Current role of human leukocyte antigen matching in kidney transplantation

A novel allele, HLA-B*51:220, identified in an individual from south of Brazil

Novel allele, HLA-B*51:220 generated by a gene conversion event was identified in a Brazilian individual.

Accuracy of Programs for the Determination of Human Leukocyte Antigen Alleles from Next-Generation Sequencing Data

The human leukocyte antigen (HLA) genes code for proteins that play a central role in the function of the immune system by presenting peptide antigens to T cells. As HLA genes show extremely high genetic polymorphism, HLA typing at the allele level is demanding and is based on DNA sequencing. Determination of HLA alleles is warranted as HLA alleles are major genetic risk factors in autoimmune diseases and are matched in transplantation. Here, we compared the accuracy of several published HLA-typing algorithms that are based on next-generation sequencing (NGS) data. As genome sequencing is becoming increasingly common in research, we wanted to test how well HLA alleles can be deduced from genome data produced in studies with objectives other than HLA typing and in platforms not especially designed for HLA typing. The accuracies were assessed using datasets consisting of NGS data produced using an in-house sequencing platform, including the full 4 Mbp HLA segment, from 94 stem cell transplantation patients and exome sequences from 63 samples of the 1000 Genomes collection. In the patient dataset, none of the software gave perfect results for all the samples and genes when programs were used with the default settings. However, we found that ensemble prediction of the results or modifications of the settings could be used to improve accuracy. For the exome-only data, most of the algorithms did not perform very well. The results indicate that the use of these algorithms for accurate HLA allele determination is not straightforward when based on NGS data not especially targeted to the HLA typing and their accurate use requires HLA expertise.

The development of D antibodies after D-mismatched kidney transplantation in a setting of reduced immunosuppression

BACKGROUND

D antigens are not taken into account in the allocation of solid organs. Female transplant recipients with D antibodies as a consequence of D-mismatched kidney transplantation may develop hemolytic disease of the fetus and newborn in future pregnancies. We examined D antibody development in transplant recipients who received D-mismatched kidney transplantation in absence of D prophylaxis and in a setting of reduced immunosuppression.

STUDY DESIGN AND METHODS

From 1993 until 2015, a total of 1355 kidney patients received transplantations in our center of whom 156 received a D-mismatched graft. A retrospective analysis was conducted; frozen stored sera obtained from transplant recipients 3 months after transplantation were tested for irregular red blood cell (RBC) antibodies using a three-cell screening and an identification panel. In the case of D antibody positivity, additional testing was performed 1 month before transplantation.

RESULTS

In seven of 156 (4.5%) transplant recipients we found irregular RBC antibodies after transplantation, of which five (3.2%) were determined to be D antibodies. We observed only one (0.6%) recipient without D antibodies before transplantation.

CONCLUSION

Although the risk of D antibody development is considerably lower after D-mismatched kidney transplantation than D-mismatched pregnancy, anti-D prophylaxis may still be advisable for female transplant recipients of childbearing age.

The impact of human leukocyte antigen mismatching on graft survival and mortality in adult renal transplantation: A protocol for a systematic review and meta-analysis

BACKGROUND

Human leukocyte antigen (HLA) was important biological barrier to a successful transplantation. Quantitative evaluations of the effect of HLA mismatching on heart, liver, umbilical cord blood, and hematopoietic stem cell transplantation, have previously been reported. In new era of immunosuppression, the reported magnitude effect of HLA mismatching on survival outcomes of kidney transplantation was controversial. In addition, the current kidney allocation guideline recommendations in different countries were inconsistent in term of HLA mismatching. We undertake this study to conduct a systematic review and meta-analysis to assess the magnitude effect of HLA mismatching in adult kidney transplantation, with a particular focus on graft survival and mortality.

METHODS

The present systematic review and meta-analysis protocol was conducted following the Meta-analysis of Observational Studies in Epidemiology protocol (MOOSE-P) and the Preferred Reporting Items for Systematic Reviews and Meta-Analysis protocol (PRISMA-P). PubMed, EMBASE, Cochrane library Database will be searched without language restriction. Studies fulfill the following criteria will be eligible: included study cohorts comprising adult recipients; reported the association between HLA mismatching (per mismatches or HLA-A, -B, -DR mismatches) and posttransplant survival outcomes; provided effect estimates of hazard ratios (HRs) with 95% confidence interval (CIs). The incidence of measured outcomes was defined according to the European Renal Best Practice Transplantation Guidelines and Kidney Disease: Improving Global Outcomes Guidelines.

RESULTS

This study will quantitatively assess the association of HLA per mismatches, DR-antigen mismatches, A-antigen mismatches, and B-antigen mismatches with survival outcomes of overall graft failure, death-censored graft failure, all-cause mortality, and mortality with a functioning graft.

