HLA matching and the United Network for Organ Sharing Allocation System: impact of HLA matching on African-American recipients of cadaveric kidney transplants

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.

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

Black kidney transplant recipients have more acute rejection (AR) and inferior graft survival. We sought to determine whether early steroid withdrawal (ESW) had an impact on AR and death-censored graft loss (DCGL) in blacks. From 2006 to 2012, AR and graft survival were analyzed in 483 kidney recipients (208 black and 275 non-black). Rates of ESW were similar between blacks (65%) and non-blacks (67%). AR was defined as early (≤3 months) or late (>3 months). The impact of black race, early AR, and late AR on death-censored graft failure was analyzed using univariate and multivariate Cox models. Blacks had greater dialysis vintage, more deceased donor transplants, and less HLA matching, yet rates of early AR were comparable between blacks and non-blacks. However, black race was a risk factor for late AR (HR: 3.48 (95% CI: 1.87-6.47)) Blacks had a greater rate of DCGL, partially driven by late AR (HR with late AR: 5.6; 95% CI: 3.3-9.3). ESW had no significant interaction with black race for risk of early AR, late AR, or DCGL. Independent of ESW, black kidney recipients had a higher rate of late AR after kidney transplantation. Late AR was highly predictive of DCGL and contributed to inferior graft survival in blacks.

Improving Medication Safety and Cardiovascular Risk Factor Control to Mitigate Disparities in African-American Kidney Transplant Recipients: Design and Methods

There is a lack of data analyzing the influence of cardiovascular disease (CVD) risk factor control on graft survival disparities in African-American kidney transplant recipients. Studies in the general population indicate that CVD risk factor control is poor in African-Americans, leading to higher rates of renal failure and major acute cardiovascular events. However, with the exception of hypertension, there is no data demonstrating similar results within transplant recipients. Recent analyses conducted by our investigator group indicate that CVD risk factors, especially diabetes, are poorly controlled in African-American recipients, which likely impacts graft loss. This study protocol describes a prospective interventional clinical trial with the goal of demonstrating improved medication safety and CVD risk factor control in adult solitary kidney transplant recipients at least one-year post-transplant with a functioning graft. This is a prospective, interventional, 6-month, pharmacist-led and technology enabled study in adult kidney transplant recipients with the goal of improving CVD risk factor outcomes by improving medication safety and patient self-efficacy. This papers describes the issues related to racial disparities in transplant, the details of this intervention and how we expect this intervention to improve CVD risk factor control in kidney transplant recipients, particularly within African-Americans.

A Comparative Effectiveness Analysis of Early Steroid Withdrawal in Black Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

There is continued debate whether early steroid withdrawal is safe to use in high-immunologic risk patients, such as blacks. The goal of this study was to use comparative effectiveness methodology to elucidate the safety of early steroid withdrawal in blacks with kidney transplants.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Our cohort study used United Network of Organ Sharing data including all adult black kidney transplant recipients from 2000 to 2009 followed through 2014. Propensity score matching was used to equalize baseline risk between continued steroid and early steroid withdrawal groups. Interaction terms were used to assess if the effect of early steroid withdrawal on outcomes varied by baseline and post-transplant factors. Of 26,582 eligible black patients with kidney transplants (5825 [21.9%] with early steroid withdrawal), 5565 patients with early steroid withdrawal were matched to 5565 blacks on continued steroid use.

RESULTS

Black patients with early steroid withdrawal had similar risk of graft loss (hazard ratio, 0.98; 95% confidence interval, 0.92 to 1.04; P=0.42) and lower risk of death (hazard ratio, 0.91; 95% confidence interval, 0.84 to 0.99; P=0.02), primarily driven by a late mortality advantage (>4 years post-transplant). Delayed graft function, cytolytic induction, tacrolimus, and mycophenolate significantly modified the effect of early steroid withdrawal on outcomes (P<0.05). Acute rejection rates were slightly higher in the continued steroid group (13.0% versus 11.3%, respectively; P<0.01), but this was not associated with graft or patient survival.

