Vascularized composite allotransplantation (VCA) has emerged as a valuable reconstructive option that enables the transfer of multiple tissue types including skin, muscle, bone, nerves, and blood vessels as a functional unit for patients with extensive tissue loss. Murine models, particularly the hind limb transplantation models, have become indispensable tools for advancing our understanding of the complex immunological and physiological aspects of VCA. This review provides a comprehensive description of established protocols for orthotopic and heterotopic hind limb transplantation in mice. It also discusses critical technical considerations, and evaluates the models' utility, impact, and limitations. By examining various aspects, including surgical techniques, immunosuppression regimens, rejection criteria, and translational relevance, this review aims to highlight best practices for the harmonization of the use of this valuable preclinical model in supporting continuous progress in the field.

Ischemia-reperfusion injury (IRI) and acute cellular rejection (ACR) are common post-operative complications that lead to poor outcomes in lung transplant recipients. The transient receptor potential vanilloid 4 (TRPV4) is a plasma membrane Ca[2+] channel that controls vascular tone and integrity. We examined whether TRPV4 influences IRI and alloimmune responses in a mouse model of orthotopic lung transplantation. Recipients receiving syngeneic lungs briefly treated with a TRPV4-specific inhibitor, or engrafted with syngeneic lungs with an endothelial cell-specific TRPV4 gene ablation (TRPV4[ΔEC]), had better graft function, reduced endothelial cell adhesion molecule expression, and lower inflammatory cytokine expression and neutrophil recruitment. TRPV4[ΔEC] lungs transplanted into immunosuppressed, major MHC-mismatched recipients had more intragraft CD25[+] Foxp3[+] CD4[+] T cells and fewer IFN-γ[+] CD8[+] T cells and were more resistant to IRI-induced ACR when compared to wildtype allografts. Finally, pharmacological inhibition of TRPV4 reduced donor-antigen-triggered production of IFN-γ and IL-17A by intragraft T cells and prevented ACR despite IRI. Our findings show that pulmonary endothelial cell TRPV4 activity couples ischemic tissue injury to T cell alloimmunity, highlighting the potential of therapies that enhance vascular integrity to promote transplant tolerance.

Alpha-gal syndrome (AGS) is an IgE-mediated hypersensitivity to the oligosaccharide galactose-α-1,3-galactose, acquired through tick bites and increasingly recognized as a cause of allergic reactions to mammalian-derived medical products. Every major transplant modality creates distinct conditions under which sensitized patients may encounter alpha-gal, yet AGS knowledge has developed almost entirely outside the transplant literature. In conventional solid organ transplantation, risk arises primarily from perioperative exposures to porcine-derived heparin, gelatin-based hemostatic agents, and other mammalian-derived materials. In xenotransplantation, the well-characterized role of alpha-gal as the principal xenoantigen has driven development of glycoprotein alpha-galactosyltransferase 1-knockout swine, but the distinct IgE-mediated pathway that defines AGS has received little attention. Hematopoietic stem cell transplantation introduces questions about conditioning-related immune remodeling of preexisting IgE sensitization, rabbit antithymocyte globulin as an underrecognized alpha-gal exposure, and transfusion-related alpha-gal syndrome when group B or AB plasma-containing blood products are transfused to susceptible patients. Cellular therapy manufacturing workflows that use animal-derived ancillary materials represent a further theoretical exposure pathway. Importantly, detectable anti-alpha-gal IgE does not invariably predict clinical reactivity, and the most appropriate clinical approach is risk stratification rather than reflexive exclusion. Generating the evidence base to support such stratification will require collaboration across allergy, transplant, and transfusion medicine.

Early post-liver transplant ischemia-reperfusion injury (IRI) in donation after circulatory death (DCD) grafts lacks therapies targeted to the immediate post-reperfusion window, in part because generic reperfusion transcription obscures IRI-selective amplification. We analyzed paired pre-/post-reperfusion liver biopsies from two cohorts (GSE151648; GSE87487) using a difference-in-differences interaction estimand (ΔΔ=(Post-Pre)IRI+ - (Post-Pre)IRI-) to define an IRI-selective early reperfusion program. Genome-wide ΔΔ effects were summarized by PROGENy, and pathway concordance was tested by permutation (B=5000). The reproducible ΔΔ footprint highlighted EGFR-MAPK signaling (Spearman ρ=0.811; P=0.001). Directional ΔΔ gene sets (interaction P<0.05) were submitted to L1000CDS[2]; cross-cohort overlap identified eight shared perturbagens, including three MEK1/2 inhibitors. In a hepatic I/R time course (GSE117915), EGFR and MAPK activities increased within 0.5 h of reperfusion, and transplant scRNA-seq (GSE189539) localized MEK/ERK engagement predominantly to parenchymal cells. A representative MEK inhibitor, PD-0325901, reduced hepatocyte OGD/R injury and, when administered at reperfusion in a rat DCD liver transplantation model (5-20 mg/kg), attenuated histologic and biochemical injury, apoptosis, and redox-inflammatory readouts and improved 7-day survival. Collectively, this biopsy-anchored ΔΔ interaction-phenotype framework, with cross-cohort concordance as a prespecified robustness gate, nominates reperfusion-timed MEK inhibition as a mechanism- and window-aligned strategy to blunt early post-liver transplant IRI.

Operational tolerance after intestinal transplantation is exceptionally rare, with few reported cases and limited mechanistic understanding. We describe a 12-year-old girl who underwent multivisceral transplantation and subsequently developed graft-versus-host disease (GvHD) followed by Epstein-Barr virus-associated post-transplant lymphoproliferative disease (PTLD). Due to severe PTLD complications, immunosuppression was withdrawn 8 months post-transplant. The patient achieved viral remission and has remained free of rejection for more than three years without immunosuppressive therapy. Comprehensive immunological analyses demonstrated stable graft function, absence of donor-specific antibodies, preserved antiviral immunity, and donor-recipient immune coexistence within the graft. Graft-resident regulatory T-cells displayed enhanced proliferative and inhibitory features despite stable frequencies. Longitudinal TCR-β repertoire analysis revealed a profound immune "reset" and reprogramming following GvHD. This case provides new evidence that GvHD-associated immune remodeling, together with functional specialization of local regulatory T-cells, may constitute the underlying mechanism of long-term graft acceptance.

Ureteral stenosis is a frequent urological complication after kidney transplantation and a relevant cause of graft dysfunction, often requiring repeated interventions due to high rates of restenosis following conventional balloon dilatation. Strategies targeting the underlying fibrotic remodeling remain limited. We report a novel clinical application of paclitaxel-coated balloon ureteroplasty in a transplanted ureter. A kidney transplant recipient developed recurrent distal ureteral stenosis at the ureterovesical anastomosis, with hydronephrosis and graft dysfunction despite standard endourological management, including balloon dilatation and ureteral stenting, complicated by recurrent urinary tract infections. Paclitaxel-coated balloon dilatation was performed as a stent-free strategy, combining mechanical expansion with local delivery of an antiproliferative agent. The procedure resulted in restoration of urinary drainage, resolution of hydronephrosis, and improvement of graft function, without the need for further stenting. This case illustrates a novel application of drug-coated balloon technology in the transplanted ureter and suggests a potential role for this minimally invasive approach in reducing restenosis of transplant ureteral strictures. By targeting fibroproliferative pathways, paclitaxel may offer a therapeutic advantage over conventional dilatation alone. Further studies are warranted to assess safety and durability in this setting.