HLA Type and the Effect of HLA Antibodies in Kidney, Liver, and Pancreas Transplantation: A Review.

Dendritic Cells Loaded With mRNA Encoding Full-length Tumor Antigens Prime CD4+ and CD8+ T Cells in Melanoma Patients

Solid organ transplantation is a life-saving medical operation that has progressed greatly because of developments in diagnostic tools and histocompatibility tests. Crossmatching for complement-dependent cytotoxicity (CDC) and human leukocyte antigen (HLA) typing are two important methods for checking graft compatibility and reducing the risk of graft rejection. HLA typing and CDC crossmatching are critical in kidney, heart, lung, liver, pancreas, intestine, and multi-organ transplantation. A systematic literature search was conducted on the internet, using PubMed, Scopus, and Google Scholar databases, to identify peer-reviewed publications about solid organ transplants, HLA typing, and CDC crossmatching. Recent advances in HLA typing have allowed for high-resolution evaluation, epitope matching, and personalized therapy methods. Genomic profiling, next-generation sequencing, and artificial intelligence have improved HLA typing precision, resulting in better patient outcomes. Artificial intelligence (AI) driven virtual crossmatching and predictive algorithms have eliminated the requirement for physical crossmatching in the context of CDC crossmatching, boosting organ allocation and transplant efficiency. This review elaborates on the importance of HLA typing and CDC crossmatching in solid organ transplantation.

Human leucocyte antigen (HLA) molecules are the principal determinants of graft antigenicity and constitute a formidable barrier to allogeneic organ transplantation.1 Clinical outcomes after kidney transplantation are particularly strongly associated with the degree of HLA matching between donor and recipient [A] [B]. Here, we collate web‐based resources related to the immunobiology and practice of HLA typing of interest to basic scientists and transplant clinicians alike. Links [A] https://www.eurotransplant.org/cms/index.php?page=et_manual [B] http://optn.transplant.hrsa.gov/policiesAndBylaws/policies.asp [C] http://www.ncbi.nlm.nih.gov/projects/gv/mhc/ [D] http://www.ebi.ac.uk/ipd/imgt/hla/ [E] http://www.allelefrequencies.net/hla6003a.asp [F] http://hla-net.eu/ [G] http://hla.alleles.org/ [H] http://epregistry.com.br/index/index [I] http://www.hlamatchmaker.net/ The HLA molecules are membrane‐bound glycoproteins that bind antigenic peptides for presentation to T cells.2 According to their structure and function, classical HLA molecules fall into 2 classes: Class I molecules comprise a single peptide‐binding, α-polypeptide chain that associates with β2‐microglobulin and an antigenic peptide to form a mature complex; class II molecules are composed of an α- and β-polypeptide, both of which contribute to binding of antigenic peptides. The HLA class I molecules are expressed by most somatic cells, whereas class II molecules are usually only expressed by specialized cell subsets with immunological function. Classic class I and II molecules are genetically encoded within the major histocompatibility complex (MHC) locus on chromosome 6p21.3, which is a region of very high gene density, extreme polymorphism and clustering of genes with related immunological functions.3 The 3 genes encoding HLA class I molecules, namely, HLA-A, HLA-B, and HLA-C, reside within the class I region alongside 2 clusters of nonclassic class I genes. Genes for the class II molecules, namely, HLA-DP, HLA-DO, HLA-DM, HLA-DQ, and HLA-DR, are located in the class II region.FigurePolymorphism is a defining feature of HLA genes.4 The IMGT/HLA database [C] at the European Bioinformatics Institute serves as an official repository for HLA allele sequences, as well as offering a selection of online tools for categorizing and comparing HLA alleles.5 The dbMHC website [D] hosted at NCBI is a publicly accessible database for HLA allele sequence and related clinical data. The catalogue of HLA allele frequencies in diverse human populations is a particularly valuable resource. For reasons that are not fully explained, the overall rate of genetic recombination in the MHC region is lower than that in the rest of the genome; as a result, many HLA alleles exist in marked linkage disequilibrium. Presumably, a felicitous consequence of inheriting HLA genes as “haplotypic blocks” is that identifying a well‐matched donor is more probable than it would otherwise be. Usefully, the dbMHC website also lists HLA haplotype frequencies in different racial groups, as does allelefrequencies.net [E]6 and hla-net.eu [F].7 Naming of HLA alleles is standardized by the World Health Organization Nomenclature Committee for Factors of the HLA System. In April 2010, the system of HLA nomenclature was changed to accommodate the large number of allelic variants in some families. An accessible source of information about the current naming of HLA alleles is available at hla.alleles.org [G]. This neatly curated website also provides up‐to‐date lists of recognized HLA alleles and proteins, as well as a convenient nomenclature conversion tool. At a molecular level, interactions between non‐self HLA molecules and T-cell receptors or antibodies are well explained. Much effort has been invested in describing epitopes of HLA‐specific antibodies, which are now being systematically named and collated in an online archive at epregistry.com.br [H], which also lists epitope frequencies, epitope‐carrying alleles in Luminex panels, and alleles with antibody‐verified epitopes.8 A practical consequence of this work is an algorithm, known as HLAMatchmaker [I], which is now used by Eurotransplant as part of its “acceptable mismatch” program.9 Assessing “epitope load” might also provide valuable information for selecting organs for nonsensitized recipients or guiding their posttransplant management.10 In summary, knowledge of the HLA system and its relevant nomenclature is important for all transplant professionals. Accurate recording of HLA typing information at the highest available resolution is very valuable, especially in the context of clinical trials. In addition to the vast specialist literature, there exist many excellent online sources of information about HLA typing and variety of helpful web‐based tools.11

