Abstract
Background: Advanced donor age paired with donation after cardiac death (DCD) increases the risk of transplantation, precluding widespread use of grafts from such donors worldwide. Our aim was to analyze outcomes of liver transplantation using grafts from older DCD donors and donation after brain death (DBD) donors.
Methods: Patients who underwent liver transplantation using grafts from deceased donors between January 2016 and December 2021 were included in the study. Short-and long-term outcomes were analyzed for 4 groups of patients: those who received DCD and DBD grafts from younger (< 50 yr) and older (≥ 50 yr) donors.
Results: Of the 807 patients included in the analysis, 44.7% (n = 361) of grafts were received from older donors, with grafts for older DCD donors comprising 4.7% of the total cohort (n = 38). Patients who received grafts from older donors had a lower incidence of biliary strictures than those who received grafts from younger donors (7.9% v. 20.0% for DCD donation, p = 0.14, and 4.9% v. 6.8% for DBD donation, p = 0.34), with a significantly lower incidence of ischemic-type biliary strictures in patients who received grafts from older versus younger DCD donors (2.6% v. 18.0%, p = 0.04). There was no difference in 1- and 3-year graft survival rates among patients who received grafts from older and younger DCD donors (92.1% v. 90.8% and 80.2% v. 80.9%, respectively) and those who received grafts from older and younger DBD donors (90.1% v. 93.2% and 85.3% v. 84.4%, respectively) (p = 0.85). Pretransplantation admission to the intensive care unit (hazard ratio [HR] 9.041, p < 0.001) and nonalcoholic steatohepatitis (HR 2.197, p = 0.02) were found to significantly affect survival of grafts from older donors.
Conclusion: Donor age alone should not be the criterion to determine the acceptability of grafts in liver transplantation. With careful selection criteria, older DCD donors could make a valuable contribution to expanding the liver donor pool, with grafts that produce comparable results to those obtained with standard-criteria grafts.
Imbalance between the demand for organs and their availability is a known hindrance to increasing liver transplantation rates across North America and has contributed to long waits for transplantation.1 To address this imbalance, there has been a steady expansion of the use of extended criteria grafts, which include organs obtained from donation after cardiac death (DCD) donors, over the last 2 or 3 decades.2 However, earlier reports describing inferior graft survival, higher rates of biliary complications, primary nonfunction and hepatic arterial complications hindered the expanded use of DCD grafts at many centres in North America and worldwide.3,4
Advanced donor age is another factor known to affect the postoperative outcome of deceased donor liver transplantation (DDLT) and is the factor that receives the highest weighting in the calculation of the donor risk index.5 When paired with DCD, the risk of complications after transplantation increases several fold, thereby precluding the use of such grafts at most centres worldwide. The downstream effects of warm ischemia inevitably associated with DCD grafts compounded by the effects of advanced age on tissue regeneration are some of the factors believed to be responsible for the risks associated with the use of such grafts.6
Grafts from DCD make up only 5%–6% of the total pool of DDLTs annually at most centres in North America.7 There has been greater acceptance of the use of DCD donors at the Toronto General Hospital, where they have made up nearly 12% of the donor pool annually since the inception of the DCD program in 2007.
The present study aims to summarize the short- and long-term outcomes of liver transplantation using grafts from older donors (≥ 50 yr) who donated after either brain death (DBD) or cardiac death (DCD) and compare them with the outcomes of liver transplantation using grafts from younger (< 50 yr) DCD and DBD donors.
Methods
Study design
This was a retrospective review of data from a prospectively maintained transplant registry at the Ajmera Transplant Centre, Toronto General Hospital, in Toronto, Canada. All patients who underwent DDLT between Jan. 1, 2016, and Dec. 31, 2021, were eligible for this study. Pediatric liver transplant recipients (< 18 yr), living donor liver transplant recipients, recipients of organs placed on an OrganOx Metra machine perfusion (part of an ongoing normothermic machine perfusion study), patients undergoing retransplantation and the recipients of multiorgan transplants were excluded from the analysis.
