Racial disparity in kidney transplant survival relates to late rejection and is independent of steroid withdrawal

Evaluating site-of-care-related racial disparities in kidney graft failure using a novel federated learning framework

OBJECTIVES

Racial disparities in kidney transplant access and posttransplant outcomes exist between non-Hispanic Black (NHB) and non-Hispanic White (NHW) patients in the United States, with the site of care being a key contributor. Using multi-site data to examine the effect of site of care on racial disparities, the key challenge is the dilemma in sharing patient-level data due to regulations for protecting patients' privacy.

MATERIALS AND METHODS

We developed a federated learning framework, named dGEM-disparity (decentralized algorithm for Generalized linear mixed Effect Model for disparity quantification). Consisting of 2 modules, dGEM-disparity first provides accurately estimated common effects and calibrated hospital-specific effects by requiring only aggregated data from each center and then adopts a counterfactual modeling approach to assess whether the graft failure rates differ if NHB patients had been admitted at transplant centers in the same distribution as NHW patients were admitted.

RESULTS

Utilizing United States Renal Data System data from 39 043 adult patients across 73 transplant centers over 10 years, we found that if NHB patients had followed the distribution of NHW patients in admissions, there would be 38 fewer deaths or graft failures per 10 000 NHB patients (95% CI, 35-40) within 1 year of receiving a kidney transplant on average.

DISCUSSION

The proposed framework facilitates efficient collaborations in clinical research networks. Additionally, the framework, by using counterfactual modeling to calculate the event rate, allows us to investigate contributions to racial disparities that may occur at the level of site of care.

CONCLUSIONS

Our framework is broadly applicable to other decentralized datasets and disparities research related to differential access to care. Ultimately, our proposed framework will advance equity in human health by identifying and addressing hospital-level racial disparities.

Extracorporeal membrane oxygenation bridge to pediatric lung transplantation: Modern era analysis

BACKGROUND

Survival outcomes of children on extracorporeal membrane oxygenation (ECMO) at time of lung transplant (LTx) remain unclear.

METHODS

Pediatric first-time LTx recipients transplanted between January 2000 and December 2020 were identified in the United Network for Organ Sharing Registry to compare post-transplant survival according to ECMO support at time of transplant. For a comprehensive analysis of the data, univariate analysis, multivariable Cox regression, and propensity score matching were performed.

RESULTS

During the study period, 954 children under 18 years of age underwent LTx with 40 patients on ECMO. We did not identify a post-LTx survival difference between patients receiving ECMO when compared to those that did not. A multivariable Cox regression model (Hazard ratio = 0.83; 95% confidence interval: 0.47, 1.45; p = .51) did not demonstrate an increased risk for death post-LTx. Lastly, a propensity score matching analysis, retaining 33 ECMO and 33 non-ECMO patients, further confirmed no post-LTx survival difference comparing ECMO to no ECMO cohorts (Hazard ratio = 0.98; 95% confidence interval: 0.48, 2.00; p = .96).

CONCLUSIONS

In this contemporary cohort of children, the use of ECMO at the time of LTx did not negatively impact post-transplant survival.

Feature Importance of Acute Rejection among Black Kidney Transplant Recipients by Utilizing Random Forest Analysis: An Analysis of the UNOS Database

Background: Black kidney transplant recipients have worse allograft outcomes compared to White recipients. The feature importance and feature interaction network analysis framework of machine learning random forest (RF) analysis may provide an understanding of RF structures to design strategies to prevent acute rejection among Black recipients. Methods: We conducted tree-based RF feature importance of Black kidney transplant recipients in United States from 2015 to 2019 in the UNOS database using the number of nodes, accuracy decrease, gini decrease, times_a_root, p value, and mean minimal depth. Feature interaction analysis was also performed to evaluate the most frequent occurrences in the RF classification run between correlated and uncorrelated pairs. Results: A total of 22,687 Black kidney transplant recipients were eligible for analysis. Of these, 1330 (6%) had acute rejection within 1 year after kidney transplant. Important variables in the RF models for acute rejection among Black kidney transplant recipients included recipient age, ESKD etiology, PRA, cold ischemia time, donor age, HLA DR mismatch, BMI, serum albumin, degree of HLA mismatch, education level, and dialysis duration. The three most frequent interactions consisted of two numerical variables, including recipient age:donor age, recipient age:serum albumin, and recipient age:BMI, respectively. Conclusions: The application of tree-based RF feature importance and feature interaction network analysis framework identified recipient age, ESKD etiology, PRA, cold ischemia time, donor age, HLA DR mismatch, BMI, serum albumin, degree of HLA mismatch, education level, and dialysis duration as important variables in the RF models for acute rejection among Black kidney transplant recipients in the United States.