CONCLUSION

This study will determine the issues on what extent HLA compatibility influenced recipient and graft survival and which HLA antigen plays a more important role in kidney transplantation.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42017071894.

Analysis of OPTN/UNOS registry suggests the number of HLA matches and not mismatches is a stronger independent predictor of kidney transplant survival

HLA matching and mismatching, while inversely related, are not exact opposites. Here we determined the independent effects of HLA matching and mismatching on outcomes in deceased donor kidney transplant recipients. The United Network for Organ Sharing database (1995-2012) was utilized and analyzed for delayed graft function, one-year acute rejection, and death-censored graft survival using combined multivariable models including HLA matching and mismatching. Sensitivity analyses were performed using the subgroup of deceased donor kidney transplant patients after 2003 with more uniform HLA nomenclature and resampling analyses using bootstrapping on complete data available from 96,236 recipients. Individually, both HLA matching and mismatching showed significant associations with graft survival. Adjusting the model to take into account both matching and mismatching simultaneously, the degree of HLA mismatching lost significance while matching continued to have a significant prediction for delayed graft function, the one-year acute rejection rate, and graft survival. Sensitivity analyses and bootstrapping showed similar results for all studied outcomes. Thus, analysis of this large cohort demonstrates the apparent greater association of HLA matching over HLA mismatching on both early allograft events as well as graft survival. Future analyses should preferentially utilize HLA matching as a covariate over mismatching for accurately reflecting impact on graft outcomes.

Two novel alleles, HLA-A*02:643N and HLA-B*53:44, identified in Brazilian individuals

Two novel alleles, HLA-A*02:643N and HLA-B*53:44, generated by different mechanisms, were identified in Brazilian individuals.

Genetic predictors of long-term graft function in kidney and pancreas transplant patients

Kidney and pancreas transplantation have helped transform the lives of people with end-stage renal failure and individuals with type 1 diabetes who have poor glycaemic control/severe secondary complications, respectively. Despite an improvement in immunosuppressive regimes, operative techniques and decreased initial rejection rates, there has been little improvement in long-term graft survival rates over the past decade. Whilst limited progress has been made in establishing clinical markers of graft function, several genetic markers of long-term graft function have been identified. These genetic markers have the potential to (i) assist in selecting marginal donor organs for transplantation, (ii) provide better understanding of the mechanisms behind graft loss enabling identification of new, or repurposing, current treatments to extend graft function and (iii) provide a window of opportunity to identify and treat individuals before graft failure has occurred. This review will discuss the different genetic variants screened for a role in predicting transplant longevity, examine their findings and limitations and introduce where the future of genetic research within the transplantation field lies.

Comparative analysis of Luminex-based donor-specific antibody mean fluorescence intensity values with complement-dependent cytotoxicity & flow crossmatch results in live donor renal transplantation

Background & objectives:

Antibodies specific to donor human leucocyte antigen (HLA) play a critical role in graft rejection and graft loss. In recent years, techniques for their detection have evolved significantly providing an ever-increasing degree of sensitivity and specificity, from the conventional cell-based assays to the advanced solid-phase system based on the Luminex platform. Consensus is still evolving on the routine employment of all these methods, either stand alone or in combination. The objective of this study was to explore the near-accurate mean fluorescence intensity (MFI) cut-off values detected on Luminex platform predicting the strength of cell-based crossmatch results.

Methods:

Serum samples from 116 primary renal transplant recipients awaiting transplantation were tested for the presence of antidonor antibodies by the complement-dependent cytotoxicity (CDC) and flow crossmatch (FCXM) methods with their corresponding donors as well as for HLA-donor-specific antibodies (DSA) detection using a sensitive single antigen bead (SAB) assay.

Results:

None of the patients having HLA Class I DSA with MFI values <1000 showed positivity for T-cell FCXM or CDC crossmatch, while in the group having MFI values between 1000 and 3000, 54 per cent showed positivity for the FCXM but none by the CDC method. However, in the group having MFI values >3000, 95 per cent of cases were positive for FCXM. Further, those groups with MFI values between 3000 and 5000, only 36 per cent were positive for CDC crossmatch, while 90 per cent showed positivity in the group with MFI >7000.

Interpretation & conclusions:

A cut-off MFI value of 3000 for Luminex SAB-based assay was found to significantly correlate with the FCXM positivity while a MFI value of 7000 and above predicted a positive CDC crossmatch. MFI cut-off value obtained as a surrogate marker for CDC and FCXM tests will help in resolving the limitations of different cell-based techniques.