Even in this era of efficient immunosuppression, a positive serological crossmatch caused by complement fixing antibodies directed against the human leukocyte antigen (HLA) mismatches of the organ donor is a contraindication for transplantation (1). The presence of this type of antibodies is known to be associated with a high incidence of hyper acute or acute-accelerated rejection (2). Highly sensitized patients have only a small chance to receive a crossmatch negative donor kidney, because they have developed antibodies against many different HLA antigens resulting from previous contacts with allogeneic cells by pregnancy, blood transfusions, or previous transplants. If no special measurements are taken, these patients will accumulate on the transplant waiting lists. More and more transplant centers are developing strategies to remove circulating HLA alloantibodies in these patients to be able to transplant the patient with a donor kidney despite a positive crossmatch (3–5). These desensitization approaches include the use of plasmapheresis, immunoabsorption, intravenous immunoglobulins, and Rituximab. Although excellent short-term results have been described with these approaches, one has to realize that desensitization includes more intensive immunosuppressive treatment associated with side effects related to the nonspecific nature of these immunosuppressive drugs that is a higher incidence of opportunistic infections and cancer. In the international organ allocation program of Eurotransplant (6), a different approach is used. The presence of donor-specific antibodies is considered a contraindication for transplantation and special efforts are given to transplant these patients with a crossmatch negative donor. First of all, these patients get priority in the standard Eurotransplant kidney allocation system (7). Allocation of kidneys within Eurotransplant is based on a transparent point system and, for every donor, which becomes available in one of the participating countries, patients receive points for among others the degree of HLA match, waiting time, the expected cold ischemia time (distance), and a match prognostic index including the degree of sensitization. Next to this standard allocation program, Eurotransplant has introduced a special program that give the highest priority to highly sensitized patients as soon as a donor becomes available, which is compatible with the patient’s antibody profile: the acceptable mismatch (AM) program (8). In this review, we describe the past, current, and future situation with respect to the application of an AM program. DEFINITION OF A HIGHLY SENSITIZED PATIENT In the past, the degree of sensitization of a patient was based on the percentage panel reactive HLA antibodies (% PRA) in the standard antibody screening. The serum of the patient was screened in complement-dependent cytotoxicity (CDC) against a panel of approximately 50 donors, and depending on the number of positive donors in the antibody screening a percentage PRA was defined. Highly sensitized patients were defined as patients with more than 85% PRA excluding the reactivity of irrelevant autoantibodies. However, this definition is not solid as quality controls have indicated that the percentage PRA is one of the most unreliable markers in histocompatibility testing. External proficiency testing programs within Eurotransplant revealed that the percentage PRA of a particular serum may vary between 10% and 90% (9). For this reason, a redefinition of a highly sensitized patient is necessary. More and more centers are introducing a virtual crossmatch, which indicates the degree of sensitization on the basis of the specificities of the HLA antibodies of a patient in relation to the frequencies of the target antigens in the donor population (10, 11). A special tool has been developed on the website of Eurotransplant to define the virtual PRA on the basis of which one can check whether a patient fulfils the criteria of a highly sensitized patient (Fig. 1).FIGURE 1.: Tool to calculate the virtual PRA on basis of the HLA phenotypes of the Eurotransplant donor population.By introducing the antibody specificities detected in the serum of the patient in the computer program, a virtual PRA will be calculated on the basis of the HLA phenotypes of more than 30,000 actual organ donors, which became available during the past 10 years within the Eurotransplant area. In this way, a uniform and more reliable definition of highly sensitized patients is established. Only patients with a virtual PRA more than 85% will be included in the AM program. So far, the virtual PRA is mainly based on HLA-A, -B, and -DR antibody specificities as all donors within Eurotransplant must be typed for these antigen specificities, whereas HLA-C and -DQ typing is only performed on voluntary basis by some centers. NEED FOR AN AM PROGRAM The standard policy in Eurotransplant is registration of the nonacceptable HLA mismatches to prevent selection of donors with HLA mismatches toward which a patient has preformed antibodies. The aim of this policy was prediction and prevention of positive crossmatches in the recipient centers. Kidneys will not be shipped to patients with specific antibodies to the donor. However, the positive identification