All of the research in this study was conducted in accordance with the declarations of Helsinki and Istanbul. The study was approved by the research ethics board of the University Health Network (CAPCR ID 21-5893). The requirement for informed consent was waived because of the retrospective nature of the study and the lack of any intervention in the study. The study design was approved in compliance with the relevant research ethics guidelines and the Ontario Personal Health Information Protection Act.8
Study population and variables
Patients in the study population were divided into 4 groups on the basis of their donor’s characteristics: DCD donors younger than 50 years, DCD donors aged 50 years and older, DBD donors younger than 50 years and DBD donors aged 50 years and older. Donor demographic and perioperative variables were retrieved from the Trillium Gift of Life Network database. Recipient demographic, perioperative and postoperative followup variables were retrieved from the prospectively maintained transplant registry. The donor risk index was calculated for all listed donors.5 The donor warm ischemia time was calculated from the time of withdrawal of life support treatment up to the initiation of cold perfusion for all DCD donors, regardless of the mean arterial pressure or the partial pressure of oxygen levels. The recipient warm ischemia time was calculated for all patients from the onset of the anhepatic phase to the reperfusion. Cold ischemia time of the graft was defined as the time of cross-clamping in the donor to the onset of portal venous reperfusion in the recipient. The United Kingdom (UK) DCD score was calculated for all DCD recipients as a predictor standard for graft outcome.9
Protocol for donation after cardiac death
All DCD grafts in the current study were from category III DCD donors according to the Maastricht classification.10 The allocation of organs from DCD donors at the Toronto General Hospital is coordinated by the Trillium Gift of Life Network. For recipients, allocation was based on the calculated Model for End-Stage Liver Disease and Sodium (MELD-Na) score, with the exception of patients listed for hepatocellular carcinoma, who received exception points. Furthermore, the selection of candidates for DCD grafts was based on minimization of the cold ischemia time to less than 8 hours, to avoid including recipients with complicated hepatectomies (retransplantation or need for vascular reconstructions) or diagnosed portal vein thrombosis or both.
Recovery of DCD grafts for our centre has been previously described.11 Briefly, an intensive care physician at the donor hospital who was completely independent of the recovery and recipient teams identified potential DCD donors and organized the process of withdrawal of life support and the declaration of donor death. Heparin (1000 U/kg) was administered before withdrawal of life support. The maximum tolerated warm ischemia time at our centre is 30 minutes. In some exceptional circumstances, the warm ischemia time was slightly expanded at the surgeons’ discretion (a maximum warm ischemia time of 33 min). All DCD graft recipients included in the current study received an injection of tissue plasminogen activator (tPA) through the hepatic artery. The tPA dose used was 100 μg/kg (donor weight) and was administered before the portal vein anastomosis (5–10 min before portal reperfusion). Grafts from donation after cardiac death with more than 10% estimated steatosis were declined for transplantation.
Technique of implantation
The preferred venous implantation procedure for all DDLT grafts at our centre has been the caval replacement technique. The arterial anastomosis is performed using the parachute technique under 3.5 times magnification. The preferred biliary anastomosis technique has been by duct-to-duct anastomosis, with a few exceptions where Roux-en-Y bilioenteric anastomosis has been preferred because of underlying liver conditions or unfavourable anatomic factors.
Post-transplantation complications
Local and systemic complications were classified according to the Clavien–Dindo (CD) grading system.12 Peak levels of aspartate transaminase (AST) were used as indicators of immediate post-transplantation graft function (within 48 h). Primary nonfunction of the graft was defined as graft failure within 48 hours of transplantation. The arterial complications were classified as hepatic artery stenosis (HAS) or hepatic artery thrombosis (HAT) and were treated with medical, radiologic (dilatation, stenting) or surgical (relaparotomy) interventions. Biliary complications were classified as leaks or strictures. The strictures were subclassified into anastomotic and ischemic. The time to development of stricture was calculated from the index surgery (transplantation). Strictures were managed by endoscopic (endoscopic retrograde cholangiopancreatography), radiologic (percutaneous cholangioscopy) or surgical (relaparotomy) techniques. Ninety-day post-transplantation mortality was calculated. Patients were followed on a regular outpatient basis, and graft and patient survival rates were calculated at 1 and 3 years after transplantation. Time of graft loss was determined by the time of listing for retransplantation or patient death, whichever date was earlier.
