#1130 Biopsy-based transcript diagnostics identify early antibody-mediated rejection phenotypes in biopsies with subclinical donor-specific antibodies

Abstract

Abstract Background and Aims Biopsy based transcript diagnostics using the molecular microscope diagnostic system (MMDx) have the potential to add diagnostic clarification in the antibody mediated rejection (AMR) continuum. While de novo donor specific antibody (dnDSA) or preformed DSA accompanied by allograft function deterioration are accepted indications for allograft biopsy with therapeutic implications, management strategy for subclinical DSA lacks consensus. MMDx might show clinical utility in this controverse scenario by helping with therapeutic decisions. Method In this single-center cohort of 326 indication kidney transplant biopsies assessed by histology and MMDx at the University Hospital Zurich, we analyzed 58 cases with subclinical DSA as biopsy indication. Cases with (n = 44) and without (n = 14) histopathologic features of AMR according to Banff 2022 were compared for molecular AMR rejection transcripts. Results When biopsied for subclinical DSA, all 14 cases without histopathologic features of AMR showed absence of molecular AMR. In contrast, molecular AMR was detected in 6/19 (32%) cases with histopathologic diagnosis of AMR and 2/25 (8%) with probable AMR (p = 0.059), Fig. 1. Microvascular inflammation below threshold with C4d negativity was significantly associated with absence of molecular AMR (p < 0.0001). Higher number of calculated epitope mismatch load for HLA class II as measured by PIRCHE II Score was significantly associated with molecular AMR (p = 0.01). In cases with molecular AMR, early AMR scores predominated (R4 vs R6, 0.0002 and R4 vs R5 0.051). Conclusion No molecular AMR was observed in absence of histopathologic AMR. Yet, in cases with histopathologic features of AMR, only 8/44 showed molecular AMR. Predominance of early AMR rejection phenotype in cases with molecular AMR transcripts allows hope for MMDx to identify treatment amenable cases with subclinical DSA. Discrepant cases call for re-biopsy to guide therapeutic decisions.