Tissue Transplantation in Plastic Surgery

Hypoxia-induced CCL2/CCR2 axis in adipose-derived stem cells (ADSCs) promotes angiogenesis by human dermal microvascular endothelial cells (HDMECs) in flap tissues

Flap expansion has become an important method widely used in wound repair and organ reconstruction. However, distal skin flap ischemic necrosis remains a problematic complication. In this study, integrative bioinformatics analyses indicated the upregulation of C-C motif chemokine ligand 2 (CCL2) and C-C motif chemokine receptor 2 (CCR2) in reperfusion-exposed skin flap tissues. In adipose-derived stem cells (ADSCs, CD90-positive, CD29-positive, CD34-negative, and CD106-negative) exposed to hypoxia, HIF-1α and CCL2 levels were significantly elevated. Conditioned medium (CM) from hypoxia-stimulated ADSCs promoted HDMEC proliferation, migration, and tube formation, partially inhibited by sh-CCL2-induced CCL2 knockdown or neutralized antibody-induced CCL2 depletion in ADSCs. Consistently, CCL2, CCR2, TNF-α, TLR2, and TLR4 protein levels in HDMECs were significantly increased by hypoxia-treated ADSCs CM, and partially decreased by sh-CCL2-induced CCL2 knockdown or neutralizing antibody-induced CCL2 knockdown in ADSCs. In the flap expansion model, ADSCs transplantation significantly improved flap survival and angiogenesis by endothelial cells in flap tissues, whereas CCL2 knockdown in ADSCs partially eliminated the improvement by ADSCs transplantation; overexpression of CCL2 in ADSCs further promoted the effects of ADSCs transplantation on skin flap. In conclusion, the CCL2/CCR2 axis in ADSCs could be induced by hypoxia, promoting HDMEC proliferation, migration, and tube formation and improving flap survival and angiogenesis in flap tissues.

Implementing Precision Medicine and Artificial Intelligence in Plastic Surgery: Concepts and Future Prospects

Precision medicine, or the individualization of evidence-based medicine, is forthcoming. As surgeons, we must be prepared for the integration of patient and system factors. Plastic surgeons regard themselves as innovators and early adopters. As such, we need our adaptability now more than ever to implement digital advancements and precision medicine into our practices. The integration of artificial intelligence (AI) technology and the capture of big data techniques should foster the next great leaps in medicine and surgery, allowing us to capture the detailed minutiae of precision medicine. The algorithmic process of artificial neural networks will guide large-scale analysis of data, including features such as pattern recognition and rapid quantification, to organize and distribute data to surgeons seamlessly. This vast digital collection of information, commonly termed “big data,” is only one potential application of AI. By incorporating big data, the cognitive abilities of a surgeon can be complemented by the computer to improve patient-centered care. Furthermore, the use of AI will provide individual patients with increased access to the broadening world of precision medicine. Therefore, plastic surgeons must learn how to use AI within the contexts of our practices to keep up with an evolving field in medicine. Although rudimentary in its practice, we present a glimpse of the potential applications of AI in plastic surgery to incorporate the practice of precision medicine into the care that we deliver.

Vascularized composite allograft rejection is delayed by intrajejunal treatment with donor splenocytes without concomitant immunosuppressants

Background. Mucosal or oral tolerance, an established method for inducing low-risk antigen-specific hyporesponsiveness, has not been investigated in vascularized composite allograft (VCA) research. We studied its effects on recipient immune responses and VCA rejection. Methods. Lewis rats (n = 12; TREATED) received seven daily intrajejunal treatments of 5 × 10⁷ splenocytes from semiallogeneic Lewis-Brown-Norway rats (LBN) or vehicle (n = 11; SHAM). Recipients' immune responses were assessed by mixed lymphocyte reaction (MLR) against donor antigen and controls. Other Lewis (n = 8; TREATED/VCA) received LBN hindlimb VCA and daily intrajejunal treatments of 5 × 10⁷ LBN splenocytes, or LBN VCA without treatment (n = 5; SHAM/VCA), until VCAs rejected. Recipients' immune responses were characterised and VCAs biopsied for histopathology. Immunosuppressants were not used. Results. LBN-specific hyporesponsiveness was induced only in treated Lewis recipients. Treatment significantly reduced MLR alloreactivity, significantly reduced VCA rejection on histopathology, and significantly delayed clinical VCA rejection (P < 0.0005; TREATED/VCA mean 9.6 versus 6.0 days for SHAM/VCA). Treatment significantly increased immunosuppressive IL-10/IL-4/TGF-β production and significantly decreased proinflammatory IFN-γ/TNF-α. Conclusion. Jejunal exposure to antigen conferred donor specific hyporesponsiveness that delayed VCA rejection. This method may offer a low-risk adjunctive treatment option to help protect VCAs from rejection.

Transgene expression in a model of composite tissue allotransplantation

BACKGROUND

Composite tissue allografting may be an ideal solution to many problems requiring reconstructive surgery. Unfortunately, complications associated with chronic immunocompromise are major impediments to widespread use of composite tissue allografting. Current immunosuppressive and immunomodulatory paradigms focus on modification of the recipient through global immunosuppression or donor/recipient chimerism. Alternatively, modifying the allograft to block rejection or promote tolerance could confine deleterious immunosuppressive effects to the graft or eliminate graft rejection. However, a technique introducing genetic information into the transplant is needed. The authors demonstrate the first model for expressing a gene of interest locally in a hind-limb transplant.

METHODS

Using a rat hind-limb transplant model, the authors tested the ability of naked DNA infusion, cationic polymer/DNA complex transfection, and adenoviral vector transduction to introduce genetic material into the composite tissue allograft. The marker genes luciferase and green fluorescent protein were used to follow gene expression.

RESULTS

Recombinant adenovirus showed rapid, high-level expression of marker genes in the graft, with no detectable expression in recipient animals. Expression was detectable at 18 hours and peaked at 7 days. Levels of expression were lower but above baseline at 4 weeks.

CONCLUSIONS

Using an adenoviral vector system, the authors have selectively introduced a marker gene (luciferase) into a transplanted hind-limb rat model. Expression was rapid and seen in a variety of cell types. Adenovirus infection had no impact on limb rejection. This method may be a powerful tool for genetically modifying composite tissue allografts and may contribute to immune tolerance and more widespread use of composite tissue allograft surgery.