Human leukocyte antigen in the allocation of kidneys from cadaveric donors in the United States

HLA Mismatching Strategies for Solid Organ Transplantation - A Balancing Act

HLA matching provides numerous benefits in organ transplantation including better graft function, fewer rejection episodes, longer graft survival, and the possibility of reduced immunosuppression. Mismatches are attended by more frequent rejection episodes that require increased immunosuppression that, in turn, can increase the risk of infection and malignancy. HLA mismatches also incur the risk of sensitization, which can reduce the opportunity and increase waiting time for a subsequent transplant. However, other factors such as donor age, donor type, and immunosuppression protocol, can affect the benefit derived from matching. Furthermore, finding a well-matched donor may not be possible for all patients and usually prolongs waiting time. Strategies to optimize transplantation for patients without a well-matched donor should take into account the immunologic barrier represented by different mismatches: what are the least immunogenic mismatches considering the patient’s HLA phenotype; should repeated mismatches be avoided; is the patient sensitized to HLA and, if so, what are the strengths of the patient’s antibodies? This information can then be used to define the HLA type of an immunologically optimal donor and the probability of such a donor occurring. A probability that is considered to be too low may require expanding the donor population through paired donation or modifying what is acceptable, which may require employing treatment to overcome immunologic barriers such as increased immunosuppression or desensitization. Thus, transplantation must strike a balance between the risk associated with waiting for the optimal donor and the risk associated with a less than optimal donor.

Kidney transplantation and the intensity of poverty in the contiguous United States

BACKGROUND

Geographic variation in kidney transplantation rates in the United States has been described previously but remains unexplained by age, race, sex, or socioeconomic status differences. Geographic variations in the concentration of poverty appear to impact end-stage renal disease care and potentially access to transplantation.

METHODS

We studied the impact of how spatial topography of poverty across geographical regions in the contiguous United States is associated with kidney transplantation in the 48 contiguous U.S. states.

RESULTS

We found considerable geographic variation in transplantation rates across the country that persisted across quartiles of county-level median household income and percentage minority population. Higher transplant rates were seen with increasing median household income and decreasing minority populations but were not influenced by education level. Transplantation rates in counties with poverty rates above the national average had low transplant rates, but these rates were influenced by the poverty level in the surrounding counties. Similarly, wealthy counties had higher transplant rates but were lowered in counties of relative wealth that were surrounded by less wealthy counties.

CONCLUSIONS

Our results underline the geographical heterogeneity of kidney transplantation in the United States and identify regions of the country most likely to benefit from interventions that may reduce disparities in transplantation.

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.

A comparative study of the traditional method, and a point-score system for allocation of deceased-donor kidneys: a national multicenter study in Mexico

BACKGROUND

The National Transplant Center in Mexico has ruled that deceased-donor kidney allocation is a function of each hospital's Internal Transplant Committee. The aim of this study was to compare and analyze results for of the traditional method and a point-score system in the allocation of deceased patient's kidneys.

METHODS

The 12 major kidney transplant centers in the country having a deceased-donor program were invited to participate. Only 3 of them replied to the invitation during 2010. A point-score system was proposed to them, comprising blood group, waiting list time, HLA type, and donor and recipient ages. Once the final recipient was chosen, an explanation of reasons for the choice was requested. Thirty-eight transplants were presented. Kappa coefficient was used to measure degree of agreement in both allocation systems. Organs donated for transplantation came from patients between 4 and 54 years old, including 52% female, 52% O+ blood type, 31% A+, and 11% B+, 44% cranial-encephalic trauma, and 44% brain hemorrhage.

RESULTS

Global agreement was 52.6% (kappa = 0.343), and partial agreement was 76.3% (weighted kappa = 0.204), assigning more intensity to extreme values, but with a lower correlation index. A more intense agreement, without discriminating by hospital, was found for "A" category (blood group), followed by "B" category (waiting list time).

DISCUSSION

Taking into consideration the determining factors for long-term graft survival, it is indispensable to include criteria such as donor and recipient ages and HLA typife in the allocation process. This first draft of a point-score system in organ allocation included waiting list time, blood group, urgency related to vascular/peritoneal access for dialysis, clinical condition, donor/recipient age ratio, and HLA antigenic compatibility.

Saving lives branch by branch: the effectiveness of driver licensing bureau campaigns to promote organ donor registry sign-ups to African Americans in Michigan

African Americans are disproportionately represented on the national waiting list for organ transplantation. Promoting organ donor registries is one way to improve the possibility that those on the waiting list can receive a life saving transplant. Driver licensing bureaus have been suggested as an efficient site for campaigns aimed at increasing state-based registry sign-ups. Previous research has suggested these campaigns work well for Caucasian populations, but there is less evidence supporting this approach in more diverse populations. To determine whether more diverse populations demonstrate similar sign-up rates when receiving a driver licensing bureau campaign, the present study used a previously successful strategy as the basis for designing and disseminating materials that would appeal to African Americans and Caucasians in two diverse counties in the state of Michigan (Wayne and Oakland Counties). Communication design and media priming served as the theoretical foundations of a three-prong campaign that used mass media, point-of-decision, and interpersonal components. Results from countywide and zip code data indicate that the campaign greatly increased sign-ups among African American residents (700% increase above baseline). Although more Caucasians still signed up than did African Americans, the inclusion of an interpersonal component resulted in similar numbers of registry sign-ups during 2 intervention months. The study provides evidence supporting the use of driver licensing bureau campaigns to promote organ donation registries to diverse audiences.