of all antibody specificities in highly sensitized patients is impossible. That is the reason why an additional policy has been introduced for highly sensitized patients: the definition of those HLA antigens toward which the patient never formed antibodies. The aim of this approach was prediction of a negative CDC crossmatch. DEFINITION OF AM The first indication of AMs comes from the analysis of the HLA types of the panel donors used in the antibody screening. Comparison of the HLA type of those panel donors, which give negative reactions with the serum of the patient, with the patient’s own HLA type leads to the identification of acceptable HLA alloantigens. However, this strategy is only useful in patients who have PRA less than 100%. Other approaches include the use of patient specific consisting of blood donors with only one HLA mismatch with the patients who facilitates the definition of AMs. However, for patients with rare HLA types, this approach is not effective as hardly any of such blood donors are available. The main problem with the use of cell-based assays for antibody screening is the fact that cells express different HLA antigens that make it difficult to define AMs. For this reason, the Eurotransplant Reference Laboratory has developed a large panel of single HLA antigen expressing cell lines for antibody screening in highly sensitized patients. By transfecting the cell line K562 with genes coding for the individual HLA class I molecules, cells are available, which express only one single HLA antigen, the so-called single antigen-expressing cell lines (12). Screening of a serum against a panel of single antigen-expressing lines will immediately reveal the AMs, which are the HLA antigens expressed on the cell lines that give negative reactions with the serum of the patient. Of course, solid-phase assays, that is ELISA or Luminex, can be used for this purpose as well, but our experience and also the experience of others is that the conformation of the HLA molecules on a cell is different from that of the isolated HLA molecules present in solid-phase assays. Especially, the recent observation that natural HLA antibodies can be detected with single-antigen beads in nonsensitized individuals supports this reasoning (13). Targets for these natural HLA antibodies are most likely epitopes present on denatured HLA molecules present on the luminex beads. For this reason, we prefer the use of cell-based assays over solid-phase assays. Other approaches that are helpful to define AMs include the analysis of the HLA types of the mothers of the highly sensitized patients because a proportion of highly sensitized patients tend not to make antibodies against the noninherited maternal HLA antigens (14). During pregnancy, the immune system of these patients is probably programmed by HLA antigens of the mothers in such a way that later in life the immune response to the maternal HLA antigens is less aggressive than the immune response to other HLA mismatches including those of the noninherited paternal HLA antigens. APPLICATION OF HLAMATCHMAKER FOR THE IDENTIFICATION OF AM In the past, the identification of AMs was based on the identification of HLA antigens toward which the patient did not make antibodies. However, in the mean time, the amino acid sequences of all HLA alleles are known and specific antibody epitopes have been defined on the different HLA antigens. Some of these epitopes are specific for a particular HLA allele whereas others are shared between different HLA alleles (15). Based on this knowledge, it is possible to identify the specific antibody epitopes on an allogeneic HLA molecule and, even more, to predict whether a certain HLA mismatch will be able to induce HLA antibodies in a specific patient. In this respect, a computer algorithm, HLAMatchmaker, has shown to be helpful (16, 17). In this program, HLA antigens are defined as a string of potential antibody epitopes (in the original version consisting of three amino acids, triplets). Some of these potential epitopes are shared between different HLA antigens and may also be present on the HLA molecules of the potential antibody producer. Therefore, an HLA mismatch should be considered in the context of the HLA phenotype of the potential antibody producer. Only those polymorphisms that are not present on the patient’s own HLA antigens can lead to a humoral immune response. That is, indeed the concept of the HLAMatchmaker algorithm (18). HLA mismatches, which only have triplets that are shared by the different HLA antigens of the antibody producer, will not lead to the induction of HLA antibodies. This theoretical concept was validated by in vitro serological crossmatches in highly sensitized patients. Both in the context of kidney graft rejection and pregnancy, a strong correlation between antibody production and the number of mismatched triplets was found. In the case of a zero mismatch or only a few triplet mismatches, the chance for the patient to be immunized is low (19, 20). For this reason, HLAMatchmaker is routinely used for the identification of potential acceptable HLA mismatches in highly sensitized patients and so far the concept has proven to be effective. THE USE FOR AM FOR THE ALLOCATION OF KIDNEYS All acceptable HLA