CONCLUSIONS

Overall, early steroid withdrawal in black kidney transplant recipients was not associated with graft loss but seemed to be associated with better long-term patient survival. Early steroid withdrawal in blacks not receiving cytolytic induction, tacrolimus, and mycophenolate or those with delayed graft function was associated with higher risk of graft loss and death.

Impact of Cardiovascular Risk Factors on Graft Outcome Disparities in Black Kidney Transplant Recipients

Although outcome inequalities for non-Hispanic black (NHB) kidney transplant recipients are well documented, there is paucity in data assessing the impact of cardiovascular disease (CVD) risk factors on this disparity in kidney transplantation. This was a longitudinal study of a national cohort of veteran kidney recipients transplanted between January 2001 and December 2007. Data included baseline characteristics acquired through the United States Renal Data System linked to detailed clinical follow-up information acquired through the Veterans Affairs electronic health records. Analyses were conducted using sequential multivariable modeling (Cox regression), incorporating blocks of variables into iterative nested models; 3139 patients were included (2095 non-Hispanic whites [66.7%] and 1044 NHBs [33.3%]). NHBs had a higher prevalence of hypertension (100% versus 99%; P<0.01) and post-transplant diabetes mellitus (59% versus 53%; P<0.01) with reduced control of hypertension (blood pressure <140/90 60% versus 69%; P<0.01), diabetes mellitus (A1c <7%, 35% versus 47%; P<0.01), and low-density lipoprotein (<100 mg/dL, 55% versus 61%; P<0.01). Adherence to medications used to manage CVD risk was significantly lower in NHBs. In the fully adjusted models, the independent risk of graft loss in NHBs was substantially reduced (unadjusted hazard ratio, 2.00 versus adjusted hazard ratio, 1.49). CVD risk factors and control reduced the influence of NHB race by 9% to 18%. Similar trends were noted for mortality, and estimates were robust across in sensitivity analyses. These results demonstrate that NHB kidney transplant recipients have significantly higher rates of CVD risk factors and reduced CVD risk control. These issues are likely partly related to medication nonadherence and meaningfully contribute to racial disparities for graft outcomes.

African-American race modifies the influence of tacrolimus concentrations on acute rejection and toxicity in kidney transplant recipients

STUDY OBJECTIVE

To determine the effect of tacrolimus trough concentrations on clinical outcomes in kidney transplantation, while assessing if African-American (AA) race modifies these associations.

DESIGN

Retrospective longitudinal cohort study of solitary adult kidney transplants.

SETTING

Large tertiary care transplant center.

PATIENTS

Adult solitary kidney transplant recipients (n=1078) who were AA (n=567) or non-AA (n=511).

EXPOSURE

Mean and regressed slope of tacrolimus trough concentrations. Subtherapeutic concentrations were lower than 8 ng/ml.

MEASUREMENTS AND MAIN RESULTS

AA patients were 1.7 times less likely than non-AA patients to achieve therapeutic tacrolimus concentrations (8 ng/ml or higher) during the first year after kidney transplant (35% vs 21%, respectively, p<0.001). AAs not achieving therapeutic concentrations were 2.4 times more likely to have acute cellular rejection (ACR) as compared with AAs achieving therapeutic concentrations (20.8% vs 8.5%, respectively, p<0.01) and 2.5 times more likely to have antibody-mediated rejection (AMR; 8.9% vs 3.6%, respectively, p<0.01). Rates of ACR (8.3% vs 6.7%) and AMR (2.0% vs 0.9% p=0.131) were similar in non-AAs compared across tacrolimus concentration groups. Multivariate modeling confirmed these findings and demonstrated that AAs with low tacrolimus exposure experienced a mild protective effect for the development of interstitial fibrosis/tubular atrophy (IF/TA; hazard ratio [HR] 0.78, 95% confidence interval [CI] 0.47-1.32) with the opposite demonstrated in non-AAs (HR 2.2, 95% CI 0.90-5.1).

CONCLUSION

In contradistinction to non-AAs, AAs who achieve therapeutic tacrolimus concentrations have substantially lower acute rejection rates but are at risk of developing IF/TA. These findings may reflect modifiable time-dependent racial differences in the concentration-effect relationship of tacrolimus. Achievement of therapeutic tacrolimus trough concentrations, potentially through genotyping and more aggressive dosing and monitoring, is essential to minimize the risk of acute rejection in AA kidney transplant recipients.

