Non-HLA antibodies worsen the histological phenotype and prognosis of antibody mediated rejection in kidney allografts

IntroductionAntibody-mediated rejection (AMR) remains a leading cause of kidney allograft failure, with both HLA and non-HLA antibodies implicated in its pathogenesis. The contribution of non-HLA antibodies (non-HLA Abs) to microvascular inflammation (MVI) and graft outcome, particularly in cases lacking donor-specific anti-HLA antibodies (HLA-DSAs), remains incompletely understood. MethodsWe analyzed 571 post-transplant serum samples from 326 patients with histological features of AMR (AMRh) and 164 stable controls. Non-HLA Abs were detected using the previously developed Non-HLA Antibody Detection Immunoassay (NHADIA), and associations were examined with histological lesions, AMRh persistence, and graft outcomes. Biopsies were scored according to Banff 2022 criteria, and patients were stratified by HLA-DSA and NHADIA status. ResultsNHADIA values were significantly higher in AMRh patients compared to controls (P=0.0001), regardless of HLA-DSA status. NHADIA values correlated with the severity of glomerulitis, peritubular capillaritis and global MVI scores. In AMRh patients with HLA-DSAs, non-HLA Abs remained independently associated with MVI severity. Follow-up biopsies revealed persistent AMR lesions in patients with both HLA-DSAs and non-HLA Abs. Allograft survival was lowest in double-positive patients, and NHADIA positivity independently predicted graft loss (HR=2.25, 95% CI: 1.03-4.92, P=0.042). Incorporating NHADIA into the Banff classification reclassified 61% of AMRh cases as "double-positive AMRh," and identified new subgroups with significant prognostic differences. ConclusionPost-transplant detection of non-HLA antibodies identifies a distinct subset of AMR with more severe histology and worse graft prognosis, particularly when coexisting with HLA-DSAs. Integrating non-HLA Ab testing into current diagnostic frameworks may refine AMR classification and improve risk stratification. TRANSLATIONAL STATEMENTThis study highlights the clinical relevance of non-HLA antibodies, identified using our innovative endothelial cell-based assay (NHADIA), in kidney transplant recipients. Their presence is associated with more severe antibody-mediated rejection (AMR) and poorer graft outcomes, even in the absence of donor-specific HLA antibodies. Incorporating non-HLA antibody detection into routine post-transplant evaluation may allow clinicians to better identify high-risk patients, including those previously classified as DSA-negative AMR. This expanded immunological profiling refines AMR diagnosis, improves risk stratification, and opens new avenues for personalized immunosuppressive strategies, ultimately enhancing long-term graft survival and patient care.