Recipient APOL1 risk alleles associate with death-censored renal allograft survival and rejection episodes

Apolipoprotein L1 (APOL1) risk-alleles in donor kidneys associate with graft loss but whether recipient risk-allele expression impacts transplant outcomes is unclear. To test whether recipient APOL1 risk-alleles independently correlate with transplant outcomes, we analyzed genome-wide SNP genotyping data of donors and recipients from two kidney transplant cohorts, Genomics of Chronic Allograft Rejection (GOCAR) and Clinical Trials in Organ Transplantation (CTOT1/17). We estimated genetic ancestry (quantified as proportion of African ancestry or pAFR) by ADMIXTURE and correlated APOL1 genotypes and pAFR with outcomes. In the GOCAR discovery set, we observed that the number of recipient APOL1 G1/G2 alleles (R-nAPOL1) associated with increased risk of death-censored allograft loss (DCAL), independent of ancestry (HR = 2.14; P = 0.006), and within the subgroup of African American and Hispanic (AA/H) recipients (HR = 2.36; P = 0.003). R-nAPOL1 also associated with increased risk of any T cell-mediated rejection (TCMR) event. These associations were validated in CTOT1/17. Ex vivo studies of peripheral blood mononuclear cells revealed unanticipated high APOL1 expression in activated CD4+/CD8+ T cells and natural killer cells. We detected enriched immune response gene pathways in risk-allele carriers vs. non-carriers on the kidney transplant waitlist and among healthy controls. Our findings demonstrate an immunomodulatory role for recipient APOL1 risk-alleles associating with TCMR and DCAL. This finding has broader implications for immune mediated injury to native kidneys.

Significance of Ethnic Factors in Immunosuppressive Therapy Management After Organ Transplantation

Clinical outcomes after organ transplantation have greatly improved in the past 2 decades with the discovery and development of immunosuppressive drugs such as calcineurin inhibitors, antiproliferative agents, and mammalian target of rapamycin inhibitors. However, individualized dosage regimens have not yet been fully established for these drugs except for therapeutic drug monitoring-based dosage modification because of extensive interindividual variations in immunosuppressive drug pharmacokinetics. The variations in immunosuppressive drug pharmacokinetics are attributed to interindividual variations in the functional activity of cytochrome P450 enzymes, UDP-glucuronosyltransferases, and ATP-binding cassette subfamily B member 1 (known as P-glycoprotein or multidrug resistance 1) in the liver and small intestine. Some genetic variations have been found to be involved to at least some degree in pharmacokinetic variations in post-transplant immunosuppressive therapy. It is well known that the frequencies and effect size of minor alleles vary greatly between different races. Thus, ethnic considerations might provide useful information for optimizing individualized immunosuppressive therapy after organ transplantation. Here, we review ethnic factors affecting the pharmacokinetics of immunosuppressive drugs requiring therapeutic drug monitoring, including tacrolimus, cyclosporine, mycophenolate mofetil, sirolimus, and everolimus.

Individual Lymphocyte Sensitivity to Steroids as a Reliable Biomarker for Clinical Outcome after Steroid Withdrawal in Japanese Renal Transplantation

Recently, steroid reduction/withdrawal regimens have been attempted to minimize the side effects of steroids in renal transplantation. However, some recipients have experienced an increase/resumption of steroid administrations and acute graft rejection (AR). Therefore, we investigated the relationship between the individual lymphocyte sensitivity to steroids and the clinical outcome after steroid reduction/withdrawal. We cultured peripheral blood mononuclear cells (PBMCs) isolated from 24 recipients with concanavalin A (Con A) in the presence of methylprednisolone (MPSL) or cortisol (COR) for four days, and the 50% of PBMC proliferation (IC₅₀) values and the PBMC sensitivity to steroids were calculated. Regarding the experience of steroid increase/resumption and incidence of AR within one year of steroid reduction/withdrawal, the IC₅₀ values of these drugs before transplantation in the clinical event group were significantly higher than those in the event-free group. The cumulative incidence of steroid increase/resumption and AR in the PBMC high-sensitivity groups to these drugs before transplantation were significantly lower than those in the low-sensitivity groups. These observations suggested that an individual’s lymphocyte sensitivity to steroids could be a reliable biomarker to predict the clinical outcome after steroid reduction/withdrawal and to select the patients whose dose of steroids can be decreased and/or withdrawn after transplantation.

Late-onset allograft rejection, cytomegalovirus infection, and renal allograft loss: Is anti-CMV prophylaxis required following late-onset allograft rejection?

Renal transplant recipients remain at risk of delayed-onset cytomegalovirus (CMV) infection occurring beyond a complete course of prophylaxis. In this retrospective cohort, all 278 patients who received renal allografts from deceased donors from 2014 to 2016 were followed until September 1, 2019. We determined the effect of early-vs late-onset acute rejection (EAR vs LAR [ie, occurring beyond 12 months after transplantation]) on CMV infection and subsequently long-term allograft outcome. Median (IQR) duration of follow-up was 1186.0 (904.7-1531.2) days. Seventy patients including 49 patients with EAR and 21 with LAR received augmented immunosuppression. In the same interval, 40 patients developed CMV infection (36 patients beyond 90 days after transplantation [90%]). In logistic regression analysis, D+/R- CMV serostatus (OR: 5.5, 95% CI: 2.5-12.2) and LAR (OR: 7.9, 95% CI: 2.8-22.2) significantly increased the risk of CMV infection. In Cox proportional hazard model, delayed-onset CMV infection (HR: 2.51, 95% CI: 1.08-5.86) and LAR (HR: 5.46, 95% CI: 2.26-13.14) significantly increased the risk of allograft loss. Patients with LAR are at risk of late-onset CMV infection. Post-LAR, targeted prophylaxis may reduce the risk of CMV infection and subsequently allograft loss. Further studies are required to demonstrate the effect of targeted prophylaxis following LAR.