Ultrastructural Insights in Renal Allograft Biopsies: Enhancing Early Diagnosis and Prognostication of Antibody-mediated Rejection

Antibody-mediated rejection (AMR) remains a critical barrier to long-term kidney allograft survival, with current diagnostic strategies relying heavily on histopathological criteria and donor-specific antibody (DSA) detection.1 The recent work by Haririan et al,2 alongside a complementary editorial by Zorn and Smith,3 underscores the transformative potential of electron microscopy (EM) in identifying subclinical endothelial injury and refining AMR prognostication. The authors should be commended for assembling a large-scale retrospective analysis of 796 biopsies from 623 high-risk patients, systematically evaluating EM features such as glomerular endothelial cell enlargement (GECE), subendothelial expansion/basement membrane duplication, and peritubular capillary multilayering. The authors demonstrate a robust association between these ultrastructural changes and the presence, class, and number of DSAs. Notably, GECE of >50% and subendothelial expansion/basement membrane duplication emerged as independent predictors of graft failure, even in biopsies that lack conventional LM markers of AMR, including microvascular inflammation and C4d positivity. These findings underscore the potential of EM to uncover subclinical endothelial injury and complement current Banff criteria,4 particularly in cases categorized as “probable AMR.” The emphasis of the study on risk stratification is particularly impactful. For instance, severe GECE in the absence of LM-detectable AMR features conferred a 2.58-fold increased risk of graft failure, highlighting the utility of EM in identifying high-risk patients who may benefit from intensified monitoring or early intervention. Similarly, the observed incremental association between DSA burden and ultrastructural changes, with odds ratios reaching as high as 8.45 in cases of GECE involving ≥4 DSAs, further reinforces the mechanistic link between antibody-mediated injury and endothelial pathology. Although the findings advocate for broader EM integration, practical challenges persist. EM requires specialized expertise, prolonged processing times, and additional costs, which may limit routine adoption. Furthermore, as Zorn and Smith caution, the retrospective design introduces potential biases, such as variability in biopsy timing and clinical management during the 20-y study span. The authors appropriately acknowledge these limitations and call for prospective validation to confirm the prognostic utility of EM in contemporary cohorts. The study also raises important questions for future research. For instance, whether early detection of ultrastructural changes can guide preemptive therapies such as complement inhibitors and B-cell depletion to mitigate the progression of AMR remains unexplored. Moreover, the interplay between EM findings and emerging biomarkers5—including gene expression profiles and donor-derived cell-free DNA—warrants further investigation to support the development of multimodal diagnostic algorithms. In summary, Haririan et al provided compelling evidence that EM enhances the diagnostic and prognostic toolkit for AMR. By bridging gaps in LM-based assessments, this work paves the way for earlier intervention and personalized management strategies in kidney transplantation. Prospective multicenter studies are now needed to validate the clinical utility of EM and define its place within multimodal diagnostic algorithms.