mismatches, which have been identified, will be added to the HLA phenotype of the recipient. It is assumed that a potential kidney donor with an HLA phenotype, which is a combination of the patient’s own HLA and one or more AMs, will have a negative CDC crossmatch with the sera of this patient. If such a donor becomes available somewhere in the Eurotransplant area, mandatory shipment of the donor kidney to the recipient center will take place. A final crossmatch will only be performed in the recipient center. Within the Eurotransplant kidney allocation system, the AM program has the highest priority followed by the allocation of kidneys to fully HLA-matched recipients, before the early described point system is applied (Fig. 2).FIGURE 2.: Priorities of kidney allocation with Eurotransplant: the acceptable mismatch program has the highest priority.INCREASED TRANSPLANTATION RATE OF HIGHLY SENSITIZED PATIENTS INCLUDED IN THE AM PROGRAM As patients within the AM program have the highest priority in the Eurotransplant kidney allocation, it is not surprising that the chance that highly sensitized patients receive a suitable crossmatch negative organ is significantly increased by their inclusion in the AM program. Approximately 60% of the highly sensitized patients will be transplanted within 2 years after inclusion in the AM program. In contrast, patients who benefit only of the extra points in the standard Eurotransplant allocation program will have approximately 20% chance to be transplanted within the same time period. Despite its success, the introduction of the AM program has also led to some ethical discussions within Eurotransplant. The consequence of giving the highest priority to highly sensitized patients is that other patients have to wait longer. Because only 1% of the patient population is highly sensitized, the impact on the waiting time of the other patients is only minor (on average their waiting time will increase with a few weeks). Taking into consideration that before introduction of the AM program many highly sensitized patients were waiting for 10 to 15 years without receiving any proper donor offer, the current policy is accepted by the Eurotransplant community. However, one can imagine that in populations with a much higher incidence of highly sensitized patients or if one would like to include other less-sensitized patients in a similar program, a different conclusion will be made. GRAFT SURVIVAL OF AM PATIENTS Inclusion in an AM program clearly facilitates transplantation of highly sensitized patients as shown by the fact that a significant proportion of the AM patients receive a graft in a short time period but according to the literature graft survival in sensitized patients is much worse than in nonsensitized patients (21). However, this is certainly not the case in patients transplanted via the AM program. Previously, we published that highly sensitized patients transplanted via the AM program have the same short-term graft survival as nonsensitized patients within Eurotransplant (22). In contrast, other sensitized patients have indeed a significantly poorer graft survival. The reason for that is probably that in the AM program the exact antibody profile of the patient is known and especially the identification of those HLA mismatches toward which the patient never formed antibodies has been proven over and over again in the laboratory. This is not the case in other sensitized patients for which these extensive laboratory studies have not been performed. These patients are transplanted on the basis of a negative crossmatch, not supported by hard laboratory data showing that the donor HLA mismatches are indeed acceptable. If such a policy will be introduced for all sensitized patients, one can assume that these graft survival will improve as well. Not only the short-term graft survival is excellent but also the long-term graft survival in these AM patients is excellent and similar to that of nonsensitized patients (Fig. 3). The degree of HLA matching in the AM cohort is comparable with that of the total Eurotransplant patient population (Table 1). No significant effect of HLA-A, -B, and -DR matching was observed in patients transplanted via the AM program.FIGURE 3.: Long-term graft survival of patients transplanted via the AM program.TABLE 1: Comparison of the degree of HLA matching between the AM and the ET cohortWHICH ANTIBODIES ARE RELEVANT? So far, the Eurotransplant AM program has only been used to predict a negative CDC crossmatch with all relevant sera of a patient. This means that antibody reactivity is mainly based on the standard CDC assay. The reason for this policy is that it is generally accepted that a positive CDC crossmatch is a contraindication for transplantation. In the meantime, sensitive antibody screening assays have become available, mainly taking advantage of solid-phase assays in which antibodies react with isolated HLA molecules in ELISA or in flow (23, 24). Especially, Luminex-based assays have gained a lot of popularity among the HLA laboratories (25, 26). Although these techniques are certainly more sensitive than CDC, the clinical relevance of the antibodies detected is not clear. Nevertheless, many centers are applying these assays already routinely for