Statistical analysis
On the basis of the distribution of the continuous variables (normal or non-normal) using the Kolmogorov–Smirnov and Shapiro–Wilk normality tests, data were expressed as either means with standard deviations (SD) or medians with range or interquartile ranges (IQR). For comparison of normally distributed data among the 2 age categories of donors (< 50 yr and ≥ 50 yr) in each of the DCD and DBD groups, the Student t test was used, and the Mann–Whitney U test was used for non-normally distributed data. Categorical variables among the 2 age categories of donors in the DCD and DBD groups were compared using χ2 or Fisher exact tests. Graft and patient survival were plotted using Kaplan–Meier curves and compared using the log rank test. A p value of less than 0.05 was set as significant. Survival times were calculated from the time of index transplantation. Graft survival time was modelled as a function of donor age at transplantation (continuously) and graft type (DCD) using the Cox proportional hazards model. The model contained main effects for donor age and type of donor (DCD) and the 2-way interaction between them. In addition, for older donors (aged ≥ 50 yr) in both the DCD and DBD groups, a Cox regression using donor predictor variables (age, body mass index, cold ischemia time) and recipient predictor variables (age at transplantation, warm ischemia time, sex, peak MELD-Na score, pretransplantation admission to the intensive care unit [ICU], requirement for pretransplantation dialysis, nonalcoholic steatohepatitis [NASH] as the cause and hepatitis C virus positivity) was performed. All statistical analyses were performed using Prism version 9.4.0 (GraphPad).
Results
Demographic characteristics
A total of 807 patients who underwent DDLT between January 2016 and December 2021 were included in the analysis. Of these, 719 patients received a graft from DBD donors (89.1%) and 88 patients received a graft from DCD donors (10.9%). Grafts from older donors (aged ≥ 50 yr) comprised 44.7% of the total cohort, with grafts from older DCD donors comprising 4.7% of the total cohort. A total of 213 patients (26.4%) received grafts from donors aged 60 years and older: 16 of these cases involved DCD donors and 197 involved DBD donors.
Table 1 summarizes the donor and recipient demographic and preoperative characteristics in the 4 groups. The oldest DCD donor was 72 years old and the oldest DBD donor was 84 years old. The median donor age in the older DCD group was 57 (range 51–72) years, while in the older DBD group it was 62 (range 50–84) years. The median donor risk index was higher for the older donors than the younger donors in the DCD (2.6 v. 2.1, p = 0.09) and DBD groups (1.7 v. 1.3, p = 0.08), although these differences were not statistically significant. There were no significant differences in the peak creatinine, alanine transaminase (ALT) and AST levels among the older and younger donors in the DCD and DBD groups. The median cold ischemia time was higher for the grafts from younger DCD donors than from older DCD donors (492 [IQR 44–1083] min v. 389 [IQR 154–600] min, p = 0.01). No difference in cold ischemia time was observed among the DBD donor groups. There was no significant difference in the recipients’ sex or peak MELD-Na score between the older and younger donor categories in both the DCD and DBD groups. The median UK DCD risk score was similar in both groups of DCD donors (7.0 v. 7.5; p = 0.80).
Perioperative outcomes and complications
Table 2 summarizes the comparison of the outcomes and perioperative systemic complications among recipients in the 4 groups. There was no significant difference in the length of postoperative stay between the recipients of grafts from older and younger donors in both the DCD and DBD groups. However, the patients in the older DBD group had a higher median length of post-transplantation ICU stay than those in the younger DBD group (2.4 [IQR 1.5–25] d v. 1.1 [IQR 1–18] d, p = 0.02). Aspartate transaminase, ALT and bilirubin levels on postoperative day 7 were similar among patients who received grafts from older and younger donors in the DCD and DBD groups. The incidence of post-transplantation infection or sepsis was higher among patients in the younger DBD group than in those in the older DBD group (15.9% [n = 63] v. 4.0% [n = 13], p < 0.001), with the most common being pneumonia or lower respiratory tract infection (6.1% v. 5.8% in the younger and older groups, respectively). There was no difference in infectious complications in the 2 DCD groups. Ninety-day mortality was similar in patients who received grafts from older and younger donors in both the DCD (13.2% v. 14.0%, p = 0.91) and DBD (6.2% v. 10.4%; p = 0.06) groups.
