Late graft failure of pig-to-rhesus renal xenografts has features of glomerulopathy and recipients have anti-swine leukocyte antigen class I and class II antibodies.

Prolonged survival in preclinical renal xenotransplantation demonstrates that early antibody mediated rejection (AMR) can be overcome. It is now critical to evaluate and understand the pathobiology of late graft failure and devise new means to improve post xenograft outcomes. In renal allotransplantation the most common cause of late renal graft failure is transplant glomerulopathy-largely due to anti-donor MHC antibodies, particularly anti-HLA DQ antibodies. We evaluated the pig renal xenograft pathology of four long-surviving (>300 days) rhesus monkeys. We also evaluated the terminal serum for the presence of anti-SLA class I and specifically anti-SLA DQ antibodies. All four recipients had transplant glomerulopathy and expressed anti-SLA DQ antibodies. In one recipient tested for anti-SLA I antibodies, the recipient had antibodies specifically reacting with two of three SLA I alleles tested. These results suggest that similar to allotransplantation, anti-MHC antibodies, particularly anti-SLA DQ, may be a barrier to improved long-term xenograft outcomes.

Immune monitoring in pediatric kidney transplant.

BACKGROUND: Long-term outcomes in pediatric kidney transplantation remain suboptimal, largely related to chronic rejection. Creatinine is a late marker of renal injury, and more sensitive, early markers of allograft injury are an active area of current research. METHODS: This is an educational review summarizing existing strategies for monitoring for rejection in kidney transplant recipients. RESULTS: We summarize supporting currently available clinical tests, including surveillance biopsy, donor specific antibodies, and donor-derived cell free DNA, as well as the potential limitations of these studies. In addition, we review the current avenues of active research, including transcriptomics, proteomics, metabolomics, and torque tenovirus levels. CONCLUSION: Advancing the use of noninvasive immune monitoring will depend on well-designed multicenter trials that include patients with stable graft function, include biopsy results on all patients, and can demonstrate both association with a patient-relevant clinical endpoint such as graft survival or change in glomerular filtration rate and a potential timepoint for intervention.

Impact of Transient and Persistent Donor-Specific Antibodies in Lung Transplantation.

Lung transplantation (LuTx) is an established treatment for patients with end-stage lung diseases, however, outcomes are limited by acute and chronic rejection. One aspect that has received increasing attention is the role of the host's humoral alloresponse, particularly the formation of de novo donor-specific antibodies (dnDSAs). The aim of this study was to investigate the clinical significance of transient and persistent dnDSAs and to understand their impact on outcomes after LuTx. A retrospective analysis was conducted using DSA screening data from LuTx recipients obtained at the Medical University of Vienna between February 2016 and March 2021. Of the 405 LuTx recipients analyzed, 205 patients developed dnDSA during the follow-up period. Among these, 167 (81%) had transient dnDSA and 38 (19%) persistent dnDSA. Persistent but not transient dnDSAs were associated with chronic lung allograft dysfunction (CLAD) and antibody-mediated rejection (AMR) (p < 0.001 and p = 0.006, respectively). CLAD-free survival rates for persistent dnDSAs at 1-, 3-, and 5-year post-transplantation were significantly lower than for transient dnDSAs (89%, 59%, 56% vs. 91%, 79%, 77%; p = 0.004). Temporal dynamics of dnDSAs after LuTx have a substantial effect on patient outcomes. This study underlines that the persistence of dnDSAs poses a significant risk to graft and patient survival.

Cellular strategies to induce immune tolerance after liver transplantation: Clinical perspectives.

Liver transplantation (LT) has become the most efficient treatment for pediatric and adult end-stage liver disease and the survival time after transplantation is becoming longer due to the development of surgical techniques and perioperative management. However, long-term side-effects of immunosuppressants, like infection, metabolic disorders and malignant tumor are gaining more attention. Immune tolerance is the status in which LT recipients no longer need to take any immunosuppressants, but the liver function and intrahepatic histology maintain normal. The approaches to achieve immune tolerance after transplantation include spontaneous, operational and induced tolerance. The first two means require no specific intervention but withdrawing immunosuppressant gradually during follow-up. No clinical factors or biomarkers so far could accurately predict who are suitable for immunosuppressant withdraw after transplantation. With the understanding to the underlying mechanisms of immune tolerance, many strategies have been developed to induce tolerance in LT recipients. Cellular strategy is one of the most promising methods for immune tolerance induction, including chimerism induced by hematopoietic stem cells and adoptive transfer of regulatory immune cells. The safety and efficacy of various cell products have been evaluated by prospective preclinical and clinical trials, while obstacles still exist before translating into clinical practice. Here, we will summarize the latest perspectives and concerns on the clinical application of cellular strategies in LT recipients.