Preemptive deceased donor kidney transplantation: considerations of equity and utility

BACKGROUND AND OBJECTIVES

There exists gross disparity in national deceased donor kidney transplant availability and practice: waiting times exceed 6 years in some regions, but some patients receive kidneys before they require dialysis. This study aimed to quantify and characterize preemptive deceased donor kidney transplant recipients and compare their outcomes with patients transplanted shortly after dialysis initiation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Using the Scientific Registry of Transplant Recipients database, first-time adult deceased donor kidney transplant recipients between 1995 and 2011 were classified as preemptive, early (on dialysis ≤1 year), or late recipients. Random effects logistic regression and multivariate Cox proportional hazards regression were used to identify characteristics of preemptive deceased donor kidney transplant and evaluate survival in preemptive and early recipients, respectively.

RESULTS

Preemptive recipients were 9.0% of the total recipient population. Patients with private insurance (adjusted odds ratio=3.15, 95% confidence interval=3.01-3.29, P<0.001), previous (nonkidney) transplant (adjusted odds ratio=1.94, 95% confidence interval=1.67-2.26, P<0.001), and zero-antigen mismatch (adjusted odds ratio=1.45, 95% confidence interval=1.37-1.54, P<0.001; Caucasians only) were more likely to receive preemptive deceased donor kidney transplant, even after accounting for center-level clustering. African Americans were less likely to receive preemptive deceased donor kidney transplant (adjusted odds ratio=0.44, 95% confidence interval=0.41-0.47, P<0.001). Overall, patients transplanted preemptively had similar survival compared with patients transplanted within 1 year after initiating dialysis (adjusted hazard ratio=1.06, 95% confidence interval=0.99-1.12, P=0.07).

CONCLUSIONS

Preemptive deceased donor kidney transplant occurs most often among Caucasians with private insurance, and survival is fairly similar to survival of recipients on dialysis for <1 year.

Transplanting kidneys without points for HLA-B matching: consequences of the policy change

In 2003, the US kidney allocation system was changed to eliminate priority for HLA-B similarity. We report outcomes from before and after this change using data from the Scientific Registry of Transplant Recipients (SRTR). Analyses were based on 108 701 solitary deceased donor kidney recipients during the 6 years before and after the policy change. Racial/ethnic distributions of recipients in the two periods were compared (chi-square); graft failures were analyzed using Cox models. In the 6 years before and after the policy change, the overall number of deceased donor transplants rose 23%, with a larger increase for minorities (40%) and a smaller increase for non-Hispanic whites (whites) (8%). The increase in the proportion of transplants for non-whites versus whites was highly significant (p < 0.0001). Two-year graft survival improved for all racial/ethnic groups after implementation of this new policy. Findings confirmed prior SRTR predictions. Following elimination of allocation priority for HLA-B similarity, the deficit in transplantation rates among minorities compared with that for whites was reduced but not eliminated; furthermore, there was no adverse effect on graft survival.

Renal transplantation in the United Kingdom for patients from ethnic minorities

BACKGROUND

To investigate any differences in access to transplant and post-transplant outcomes for ethnic minority patients in the United Kingdom, national data on ethnicity of patients on the waiting list, those receiving a transplant, and deceased donors were analyzed.

METHODS

Adult patients and donors were included. Ethnic origin was classified as white, Asian, black, or "other." National data were analyzed, and 2001 U.K. National census data were used for comparative purposes. Median waiting times to transplant were obtained from Kaplan-Meier estimates for patients registered 1998-2000. Transplant survival was estimated for patients transplanted from 1998 to 2003.

RESULTS

A total of 92% of the U.K. population was white, compared with 77% of waiting list patients, 88% of transplant recipients, and 97% of deceased donors. Median waiting time to transplantation for white patients was 719 days (95% confidence interval 680-758) compared with 1368 (1131-1605) days for Asian patients and 1419 (1165-1673) days for black patients. The degree of human leukocyte antigen matching achieved was inferior for Asian and black patients. There is some evidence of inferior 3-year transplant survival for black patients compared with white and Asian patients (P=0.03).

