs/tissues. However, questions remain regarding the outcome of allogeneic grafts in terms of persistence of allogeneic cells, tolerance and the host immune reaction against the tissue after implantation. To evaluate graft tolerance of engineered-tissues containing non-autologous fibroblasts, tissue-engineered skin substitutes (TESs) produced with syngeneic, allogeneic or xenogeneic fibroblasts associated with syngeneic, allogeneic or xenogeneic epithelial cells were grafted in mice as primary and secondary grafts. The immune response was evaluated by histological analysis and immunodetection of M2 macrophages, CD4- and CD8-positive T cells, 15, 19, 35 and 56 days after grafting. Tissue-engineered skin composed of non-autologous epithelial cells were rejected. In contrast, TESs composed of non-autologous fibroblasts underlying syngeneic epithelial cells were still present 56 days after grafting. This work shows that TES composed of non-autologous fibroblasts and autologous epithelial cells are not rejected after grafting. STATEMENT OF SIGNIFICANCE: We found that tissue-engineered skin substitutes produced by a scaffold-free cell-based approach from allogeneic fibroblasts and autologous epithelial cells are not rejected after grafting and allow for the permanent coverage of a full-thickness skin wounds. In the field of tissue engineering, these findings open the possibility of selecting a human fibroblastic or stromal cell population based on its biological properties and adequate biosafety, banking it, in order to produce "ready-to-use" bioengineered organs/tissues that could be grafted to any patient without eliciting immune reaction after grafting. Our results can be generalized to any organs produced from fibroblasts. Thus, it is a great step with multiple applications in tissue engineering and transplantation.

Accommodation and related conditions in vascularized composite allografts

PURPOSE OF REVIEW

The outcome of vascularized composite allografts (VCA) often appear unrelated to the presence of donor-specific antibodies (DSA) in blood of the recipient or deposition of complement in the graft. The attenuation of injury and the absence of rejection in other types of grafts despite manifest donor-specific immunity have been explained by accommodation (acquired resistance to immune-mediated injury), adaptation (loss of graft antigen) and/or enhancement (antibody-mediated antigen blockade). Whether and how accommodation, adaptation and/or enhancement impact on the outcome of VCA is unknown. Here we consider how recent observations concerning accommodation in organ transplants might advance understanding and resolve uncertainties about the clinical course of VCA.

RECENT FINDINGS

Investigation of the mechanisms through which kidney allografts avert antibody-mediated injury and rejection provide insights potentially applicable to VCA. Interaction of DSA can facilitate replacement of donor by recipient endothelial cells, modulate or decrease synthesis of antigen, mobilize antigen that in turn blocks further immune recognition and limit the amount of bound antibody, allowing accommodation to ensue. These processes also can explain the apparent dissociation between the presence and levels of DSA in blood, deposition of C4d in grafts and antibody-mediated rejection. Over time the processes might also explain the inception of chronic graft changes.

SUMMARY

The disrupted tissue in VCA and potential for repopulation by endothelial cells of the recipient establish conditions that potentially decrease susceptibility to acute antibody-mediated rejection. These conditions include clonal suppression of donor-specific B cells, and adaptation, enhancement and accommodation. This setting also potentially highlights heretofore unrecognized interactions between these 'protective' processes.