Recombinant human IL-37 attenuates acute cardiac allograft rejection in mice.

BACKGROUND: Allograft rejection remains a major obstacle to long-term graft survival. Although previous studies have demonstrated that IL-37 exhibited significant immunomodulatory effects in various diseases, research on its role in solid organ transplantation has not been fully elucidated. In this study, the therapeutic effect of recombinant human IL-37 (rhIL-37) was evaluated in a mouse cardiac allotransplantation model. METHODS: The C57BL/6 recipients mouse receiving BALB/c donor hearts were treated with rhIL-37. Graft pathological and immunohistology changes, immune cell populations, and cytokine profiles were analyzed on postoperative day (POD) 7. The proliferative capacities of Th1, Th17, and Treg subpopulations were assessed in vitro. Furthermore, the role of the p-mTOR pathway in rhIL-37-induced CD4+ cell inhibition was also elucidated. RESULTS: Compared to untreated groups, treatment of rhIL-37 achieved long-term cardiac allograft survival and effectively alleviated allograft rejection indicated by markedly reduced infiltration of CD4+ and CD11c+ cells and ameliorated graft pathological changes. rhIL-37 displayed significantly less splenic populations of Th1 and Th17 cells, as well as matured dendritic cells. The percentages of Tregs in splenocytes were significantly increased in the therapy group. Furthermore, rhIL-37 markedly decreased the levels of TNF-α and IFN-γ, but increased the level of IL-10 in the recipients. In addition, rhIL-37 inhibited the expression of p-mTOR in CD4+ cells of splenocytes. In vitro, similar to the in vivo experiments, rhIL-37 caused a decrease in the proportion of Th1 and Th17, as well as an increase in the proportion of Treg and a reduction in p-mTOR expression in CD4+ cells. CONCLUSIONS: We demonstrated that rhIL-37 effectively suppress acute rejection and induce long-term allograft acceptance. The results highlight that IL-37 could be novel and promising candidate for prevention of allograft rejection.

Memory B-cell derived donor-specific antibodies do not predict outcome in sensitized kidney transplant recipients: a retrospective single-center study.

Background: Repeated exposure to sensitizing events can activate HLA-specific memory B cells, leading to the production of donor-specific memory B cell antibodies (DSAm) that pose a risk for antibody-mediated rejection (ABMR) in kidney transplant recipients (KTRs). This single-center retrospective study aimed to identify DSAm and assess their association with outcomes in a cohort of KTRs with pretransplant serum donor-specific antibodies (DSA). Methods: We polyclonally activated pretransplant peripheral blood mononuclear cells (PBMCs) from 60 KTRs in vitro, isolated and quantified IgG from the culture supernatant using ELISA, and analyzed the HLA antibodies of eluates with single antigen bead (SAB) assays, comparing them to the donor HLA typing for potential DSAm. Biopsies from 41 KTRs were evaluated for rejection based on BANFF 2019 criteria. Results: At transplantation, a total of 37 DSAm were detected in 26 of 60 patients (43%), of which 13 (35%) were found to be undetectable in serum. No significant association was found between pretransplant DSAm and ABMR (P=0.53). Similar results were observed in a Kaplan-Meier analysis for ABMR within the first year posttransplant (P=0.29). Additionally, MFI levels of DSAm showed no significant association with ABMR (P=0.28). Conclusion: This study suggests no significant association between DSAm and biopsy-proven clinical ABMR. Further prospective research is needed to determine whether assessing DSAm could enhance existing immunological risk assessment methods for monitoring KTRs, particularly in non-sensitized KTRs.

Maximizing matching, equity and survival in kidney transplantation using molecular HLA immunogenicity quantitation.