Effect of eliminating priority points for HLA-B matching on racial disparities in kidney transplant rates

BACKGROUND

African Americans have lower rates of obtaining a deceased donor kidney transplant (DDKT) compared with their white counterparts. One proposed mechanism is differential HLA distributions between African Americans and whites. In May 2003, the United Network for Organ Sharing/Organ Procurement and Transplantation Network changed kidney allocation policy to eliminate priority based on HLA-B matching in an effort to address this disparity. The objective of this study was to quantify the effect of the change in policy regarding priority points for HLA-B matching.

STUDY DESIGN

Observational cohort study.

SETTING & PARTICIPANTS

A cohort of 178,902 patients registered for a DDKT between January 2000 and August 2009.

FACTORS

African Americans versus whites before and after the policy change. Cox models were adjusted for age, sex, diabetes, dialysis type, insurance status, education, panel-reactive antibody level, and blood type.

OUTCOMES

Adjusted relative rates (aRRs) of deceased donor kidney transplant for African Americans compared with whites.

MEASUREMENTS

Time from initial active wait listing to DDKT, censored for living donor kidney transplant and death.

RESULTS

Before the policy change, African Americans had 37% lower rates of DDKT (aRR, 0.63; 95% CI, 0.60-0.65; P < 0.001). After the policy change, African Americans had 23% lower rates of DDKT (aRR, 0.77; 95% CI, 0.76-0.79; P < 0.001). There was a 23% reduction in the disparity between African Americans and whites after the policy change (interaction aRR, 1.23; 95% CI, 1.18-1.29; P < 0.001).

LIMITATIONS

As an observational study, findings could have been affected by residual confounding or other changes in practice patterns.

CONCLUSIONS

Racial disparity in rates of DDKT was decreased by the HLA-B policy change, but parity was not achieved. There are unaddressed factors in kidney allocation that lead to continued disparity on the kidney transplant waiting list.

Predicting HLA class I alloantigen immunogenicity from the number and physiochemical properties of amino acid polymorphisms

BACKGROUND

Knowledge of the human leukocyte antigen (HLA) amino acid (AA) sequence combined with crystallographic structural data may enable prediction of the relative immunogenicity of individual donor/recipient HLA mismatches.

METHODS

Multiple sera from 32 highly sensitized patients awaiting kidney transplantation were screened using Luminex/single-antigen beads to determine the HLA-specific antibody levels against mismatched HLA class I specificities. A computer program was developed to allow intralocus and interlocus comparison of mismatched HLA-A and -B specificities with corresponding recipient HLA class I type, and to determine the number, position, and physiochemical disparity (hydrophobicity and electrostatic charge) of polymorphic AA.

RESULTS

HLA-specific antibody was detected against 1666 (85%) of the 1964 mismatched HLA specificities evaluated, with a close correlation between increasing number of AA polymorphisms and the presence and magnitude of the alloantibody response (P<0.0001). Hydrophobicity and electrostatic charge disparity scores were independent predictors of alloantibody production (adjusted P=0.0009 and P=0.0005, respectively). Mismatched specificities with physiochemical scores within the first decile of the scale led to weak alloantibody responses (median fluorescence intensity 2330), whereas those with scores above the sixth decile led to strong alloantibody production (median fluorescence intensity >10,000).

CONCLUSION

Differences in AA number, hydrophobicity, and electrostatic charge between HLA class I specificities enable prediction of donor HLA class I types with low immunogenicity for a given recipient.

Renal Transplantation in High-Risk Patients

Renal transplantation in high-risk patients is a growing phenomenon. More patients are progressing to endstage renal failure, in the setting of an increased incidence of diabetes mellitus and cardiovascular disease. Current organ shortages and the use of more marginal donors have affected both patient and graft survival. Acute rejection has been minimised under modern immunosuppression; however, patient and long-term allograft outcomes have not improved concurrently. Specific understanding of donor, recipient and allograft variables associated with stratification of patients as 'high risk for renal transplantation' is necessary to facilitate appropriate peri- and post-transplant pharmacotherapy. Induction and maintenance immunosuppression choices are different for high-risk patients and must be made to ensure optimal immunosuppression, while limiting patient and allograft toxicity.