Alloimmune T cells in transplantation

Alloimmune T cells are central mediators of rejection and graft-versus-host disease in both solid organ and hematopoietic stem cell transplantation. Unique among immune responses in terms of its strength and diversity, the T cell alloresponse reflects extensive genetic polymorphisms between allogeneic donors and recipients, most prominently within the major histocompatibility complex (MHC), which encodes human leukocyte antigens (HLAs) in humans. The repertoire of alloreactive T cell clones is distinct for every donor-recipient pair and includes potentially thousands of unique HLA/peptide specificities. The extraordinary magnitude of the primary alloresponse and diversity of the T cell population mediating it have presented technical challenges to its study in humans. High-throughput T cell receptor sequencing approaches have opened up new possibilities for tackling many fundamental questions about this important immunologic phenomenon.

The Risk of Transplant Failure With HLA Mismatch in First Adult Kidney Allografts From Deceased Donors

BACKGROUND

Since the beginning of the technology, there has been active debate about the role of human leucocyte antigen (HLA) matching in kidney allograft survival. Recent studies have reported diminishing importance of HLA matching, which have, in turn, been challenged by reports that suggest the continuing importance of these loci. Given the controversies, we examined the effect of HLA compatibility on kidney allograft survival by studying all first adult kidney transplants in the United States from a deceased donor.

METHODS

Using the United Network for Organ Sharing data, we identified first deceased donor kidney transplants between October 1, 1987, and December 31, 2013. Recipients were classified by their number of HLA mismatches. Cox multivariate regression analyses adjusting for recipient and donor transplant characteristics were performed to determine the impact of HLA compatibility on kidney allograft survival.

RESULTS

Study cohort included 189 141 first adult kidney alone transplants, with a total of 994 558 years of kidney allograft follow-up time. Analyses adjusted for recipient and donor characteristics demonstrated a 13% higher risk (hazard ratio, 1.13; 95% confidence interval, 1.06-1.21) with 1 mismatch and a 64% higher risk (hazard ratio, 1.64, 95% confidence interval, 1.56-1.73) with 6 mismatches. Dividing the mismatch categories into 27 ordered permutations, and testing their 57 within mismatch category differences, demonstrated that all but 1 were equal, independent of locus.

CONCLUSIONS

A significant linear relationship of hazard ratios was associated with HLA mismatch and affects allograft survival even during the recent periods of increasing success in renal transplantation.

Association Between HLA Antibodies and Different Sensitization Events in Renal Transplant Candidates

BACKGROUND

Human leukocyte antigen (HLA) allo-immunization is caused by various events such as blood transfusions, pregnancies, or organ transplantations, which can lead to sensitization. In this retrospective study, we evaluated different sensitization models and their effects on panel-reactive antibody (PRA) profiles of renal transplantation candidates.

METHODS

Anti-HLA class I/II antibody screening tests were performed in 906 renal transplantation candidates with the use of a microbead-based assay (Luminex).

RESULTS

Two hundred ninety-seven (32.8%) of the patients were determined as positive in terms of PRA, and 609 (67.2%) were negative. Sensitized and non-sensitized patients were compared separately in terms of each sensitization type. The anti-HLA class I, II, and I+II positivity rates in patients sensitized only by blood transfusion were 13.1%, 6.3%, and 14.1%, the rates with pregnancy sensitization were 35.5%, 29%, and 45.2%, and rates with previous transplantation sensitization were 15.6%, 34.4%, and 38.9%, respectively. Prevalence of PRA positivity was significantly higher in patients with previous pregnancy than with transplantation and transfusion (odds ratio, 1.003; 95% confidence interval, 0.441-2.281; P = .031). The risk of developing HLA class I antibodies was higher in pregnancies (P < .001), and the risk of developing anti-HLA class II antibodies was higher in patients who had undergone a previous transplantation (P < .001). The rate of developing HLA-B antibodies in patients sensitized by pregnancy were significantly higher compared with sensitization after transfusion (P = .015), as was the rate of developing HLA-DQ antibodies in patients sensitized by previous transplantation compared with sensitization through pregnancy (P = .042).

CONCLUSIONS

In patients who are waiting for kidney transplantation, sensitization by pregnancy and transplantation have a significant impact on development of HLA class I and class II antibodies.

