🎗Lipid-associated macrophage polarization and APOE–SDC2 signaling underlies chronic xenograft fibrosis

Introduction: Chronic injury of kidney xenografts, characterised by interstitial fibrosis and tubular atrophy (IF/TA), remains a primary barrier to long-term survival in pig-to-nonhuman primate (NHP) xenotransplantation despite substantial advancements in genetic modifications and immunosuppressive regimens. The molecular and cellular mechanisms driving this transition toward chronic rejection are poorly understood.
Methods: We assessed kidney xenografts from genetically engineered porcine donors (knockouts for three or four major xenoantigens [GGTA1, CMAH, B4GalNT2 ± iGb3s] and knockins for two or four human complement- or coagulation-regulatory genes [CD39, CD55, CD46, TBM]) transplanted into cynomolgus monkeys (n = 12) under five immunosuppressive regimens. A multi-modal approach was employed across multiple time points, integrating single-nucleus RNA sequencing, spatial transcriptomics, and proteomics to profile the molecular and spatial landscapes of chronic injury. Histopathology and Banff scoring were used to assess graft injury and fibrosis.
Results: Increasing Banff fibrosis scores significantly correlate with macrophage polarisation toward pro-fibrotic lipid-associated macrophage (LAM) and M2a phenotypes, with systemic OLR1 elevation reflecting ongoing vascular stress as an upstream driver of this polarisation. Spatial transcriptomics delineated pro-fibrotic immune–fibroblast and immune-adaptive epithelium niches enriched near glomeruli and arterioles. The APOE–SDC2 signalling axis emerged as a conserved mediator of macrophage-driven epithelial-mesenchymal transition (EMT). Cross-species validation in human allografts confirmed epithelial cells as the conserved target of this axis. Furthermore, a triple-blockade regimen targeting CD154, CD80/86, and IL-6 signaling significantly mitigated fibrosis by dismantling these niches and suppressing the APOE–SDC2 axis.
Conclusion: Our findings identify OLR1-mediated vascular stress as an upstream trigger that drives macrophage polarization toward pro-fibrotic LAM phenotypes, culminating in the APOE–SDC2 signaling axis as a universal pathogenic mechanism of chronic kidney injury. Despite current immunosuppressive regimens, this innate immune-driven fibrotic cascade persists, underscoring the need for targeted intervention. Blocking the APOE–SDC2 axis and associated pro-fibrotic niches through multi-axis immune modulation offers a promising therapeutic strategy to improve long-term outcomes in xenotransplantation, with OLR1 serving as a potential upstream biomarker of fibrotic progression.