their patient care and patients are not transplanted, or desensitized, when noncomplement fixing donor-specific antibodies only detectable in Luminex are present. To check the possible clinical relevance of donor-specific antibodies, only detectable in Luminex, a retrospective analysis was performed by the group of Van den Berg-Loonen et al. (27). They reanalyzed the original peak sera of patients transplanted in the AM program only based on a negative CDC crossmatch by single-antigen Luminex beads. Patients who had donor-specific antibodies in Luminex had a higher incidence of acute graft rejection in the first 6 months after transplantation (biopsy proven) but graft survival was similar in patients with and without donor-specific antibodies in Luminex. This led to the preliminary conclusion that patients with donor-specific HLA antibodies detected by Luminex only tend to undergo more acute rejections but these antibodies do not have a detrimental effect on graft survival. Of course, confirmation in a larger patient group is necessary before final conclusions are drawn, but it is clear from this and many other studies (28–30) that the presence of donor-specific antibodies in Luminex does not have the same detrimental effect as donor-specific antibodies detectable by CDC. Donor-specific antibodies in Luminex may be considered a risk factor but are certainly not a contraindication for transplantation (1, 31). That is the reason why so far within Eurotransplant the AM program is only available for patients with CDC antibodies. Future studies are necessary to reveal which subpopulation of antibodies, detectable in Luminex (possibly dependent on antibody titer, immunoglobin class, or kind of sensitization), have a similar detrimental effect as CDC antibodies. Only these relevant antibodies should be taken into consideration in the decision whether a patient should be included in the AM program. Without this restriction, the exclusivity of the program would change enormously as many patients will end up to be highly sensitized if all positive reactions in Luminex are considered relevant. Recent adaptations of the luminex antibody detection such as monitoring of C4d-fixing antibodies (32) or IgG subclasses (33) may be useful in this perspective. OTHER OPTIONS The AM has proven to be a useful tool to transplant a large proportion of the highly sensitized patients in a short period of time. However, approximately 40% of the highly sensitized patients cannot be helped by the current procedure because no compatible donor will become available within the Eurotransplant population. A special tool has been developed on the Eurotransplant website to estimate the chance that a patient will be transplanted within the AM program (Fig. 4).FIGURE 4.: Website-based tool to calculate the chance that a compatible donor will become available for a patient included in the AM program.After introducing the patient’s own HLA antigens and the AMs, the program will calculate the chance that a compatible donor will be available within the Eurotransplant donor population. On the basis of this information, the clinician can decide whether it is worthwhile to wait until the patient will get a transplant via the AM program or whether alternative approaches should be used. At the moment, the only available alternatives are desensitization or for a limited number of patients in the Netherlands the National Paired Donor exchange program (34). However, to our opinion, there is a good opportunity to create an additional option for these patients. Based on the success of the Eurotransplant AM program, similar programs have recently been implemented in France and Greece, whereas implementation is in progress in Scandia transplant, Switzerland, and even Canada. It is to be expected that in the near future many more countries within Europe will implement a similar approach. This would open the possibility to introduce a common solution for patients who cannot be transplanted within the own allocation program. The alternative that we have in mind and that is currently investigated is the setup of an AM program Europe wide. Patients for whom the AMs have been determined but who cannot be transplanted in a reasonable time period within the local allocation program will be registered on one common European waiting list. When somewhere within Europe a donor becomes available, which is compatible with the HLA profile of an AM patient, the kidney should be mandatorily shipped to the recipient center, similar to the current protocol within Eurotransplant. This would mean an enormous extension of the donor population, and especially of the number of HLA phenotypes within the donor population, and related to that a significantly increased chance that one of these donors is compatible with a highly sensitized patient. The logistics of such an effort is a challenge but will be investigated in the near future. The long-lasting experience of Eurotransplant with international organ allocation will be certainly of benefit for the set up of such an exercise. ACKNOWLEDGMENTS The authors thank all transplantation centers and HLA laboratories within the Eurotransplant area for their constructive collaboration and participation in the acceptable mismatch program.

