To discard or not to discard: transplantation and the art of scoring

Untargeted metabolomics of perfusate and their association with hypothermic machine perfusion and allograft failure

Although hypothermic machine perfusion (HMP) is associated with improved kidney graft viability and function, the underlying biological mechanisms are unknown. Untargeted metabolomic profiling may identify potential metabolites and pathways that can help assess allograft viability and contribute to organ preservation. Therefore, in this multicenter study, we measured all detectable metabolites in perfusate collected at the beginning and end of deceased-donor kidney perfusion and evaluated their associations with graft failure. In our cohort of 190 kidney transplants, 33 (17%) had death-censored graft failure over a median follow-up of 5.0 years (IQR 3.0-6.1 years). We identified 553 known metabolites in perfusate and characterized their experimental and biological consistency through duplicate samples and unsupervised clustering. After perfusion-time adjustment and false discovery correction, six metabolites in post-HMP perfusate were significantly associated with death-censored graft failure, including alpha-ketoglutarate, 3-carboxy-4-methyl-5-propyl-2-furanpropanoate, 1-carboxyethylphenylalanine, and three glycerol-phosphatidylcholines. All six metabolites were associated with an increased risk of graft failure (Hazard Ratio per median absolute deviation range 1.04-1.45). Four of six metabolites also demonstrated significant interaction with donation after cardiac death with notably greater risk in the donation after cardiac death group (Hazard Ratios up to 1.69). Discarded kidneys did not have significantly different levels of any death-censored graft failure-associated metabolites. On interrogation of pathway analysis, production of reactive oxygen species and increased metabolism of fatty acids were upregulated in kidneys that subsequently developed death-censored graft failure. Thus, further understanding the role of these metabolites may inform the HMP process and help improve the objective evaluation of allograft offers, thereby reducing the discard of potentially viable organs.

Preoperative Function Assessment of Ex Vivo Kidneys with Supervised Machine Learning Based on Blood and Urine Markers Measured during Normothermic Machine Perfusion

Establishing an objective quality assessment of an organ prior to transplantation can help prevent unnecessary discard of the organ and reduce the probability of functional failure. In this regard, normothermic machine perfusion (NMP) offers new possibilities for organ evaluation. However, to date, few studies have addressed the identification of markers and analytical tools to determine graft quality. In this study, function and injury markers were measured in blood and urine during NMP of 26 porcine kidneys and correlated with ex vivo inulin clearance behavior. Significant differentiation of kidneys according to their function could be achieved by oxygen consumption, oxygen delivery, renal blood flow, arterial pressure, intrarenal resistance, kidney temperature, relative urea concentration, and urine production. In addition, classifications were accomplished with supervised learning methods and histological analysis to predict renal function ex vivo. Classificators (support vector machines, k-nearest-neighbor, logistic regression and naive bayes) based on relevant markers in urine and blood achieved 75% and 83% accuracy in the validation and test set, respectively. A correlation between histological damage and function could not be detected. The measurement of blood and urine markers provides information of preoperative renal quality, which can used in future to establish an objective quality assessment.

Donor characteristics and their impact on kidney transplantation outcomes: Results from two nationwide instrumental variable analyses based on outcomes of donor kidney pairs accepted for transplantation

BACKGROUND

Donor-characteristics and donor characteristics-based decision algorithms are being progressively used in the decision process whether or not to accept an available donor kidney graft for transplantation. While this may improve outcomes, the performance characteristics of the algorithms remains moderate. To estimate the impact of donor factors of grafts accepted for transplantation on transplant outcomes, and to test whether implementation of donor-characteristics-based algorithms in clinical decision-making is justified, we applied an instrumental variable analysis to outcomes for kidney donor pairs transplanted in different individuals.

METHODS

This analysis used (dis)congruent outcomes of kidney donor pairs as an instrument and was based on national transplantation registry data for all donor kidney pairs transplanted in separate individuals in the Netherlands (1990-2018, 2,845 donor pairs), and the United Kingdom (UK, 2000-2018, 11,450 pairs). Incident early graft loss (EGL) was used as the primary discriminatory factor. It was reasoned that a scenario with a dominant impact of donor variables on transplantation outcomes would result in high concordance of EGL in both recipients, whilst dominance of asymmetrical outcomes could indicate a more complex scenario, involving an interaction of donor, procedural and recipient factors.