Graft-related complications
Table 3 summarizes graft-related complications in the younger and older donor groups in the DCD and DBD groups. There was no significant difference in the incidence of major graft-related complications such as primary nonfunction, small-for-size syndrome (SFSS) and early (< 30 d) and delayed graft rejection among patients receiving grafts from older and younger donors in either the DCD or DBD group. The overall incidence of hepatic arterial complications was 1.2% (n = 10). In the DCD group, there was no significant difference in the rate of these complications between patients who received grafts from older and younger donors (5.2% [n = 2] v. 0% [n = 0], p = 0.18). However, in the DBD group, there was a significantly higher incidence in patients who received grafts from younger donors than from older donors (2.0% [n = 8] v. 0% [n = 0], p = 0.009). The overall incidence of biliary complications was 14.7% (n = 13) in the DCD cohort and 6.0% (n = 43) in the DBD cohort. The incidence of biliary stricture was lower in the older DCD group than in the younger group, although the difference was not statistically significant (7.9% [n = 3] v. 20.0% [n = 10], p = 0.14). Ischemic strictures were more common than anastomotic strictures; the incidence of the former was significantly lower in the older DCD group than in the younger DCD group (2.6% [n = 1] v. 18.0% [n = 9], p = 0.04). The findings were similar in the DBD group, with a lower incidence of biliary strictures among recipients of grafts from older donors than younger donors, although again the difference was not significant (4.9% [n = 16] v. 6.8% [n = 27], p = 0.34).
Post-transplantation graft and patient survival
One- and 3-year patient survival (Figure 1 and Table 4) was similar between recipients of grafts from older and younger donors in the DCD group (94.7% v. 93.2% and 86.1% v. 83.3%, respectively) and in the DBD group (89.2% v. 92.9% and 83.1% v. 87.1%, respectively) with no statistically significant difference (p = 0.52). One- and 3-year graft survival rate (Figure 2 and Table 5) was also similar between patients who received grafts from older and younger donors in the DCD group (92.1% v. 90.8% and 80.2% v. 80.9%, respectively) and in the DBD group (90.1% v. 93.2% and 85.3% v. 84.4%, respectively), with no significant difference (p = 0.86). A Cox regression analysis evaluating the predictors of graft failure for older donors (361 donors aged ≥ 50 yr, DCD and DBD groups combined) was performed (Table 6). Pretransplantation ICU admission of the recipient (hazard ratio [HR] 9.041, 95% confidence interval [CI] 3.661–19.760, p < 0.001) and the presence of NASH (HR 2.197, 95% CI 1.098–4.310, p = 0.02) in the recipient were found to significantly affect graft survival outcomes in recipients receiving grafts from older donors. Further multivariate analysis using Cox proportional hazards modelling (main effects and 2-way interaction model) was performed to examine the effect of donor age and donor type on graft survival in the entire study population (Table 7). The risk of graft failure was not found to be statistically significant with donor type (DCD v. DBD, HR 1.811, 95% CI 0.331–7.915, p = 0.46) or with the age of the donor (HR 0.999, 95% CI 0.987–1.011, p = 0.91) in either the DCD or DBD group.
Discussion
Despite the initial discouraging results for the use of DCD grafts and the associated skepticism, more recent studies have shown good long-term outcomes in the form of patient and graft survival. However, even with an increase in the utilization of DCD grafts and the laxity of selection criteria for DBD grafts across North America, the gap between demand for organs and availability is still far from being bridged.13 This has led to continued consideration of pushing the age limits of organ donors in many centres to augment the donor pool. The DCD program at the Toronto General Hospital has been steadily increasing its acceptance of grafts from older DCD donors, pushing the boundaries in DCD since 2007.14 The results of our single-centre study revealed comparable outcomes of DDLT using grafts from donors aged 50 years and older and donors aged less than 50 years in both the DCD and DBD groups, in terms of graft and patient survival rates.
With an aging population in North America, the number of potential elderly donors is expected to rise.15 However, there exists a theoretical risk of lower regenerative potential and higher incidence of graft failure with grafts from older donors, given the physiologic changes in liver associated with aging, including increased apoptosis, decreased mitochondrial counts, increased oxidative stress and polyploidy.16 The risk increases further in the setting of DCD grafts where the insult to the graft is felt to be more severe. This had been substantiated in several studies. In 2006, Mateo and colleagues17 analyzed the outcome of liver transplantation from DCD donors versus DBD donors by formulating a recipient cumulative relative risk algorithm. They reported significantly inferior graft and patient survival outcomes from DCD versus DBD donors at 1 and 3 years respectively (71% v. 80% and 60% v. 72%, respectively, p < 0.001). The risk increased further with the use of elderly donors and ones with longer warm ischemia time and cold ischemia time. In 2009, de Vera and colleagues18 reported similar results, showing that donation from DCD donors older than 60 years was associated with a worse survival outcome than donation from DCD donors younger than 60 years. Subsequently, a retrospective study by Firl and colleagues19 reported the results for a matched cohort of 92 recipients each in the DCD and DBD groups; their findings revealed significantly worse 1-, 3- and 5-year graft survival rates in the former than in the latter group (82%, 71% and 66% v. 92%, 87% and 85%, respectively, p = 0.03). They also reported a higher incidence of ischemic-type biliary strictures among recipients in the DCD group. However, the authors found no association between biliary strictures and advanced donor age. Also, they reported similar graft survival rates at 1, 3 and 5 years in patients receiving DCD grafts from older (> 45 yr) and younger (< 45 yr) donors. Advanced donor age and use of DCD grafts were identified as unfavourable factors for graft survival.
