Congress Abstracts 2018 th th 14 to 16 March, Brighton Centre, Brighton Medawar medal presentations 10:45 Thursday 15th March – The Auditorium M01 Chronic renal histological changes at implantation and subsequent deceased donor kidney transplant outcomes: a single-centre analysis Benedict Phillips1, Kerem Atalar1, Hannah Wilkinson1, Nicos Kessaris1, Naomi Simmonds2, Theodoros Kasimatis1, Rachel Hilton1, Catherine Horsfield2, Chris Callaghan1 1Department of Nephrology and Transplantation, Guy's and St. Thomas' NHS Foundation Trust, London, United Kingdom. 2Department of Pathology, Guy's and St. Thomas' NHS Foundation Trust, London, United Kingdom. Introduction: Chronic histological changes within kidneys at transplantation may predict graft outcomes, suggesting that pre- implantation biopsies can inform organ utilisation decisions. Analyses from Cambridge have shown an inconsistent association between the Remuzzi score on wedge biopsy and graft survival. We sought to determine whether histological changes at transplantation were predictive of graft outcomes. Methods: We performed a retrospective analysis of adult single deceased donor kidney-only transplants between 2005-2015. Core biopsies (16G) taken after re-perfusion were examined by consultant renal histopathologists, and a Karpinski (K) score was assigned (0-12). Donor and recipient variables were collected; 1-, 3-, and 5-year graft function (eGFR – 4 variable MDRD) and death-censored graft survival (DCGS) were recorded. Recipients were grouped by K-score threshold (group A <4; group B 4+; group C <5; group D 5+). Multivariate and linear regression analyses were performed to determine independent risk factors for DCGS and 1-year eGFR, respectively. Results: 587 recipients had biopsies performed. 401 (68%) were adequate for K-scoring (DBD/DCD 267/134; median (IQR) donor age 51 (41-59) years; K-score 4 (2-5)). There were no differences in DCGS between groups A and B (p=0.17) or C and D (p=0.14), but 1-year eGFR trended downwards with increasing K-score (A 52.7 (40.0-67.0); B 42.0 (30.8-54.9) – p<0.01) (C 51.7 (37.8-65.0); D 40.5 (29.9-51.5) – p<0.01). Cold ischaemia time (CIT) was the only independent predictor of reduced DCGS (p=0.01). K-score, CIT and UKKDRI were independently associated with lower 1-year eGFR (p<0.01; p=0.03; p<0.01, respectively). Conclusion: This large risk-adjusted analysis does not demonstrate a clear association between K score thresholds and deceased donor kidney transplant DCGS, though increasing K score was associated with lower 1-year eGFR. Variations between single-centre studies might be explained by differences in biopsy and scoring techniques, or histological interpretation. M02 Accurate viability assessment and cryopreservation of pancreatic islets requires prolonged incubation with viability dyes and cryoprotectants for more than 12 hours Nikola Dolezalova1,2, Till Moreth3, Kevin O'Holleran4, Martin Lenz4, Krishnaa Mahbubani1, John Casey5, Francesco Pampaloni3, Nigel Slater2, Kourosh Saeb-Parsy1 1Department of Surgery, University of Cambridge, Cambridge, United Kingdom. 2Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, United Kingdom. 3Buchman Institute for Molecular Life Science, Goethe University Frankfurt, Frankfurt, Germany. 4Cambridge Advanced Imaging Centre, University of Cambridge, Cambridge, United Kingdom. 5Department of Surgery, University of Edinburgh, Edinburgh, United Kingdom. Introduction: Determining diffusion kinetics of dyes and cryoprotectants into the core of pancreatic islets is essential for accurate viability assessment and improved cryopreservation. We examined the impact of incubation time on solute diffusion into islets as a prelude to improving islet viability assessment and cryopreservation. Methods: Mouse pancreatic islets were incubated with Hoechst 33342 nuclear dye for 15min, 6h or 12h and cryosectioned for confocal microscopy. Live islets were stained with Hoechst 33342, fluorescein diacetate and propidium iodide for up to 24h and imaged using confocal, two-photon and light-sheet microscopy. To examine the impact of cryoprotectant incubation time on post-thaw viability, human islets were cryopreserved after 2h or 24h incubation with cryoprotectant trehalose. Results: Viability staining and imaging of islets by confocal microscopy revealed that short incubation periods used in current viability staining protocols only assess surface cells, with minimal staining of the core seen by two-photon and light-sheet microscopy. Dye gradient towards the core was present even after 24h of incubation. Sectioning confirmed that fluorescence intensity equilibrated only to a depth of ~10µm by 15min and continued to increase at the core beyond 12h:fluorescence intensity was 1.35±0.20, 