Donor-specific alloreactive T cells can be quantified from whole blood, and may predict cellular rejection after renal transplantation

Preformed cellular alloreactivity can exist prior to transplantation and may contribute to rejection. Here, we used a rapid flow-cytometric whole-blood assay to characterize the extent of alloreactive T cells among 1491 stimulatory reactions from 61 renal transplant candidates and 75 controls. The role of preformed donor-specific alloreactive T cells in cellular rejection was prospectively analyzed in 21 renal transplant recipients. Alloreactive CD8⁺ T cells were more frequent than respective CD4⁺ T cells, and these levels were stable over time. CD8⁺ T cells were effector-memory T cells largely negative for expression of CD27, CD62L, and CCR7, and were susceptible to steroid and calcineurin inhibitor inhibition. Alloreactivity was more frequent in samples with higher number of HLA mismatches. Moreover, the percentage of individuals with alloreactive T cells was higher in transplant candidates than in controls. Among transplant candidates, 5/61 exhibited alloreactive CD8⁺ T cells against most stimulators, 23/61 toward a limited number of stimulators, and 33/61 did not show any alloreactivity. Among 21 renal transplant recipients followed prospectively, one had donor-specific preformed T-cell alloreactivity. She was the only patient who developed cellular rejection posttransplantation. In conclusion, donor-specific alloreactive T cells may be rapidly quantified from whole blood, and may predict cellular rejection after transplantation.

Herpesvirus microRNAs for use in gene therapy immune-evasion strategies

Transplantation of allogeneic cells as well as of genetically corrected autologous cells are potent approaches to restore cellular functions in patients suffering from genetic diseases. The recipient's immune responses against non-self-antigens may compromise the survival of the grafted cells. Recipients of the graft may therefore require lifelong treatment with immunosuppressive drugs. An alternative approach to reduce graft rejection could involve the use of immune-evasion molecules. Expression of such molecules in cells of the graft may subvert recognition by the host's immune system. Viruses in particular are masters of exploitation and modulation of their hosts immune response. The Herpesviridae family provides a proof of concept for this as these viruses are capable to establish latency and a lifelong persistence in the infected hosts. While several viral proteins involved in immune evasion have been characterized, the Herpesviridae also encode a multitude of viral microRNA (miRNAs). Several of these miRNAs have been demonstrated to reduce the sensitivity of the infected cells to the destructive action of the host's immune cells. In this review, the miRNAs of some common herpesviruses that are associated with immune modulation will be discussed with a focus on their potential use in strategies aiming at generating non-immunogenic cells for transplantation.

Computational Approaches to Facilitate Epitope-Based HLA Matching in Solid Organ Transplantation

Epitope-based HLA matching has been emerged over the last few years as an improved method for HLA matching in solid organ transplantation. The epitope-based matching concept has been incorporated in both the PIRCHE-II and the HLAMatchmaker algorithm to find the most suitable donor for a recipient. For these algorithms, high-resolution HLA genotype data of both donor and recipient is required. Since high-resolution HLA genotype data is often not available, we developed a computational method which allows epitope-based HLA matching from serological split level HLA typing relying on HLA haplotype frequencies. To validate this method, we simulated a donor-recipient population for which PIRCHE-II and eplet values were calculated when using both high-resolution HLA genotype data and serological split level HLA typing. The majority of the serological split level HLA-determined ln(PIRCHE-II)/ln(eplet) values did not or only slightly deviate from the reference group of high-resolution HLA-determined ln(PIRCHE-II)/ln(eplet) values. This deviation was slightly increased when HLA-C or HLA-DQ was omitted from the input and was substantially decreased when using two-field resolution HLA genotype data of the recipient and serological split level HLA typing of the donor. Thus, our data suggest that our computational approach is a powerful tool to estimate PIRCHE-II/eplet values when high-resolution HLA genotype data is not available.

Kidney Transplantation With Ultralong-Term (42 Years) Survival of a 100-Year-Old Graft

BACKGROUND

In kidney transplantation, long-term graft survival has improved over the last few decades. Study to understand ultralong-term graft survival with graft functioning is rare, but a few researchers have tried to explain the factors involved in long-term graft survival. In this report, we explore the predictive factors that can be involved in ultralong-term graft survival.

MATERIAL AND METHODS

Immunologic evaluations of the patients were performed using crossmatch (XM), serological, and high-resolution HLA typing for 8 loci. A transplant recipient was treated with azathioprine as immunosuppressive monotherapy for 42 years. Donor-specific antibodies (DSAs) were identified using panel reactive antibody single antigen beads (PRA-SAB) followed by EpVix and Matchmaker epitope analysis to define the immunogenic mismatch eplets.

RESULTS

The patient and donor were haploidentical for 7 loci and identical at the HLA-DPA1* locus. Among 61 identified eplet mismatches, DSAs were not detected against 59 eplets after 42 years of exposure to the patient's immune system with the exceptions of antibodies against the public eplets 9Y and 9YL from allele HLA-DPB1*03:01, and the transplanted kidney exhibited preserved structures.

