Clinical, Histopathologic, and Molecular Characterization of Allograft Mesangial Glomerulopathy

Background: Donor-derived cell-free DNA (dd-cfDNA) is a non-invasive biomarker used to detect allograft rejection. In the absence of other signs of graft dysfunction elevated levels of dd-cfDNA can prompt allograft biopsy. We describe three donor specific antibody (DSA)-negative, dd-cfDNA positive patients with an allograft mesangial glomerulopathy that is histologically distinct from traditional transplant glomerulitis (Figure 1). Methods: Kidney allograft biopsies from 2018-2022 that had dd-cfDNA testing were reviewed to identify DSA-negative, dd-cfDNA-positive cases with mesangial proliferative glomerulopathy. Clinical and pathologic data were collected. Biopsy material from mesangial proliferative glomerulopathy cases were analyzed using digital spatial profiling (GeoMx, Nanostring) and compared to DSA-negative, dd-cfDNA positive and without obvious transplant glomerulopathy. Biopsies were hybridized with the Whole Transcriptome Atlas and bound probes were collected, sequenced and quantified from glomerular and tubulointerstitial regions of interest (ROI). Results: Patients with mesangial glomerulopathy had fluctuating dd-cfDNA levels but maintained stable renal function (follow-up period 5-7 years post-transplant). The biopsies demonstrated a histologically unique form of allograft mesangial glomerulopathy. Analysis of glomerular ROI from control (17), mesangial glomerulopathy (11) and DSA-/cfDNA+ patients without glomerulopathy (37) revealed PD-L1 signaling as the most enriched pathway for differentially expressed genes in allograft mesangial glomerulopathy. Conclusion: This smallcohort of patients with allograft mesangial glomerulopathy exhibited fluctuating levels of dd-cfDNA, but stable allograft function. DSP analysis supports a distinct molecular pathophysiology for allograft mesangial glomerulopathy compared to DSA-/cfDNA+ glomerulitis.Figure 1. DSP uncovers gene expression differences in allograft mesangial glomerulopathy. A) Glomerulus from a patient with allograft mesangial glomerulopathy. B) Glomerulus from a patient with DSA-/cfDNA+ glomerulitis.