P.420 Donor-Derived Cell-Free DNA as Minimally Invasive Tool to Diagnose Acute Rejection after Kidney Transplantation Karin Boer 1 , Carla C Baan 1 , Nadine van Donk 2 , Evert de Jonge 2 , Marian C Clahsen-van Groningen 3 , Dennis A Hesselink 1 , Ron H.N. van Schaik 2 1 Internal Medicine - Nephrology and Transplantation, Erasmus Medical Center, Rotterdam, Netherlands; 2 Clinical Chemistry, Erasmus Medical Center, Rotterdam, Netherlands; 3 Pathology, Erasmus Medical Center, Rotterdam, Netherlands. Introduction: Acute rejection after kidney transplantation, which occurs in 15-20% of recipients, is diagnosed by means of a kidney biopsy which is an invasive procedure. Here we evaluated a novel, minimally invasive approach to diagnose acute rejection by measuring donor-derived cell free DNA (dd-cfDNA) in plasma of kidney transplant recipients. Methods: In total, 18 kidney transplant recipients were studied. Ten recipi- ents experienced a decline in kidney function and underwent a ‘for cause’ bi- opsy. Of these ten, seven recipients had a biopsy proven acute rejection (BPAR) within the first 4 months after transplantation, while the other three recipients had an urinary tract infection (UTI). Plasma was collected before transplantation, at 3, 6 and 12 months after transplantation and at moment of biopsy. DNA of all 18 donor-recipient pairs was genotyped for 10 highly variable single nucleotide polymorphism (SNP)s. Digital droplet PCR for at least 2 discriminative SNPs between donor and recipient was performed to quantify the level of dd-cfDNA at the different time points. Results: Two recipients with a severe rejection resulting in graft loss, demon- strated a clear dd-cfDNA signal at the moment of rejection with a ratio of dd- cfDNA to total cfDNA of 14.5% and 4%, respectively. The ratio of dd-cfDNA in the other 5 recipients with BPAR was lower with a median of 0.3% (range 0.09 -1.7%), though these percentages corresponded to a significant number of positive dd-cfDNA droplets (median number of droplets: 17; range 9-31). There was a positive correlation between the number of positive dd-cfDNA droplets and serum creatinine concentrations of the recipients with BPAR (r=0.86, p=0.02). The number of positive dd-cfDNA droplets in recipients with- out BPAR or UTI was low (1; range 0-12) at all time points (n=29 samples). Two recipients with an UTI demonstrated a ratio of 0.4% and 0.04% dd-cfDNA corresponding with 12 and 6 positive dd-cfDNA droplets, while the third pa- tient who experienced a recurring UTI had high levels of dd-cfDNA with a ratio of 11% dd-cfDNA representing 168 dd-cfDNA droplets. Conclusion: Our first data show that dd-cfDNA is a potential minimally inva- sive marker for acute rejection after kidney transplantation. Nevertheless, the discriminative capacity of dd-cfDNA as marker for rejection from other causes of graft damage or clinical problems as urinary tract infection needs to be elucidated. P.423 Differential Expression of Metallothioneins and Slc Family Genes in Accommodation and Subclinical Antibody Mediated Rejection Petra Hruba 1 , Zdenek Krejcik 2 , Viktor Stranecky 3 , Faikah Gueler 4 , Wilfried Gwinner 4 , Alena Parikova 5 , Janka Slatinska 5 , Mariana Wohlfahrtova 5 , Ilja Striz 6 , Jiri Fronek 7 , Jana Maluskova 8 , Eva Honsova 8 , Ondrej Viklicky 1,5 1 Transplant laboratory, Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Prague, Czech Republic; 2 Department of Genomics, Institute of Hematology and Blood Transfusion, Prague, Czech Republic; 3 Institute of Inherited Metabolic Disorders, Prague, Czech Republic; 4 Department of Nephrology, Hannover Medical School, Hannover, Germany; 5 Department of Nephrology and Transplant Center, Institute for Clinical and Experimental Medicine, Prague, Czech Republic; 6 Department of Clinical and Transplant Immunology, Institute for Clinical and Experimental Medicine, Prague, Czech Republic; 7 Transplant Surgery Department, Institute for Clinical and Experimental Medicine, Prague, Czech Republic; 8 Department of Clinical and Transplant Pathology, Institute for Clinical and Experimental Medicine, Prague, Czech Republic. Introduction: Accommodation in ABOi kidney transplantation has been de- fined as persistence of hemagglutinins on endothelial cells (C4d positivity in protocol biopsies) without deleterious effect on graft dysfunction in long-term. In subclinical antibody mediated rejection, C4d deposition in protocol biopsies caused by donor specific anti-HLA antibodies binding to endothelial cells sub- stantially influence graft function. With the aim to elucidate the mechanism of accommodation, molecular processes involved in those two different ways of complement activation were studied. Methods: Transcriptome of 3-months C4d positive protocol biopsies in ABOi patients (n=11) and in HLAi cohort with positive donor specific antibodies (n=7) was assessed using Illumina Human HT-12 v4 Expression BeadChips. Moreover, transcriptome of both groups was compared to C4d negative pro- tocol biopsies with normal histological findings (n=8, controls). ABOi and HLAi groups did not differ in Banff scores. Biopsies of controls had besides C4d negativity lower cv score. Differentially expressed genes were defined as those with fold change ≥2 and p<0.05. The enrichment of deregulated genes in biological processes was analyzed using DAVID database and results were validated using real-time qPCR at the independent cohort (n=24). Results: The hierarchical clustering of gene expression profiles of samples from HLAi, ABOi and control groups did not result in formation of 3 main clus- ters. Instead 4 clusters were formed: 2 clusters included exclusively ABOi and control samples and 2 clusters included samples from all groups. This sug- gests no major clear difference among transcriptome profiles of all 3 groups. GO terms with the highest fold enrichment for deregulated genes between ABOi and HLAi group were represented by cadmium ion binding (p=0.0016), apical plasma membrane (p=0.008) and anion transmembrane transporter activity (p=0.032). Majority of deregulated genes between both groups be- longs to metallothioneins (MT) and solute carrier family (Slc) genes. The de- creased expression of 5 Slc family genes (SLC4A1; SLC4A9; SLC17A3; SLC12A3; SLC30A2 and 3 metallothioneins of class1 (MT1F, MT1G and MT1X) in ABOi compared to HLAi group was verified by RT-qPCR. When transcriptomes of HLAi or ABOi were compared to C4d negative controls, in both HLAi and ABOi group genes including in GO term mitochon- drion (p=0.021 and 0.0075, respectively) were upregulated. In controls com- pared to HLAi group were upregulated genes from GO terms: extracellular matrix (p=2.3 E-06), proteinaceous extracellular matrix (p= 4.30E-06) and cell adhesion (p= 0.0012). Conclusion: Contrary to hemagglutinins, anti-HLA antibodies activate both MTs of class 1 and Slc genes. Dysregulation of MTs and distinct Slc family genes might be involved in ABOi accommodation. Supported by Ministry of Health of the Czech Republic (MZO 00023001) and by the Grant Agency of the Ministry of Health of the Czech Republic (No. 15-26865A). © 2018 Wolters Kluwer Abstract S689 Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.