HLA matching improves long-term outcomes of kidney transplantation, yet implementation challenges persist, particularly within the African American (Black) patient demographic due to donor scarcity. Consequently, kidney survival rates among Black patients significantly lag behind those of other racial groups. A refined matching scheme holds promise for improving kidney survival, with prioritized matching for Black patients potentially bolstering rates of HLA-matched transplants. To facilitate quantity, quality and equity in kidney transplants, we propose two matching algorithms based on quantification of HLA immunogenicity using the hydrophobic mismatch score (HMS) for prospective transplants. We mined the national transplant patient database (SRTR) for a diverse group of donors and recipients with known racial backgrounds. Additionally, we use novel methods to infer survival assessment in the simulated transplants generated by our matching algorithms, in the absence of actual target outcomes, utilizing modified unsupervised clustering techniques. Our allocation algorithms demonstrated the ability to match 87.7% of Black and 86.1% of White recipients under the HLA immunogenicity threshold of 10. Notably, at the lowest HMS threshold of 0, 4.4% of Black and 12.1% of White recipients were matched, a marked increase from the 1.8% and 6.6% matched under the prevailing allocation scheme. Furthermore, our allocation algorithms yielded similar or improved survival rates, as illustrated by Kaplan-Meier (KM) curves, and enhanced survival prediction accuracy, evidenced by C-indices and Integrated Brier Scores.

The balance between memory and regulatory cell populations in kidney transplant recipients with operational tolerance.

Donor-reactive memory cells represent a barrier to long-term kidney graft survival. A better understanding of regulatory mechanisms that counterbalance alloreactive memory responses may help to identify patients with operational tolerance. This prospective study investigated the equilibrium between memory T-cell subsets and regulatory T or B cells (Tregs, Bregs) in peripheral blood of kidney transplant recipients with operational tolerance (N = 8), chronic rejection (N = 8), and different immunosuppressive treatment regimens (N = 81). Patients on hemodialysis and healthy individuals served as controls (N = 50). In addition, the expression of Treg- and Breg-associated molecule genes was analyzed. Patients with chronic rejection showed a disrupted memory T-cell composition with a significantly higher frequency of circulating CD8+ terminally differentiated effector memory (TEMRA) T cells than patients with operational tolerance, patients on hemodialysis, or healthy controls (P < 0.001). Low frequency of CD8+ TEMRA and high frequency of Tregs and transitional Bregs were found in operationally tolerant patients. Consequently, operationally tolerant patients showed, as compared to all other transplant recipients with different immunosuppressive regiments, the lowest ratios between CD8+ TEMRA T cells and Tregs or Bregs (for both P < 0.001). Moreover, a specific peripheral blood transcription pattern was found in operationally tolerant patients with an increased expression of Breg- and Treg-associated genes CD22 and FoxP3 and a decreased FcγRIIA/FcγRIIB transcript ratio (for all P < 0.001). In conclusion, monitoring the balance between circulating CD8+ TEMRA T cells and regulatory cell subsets and their transcripts may help to distinguish transplant recipients with operational tolerance from recipients at risk of graft loss.

Pigs in Transplantation Research and Their Potential as Sources of Organs in Clinical Xenotransplantation.

The pig has long been used as a research animal and has now gained importance as a potential source of organs for clinical xenotransplantation. When an organ from a wild-type (i. e., genetically unmodified) pig is transplanted into an immunosuppressed nonhuman primate, a vigorous host immune response causes hyperacute rejection (within minutes or hours). This response has been largely overcome by 1) extensive gene editing of the organ-source pig and 2) the administration to the recipient of novel immunosuppressive therapy based on blockade of the CD40/CD154 T cell costimulation pathway. Gene editing has consisted of 1) deletion of expression of the 3 known carbohydrate xenoantigens against which humans have natural (preformed) antibodies and 2) the introduction of human 'protective' genes. The combination of gene editing and novel immunosuppressive therapy has extended life-supporting pig kidney graft survival to greater than 1 y and of pig heart survival to up to 9 mo. This review briefly describes the techniques of gene editing, the potential risks of transfer of porcine endogenous retroviruses with the organ, and the need for breeding and housing of donor pigs under biosecure conditions.

DQB1 antigen matching improves rejection-free survival in pediatric heart transplant recipients.

