Abstract Introduction Acute rejection (AR) is a major obstacle to successful lung transplantation (LTx), driving early immune-mediated injury and contributing to chronic lung allograft dysfunction (CLAD). AR impairs airway microvasculature and epithelial integrity, yet predictive biomarkers and therapies that promote immune regulation and repair remain limited. Tumor necrosis factor-stimulated gene-6 (TSG-6), an anti-inflammatory protein secreted by mesenchymal stromal cells and macrophages in response to TNF-α and IL-1β, plays key roles in tissue repair and immune modulation, but its role in LTx is poorly understood. To address this, we investigated TSG-6 in a murine tracheal transplant model and correlated its expression with human lung transplant biopsies, comparing samples from patients with acute rejection versus those without. Methods In a murine orthotopic tracheal transplant model (BALB/c → C57BL/6), allograft recipients (n = 9) received intranasal TSG-6 (5 µg per dose per transplant) on days −1, 2, 5, and 8 post-transplantation. On day 10—corresponding to the onset of microvascular loss—grafts were evaluated for M2 macrophage infiltration, microvascular perfusion, and epithelial integrity (β-catenin, FOXJ1) in comparison to untreated controls. To assess clinical relevance, TSG-6 expression was examined in transbronchial lung biopsies from transplant recipients within the first postoperative month—those with acute rejection (n = 6) and those without (n = 6)—using immunohistochemistry and quantitative image analysis. Results Syngeneic grafts demonstrated elevated TSG-6 expression following transplantation compared to rejecting allografts. Treatment of murine allografts with exogenous TSG-6 significantly (p 0.05) reduced subepithelial mononuclear cell infiltration, enhanced recruitment of M2 macrophages and regulatory T cells, and upregulated transcripts associated with tissue repair (Figure 1A-B). At day 10 post-airway transplantation, TSG-6 also significantly preserved microvascular perfusion and epithelial architecture, maintained β-catenin and FOXJ1 expression, and reduced subepithelial mononuclear cell deposition and fibrosis. In human biopsies, TSG-6 expression was significantly higher in non-rejected samples (20-37 units; 88-100% positive cells) compared to rejected grafts (0-12 units; 0-60% positive cells), with a 3-fold increase in per-cell staining (p 0.05). Despite the small sample size, the frequency of TSG-6-positive cells was significantly higher in the non-rejection group, with a large effect size suggesting strong biological relevance (Figure 1C). Conclusion These findings demonstrate that TSG-6 promotes immune regulation, preserves graft integrity, and reduces airway fibrosis in a preclinical LTx model. Clinically, higher TSG-6 expression correlates with rejection-free grafts, supporting its potential as a predictive biomarker and therapeutic target to prevent acute rejection and enhance repair. This abstract is funded by: National Institute of Allergy and Infectious Diseases (NIAID)
Khan et al. (Fri,) studied this question.