In contrast, a retrospective analysis comparing outcomes in 108 DCD liver recipients with those in 1328 DBD liver recipients between 1998 and 2006 by Grewal and colleagues20 revealed similar 1-, 3- and 5-year graft and patient survival rates in the 2 groups. Outcomes were not significantly different among DCD donors older than 60 years of age, DCD donors younger than 60 years of age and DBD donors. More recently, another study by Schlegel and colleagues21 in 2017 compared outcomes in recipients who received DCD grafts from donors 60 years of age and younger (n = 222) and from donors over 60 years of age (n = 93) over 10 years. They found similar graft and patient survival rates between the 2 groups, with no significant difference in the incidence of vascular and biliary complications. In another multicentre analysis by Croome and colleagues22 in 2018, the authors compared the outcomes of DCD graft recipients over 15 years by dividing them into 2 groups: those whose grafts were from donors aged 50 years and older (n = 155) and those whose grafts were from donors aged less than 50 years (n = 316). Graft survival at 1, 3 and 5 years was 87%, 75.6% and 71.8%, respectively, in the older DCD group, compared with 85.8%, 76% and 70.4%, respectively, in the younger DCD group, with no significant difference (p = 0.99). They reported a higher rate of anastomotic biliary strictures in the older DCD cohort than in the younger cohort (16.1% v. 8.2%, p = 0.01), with no difference in the incidence of ischemic-type biliary strictures between the 2 groups.
In the present study we reported similar findings in terms of the comparison of 1- and 3-year patient and graft survival in recipients of grafts from older versus younger DCD and DBD donors. However, contrary to most earlier reports on DCD, the incidence of hepatic arterial complications was higher among DBD graft recipients than among DCD graft recipients, with a significantly higher occurrence in the younger DBD group than in the older group. This is similar to the findings reported by Kollmann and colleagues14 from our centre in 2018, where the authors found hepatic arterial complication to be the major indication for retransplantation in DBD recipients and biliary complications to be the main indication for retransplantation in DCD graft recipients. Measures such as donor heparinization, minimizing cold ischemia time and administration of tissue plasminogen activator during graft reperfusion constitute the routine protocol for DCD graft transplantation at the Toronto General Hospital, which could contribute to a lower incidence of arterial complications in those recipients. There was no significant difference in the rate of biliary complications in recipients of grafts from older versus younger donors in both the DCD and DBD groups. Contrary to most studies, in both the DCD and DBD groups we found a significantly higher incidence of ischemic-type biliary strictures in the recipients of grafts from younger donors than from older ones. A possible explanation of this could be the significantly longer cold ischemia time in our study in grafts from younger DCD donors than from older donors, a factor that could contribute to the higher incidence of ischemic cholangiopathy.
Croome and colleagues22 also found MELD scores of 30 or above, prolonged mechanical ventilation in the ICU before transplantation and longer cold ischemia time to be significant predictors of graft failure in recipients of grafts from older (> 50 yr) DCD donors. Given that the numbers of patients in our older DCD group were too small for accurate analysis, we used a Cox proportional hazards model for the recipients of grafts from older DCD and DBD donors combined (n = 361). In addition to pretransplantation ICU admission, we also found NASH in the recipient to significantly affect graft survival when the graft was from an older donor. A recent study from our institute by Minich and colleagues23 identified advanced recipient age (HR 2.07, 95% CI 1.7–2.5) and pretransplantation diabetes mellitus (HR 1.18, 95% CI 1.08–1.28) to be significant predictors of patient mortality across 25 studies included in their systematic review and 5 in their meta-analysis. However, to our knowledge, no association between NASH in recipients and advanced donor age has been identified in the past.
Croome and colleagues22 also found that recipients with lower MELD scores received preferential DCD graft allocation across all 3 centres studied. This finding is similar to our observation in the present study that the median MELD-Na score in the older DCD group was lower than in the other 3 groups (although the difference was not statistically significant), with hepatocellular carcinoma (low MELD score) being the indication for transplantation in 50% of the patients in that group.