Organ donation and transplantation trends in the USA, 2003

Hiding in Plain Sight-A New Look at HLA Epitopes: A Case Report.

Antibody mediated rejection (ABMR) is the most common cause of long-term allograft loss in kidney transplantation (KT). Therefore, a low human leukocyte antigen (HLA) mismatch (MM) load is favorable for KT outcomes. Hitherto, serological or low-resolution molecular HLA typing have been adapted in parallel. Here, we aimed to identify previously missed HLA mismatches and corresponding antibodies by high resolution HLA genotyping in a living-donor KT cohort. 103 donor/recipient pairs transplanted at the University of Leipzig Medical Center between 1998 and 2018 were re-typed using next generation sequencing (NGS) of the HLA loci -A, -B, -C, -DRB1, -DRB345, -DQA1, -DQB1, -DPA1, and -DPB1. Based on these data, we compiled HLA MM counts for each pair and comparatively evaluated genomic HLA-typing with pre-transplant obtained serological/low-resolution HLA (=one-field) typing results. NGS HLA typing (=two-field) data was further used for reclassification of de novo HLA antibodies as "donor-specific". By two-field HLA re-typing, we were able to identify additional MM in 64.1% (n=66) of cases for HLA loci -A, -B, -C, -DRB1 and -DQB1 that were not observed by one-field HLA typing. In patients with biopsy proven ABMR, two-field calculated MM count was significantly higher than by one-field HLA typing. For additional typed HLA loci -DRB345, -DQA1, -DPA1, and -DPB1 we observed 2, 26, 3, and 23 MM, respectively. In total, 37.3% (69/185) of de novo donor specific antibodies (DSA) formation was directed against these loci (DRB345 ➔ n=33, DQA1 ➔ n=33, DPA1 ➔ n=1, DPB1 ➔ n=10). Our results indicate that two-field HLA typing is feasible and provides significantly more sensitive HLA MM recognition in living-donor KT. Furthermore, accurate HLA typing plays an important role in graft management as it can improve discrimination between donor and non-donor HLA directed cellular and humoral alloreactivity in the long range. The inclusion of additional HLA loci against which antibodies can be readily detected, HLA-DRB345, -DQA1, -DQB1, -DPA1, and -DPB1, will allow a more precise virtual crossmatch and better prediction of potential DSA. Furthermore, in living KT, two-field HLA typing could contribute to the selection of the immunologically most suitable donors.

Antibody-mediated rejection: analyzing the risk, proposing solutions.