FINDINGS

Incidences of congruent EGL (Netherlands: 1·2%, UK: 0·7%) were slightly lower than the arithmetical (stochastic) incidences, suggesting that once a graft has been accepted for transplantation, donor factors minimally contribute to incident EGL. A long-term impact of donor factors was explored by comparing outcomes for functional grafts from donor pairs with asymmetrical vs. symmetrical outcomes. Recipient survival was similar for both groups, but a slightly compromised graft survival was observed for grafts with asymmetrical outcomes in the UK cohort: (10-years Hazard Ratio for graft loss: 1·18 [1·03-1·35] p<0·018); and 5 years eGFR (48·6 [48·3-49·0] vs. 46·0 [44·5-47·6] ml/min in the symmetrical outcome group, p<0·001).

INTERPRETATION

Our results suggest that donor factors for kidney grafts deemed acceptable for transplantation impact minimally on transplantation outcomes. A strong reliance on donor factors and/or donor-characteristics-based decision algorithms could result in unjustified rejection of grafts. Future efforts to optimize transplant outcomes should focus on a better understanding of the recipient factors underlying transplant outcomes.

FUNDING

None.

The Independent Effects of Procurement Biopsy Findings on Ten-Year Outcomes of Extended Criteria Donor Kidney Transplants

Introduction

Methods

Results

Conclusion

Hyperspectral Imaging during Normothermic Machine Perfusion—A Functional Classification of Ex Vivo Kidneys Based on Convolutional Neural Networks

Facing an ongoing organ shortage in transplant medicine, strategies to increase the use of organs from marginal donors by objective organ assessment are being fostered. In this context, normothermic machine perfusion provides a platform for ex vivo organ evaluation during preservation. Consequently, analytical tools are emerging to determine organ quality. In this study, hyperspectral imaging (HSI) in the wavelength range of 550–995 nm was applied. Classification of 26 kidneys based on HSI was established using KidneyResNet, a convolutional neural network (CNN) based on the ResNet-18 architecture, to predict inulin clearance behavior. HSI preprocessing steps were implemented, including automated region of interest (ROI) selection, before executing the KidneyResNet algorithm. Training parameters and augmentation methods were investigated concerning their influence on the prediction. When classifying individual ROIs, the optimized KidneyResNet model achieved 84% and 62% accuracy in the validation and test set, respectively. With a majority decision on all ROIs of a kidney, the accuracy increased to 96% (validation set) and 100% (test set). These results demonstrate the feasibility of HSI in combination with KidneyResNet for non-invasive prediction of ex vivo kidney function. This knowledge of preoperative renal quality may support the organ acceptance decision.

Estimating Nephron Number from Biopsies: Impact on Clinical Studies

BACKGROUND

Accumulating evidence supports an association between nephron number and susceptibility to kidney disease. However, it is not yet possible to directly measure nephron number in a clinical setting. Recent clinical studies have used glomerular density from a single biopsy and whole kidney cortical volume from imaging to estimate nephron number and single nephron glomerular filtration rate. However, the accuracy of these estimates from individual subjects is unknown. Furthermore, it is not clear how sample size or biopsy location may influence these estimates. These questions are critical to study design, and to the potential translation of these tools to estimate nephron number in individual subjects.

METHODS

We measured the variability in estimated nephron number derived from needle or virtual biopsies and cortical volume in human kidneys declined for transplantation. We performed multiple needle biopsies in the same kidney, and examined the three-dimensional spatial distribution of nephron density by magnetic resonance imaging. We determined the accuracy of a single-kidney biopsy to predict the mean nephron number estimated from multiple biopsies from the same kidney.

RESULTS

A single needle biopsy had a 15% chance and virtual biopsy had a 60% chance of being within 20% of the whole-kidney nephron number. Single needle biopsies could be used to detect differences in nephron number between large cohorts of several hundred subjects.

CONCLUSIONS

The number of subjects required to accurately detect differences in nephron number between populations can be predicted on the basis of natural intrakidney variability in glomerular density. A single biopsy is insufficient to accurately predict nephron number in individual subjects.

