The New Distance-Based Kidney Allocation System: Implications for Patients, Transplant Centers, and Organ Procurement Organizations

Effects of the March 2021 Allocation Policy Change on Key Deceased-donor Kidney Transplant Metrics

BACKGROUND

A major change to deceased-donor kidney allocation in the United States, Kidney Allocation System 250 (KAS250), was implemented on March 15, 2021. Evaluating the consequences of this policy on critical system performance metrics is critical to determining its success.

METHODS

We performed a retrospective analysis of critical performance measures of the kidney transplant system by reviewing all organs procured during a 4-y period in the United States. To mitigate against possible effects of the COVID-19 pandemic, Scientific Registry of Transplant Recipients records were stratified into 2 pre- and 2 post-KAS250 eras: (1) 2019; (2) January 1, 2020-March14, 2021; (3) March 15, 2021-December 31, 2021; and (4) 2022. Between-era differences in rates of key metrics were analyzed using chi-square tests with pairwise z -tests. Multivariable logistic regression and analysis of variations methods were used to evaluate the effects of the policy on rural and urban centers.

RESULTS

Over the period examined, among kidneys recovered for transplant, nonuse increased from 19.7% to 26.4% (all between-era P < 0.05) and among all Kidney Donor Profile Index strata. Cold ischemia times increased ( P < 0.001); however, the distance between donor and recipient hospitals decreased ( P < 0.05). Kidneys from small-metropolitan or nonmetropolitan hospitals were more likely to not be used over all times ( P < 0.05).

CONCLUSIONS

Implementation of KAS250 was associated with increased nonuse rates across all Kidney Donor Profile Index strata, increased cold ischemic times, and shorter distance traveled.

Inconsistent values and algorithmic fairness: a review of organ allocation priority systems in the United States

BACKGROUND

The Organ Procurement and Transplant Network (OPTN) Final Rule guides national organ transplantation policies, mandating equitable organ allocation and organ-specific priority stratification systems. Current allocation scores rely on mortality predictions.

METHODS

We examined the alignment between the ethical priorities across organ prioritization systems and the statistical design of the risk models in question. We searched PubMed for literature on organ allocation history, policy, and ethics in the United States.

RESULTS

We identified 127 relevant articles, covering kidney (19), liver (60), lung (24), and heart transplants (23), and transplant accessibility (1). Current risk scores emphasize model performance and overlook ethical concerns in variable selection. The inclusion of race, sex, and geographical limits as categorical variables lacks biological basis; therefore, blurring the line between evidence-based models and discrimination. Comprehensive ethical and equity evaluation of risk scores is lacking, with only limited discussion of the algorithmic fairness of the Model for End-Stage Liver Disease (MELD) and the Kidney Donor Risk Index (KDRI) in some literature. We uncovered the inconsistent ethical standards underlying organ allocation scores in the United States. Specifically, we highlighted the exception points in MELD, the inclusion of race in KDRI, the geographical limit in the Lung Allocation Score, and the inadequacy of risk stratification in the Heart Tier system, creating obstacles for medically underserved populations.

CONCLUSIONS

We encourage efforts to address statistical and ethical concerns in organ allocation models and urge standardization and transparency in policy development to ensure fairness, equitability, and evidence-based risk predictions.

Outcomes of Older Primary Kidney Transplant Recipients by Induction Agent and High-risk Viral Discordance Status in the United States

Background

The impact of induction type or high-risk viral discordance on older kidney transplant recipients is unclear. Herein, we analyzed the association between induction type, viral discordance, and outcomes for older recipients.

Methods

We analyzed the Scientific Registry of Transplant Recipients standard analysis file for all primary kidney transplant recipients older than 55 y who were transplanted between 2005 and 2022. All transplants were crossmatch negative and ABO-compatible. Recipients were discharged on tacrolimus and mycophenolate ± steroids. Recipients were categorized into 3 groups by induction received: rabbit antithymocyte globulin (r-ATG; N = 51 079), interleukin-2 receptor antagonist (IL-2RA; N = 22 752), and alemtuzumab (N = 13 465). Kaplan-Meier curves were generated for recipient and graft survival, and follow-up was censored at 10 y. Mixed-effect Cox proportional hazard models examined the association between induction type, high-risk viral discordance, and outcomes of interest. Models were adjusted for pertinent recipient and donor characteristics.

Results

Induction type did not predict recipient survival in the multivariable model, whereas Epstein-Barr virus high-risk discordance predicted 14% higher mortality (1.14 [1.07-1.21], P < 0.01). In the multivariable model for death-censored graft survival, alemtuzumab, but not IL-2RA, was associated with an increased risk of graft loss (1.18 [1.06-1.29], P < 0.01) compared with r-ATG. High-risk cytomegalovirus discordance predicted 10% lower death-censored graft survival (1.10 [1.01-1.19], P < 0.02). Live donor and preemptive transplantation were favorable predictors of survival.

Conclusions

In this large cohort of older transplant recipients, alemtuzumab, but not IL-2RA, induction was associated with an increased risk of graft loss compared with r-ATG. Cytomegalovirus and Epstein-Barr virus high-risk viral discordance portended poor graft and recipient survival, respectively.