Over the decade between 2003 and 2012, the UK has seen major changes in how organ donation and transplantation is delivered. The number of deceased organ donors has increased from 709 (12.0 per million population [pmp]) to 1,164 (18.3 pmp); this increase has been predominantly a result of an increase in donors after circulatory death (DCD) (from 1.1 pmp to 7.9 pmp) while the numbers of donors after brain death (DBD) has remained broadly stable (around 10.5 pmp). The donor population has become older (from 14% 60 years or over to 35%) and heavier (from 14% with body mass index >=30 kg/m2 to 23%). Despite these changes in demographic factors, the number of organs retrieved from DBD donors has risen from a mean of 3.6 to 4.0 per donor and for DCD donors from 2.2 to 2.6. The number of transplants in adults in 2012 was 2,709 (967 DBD, 708 DCD, and 1,034 living) for kidney alone, 246 pancreas (including 172 kidney and pancreas), 792 (611 DBD, 142 DCD, 36 living, and 3 domino) for liver, 136 for heart only, and 179 (145 DBD and 34 DCD) for lung only. Median waiting times to transplant for adult patients were 1,167, 339, 141, 293, and 311 days, respectively. The proportion of adult non-urgent registrants in 2009 (2007 for kidneys) who were removed from the waiting list or died awaiting a graft within 1 year was 3% for kidneys, 6% for pancreas, 19% for liver, 27% for heart, and 24% for lung. Outcomes after solid organ transplants are improving; for adult patients grafted between 2003 and 2005, 5-year graft survival for kidney is 84% (DBD), 87% (DCD), and 92% (living donor), for simultaneous kidney and pancreas 72%, and for pancreas alone 50% (DBD). Five-year patient survival for liver is 77% (DBD) and 68% (DCD), heart 67%, and lung 52% (DBD). Although rates of organ donation and transplantation have increased in the UK, this has been almost solely because of a rise in DCD donation. Although donor age and weight is increasing, graft survival has generally improved. Despite a recent fall in the number of patients on the transplant waiting list, there remains a significant gap between the need for transplantation and the number of organs available from deceased and living donors. The implementation of a new strategy following the recommendations of the Organ Donation Task Force in 2008 has had a major impact in bringing together clinicians involved in both organ donation and transplantation, and these changes and clinical enthusiasm have been instrumental in achieving success. With an emphasis on the need to increase the family consent rate for organ donation, which has failed to show any improvement over the last 5 years, a new UK strategy for organ donation and transplantation, introduced in 2013, will further increase organ transplantation in the UK.

Molecular characterisation of the monocytic cell line THP‐1 demonstrates a discrepancy with the documented HLA type

Simultaneous en-bloc pancreas and kidney transplantation from a small pediatric donor after circulatory death.

Rejection after spontaneous pancreas and kidney transplantation (SPK), especially the antibody-mediated rejection, is the main cause of allografts loss. Human leukocyte antigen (HLA) typing plays a crucial role in defense against the injury to the allograft by immune system of recipients. HLA antigen typing, especially the HLA molecular typing, could help to choose a compatible allograft for transplantation; and it might have a role in preventing and circumventing rejection, predicting the risk of immunogenicity posttransplantation, as well as guiding posttransplant immunosuppression strategies; thus, improving the allograft function. This paper tries to discuss the reseach progress of the function of HLA typing in SPK and clinical application of HLA typing for organ selection in SPK. Key words: Human leukocyte antigen typing; Spontaneous pancreas and kidney transplantation; Donor specific antibody; Rejection

OPTN/SRTR 2020 Annual Data Report: Introduction

Human leukocyte antigens (HLA) are unique proteins expressed on the surface of human cells, playing a pivotal role in the immune system, particularly in the contexts of infection, cancer, and transplantation. The widespread adoption of HLA typing methods has become an essential component in assessing donor-recipient compatibility, a crucial limiting factor in solid organ transplantation. In general, the greater the disparity between a donor's and recipient's HLA types, the higher the likelihood of provoking an alloimmune response, which frequently results in alloimmune graft rejection. With significant advancements in organ transplantation techniques, immunosuppressive medications, and surgical procedures, attention has increasingly turned toward understanding and managing humoral rejection processes. Pre-transplant antibody screening plays a critical role in identifying individuals with elevated levels of antibodies against potential donor antigens. This screening aids in risk assessment and planning to mitigate the risk of antibody-mediated rejection (AbMR). Several methods are available for assessing circulating antigen-specific antibodies and HLA tissue typing, including cell-based assays like serological assays, complement-dependent cytotoxicity, and flow cytometry. However, non-cell-based approaches, such as molecular methods, HLA imputation techniques and high-throughput HLA-matchmaker assays have gained significant popularity due to their ability to provide higher resolution and robust donor-recipient matching. Despite the advancements in precision and sensitivity observed in HLA cutting-edge technologies, numerous challenges still persist. These challenges involve complexities linked to allelic ambiguities, the differentiation of closely related alleles, and the ongoing effort to establish a standardized HLA testing methodology across diverse laboratories. Additionally, correlating the HLA crossmatch results with the clinical outcomes for transplant donors poses another important aspect that warrants attention and requires expert analysis. In this review, we will enumerate the different methods of HLA typing and DSA screening and discuss the unmet needs and future directions for HLA typing methods.

Transfusion-associated graft-versus-host disease.