Inulin Clearance During Ex vivo Normothermic Machine Perfusion as a Marker of Renal Function

Normothermic machine perfusion (NMP) offers a unique opportunity to objectively assess donor organ quality. This study describes the evaluation of inulin clearance as a potential marker for the ex vivo function of porcine kidneys during NMP. The function assessment was performed in both kidneys from slaughterhouse pigs (n = 20) and kidneys from pigs in a laboratory setting (n = 28). The kidneys were exposed to different warm ischemia times (WIT). After a period of static cold storage, the kidneys underwent a 4-hour NMP with autologous whole blood. Inulin clearance, hemodynamic parameters, and urine output were measured. Based on the inulin excretion behavior laboratory pig kidneys were assigned to three classes (functional, limited functional, and nonfunctional), slaughterhouse pig kidneys to two classes (limited functional and nonfunctional), respectively. Contrary to the marginal kidneys of the slaughterhouse pigs, the functional variation of kidneys of the laboratory pigs was associated with the WIT. A correlation between functional kidneys and a WIT less than 25 min was shown. Because none of the slaughterhouse pig kidneys could be assigned to the functional class, only the laboratory pig kidneys were used for examinations with functional markers. Renal blood flow and urine output during NMP correlated significantly (p < 0.01) with ex vivo kidney function. This study demonstrated that inulin is a marker of high quality for the evaluation of suggested kidney function after NMP with whole blood. Furthermore, surrogate markers measured during NMP can be used to describe and predict the physiologic behavior of kidneys before transplantation.

Macroscopic assessment of the quality of cold perfusion after deceased-donor kidney procurement: A United Kingdom population-based cohort study

Concern regarding the quality of cold perfusion (QOP) during macroscopic assessment of procured kidneys is a common reason for discard. In the UK, QOP is routinely graded by both retrieving and implanting teams during back-bench surgery as: 1 (good), 2 (fair), 3 (poor) or 4 (patchy). We evaluated the association of this grading with organ utilization, graft outcomes, and agreement between teams. Data on all deceased-donor kidneys procured between January 2000 and December 2016 were analyzed for discard rates, while association with graft outcomes was studied in single adult transplants. Of 31,167 kidneys procured, 90.6%, 5.7%, 1.7%, and 2.1% were assigned grades 1, 2, 3, and 4, respectively, at retrieval. QOP was an independent risk factor of discard, with the highest rates observed in grade 3 kidneys (41.8%), compared to 6.5% in grade 1 (aOR 7.67, 95% CI 5.44-10.82, p < .001). Grading at retrieval was an independent predictor of delayed graft function (p = .019) and primary non-function (p = .001), but not long-term graft survival (p = .111). Implanting grade was an independent predictor of all three outcomes (p < .001, p < .001, and p = .002, respectively). Consistency of grading between teams was poor (Kappa = 0.179). QOP influences utilization and predicts outcomes, but a standardized and validated scoring system is required.

Impact of acute kidney injury in deceased donors with high Kidney Donor Profile Index on posttransplant clinical outcomes: a multicenter cohort study

BACKGROUND

This study evaluated the impact of acute kidney injury (AKI) on posttransplant clinical outcomes for deceased donor (DD) kidney transplantation (KT) using the Kidney Donor Profile Index (KDPI) system.

METHODS

Overall, 657 kidney transplant recipients (KTRs) receiving kidneys from 526 DDs from four transplant centers were included. We divided them into the high and low KDPI donor groups by 65%, the KDPI score, and both groups were subdivided into the AKI-DDKT and non-AKI-DDKT subgroups according to AKI in DDs.

RESULTS

There was no significant difference in the incidence of delayed graft function (DGF) between the high and low KDPI-KTR groups; however, the AKI-DDKT subgroup showed significantly higher incidence of DGF than the non-AKI-DDKT subgroup in both groups (p = 0.001, p < 0.001, respectively). The death-censored graft survival rate was significantly lower in the high KDPI-KTR group than in the low KDPI-KTR group (p = 0.005). Only in the high KDPI-KTR group, the death-censored graft survival rate was significantly lower in the KT from DDs with AKI stage 3 than KT from DDs with non-AKI or AKI stage 1 or 2 (p = 0.040). The interaction between AKI stage 3 in DDs and high KDPI on the allograft outcome was significant (p = 0.002).

CONCLUSION

KTs from DDs with AKI stage 3 showed an adverse impact on the allograft outcome in the high KDPI-KTR group. Therefore, DDs with a high KDPI score should be managed carefully so that severe AKI does not occur prior to KT.

Organ donation and transplantation: a multi-stakeholder call to action

Although overall donation and transplantation activity is higher in Europe than on other continents, differences between European countries in almost every aspect of transplantation activity (for example, in the number of transplantations, the number of people with a functioning graft, in rates of living versus deceased donation, and in the use of expanded criteria donors) suggest that there is ample room for improvement. Herein we review the policy and clinical measures that should be considered to increase access to transplantation and improve post-transplantation outcomes. This Roadmap, generated by a group of major European stakeholders collaborating within a Thematic Network, presents an outline of the challenges to increasing transplantation rates and proposes 12 key areas along with specific measures that should be considered to promote transplantation. This framework can be adopted by countries and institutions that are interested in advancing transplantation, both within and outside the European Union. Within this framework, a priority ranking of initiatives is suggested that could serve as the basis for a new European Union Action Plan on Organ Donation and Transplantation.