Geography, inequities, and the social determinants of health in transplantation

Among the causes of inequity in organ transplantation, geography is oft-cited but rarely defined with precision. Traditionally, geographic inequity has been characterized by variation in distance to transplant centers, availability of deceased organ donors, or the consequences of allocation systems that are inherently geographically based. Recent research has begun to explore the use of measures at various geographic levels to better understand how characteristics of a patient's geographic surroundings contribute to a broad range of transplant inequities. Within, we first explore the relationship between geography, inequities, and the social determinants of health. Next, we review methodologic considerations essential to geographic health research, and critically appraise how these techniques have been applied. Finally, we propose how to use geography to improve access to and outcomes of transplantation.

Individual- and Community-Level Socioeconomic Status and Deceased Donor Renal Transplant Outcomes

BACKGROUND

This study examined the relationship between socioeconomic status (SES), race, and ethnicity and clinical outcomes following deceased donor kidney transplant (DDKT) at a high-volume transplant center.

METHODS

This retrospective cohort study used regression models and survival analyses to examine the relationship between individual- and community-level SES, race, and ethnicity and DDKT outcomes (i.e., delayed graft function, graft failure, mortality) adjusting for potential confounders.

RESULTS

The analytic sample included 3366 patients; 40.7% (n = 1370) were female, the mean age was 54.7 (SD = 13.3) years, 49.3% were non-Hispanic White, and the median follow-up time was 39.5 months (IQR = 24.2-68.1). Patients living in the most disadvantaged communities (using the US Census data) had a higher likelihood of delayed graft function (adjusted relative risk [RR] = 1.12, p = 0.042) and a higher hazard of mortality (adjusted hazard ratio [HR] = 1.32, p = 0.025) compared to patients living in the least disadvantaged communities. Patients without a high school diploma had a higher risk of delayed graft function compared to patients with an associate degree or more (RR = 1.37, p < 0.001). Patients with public insurance coverage had a higher risk of delayed graft function (RR = 1.24, p < 0.001) and a higher hazard of mortality (HR = 1.37, p < 0.001) and graft failure (HR = 1.71, p < 0.001) compared to patients without public insurance. There were no differences in graft failure or mortality by race and ethnicity.

CONCLUSIONS

SES was not consistently associated with outcomes following DDKT; however, many of the predictors were associated with delayed graft function. With a large and diverse sample size, these findings further the heterogeneity of the present renal transplant research suggesting the need for further investigation to guide implementation of innovative strategies and interventions.

Hedgehog costimulation during ischemia-reperfusion injury potentiates cytokine and homing responses of CD4+ T cells

Introduction

Ischemia reperfusion injury (IRI) confers worsened outcomes and is an increasing clinical problem in solid organ transplantation. Previously, we identified a "PtchHi" T-cell subset that selectively received costimulatory signals from endothelial cell-derived Hedgehog (Hh) morphogens to mediate IRI-induced vascular inflammation.

Methods

Here, we used multi-omics approaches and developed a humanized mouse model to resolve functional and migratory heterogeneity within the PtchHi population.

Results

Hh-mediated costimulation induced oligoclonal and polyclonal expansion of clones within the PtchHi population, and we visualized three distinct subsets within inflamed, IRI-treated human skin xenografts exhibiting polyfunctional cytokine responses. One of these PtchHi subsets displayed features resembling recently described T peripheral helper cells, including elaboration of IFN-y and IL-21, expression of ICOS and PD-1, and upregulation of positioning molecules conferring recruitment and retention within peripheral but not lymphoid tissues. PtchHi T cells selectively homed to IRI-treated human skin xenografts to cause accelerated allograft loss, and Hh signaling was sufficient for this process to occur.

Discussion

Our studies define functional heterogeneity among a PtchHi T-cell population implicated in IRI.

Beyond donation to organ utilization in the USA

PURPOSE OF REVIEW

The deceased donor organ pool has broadened beyond young, otherwise healthy head trauma victims. But an abundance of donated organs only benefits patients if they are accepted, expeditiously transported and actually transplanted. This review focuses on postdonation challenges and opportunities to increase the number of transplants through improved organ utilization.

RECENT FINDINGS

We build upon recently proposed changes in terminology for measuring organ utilization. Among organs recovered for transplant, the nonuse rate (NUR REC ) has risen above 25% for kidneys and pancreata. Among donors, the nonuse rate (NUR DON ) has risen to 40% for livers and exceeds 70% for thoracic organs. Programme-level variation in offer acceptance rates vastly exceeds variation in the traditional, 1-year survival benchmark. Key opportunities to boost utilization include donation after circulatory death and hepatitis C virus (HCV)+ organs; acute kidney injury and suboptimal biopsy kidneys; older and steatotic livers.

SUMMARY

Underutilization of less-than-ideal, yet transplant-worthy organs remains an obstacle to maximizing the impact of the U.S. transplant system. The increased risk of inferior posttransplant outcomes must always be weighed against the risks of remaining on the waitlist. Advanced perfusion technologies; tuning allocation systems for placement efficiency; and data-driven clinical decision support have the potential to increase utilization of medically complex organs.