Allograft pathology, antibody-tissue interaction as demonstrated by C4d deposition, and serologic evidence of donor-specific antibodies (DSA) are the cardinal diagnostic features of antibody-mediated lesions (AML) in kidney transplantation. However, discrepancy between histologic and serologic findings is common, and more reliable diagnostic tools are called for. Here we asked whether the in situ detection of DSA could serve as marker for the diagnosis of AML. To that end, 51 graft biopsies performed for cause were retrospectively examined for intragraft DSA (gDSA). After acidic elution from the graft tissue using class I and II single antigen bead-based assays on a Luminex platform, the intragraft antibody profiles were correlated to serum DSA (sDSA), histologic data and transplant outcome. Although the prevalence and the mean number of gDSA were lower than that of sDSA (15/51 gDSA+ versus 46/51 sDSA+ patients; 1.64 gDSA versus 2.24 sDSA per patient), DSA were detected in all anti-HLA antibody-positive biopsies (15/15), which was not the case in serum (37/46). While no difference in estimated GFR (eGFR) was observed between gDSA+ and gDSA- patients, the presence of gDSA was significantly associated with microcirculation lesions (peritubular capillaritis (ptc)>0, p=0.05; glomerulitis (g)>0, p=0.01; and transplant glomerulopathy (cg)>0, p=0.002), C4d positivity (p=0.01) and a worse short-term transplant outcome (p<0.05). These associations were not found for patients presenting only sDSA. Taken together, these results indicate that the presence of gDSA in graft biopsy eluates could be a valuable biomarker of active antibody-mediated pathogenic processes.

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