We made a similar observation when we computed the UK DCD risk scores for the 2 groups of DCD graft recipients. There was a preferential allocation of grafts from younger DCD donors with lower body mass index or shorter warm ischemia time to recipients who were older and had worse MELD-Na scores, and grafts from donors with more borderline characteristics were preferentially allocated to younger recipients with better MELD-Na scores, thereby accounting for the finding that the median UK DCD scores were similar in the 2 DCD groups. As an institutional protocol, DCD grafts from older donors (> 50 yr) with evident macroscopic steatosis based on visual examination were mostly discarded and deemed unsuitable for implantation. However, the incidence of primary nonfunction and ischemic cholangiopathy was 0% and 2.6%, respectively, in the older DCD group, with a median UK DCD score of 7.5 (IQR 5–10), less than the incidence of 1% and 3%, respectively, predicted by the UK DCD model.9 This finding could be attributed to careful selection of DCD donors complemented by meticulous donor–recipient matching during allocation of grafts at our centre. Conversely, there was no preferential selection of donors on the basis of their underlying comorbidities, as evidenced by the fact that 42% (n = 16) of the DCD donors aged 50 years or older had had some underlying comorbidities in the form of hypertension, diabetes mellitus, chronic obstructive pulmonary disease or a history of cerebrovascular accident at some point in their life.
Limitations
The study had some limitations, the main one being the small size of the sample of DCD donors, which meant that the sample size for the comparison of the older and younger groups in the DCD cohort was also small. Setting the cut-off at 60 years would have further limited the sample size in the older DCD age group (n = 16) and compromised the power of the study and the reliability of the Cox proportional hazards model. In addition, very stringent selection of DCD donors (as evidenced by the UK DCD scores) by our institution could perhaps account for certain observations such as the very low rate of ischemic cholangiopathy in our DCD group compared with the world literaure. Selection of grafts from older DCD donors on the basis of lower comorbilities in the donor or even the donor’s geographic proximity to the centre of transplantation could account for the shorter cold ischemia times for grafts from older DCD donors as well as the very good clinical outcomes for the recipients of these grafts. This selection bias should be accounted for when extrapolating the results of this study to a more heterogeneous cohort of DCD donors who probably have characteristics that are considered to be associated with higher risk. Another possible limitation is the retrospective nature of the study and the short follow-up period, which was less than 5 years for most patients.
Conclusion
The results of this study suggest that in appropriately selected donors and recipients, the graft type (DCD v. DBD) and the age of the donor should not be contraindications to utilization of the graft for liver transplantation, as evidenced by the incidence of vasculobiliary complications and the graft and patient survival rates in the recipients of liver grafts from older donors. However, minimizing cold ischemia time, properly selecting recipients on the basis of comorbidities and MELD score, appropriately matching donors and recipients and administering heparin to donors during retrieval are some of the measures to improve the outcomes for such high-risk grafts.
Acknowledgement
The authors thank data analyst Vibha Bhat for help with data collection.
Footnotes
Presented at the 29th International Congress of the Transplantation Society, Sept. 10–14, 2022, Buenos Aires, Argentina
Competing interests: G. Sapisochin has received consulting fees from AstraZeneca, Roche, Chiesi Farmaceutici, HepaRegeniX and Novartis and a grant from Roche, all unrelated to the current study. C. Tsien has received consulting fees from Paladin Labs and speaker fees from Lupin Pharma Canada, unrelated to the current study. No other competing interests were declared.
Contributors: C. Shwaartz, N. Selzner, M. Selzner and T. Reichman conceived the study. B. Sayed, L. Lilly and N. Selzner acquired the data, which S. Ray, G. Sapisochin, A. Ghanekar, I. McGilvray, M. Cattral, C. Tsien, M. Bhat and E. Jaeckel analyzed. S. Ray wrote the article, which C. Shwaartz, B. Sayed, G. Sapisochin, A. Ghanekar, I. McGilvray, M. Cattral, L. Lilly, N. Selzner, C. Tsien, M. Bhat, E. Jaeckel, M. Selzner and T. Reichman critically revised. All authors gave final approval of the version to be published.
Funding: This work was supported by the Trillium Gift of Life Network (Ontario Health) [2016-21], Toronto, Ontario. The researchers’ interpretations and statements in this publication are those of the researchers only and not those of the Trillium Gift of Life Network (Ontario Health).
- Accepted September 6, 2023.
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