CONCLUSION

The transplanted kidney has the preserved structure based on magnetic resonance imaging, the 2 DSAs were not deleterious to the graft until now, and the eplet mismatches were considered acceptable. The patient is in good clinical condition living with a 100-year-old graft, a serum creatinine level of 1.5 mg/dL, and an estimated glomerular filtration rate of 50 mL/1.72 m².

A Previous Miscarriage and a Previous Successful Pregnancy Have a Different Impact on HLA Antibody Formation during a Subsequent Successful Pregnancy

Inherited paternal HLA antigens from the semi-allogeneic fetus may trigger maternal immune responses during pregnancy, leading to the production of child-specific HLA antibodies. The prevalence of these HLA antibodies increases with the number of successful pregnancies. In the present study, we investigated the effect of a single prior miscarriage on HLA antibody formation during a subsequent successful pregnancy. Women with a successful pregnancy with one or more prior miscarriages (n = 229) and women with a successful pregnancy without a prior miscarriage (n = 58), and their children were HLA typed. HLA antibody analyses were performed in these women to identify whether HLA antibodies were formed against mismatched HLA class-I antigens of the last child. The percentage of immunogenic antigens was significantly lower after a single successful pregnancy that was preceded by a single miscarriage (n = 18 women) compared to a successful pregnancy that was preceded by a first successful pregnancy (n = 62 women). Thus, our data suggest that a previous miscarriage has a different impact on child-specific HLA antibody formation during a subsequent successful pregnancy than a previous successful pregnancy. The lower immunogenicity in these women cannot be explained by reduced numbers of immunogenic B-cell and T-cell epitopes. In conclusion, our observations indicate that increasing gravidity is not related to an increased prevalence of HLA antibodies in a single successful pregnancy that was preceded by a single prior miscarriage.

[Chronic kidney disease and kidney transplantation]

OBJECTIVES

To report epidemiology and characteristics of end-stage renal disease (ESRD) patients and renal transplant candidates, and to evaluate access to waiting list and results of renal transplantation.

MATERIAL AND METHODS

An exhaustive systematic review of the scientific literature was performed in the Medline database (http://www.ncbi.nlm.nih.gov) and Embase (http://www.embase.com) using different associations of the following keywords: "chronic kidney disease, epidemiology, kidney transplantation, cost, survival, graft, brain death, cardiac arrest, access, allocation". French legal documents have been reviewed using the government portal (http://www.legifrance.gouv.fr). Articles were selected according to methods, language of publication and relevance. The reference lists were used to identify additional historical studies of interest. Both prospective and retrospective series, in French and English, as well as review articles and recommendations were selected. In addition, French national transplant and health agencies (http://www.agence-biomedecine.fr and http://www.has-sante.fr) databases were screened using identical keywords. A total of 3234 articles, 6 official reports and 3 newspaper articles were identified; after careful selection 99 publications were eligible for our review.

RESULTS

The increasing prevalence of chronic kidney disease (CKD) leads to worsen organ shortage. Renal transplantation remains the best treatment option for ESRD, providing recipients with an increased survival and quality of life, at lower costs than other renal replacement therapies. The never-ending lengthening of the waiting list raises issues regarding treatment strategies and candidates' selection, and underlines the limits of organ sharing without additional source of kidneys available for transplantation.

CONCLUSION

Allocation policies aim to reduce medical or geographical disparities regarding enrollment on a waiting list or access to an allotransplant.

Renal transplant immunology in the last 20 years: A revolution towards graft and patient survival improvement

To deride the hope of progress is the ultimate fatuity, the last word in poverty of spirit and meanness of mind. There is no need to be dismayed by the fact that we cannot yet envisage a definitive solution of our problems, a resting-place beyond which we need not try to go. -P.B. Medawar, 1969 * Thomas E. Starlz, also known as the Father of Clinical Transplantation, once said that organ transplantation was the supreme exception to the rule that most major advances in medicine spring from discoveries in basic science [Starzl T. The mystique of organ transplantation. J Am Coll Surg 2005 Aug;201(2):160-170]. In fact, the first successful identical-twin kidney transplantation performed by Murray's team in December 1954 (Murray J et al. Renal homotransplantations in identical twins. Surg Forum 1955;6:432-436) was the example of an upside down translation medicine: Human clinical transplantation began and researchers tried to understand the underlying immune response and how to control the powerful rejection pathways through experimental models. In the last 20 years, we have witnessed an amazing progress in the knowledge of immunological mechanisms regarding alloimmune response and an outstanding evolution on the identification and characterization of major and minor histocompatibility antigens. This review presents an historical and clinical perspective of those important advances in kidney transplantation immunology in the last 20 years, which contributed to the improvement in patients' quality of life and the survival of end-stage renal patients. In spite of these significant progresses, some areas still need substantial progress, such as the definition of non-invasive biomarkers for acute rejection; the continuous reduction of immunosuppression; the extension of graft survival, and finally the achievement of real graft tolerance extended to HLA mismatch donor: recipient pairs.