Ageism and kidney transplantation

The growing shortage of deceased-donor kidneys and the rapid growth in the number of patients with end-stage renal failure aged 65 years and older is impacting the current policies for allocation of allografts. The utilitarian and egalitarian philosophies may clash in times of limited resources. Organ transplantation can be viewed as a microcosm concerning healthcare issues facing an aging population and limited resources. The limited resources in organ transplantation are not merely financial. The limits on supply of deceased-donor organs will force the transplant community to deal with allocation issues before the more general population faces other limits in health care. Our discussions may clarify some of the problems.

Predictive value of human leucocyte antigen epitope matching using HLAMatchmaker for graft outcomes in a predominantly African-American renal transplant cohort

The HLAMatchmaker program is based on the donor/recipient comparison of the polymorphic triplet amino-acid sequences of the antibody-accessible regions on the human leucocyte antigen (HLA) molecule. The previous reports on its predictive value for renal allograft outcomes are conflicting. We conducted a retrospective study in a predominantly African-American (AA) cohort (N = 101, 94% AA). HLA typing was performed by molecular methods and triplet matching using HLAMatchmaker. Study end points included graft survival and incidence of acute rejection. The relationship between the number of triplet mismatches (TMM) and the degree of HLA antigen MM was evaluated using Pearson's correlation coefficient. Logistic regression models were used to examine the association between triplet matching and the study end points. Kaplan-Meier and Cox proportional hazard models were used for graft survival analysis. The strongest relationship between the number of TMM and HLA antigen MM was observed for HLA-DQ (r = 0.88). The association between triplet matching at HLA-A, -B, -DR and -DRw HLA loci and the study end points was not statistically significant. However, after grouping, the unadjusted estimates of graft survival for those with more than 10 Class I TMM were significantly worse than the others (p = 0.03). Adjusting for the effect of donor source, recipient characteristics and the immunosuppressive regimen did not change this association (hazard ratio = 0.2, confidence interval = 0.04-1.1). We conclude that triplet matching using HLAMatchmaker can provide useful prognostic information in kidney transplantation and that more than 10 donor/recipient Class I HLA TMM is predictive of worse graft outcome.

Les nouvelles règles de répartition des greffons rénaux en France

The French rules for the attribution of a kidney transplant are regularly evaluated and modified according to scientific progress, evolution of the waiting list and of health policies. Modifications, initiated by the Transplantation Commission of the French-speaking Society of Nephrology, have been introduced in 2004 by the Etablissement français des Greffes and aim at decreasing the number of patients on the waiting list having difficult access to transplantation because of their immunogenetic characteristics (rare ABO or HLA group, HLA immunization). Four points are concerned: 1/ better definition of hyperimmunisation; 2/ introduction of a program based on "acceptable mismatches" as a new priority for hyperimmunized patients; 3/ suppression of the full-match priority to non-immunized patients; 4/ attribution to immunized patients (anti-HLA antibodies=5-80%) who have difficult access to a transplant, of priorities similar to those followed for hyperimmunized patients. This article presents the new rules for the allocation of a kidney transplant and the rationale for the current modifications.

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.

Application of human leukocyte antigen matching in the allocation of kidneys from cadaveric organ donors in the Nordic countries

The Nordic organ exchange organization Scandiatransplant was founded in 1969. It covers a population of 24.41 million inhabitants in five countries: Denmark (5.45 million), Finland (5.19 million), Iceland (0.29 million), Norway (4.54 million), and Sweden (8.94 million). Initially, the purpose of Scandiatransplant was to establish and maintain a common waiting list for all Nordic patients with end-stage renal failure waiting for a cadaveric kidney transplant. The basis of maintaining a common Nordic waiting list was the recognition of the wide polymorphism of the human leukocyte antigen system, which demands a substantial pool of waiting patients to provide optimal histocompatibility matching between organ donor and recipient. Thus, one of the major tasks of the organization was and still is to specify rules for the exchange of kidneys between the participating transplant centers. Scandiatransplant includes the cooperation of all 10 Nordic kidney transplant centers in addition to eight immunology laboratories. Denmark has four transplant centers located in Copenhagen, Herlev, Odense, and Aarhus. Finland has one center in Helsinki. Norway has one center located in Oslo. Sweden has four kidney transplantation centers located in each of the university hospitals in Göteborg, Malmö, Stockholm, and Uppsala. The fifth Nordic country, Iceland, is participating fully in organ donation but has no individual transplant center. Organ transplantation in Icelandic patients is performed in other Nordic countries.

Allocation of cadaver donor kidneys in Australia

The national allocation of kidneys in Australia is based on a combination of human leukocyte antigen (HLA) matching and equity factors designed to make transplantation accessible to as many patients as possible. A points system has been designed that deducts points for HLA mismatches but adds points for factors such as levels of HLA sensitization, waiting time on dialysis, and a loading for pediatric patients. Kidneys that do not reach the level of matching required for national allocation are transplanted in the donor state using both matching and waiting time criteria, which caters to minority groups with rare HLA types.