Development and external validation study combining existing models and recent data into an up-to-date prediction model for evaluating kidneys from older deceased donors for transplantation

With a rising demand for kidney transplantation, reliable pre-transplant assessment of organ quality becomes top priority. In clinical practice, physicians are regularly in doubt whether suboptimal kidney offers from older donors should be accepted. Here, we externally validate existing prediction models in a European population of older deceased donors, and subsequently developed and externally validated an adverse outcome prediction tool. Recipients of kidney grafts from deceased donors 50 years of age and older were included from the Netherlands Organ Transplant Registry (NOTR) and United States organ transplant registry from 2006-2018. The predicted adverse outcome was a composite of graft failure, death or chronic kidney disease stage 4 plus within one year after transplantation, modelled using logistic regression. Discrimination and calibration were assessed in internal, temporal and external validation. Seven existing models were validated with the same cohorts. The NOTR development cohort contained 2510 patients and 823 events. The temporal validation within NOTR had 837 patients and the external validation used 31987 patients in the United States organ transplant registry. Discrimination of our full adverse outcome model was moderate in external validation (C-statistic 0.63), though somewhat better than discrimination of the seven existing prediction models (average C-statistic 0.57). The model's calibration was highly accurate. Thus, since existing adverse outcome kidney graft survival models performed poorly in a population of older deceased donors, novel models were developed and externally validated, with maximum achievable performance in a population of older deceased kidney donors. These models could assist transplant clinicians in deciding whether to accept a kidney from an older donor.

Kidney nonprocurement in solid organ donors in the United States

There are limited data on the nonprocurement of kidneys from solid organ donors. Analysis of Standard Transplant Analysis and Research files was undertaken on all deceased donors in the United States with at least 1 solid organ recovered. From 2000 to 2018, 21 731 deceased donor kidneys (averaging 1144 kidneys per year) were not procured. No kidneys were procured from 8% of liver donors, 3% of heart donors, and 3% of lung donors. Compared to donors with all kidneys procured, those with none procured were older and more likely obese, black, hypertensive, diabetic, hepatitis C positive, smokers, Public Health Service - Increased Risk designated, deceased after cardiac death, or deceased after cerebrovascular accident. Although these donors had lower quality kidneys (median Kidney Donor Risk Index (interquartile range) 1.9 (1.0) vs 1.2 (0.7)), there was substantial overlap in quality between nonprocured and procured kidneys. Nearly one third of nonprocurements were attributed to donor history. Donors with elevated terminal creatinine likely resulting from acute kidney injury (AKI) had higher odds of kidney nonprocurement. Nonprocurement odds varied widely across Organ Procurement and Transplantation Network regions, with a positive correlation between donor kidney nonprocurements and kidney discards at the donation service area level. These findings suggest current discard rates underestimate the underutilization of deceased donor kidneys and more research is needed to optimize safe procurement and utilization of kidneys from donors with AKI.

Algorithm for Mapping Kidney Tissue Water Content during Normothermic Machine Perfusion Using Hyperspectral Imaging

The preservation of kidneys using normothermic machine perfusion (NMP) prior to transplantation has the potential for predictive evaluation of organ quality. Investigations concerning the quantitative assessment of physiological tissue parameters and their dependence on organ function lack in this context. In this study, hyperspectral imaging (HSI) in the wavelength range of 500–995 nm was conducted for the determination of tissue water content (TWC) in kidneys. The quantitative relationship between spectral data and the reference TWC values was established by partial least squares regression (PLSR). Different preprocessing methods were applied to investigate their influence on predicting the TWC of kidneys. In the full wavelength range, the best models for absorbance and reflectance spectra provided Rp2 values of 0.968 and 0.963, as well as root-mean-square error of prediction (RMSEP) values of 2.016 and 2.155, respectively. Considering an optimal wavelength range (800–980 nm), the best model based on reflectance spectra (Rp2 value of 0.941, RMSEP value of 3.202). Finally, the visualization of TWC distribution in all pixels of kidneys’ HSI image was implemented. The results show the feasibility of HSI for a non-invasively and accurate TWC prediction in kidneys, which could be used in the future to assess the quality of kidneys during the preservation period.