Alloreactive T Cells to Identify Risk HLA Alleles for Retransplantation After Acute Accelerated Steroid-Resistant Rejection

The risk of rejection by cellular alloreactivity to the transplant donor is not routinely assessed. Here we analyzed alloreactive T cells in kidney transplant recipients and report how their detection may have helped to prevent rejection of a second kidney graft in a patient with a history of acute accelerated steroid-resistant nonhumoral rejection. Alloreactive CD4 and CD8 T cells were quantified using a flow-cytometric mixed lymphocyte reaction assay based on interferon-γ induction. A group of 16 nonrejecting transplant recipients did not show any alloreactive T-cell immunity to their respective donors, whereas alloreactivity to third-party controls was detectable. In the patient with rejection, HLA-specific antibodies were not detectable before and shortly after rejection, but after transplantation the patient showed exceptionally high frequencies of alloreactive T cells against 2 of 11 HLA-typed controls (0.604% and 0.791% alloreactive CD4 T cells and 0.792% and 0.978% alloreactive CD8 T cells) who shared HLA alleles (HLA-A*24, -B*44, -C*02, -DQB1*5) with the kidney donor. These HLA alleles were subsequently excluded for allocation of a second graft. No alloreactive T cells were observed toward the second kidney donor, and this transplantation was performed successfully. Thus, shared HLA alleles between the donor and third-party controls may suggest that alloreactive T cells had contributed to rejection of the first graft. The rejecting patient highlights that determination of cellular alloreactivity before transplantation may be applied to identify unacceptable mismatches and to reduce the risk for acute cellular rejection episodes.

Clinical Use of Tolerogenic Dendritic Cells-Harmonization Approach in European Collaborative Effort

The number of patients with autoimmune diseases and severe allergies and recipients of transplants increases worldwide. Currently, these patients require lifelong administration of immunomodulatory drugs. Often, these drugs are expensive and show immediate or late-occurring severe side effects. Treatment would be greatly improved by targeting the cause of autoimmunity, that is, loss of tolerance to self-antigens. Accumulating knowledge on immune mechanisms has led to the development of tolerogenic dendritic cells (tolDC), with the specific objective to restrain unwanted immune reactions in the long term. The first clinical trials with tolDC have recently been conducted and more tolDC trials are underway. Although the safety trials have been encouraging, many questions relating to tolDC, for example, cell-manufacturing protocols, administration route, amount and frequency, or mechanism of action, remain to be answered. Aiming to join efforts in translating tolDC and other tolerogenic cellular products (e.g., Tregs and macrophages) to the clinic, a European COST (European Cooperation in Science and Technology) network has been initiated-A FACTT (action to focus and accelerate cell-based tolerance-inducing therapies). A FACTT aims to minimize overlap and maximize comparison of tolDC approaches through establishment of minimum information models and consensus monitoring parameters, ensuring that progress will be in an efficient, safe, and cost-effective way.

Analysis of the Influence of HLA-A Matching Relative to HLA-B and -DR Matching on Heart Transplant Outcomes

Background

There are conflicting reports on the effect of donor-recipient HLA matching on outcomes in heart transplantation. The objective of this study was to investigate the effects of HLA-A matching relative to HLA-B and -DR matching on long-term survival in heart transplantation.

Methods

A total of 25 583 patients transplanted between 1988 and 2011 were identified from the International Society for Heart and Lung Transplantation registry. Transplants were divided into 2 donor-recipient matching groups: HLA-A–compatible (no HLA-A mismatches) and HLA-A–incompatible (1-2 HLA-A mismatches). Primary outcome was all-cause mortality. Secondary outcomes were graft failure-, cardiovascular-, infection-, or malignancy-related deaths.

Results

The risk of all-cause mortality 15 years after transplantation was higher for HLA-A–compatible (vs HLA-A–incompatible) grafts in patients who had HLA-B–, HLA-DR–, or HLA-B,DR–incompatible grafts (P = 0.027, P = 0.007, and P = 0.002, respectively) but not in HLA-B– and/or HLA-DR–compatible grafts. This was confirmed in multivariable Cox regression analysis where HLA-A compatibility (vs HLA-A incompatibility) was associated with higher mortality in transplants incompatible for HLA-DR or HLA-B and -DR (hazard ratio [HR], 1.59; 95% confidence interval [95% CI], 1.11-2.28; P = 0.012 and HR, 1.69; 95% CI, 1.17-2.43; P = 0.005, respectively). In multivariable analysis, the largest compromise in survival for HLA-A compatibility (vs HLA-incompatibility) was for chronic rejection in HLA-B– and -DR–incompatible grafts (HR, 1.91; 95% CI, 1.22-3.01; P = 0.005).