21.40±3.00 and 34.38±4.21 RFUs at depth of ~45µm after 15min, 6h and 12h of incubation respectively, demonstrating ongoing dye diffusion into the core (p<0.0001). Incubation of human islets with trehalose for 24h vs. 2h significantly enhanced post-thaw viability (22.2±9.3% vs. 3.4±3.2%, p=0.036). Discussion: Results suggest that solute diffusion into islet tissue can take up to 24h. Current viability assessment and cryopreservation protocols, fail to target the core of pancreatic islets and do not accurately assess whole-islet viability. Incubation times with viability dyes and cryoprotectants should be prolonged to ensure exposure of cells in the core of islets to the minimal effective concentration. M03 The likelihood of re-transplantation in patients undergoing allograft nephrectomy Gaetano Lucisano1, Paul Brookes2, Eva Santos-Nunez2, Nicola Firmin2, Nicola Gunby2, Sevda Hassan1, Alexander Gueret-Wardle1, Michelle Willicombe1, David Taube1 1Renal and Transplant Centre, Imperial College Healthcare NHS Trust, London, United Kingdom. 2Histocompatibility and Immunogenetics, Imperial College Healthcare NHS Trust, London, United Kingdom Introduction: Transplant nephrectomy (NX) is a known cause of allosensitisation after graft failure. As yet, there is no consensus for the management of the patient with a failed graft returning to dialysis with respect to NX and the potential impact of NX on the likelihood of re-transplantation has not been hitherto investigated. Methods: Patients were divided into two groups according to whether they underwent NX after transplant failure (NX+, n=61) or not (NX-, n=48). Sera were assessed for HLA-A/B/Cw/DR/DQ at the time of NX/transplant failure and after 3, 6, 12 and 24 months using the single antigen Luminex assay. Matchability analysis estimates the relative ease (high score) or difficulty (low score) a patient may have in finding a good HLA matched donor taking into account blood group, HLA type and unacceptable class I and II HLA antigens. Transplant matchability was calculated using the tool provided by the Organ Donation and Transplantation UK. Results: Matchability analysis did not differ at the time of NX/failure and 3 months, although we found a significant difference in the matchability score starting from the 6-month time point (Figure 1), which resulted in a significantly higher prevalence of patients with “difficult” match in the NX+ group compared to NX-, persisting up to 24 months later. Discussion: NX leads to significant long-term allosensitization and this negatively impacts on the likelihood of receiving a second transplant. NX after allograft failure should only be undertaken if clinically indicated. Figure 1: M04 Shared HLA specificities between the blood and transplant donor increases the risk of de novo DSA development following transfusion in transplant recipients Sevda Hassan1, Fiona Regan2,3, Colin Brown4, Andrea Harmer3, Nicky Anderson3, Paul Brookes5, David Taube1, Michelle Willicombe1 1Renal and Transplant Centre, Imperial College Healthcare NHS Trust, London, United Kingdom. 2Haematology, Imperial College Healthcare NHS Trust, London, United Kingdom. 3Haematology, NHS Blood and Transplant, London, United Kingdom. 4Histocompatibility and Immunogenetics, NHS Blood and Transplant, London, United Kingdom. 5Histocompatibility and Immunogenetics, Imperial College Healthcare NHS Trust, London, United Kingdom Introduction: Blood transfusions post-transplant have been shown to be associated with the development of de novo DSA and inferior allograft outcomes. The mechanisms behind this phenomenon are not understood. Methods: We performed HLA typing on 244 blood donors of transfusions received by 86 renal transplant recipients. Sequential screening of a de novo alloimmune response against the blood (transfusion specific antibody, TSA) and transplant donor (DSA) was performed and analysed. Results: TSAs developed against 150/244 (61.5%) blood donors. 80/150 (53.3%) were TSAs alone, whilst 70/150 (46.7%) were TSAs in conjunction with DSA. 86/150 (57.3%) TSAs were HLA class I, 35/150 (23.3%) class II and 29/150 (19.3%) class I+II. TSA+DSA- patients were more likely to have class I HLA Abs compared with TSA+DSA+ patients, HR:4.66 (2.0-10.9), p<0.01. There was no difference in the overall ABDR mismatch between the blood donor and recipient in the TSA+ and TSA- groups. However, mismatching between the blood donor and recipient at HLA-B and HLA-DQ was higher in TSA+ compared with TSA- patients, p=0.02 and 0.014 respectively. Importantly, the ABDR HLA match between the blood and transplant donor was greater in the TSA+DSA+ compared with TSA+DSA- patients, p<0.0001. There was no difference in the baseline demographics between the TSA+ and TSA- recipients.