Impact of pre-transplant biopsy on 5-year outcomes of expanded criteria donor kidney transplantation

AIM

Compared to Standard Criteria Donors (SCD), Expanded Criteria Donor (ECD) kidneys are associated with poorer outcomes, although pre-transplant biopsy may mitigate risks. This study assessed 5-year outcomes of deceased-donor kidney transplant recipients, comparing recipients of ECD allografts evaluated histologically to recipients of SCD and ECD kidneys assessed clinically.

METHODS

This is a single-centre retrospective study. From November 2005 to December 2009 (Era 1), donors were assessed clinically for suitability for kidney donation. From December 2009 to October 2017 (Era 2), kidneys from ECDs and diabetics underwent pre-transplant biopsy and were allocated based on Remuzzi score. Outcomes of Era 1 and 2 recipients were compared.

RESULTS

ECD kidney transplantation increased from 30.4% to 40.0% from Era 1 to 2. Univariable Cox regression, stratified by transplant era, found that 5-year graft loss was highest with Era 1 ECD (HR 2.5, 95% CI 1.1-5.5, P = .027) while graft loss for Era 2 ECD recipients was similar to SCD recipients. There was no difference in 5-year recipient survival. Amongst Era 1 ECD recipients, 51.2% experienced rejection compared to 30.8-41.5% for other subgroups. Five-year eGFR was higher with Era 2 ECD at 48.4 (33.3-60.7) ml/min/1.73 m² compared to 42.2 (35.8-57.3) ml/min/1.73 m² for Era 1 ECD. However, these differences were not statistically significant.

CONCLUSION

Introduction of pre-transplant biopsy assessment may be associated with improved outcomes of ECD kidney recipients such that they are now comparable to SCD kidney recipients, with benefits persisting over 5 years.

Improving HLA matching in living donor kidney transplantation using kidney paired exchange program

BACKGROUND

The inclusion of compatible pairs within kidney paired exchange programs has been described as a way to enhance these programs. Improved immunological matching for the recipient in compatible pair has been described to be a possible benefit.

METHODS

The main purpose of our study was to determine if the introduction of compatible pairs in the Portuguese kidney paired exchange program would result in a better match for these patients, but also to assess if this strategy would increase the number of incompatible pairs with a possible match. We included 17 compatible pairs in kidney paired exchange pool of 35 pairs and performed an in-silico simulation determining HLA eplet mismatch load between the co-registered and matched pairs using HLA MatchMaker, version 3.0.

RESULTS

Our study showed that the inclusion of fully HLA-A, -B, -DR mismatched compatible pairs within the national Portuguese KEP increased matched rate within ICP (0.71%) and improved HLA eplet matching within compatible pairs. 16 of 17 (94.12%) of the CP obtained one or more transplants possibilities and 13 (81.25%) would have been transplanted with significantly lower HLA class I and class II total and antibody-verified eplet mismatch load (83.9 ± 16.9 vs. 59.8 ± 12.2, P = .002 and 30.1 ± 5.5 vs. 21.2 ± 3.0, P = .003, respectively).

CONCLUSIONS

This strategy is a viable alternative for compatible pairs seeking a better matched kidney and Portuguese KEP program should allow them this possibility.

Kidney Donor Profile Index in a Transplant Center in Mexico

BACKGROUND

The Kidney Donor Profile Index (KDPI) was created in 2014 to measure the likelihood of graft failure for a given donor compared with the median kidney donor from the previous year. This scale is based on the American population only. Mexico is one of the countries with greater incidence of chronic kidney disease, a long waiting list, and not enough kidney donors with KDPI smaller than 80%. This has led transplant centers to take kidney grafts with a higher KDPI.

OBJECTIVE

To investigate the agreement between the KDPI and histologic scores (preimplantation renal biopsy) and assess the relationship between the Kidney Donor Risk Index (KDRI), KDPI, and the histologic score on graft survival.

METHODS

A retrospective, analytical, transversal study was performed. Data were collected from patients with kidney grafts from deceased donors from January 1, 2011, to June 30, 2019, at our hospital. The variables analyzed were age, weight, height, sex, race and/or ethnicity, history of hypertension or diabetes, cause of death, serum creatinine, KDPI, KDRI, and biopsy result from each graft prior to transplant.

RESULTS

The total population was 59 deceased kidney donors. For our patients, a high KDPI did not increase mortality rate; it provided greater benefit than staying on dialysis.

CONCLUSIONS

We conclude that the use of KDRI should only be considered to assess the degree of fibrosis, not to rule out a transplantable kidney, in addition to the consistent demonstration that high KDPI kidneys (even 91%-100%) confer greater survival benefits to patients regarding the waiting list.