Molecular signatures of chronic antibody-mediated rejection in human liver transplants

Background&Aims The role of antibody-mediated rejection (ABMR) after liver transplantation (LT) remains controversial. Chronic ABMR (cABMR) is often subclinical and potentially missed without surveillance biopsies (svLbx). Transcriptome analysis previously characterized molecular changes in T cell-mediated rejection (TCMR) after solid organ transplantation. We aimed to identify molecular cABMR signatures after LT. Methods Indication and svLbx from two prospective institutional biorepositories were screened. We performed RNA-sequencing on liver biopsies (discovery cohort: n=71; Hannover validation cohort: n=58; Barcelona validation cohort: n=29). Downstream analyses explored the molecular features of cABMR, clinical (clinTCMR), subclinical TCMR (subTCMR) and chronic ductopenic rejection compared to no histological rejection (NHR). Results Nineteen percent of LT recipients with donor-specific antibodies had cABMR in the training cohort. Fifty seven percent of cABMR patients had normal/near normal liver enzymes, recognized only by svLbx. CABMR was associated with subsequent cirrhosis development in 40-50% and displayed differentially expressed genes (DEGs) uniquely enriched in fibrogenesis-, complement activation- and TNFα-signaling-related pathways. ClinTCMR showed no such recurrent cirrhosis and DEGs uniquely enriched in antigen presentation-, interferon-signaling-, and T cell receptor-signaling-related pathways. SubTCMR was molecularly almost indistinguishable from NHR. There was a high degree of correlation in the DEGs between the training and two independent validation cohorts. Conclusions We report transcriptome features of cABMR that is a unique molecular identity associated with inflammation and fibrogenesis as described in other solid organ transplantations and being linked to a high rate of liver graft failure. Impact and Implications - Chronic antibody-mediated rejection (ABMR) is a recognized relevant cause of graft injury and unfavorable patient outcomes after kidney, heart and lung transplantation but the role of chronic ABMR after liver transplantation (LT) remains controversial, despite a recurrent cirrhosis rate of 40-50% in the present study. Therefore, we aimed to characterize rejection phenotypes after LT on a molecular basis, as done in other solids organ transplants, to identify unique features of chronic ABMR. - Our findings highlight chronic ABMR to be a molecularly distinct clinical phenotype of rejection after LT that often presents with normal liver enzymes validated in three independent cohorts. - Therefore, our work emphasizes the usage of surveillance graft biopsies for the detection of a fibrosis associated phenotype of chronic ABMR. The molecular signature may be used in the future by researchers and clinicians to discriminate chronic ABMR from graft injury of other causes.