CONCLUSIONS

There are imbalances in the ethnic make up of the waiting list, the donor pool, and renal transplant recipients. There are significant differences in both post-transplant outcomes and time to transplantation between patients of different ethnic origin. Waiting times are influenced by allocation schemes, and the 2006 U.K. National Kidney Allocation Scheme is designed to achieve greater equity of access to transplant for all patients, regardless of geography, blood group, or ethnicity.

Access to Kidney Transplantation in France of Non-French Patients and French Patients Living in Overseas Territories

BACKGROUND

In France, foreign patients, whether resident or not in France, can register on the national waiting list under certain conditions. We compared waiting time to kidney transplantation, the level of HLA matching and graft cold ischemia time between foreign patients and French patients living in mainland France or in French overseas territories (FOT).

METHODS

We performed a retrospective cohort survey using the nationwide registry. Between 1996 and 2003, 18,595 patients were registered on the French waiting list. Of these, 9.9% were of non-French nationality (0.7% Greek, 1.4% Italian, 1.5% other European, 3.7% North African, 1.8% sub-Saharan African and 0.9% other), and 3.8% were French nationals living in FOT.

RESULTS

Median waiting time differed significantly between groups, from 13.8 months for mainland French patients to 39.5 months for sub-Saharan African patients. After adjustment for other factors significantly linked to waiting time, French residents of FOT (RR=0.83; P<0.001) and patients from sub-Saharan Africa (RR=0.75; P<0.0001) were found to wait significantly longer than other patients. HLA matching level, particularly HLA-A and HLA-B, was worse for African patients. After adjustment for the transplant team, cold ischemia time was found to be longer for Greeks (30.4 hr, P<0.0001) and French patients living in FOT (33.3 hr, P<0.0001) than for mainland French patients (21.2 hr). CONCLUSIONS.: Programs promoting organ donation aimed at minorities of African origin should improve their access to transplantation in France. We also need to strengthen international cooperation programs in certain countries to assist access to transplantation and to increase graft quality.

Significant differences in the efficacy of kidney transplantation between Hungarian Caucasians and Gypsies

In a retrospective study we examined the differences between Caucasian (Group A) and Gypsy (Group B) renal allograft recipients transplanted in Hungary. From 1983 to 2001, 1918 transplants were performed in Budapest (1825 Caucasian and 93 Gypsy recipients). Group B patients were younger (34 +/- 12 vs 42 +/- 14 years of age; P < .01) and Group A had more polycystic kidney disease (12% vs 3%; P < .025). Blood group B was more common in Group B (27% vs 19%; P = NS) than in Group A patients, and Group A had seemingly more diabetes (5% vs 1%; P = NS) than did Group B. There were no differences in HLA mismatches or panel reactive antibodies (PRA). No differences were seen in Group A vs Group B patient survivals at 1, 3, 5, or 10 years' posttransplant (98% vs 95%; 90% vs 93%; 85% vs 88%; and 74% vs 82%, respectively). However, Group A graft survivals were significantly better than Group B at 1, 3, 5, and 10 years' posttransplant (89% vs 77%; 82% vs 66%; 76% vs 54%; and 57% vs 34%; each comparison P < .01). Group B recipients experienced a greater number of acute rejection episodes (66% vs 49%; P < .01), irreversible acute rejections (15% vs 6%; P < .001), chronic rejections (34% vs 18%; P < .001), and graft loss due to immunosuppression noncompliance (5% vs 1%; P < .05) than did Group A recipients. As has been previously described for other non-Caucasian ethnic groups (eg, African-Americans), Hungarian Gypsies appear to be at a greater immunological risk for rejection and poorer long-term graft survival.

