GENOMICS AND BIOMARKERS

F. Bohne¹, M. Martinez-llordella¹, J.J. Lozano², M. Lopez², C. Benitez², R. Miquel³, G. Tisone⁴, A. Rimola⁵, A. Sanchez-fueyo^2
1Liver Transplant Unit, Hospital Clinic/IDIBAPS/Ciberehd, Barcelona/SPAIN, ²Immunology Of Liver Transplantation, Hospital Clinic/IDIBAPS/Ciberehd, Barcelona/SPAIN, ³Pathology Department, Hospital Clinic Barcelona, Barcelona/SPAIN, ⁴General And Transplant Surgery, Tor Vergata University of Rome, Rome/ITALY, ⁵Unitat De Transplantament De Fetge I Viabilitat De L’empelt, Institut d´Investigacions Biomèdiques August Pi i Sunyer-CIBERehd, Barcelona/SPAIN

Body: Introduction: Complete cessation of immunosuppressive therapy (IS) is feasible in selected liver transplant (tx) recipients who are considered operationally tolerant (TOL) and exhibit specific blood cell gene expression patterns. The intragraft molecular pathways associated with liver operational tolerance however have not been thoroughly analysed before. Methods: 104 liver recipients (>3 years after tx) were enrolled in a prospective European multi-center IS withdrawal clinical trial. IS was gradually discontinued over a 6-9 month period and recipients were then followed-up for 12 months and considered TOL if no rejection was detected over the entire duration of the study. Liver biopsies were obtained at baseline and at the end of the study in TOL recipients, and at baseline and at the time of rejection in non-TOL recipients. For the current study we employed cryopreserved liver tissue samples collected from 28 TOL and 33 non-TOL recipients at baseline, 14 non-TOL recipients at the time of rejection, and 7 TOL at the end of the study. In addition, the following comparison groups were also included: early acute cellular rejection (n=9), recurrent HCV infection (n=12), 1-year post-tx protocol biopsies (n=7) and normal liver tissue from surgical resections (n=10). We conducted whole-genome transcriptional profiling employing Illumina arrays on all 129 liver tissue samples, and Affymetrix and real-time TaqMan PCR (98-gene LDA plate) validation experiments on a selected group of biopsies. In addition, baseline Affymetrix blood cell expression data from all TOL and non-TOL recipients were available for comparison. Results: As expected, marked differences in gene expression were noted between recurrent HCV, acute cellular rejection and normal liver. In contrast, comparison of TOL and non-TOL recipients at baseline showed small differences in gene expression with only 21 genes displaying FDR<5%. The most relevant functional pathway among the differentially expressed data set was related to iron homeostasis, followed by T cell activation and cytoskeletal motility/mitochondrial movement. In TOL recipients no significant expression differences between pre- and post-weaning samples were detected. Results were replicated employing both Affymetrix and real-time PCR. In contrast, comparison of blood and liver tissue expression patterns in TOL and Non-TOL recipients revealed no obvious similarities. Conclusion: We report here on the first whole-genome molecular profiling study conducted on allograft tissue collected from tolerant human transplant recipients. Our findings reveal a previously unknown liver allograft gene expression pattern that suggests a role for iron metabolism-related genes in the pathogenesis of operational tolerance in clinical liver transplantation.

Disclosure: All authors have declared no conflicts of interest.