Conclusions

Decreased long-term survival in heart transplantation was associated with HLA-A compatibility in HLA-B,DR–incompatible grafts.

HLA sensitisation: can it be prevented?

Human leukocyte antigen (HLA) sensitisation occurs after transfusion of blood products and transplantation. It can also happen spontaneously through cross-sensitisation from infection and pro-inflammatory events. Patients who are highly sensitised face longer waiting times on organ allocation programmes, more graft rejection and therefore more side effects of immunosuppression, and poorer graft outcomes. In this review, we discuss these issues, along with the limitations of modern HLA detection methods, and potential ways of decreasing HLA antibody development. We do not discuss the removal of antibodies after they have developed.

Utility of HLA Antibody Testing in Kidney Transplantation

HLA antigens are polymorphic proteins expressed on donor kidney allograft endothelium and are critical targets for recipient immune recognition. HLA antibodies are risk factors for acute and chronic rejection and allograft loss. Solid-phase immunoassays for HLA antibody detection represent a major advance in sensitivity and specificity over cell-based methods and are widely used in organ allocation and pretransplant risk assessment. Post-transplant, development of de novo donor-specific HLA antibodies and/or increase in donor-specific antibodies from pretransplant levels are associated with adverse outcomes. Although single antigen bead assays have allowed sensitive detection of recipient HLA antibodies and their specificities, a number of interpretive considerations must be appreciated to understand test results in clinical and research contexts. This review, which is especially relevant for clinicians caring for transplant patients, discusses the technical aspects of single antigen bead assays, emphasizes their quantitative limitations, and explores the utility of HLA antibody testing in identifying and managing important pre- and post-transplant clinical outcomes.

Now or never? The case for cell-based immunosuppression in kidney transplantation

By exploiting mechanisms of immunological regulation against donor alloantigen, it may be possible to reduce the dependence of kidney transplant recipients upon calcineurin inhibitor-based maintenance immunosuppression. One means to strengthen regulatory responses is treating recipients with preparations of regulatory cells obtained by ex vivo manipulation. This strategy, which is a well-established experimental method, has been developed to the point that early-phase clinical trials in kidney transplantation are now feasible. Cell-based therapies represent a radical departure from conventional treatment, so what grounds are there for this new approach? This article offers a three-part justification for trialing cell-based therapies in kidney transplantation: first, a clinical need for alternatives to standard immunosuppression is identified, based on the inadequacies of calcineurin inhibitor-based regimens in preventing late allograft loss; second, a mechanistic explanation of how cell-based therapies might address this clinical need is given; and third, the possible benefit to patients is weighed against the potential risks of cell-based immunosuppressive therapy. It is concluded that the safety of cell-based immunosuppressive therapy will not be greatly improved by further basic scientific and preclinical development. Only trials in humans can now tell us whether cell-based therapy is likely to benefit kidney transplant recipients, but these should be conservative in design to minimize any potential harm to patients.

Use of pharmacogenomics in pediatric renal transplant recipients

Transplant recipients receive potent immunosuppressive drugs in order to prevent graft rejection. Therapeutic drug monitoring is the current approach to guide the dosing of calcineurin inhibitors, mammalian target of rapamycin inhibitors (mTORi) and mofetil mycophenolate. Target concentrations used in pediatric patients are extrapolated from adult studies. Gene polymorphisms in metabolizing enzymes and drug transporters such as cytochromes CYP3A4 and CYP3A5, UDP-glucuronosyl transferase, and P-glycoprotein are known to influence the pharmacokinetics and dose requirements of immunosuppressants. The implications of pharmacogenomics in this patient population is discussed. Genetic information can help with achieving target concentrations in the early post-transplant period, avoiding adverse drug reactions and drug-drug interactions. Evidence about genetic studies and transplant outcomes is revised.

Human leukocyte antigens and alloimmunization in heart transplantation: an open debate

Considerable advances in heart transplantation outcome have been achieved through the improvement of donor-recipient selection, better organ preservation, lower rates of perioperative mortality and the use of innovative immunosuppressive protocols. Nevertheless, long-term survival is still influenced by late complications. We support the introduction of HLA matching as an additional criterion in the heart allocation. Indeed, allosensitization is an important factor affecting heart transplantation and the presence of anti-HLA antibodies causes an increased risk of antibody-mediated rejection and graft failure. On the other hand, the rate of heart-immunized patients awaiting transplantation is steadily increasing due to the limited availability of organs and an increased use of ventricular assist devices. Significant benefits may result from virtual crossmatch approach that prevents transplantation in the presence of unacceptable donor antigens. A combination of both virtual crossmatch and a tailored desensitization therapy could be a good compromise for a favorable outcome in highly sensitized patients. Here, we discuss the unresolved issue on the clinical immunology of heart transplantation.