Significant HLA matching effect in a large urban transplant center composed primarily of minorities

In more than 1300 deceased donor transplants, including 75% Hispanics, African-Americans, and Asians, a significant effect of mismatching (MM) was observed for zero to three MM compared to more than three MM (P < .02). There was a significantly better patient survival (P < .002), shorter hospital stay (P < .001), and a trend toward lowered immunosuppression. Zero to three MM were present in 48% of the recipient population in part due to the pre-UNOS algorithm that assigns points for zero MM and other MM grades. However, recently only zero MM receive points, therefore fewer zero to three MM recipients would be expected. The largest minority population is Hispanic. We postulated that at least part of the effect was associated with socioeconomic status and English as a second language parameters of our Hispanic population. Zero to three MM was found to decrease risk and should be used prospectively in minority donor/recipient combinations.

Health disparities in transplantation: focus on the complexity and challenge of renal transplantation in African Americans

The field of renal transplantation has grown exponentially as a result of a greater understanding of the immune system and the advent of numerous immunosuppressive agents. Although African Americans and whites have benefited from these advances, equivalent long-term success eludes African Americans who are disadvantaged in gaining access to renal transplantation. This review summarizes the obstacles for African Americans to end-stage renal disease(ESRD) care, focusing on transplantation. Factors that predispose African Americans for ESRD, impede this ethnic group from timely transplantation, and negatively influence graft survival are examined. Possible solutions to these persistent problems are offered.

???Don???t Know Enough about It!???: Awareness and Attitudes Toward Organ Donation and Transplantation among the Black Caribbean and Black African Population in Lambeth, Southwark, and Lewisham, United Kingdom

BACKGROUND

The current demand for transplant organs, particularly kidneys, far outweighs the supply in the United Kingdom. This problem is particularly severe for the black African and black Caribbean population, who have been shown to have a disproportionately greater presentation on kidney transplant waiting lists in some regions of the United Kingdom. The situation is clear: There is an urgent need to address the number of black African and black Caribbean patients requiring a kidney transplant, otherwise the human and economic costs will be high.

METHODS

An exploratory study was undertaken to assess the current awareness of organ donation and transplantation and to explore attitudes toward these issues in a cross-section of the black African and black Caribbean population in Lambeth, Southwark, and Lewisham.

RESULTS

It was found that there was a lack of available information for the black African and black Caribbean communities. This precipitated low levels of awareness about organ donation and transplantation issues.

CONCLUSIONS

In an effort to redress this, effective methods for targeting black African and black Caribbean groups are required. From this study, there are indications that appeals for organ donors may be more effectively communicated by using a grass-roots, community-network approach. For this reason, consideration should be given to language and cultural needs, and to the provision of culturally sensitive material and information.

The case to abandon human leukocyte antigen matching for kidney allocation: would it be wise to throw out the baby with the bathwater?

Since major histocompatibility (MHC) antigen matching was introduced in the early 1970s as the key factor determining kidney transplant allocation, several studies, mainly arising from organ-sharing organizations in the United States and Europe, have debated this complex issue. The first fundamental concern is the interaction of human leukocyte antigen matching with other transplant outcome risk factors, for example, prolongation of ischemia and matching for age. Much concordant data advocate restraining MHC antigen-based allocation in terms of space and time limits. The second fundamental concern is the balancing of the advantages of better antigen matching in terms of improved graft survival and the improved transplantation rate in immunologically high-risk patients with the major drawback of inequitable access for ethnic minorities and patients with rare MHC haplotypes. These issues have led to considering renewed kidney allocation rules, discarding human leukocyte antigen matching from algorithms, or modifying the specificity allocation level by using cross-reactive group matching or class II MHC antigen matching. The evolving concepts in the field of histocompatibility support the need for periodically updated, flexible, and hybrid allocation systems, as designed in France by the Etablissement français des Greffes.

Human leukocyte antigen and the allocation of kidneys from cadaver donors in the United Kingdom

The national scheme currently used for the allocation of cadaver kidneys in the United Kingdom includes factors demonstrated to improve transplant outcome and promote equity in organ allocation. Introduced in 1998, the scheme is based on human leukocyte antigen matching, gives priority to children and highly sensitized patients, and incorporates features to assist transplantation in patients who are difficult to match. The scheme is open and transparent and subject to continuous audit and review to address any inequities in access to transplant that become apparent.