Impact of donor kidney function and donor age on poor outcome of living-unrelated kidney transplantation (KT) in comparison with living-related KT

Living-unrelated donors (LURD) have been widely used for kidney transplantation (KT). We retrospectively reviewed 779 patients who underwent living-donor KT from 2000 to 2012, to compare outcomes of 264 KT from LURD and 515 from living-related donors (LRD), and to identify risk factors for living KT. Median follow-up was 67 months. Mean donor age, total human leukocyte antigen (HLA) mismatches, and HLA-DR mismatches were higher, and mean estimated glomerular filtration rate (eGFR) was lower in LURD. Acute rejection (AR)-free survival (p = 0.018) and graft survival (p = 0.025) were lower for LURD than LRD, whereas patient survival rate was comparable. Cox regression analysis showed HLA-DR mismatches (OR 1.75 for one mismatch; OR 2.19 for two mismatches), recipient age ≤ 42 yr, and donor age > 50 yr were significant risk factors for acute rejection. For graft survival, AR and donor eGFR (OR 1.90, p = 0.035) were significant. We also identified significant impact of recipient age > 50 yr and diabetes for patient survival. However, KT from LURD was not a significant risk factor for AR (p = 0.368), graft survival (p = 0.205), and patient survival (p = 0.836). Our data suggest that donor eGFR and donor age are independent risk factors for clinical outcomes of living KT, which can be related with poor outcome of KT from LURD.

Vascularized Composite Allografts: Procurement, Allocation, and Implementation

Vascularized composite allotransplantation is a continuously evolving area of modern transplant medicine. Recently, vascularized composite allografts (VCAs) have been formally classified as 'organs'. In this review, key aspects of VCA procurement are discussed, with a special focus on interaction with the procurement of classical solid organs. In addition, options for a matching and allocation system that ensures VCA donor organs are allocated to the best-suited recipients are looked at. Finally, the different steps needed to promote VCA transplantation in society in general and in the medical community in particular are highlighted.

Human leukocyte antigen matching in heart transplantation: systematic review and meta-analysis

Allocation of donors with regard to human leukocyte antigen (HLA) is controversial in heart transplantation. This paper is a systematic review and meta-analysis of the available evidence. PubMed, Embase, and the Cochrane Library were searched systematically for studies that addressed the effects of HLA matching on outcome after heart transplantation. Fifty-seven studies met the eligibility criteria. 34 studies had graft rejection as outcome, with 26 of the studies reporting a significant reduction in graft rejection with increasing degree of HLA matching. Thirteen of 18 articles that reported on graft failure found that it decreased significantly with increasing HLA match. Two multicenter studies and nine single-center studies provided sufficient data to provide summary estimates at 12 months. Pooled comparisons showed that graft survival increased with fewer HLA-DR mismatches [0-1 vs. 2 mismatches: risk ratio (RR) = 1.09 (95% confidence interval (CI): 1.01-1.19; P = 0.04)]. Having fewer HLA-DR mismatches (0-1 vs. 2) reduced the incidence of acute rejection [(RR = 0.81 (0.66-0.99; P = 0.04)]. Despite the considerable heterogeneity between studies, the short observation time, and older data, HLA matching improves graft survival in heart transplantation. Prospective HLA-DR matching is clinically feasible and should be considered as a major selection criterion.

Successful three-way kidney paired donation with compatible pairs to increase donor pool

Despite heightened international interest in performing living donor kidney paired donation (KPD) transplantation after the publication of a research protocol by Ross and colleagues in 1997, only a few hundred have been performed worldwide. The major obstacle is that many individuals in end-stage renal disease are of blood type O and can only receive an organ from a donor of blood type O, whereas blood type O donors are "universal donors" and will be able to donate directly with an intended recipient of any blood type unless there is a positive crossmatch. To overcome this, patients with compatible but non-HLA identical donors over 45 years of age should be approached for inclusion in KPD program especially O blood group donors. Inclusion of all these additional pairs into the algorithm greatly increases chances of possible matches for O blood group recipients. We report successful three-way KPD transplantation resulting in transplantation of O blood group patient using compatible O blood group donor from India. None of the patients had delayed graft function or rejection and all had stable graft function on discharge without any medical and surgical complications. We need to allocate O blood group kidneys from compatible donors to overcome the barrier of HLA, non-HLA antibodies and other donor related factors to improve transplant quality and long term outcomes. This will increase transplantation of O blood group patients.