BACKGROUND: Presence of donor-specific antibodies (DSAs), particularly to class II antigens, remains a major challenge in pediatric heart transplantation. Donor-recipient human leukocyte antigen (HLA) matching is a potential strategy to mitigate poor outcomes associated with DSAs. We evaluated the hypothesis that antigen mismatching at the DQB1 locus is associated with worse rejection-free survival. METHODS: Data were collected from Scientific Registry of Transplant Recipients for all pediatric heart transplant recipients 2010-2021. Only transplants with complete HLA typing at the DQB1 locus for recipient and donor were included. Primary outcome was rejection-free graft survival through 5 years. RESULTS: Of 5,115 children, 4,135 had complete DQB1 typing and were included. Of those, 503 (12%) had 0 DQB1 donor-recipient mismatches, 2,203 (53%) had 1, and 1,429 (35%) had 2. Rejection-free survival through 5 years trended higher for children with 0 DQB1 mismatches (68%), compared to those with 1 (62%) or 2 (63%) mismatches (pairwise p = 0.08 for both). In multivariable analysis, 0 DQB1 mismatches remained significantly associated with improved rejection-free graft survival compared to 2 mismatches, while 1 DQB1 mismatch was not. Subgroup analysis showed the strongest effect in non-Hispanic Black children and those undergoing retransplant. CONCLUSIONS: Matching at the DQB1 locus is associated with improved rejection-free survival after pediatric heart transplant, particularly in Black children, and those undergoing retransplant. Assessing high-resolution donor typing at the time of allocation may further corroborate and refine this association. DQB1 matching may improve long-term outcomes in children stabilized either with optimal pharmacotherapy or supported with durable devices able to await ideal donors.

T-cell receptor sequencing reveals selected donor-reactive CD8+ T cell clones resist antithymocyte globulin depletion after kidney transplantation.

High frequencies of donor-reactive memory T cells in the periphery of transplant candidates prior to transplantation are linked to the development of posttransplant acute rejection episodes and reduced allograft function. Rabbit antithymocyte globulin (rATG) effectively depletes naïve CD4+ and CD8+ T cells for >6 months posttransplant, but rATG's effects on human donor-reactive T cells have not been carefully determined. To address this, we performed T cell receptor ß-chain sequencing on peripheral blood mononuclear cells aliquots collected pretransplant and serially posttransplant in 7 kidney transplant recipients who received rATG as induction therapy. We tracked the evolution of the donor-reactive CD4+ and CD8+ T cell repertoires and identified stimulated pretransplant, CTV-(surface dye)-labeled, peripheral blood mononuclear cells from each patient with donor cells or third-party cells. Our analyses showed that while rATG depleted CD4+ T cells in all tested subjects, a subset of donor-reactive CD8+ T cells that were present at high frequencies pretransplant, consistent with expanded memory cells, resisted rATG depletion, underwent posttransplant expansion and were functional. Together, our data support the conclusion that a subset of human memory CD8+ T cells specifically reactive to donor antigens expand in vivo despite induction therapy with rATG and thus have the potential to mediate allograft damage.

Natural killer cell functional genetics and donor-specific antibody-triggered microvascular inflammation.

Antibody-mediated rejection (ABMR) is a leading cause of graft failure. Emerging evidence suggests a significant contribution of natural killer (NK) cells to microvascular inflammation (MVI). We investigated the influence of genetically determined NK cell functionality on ABMR development and activity. The study included 86 kidney transplant recipients subjected to systematic biopsies triggered by donor-specific antibody detection. We performed killer immunoglobulin-like receptor typing to predict missing self and genotyped polymorphisms determining NK cell functionality (FCGR3AV/F158 [rs396991], KLRC2wt/del, KLRK1HNK/LNK [rs1049174], rs9916629-C/T). Fifty patients had ABMR with considerable MVI and elevated NK cell transcripts. Missing self was not related to MVI. Only KLRC2wt/wt showed an association (MVI score: 2 [median; interquartile range: 0-3] vs 0 [0-1] in KLRC2wt/del recipients; P = .001) and remained significant in a proportional odds multivariable model (odds ratio, 7.84; 95% confidence interval, 2.37-30.47; P = .001). A sum score incorporating all polymorphisms and missing self did not outperform a score including only KLRC2 and FCGR3A variants, which were predictive in univariable analysis. NK cell genetics did not affect graft functional decline and survival. In conclusion, a functional KLRC2 polymorphism emerged as an independent determinant of ABMR activity, without a considerable contribution of missing self and other NK cell gene polymorphisms.

Co-transplantation of autologous Treg cells in a cell therapy for Parkinson's disease.

The specific loss of midbrain dopamine neurons (mDANs) causes major motor dysfunction in Parkinson's disease, which makes cell replacement a promising therapeutic approach1-4. However, poor survival of grafted mDANs remains an obstacle to successful clinical outcomes5-8. Here we show that the surgical procedure itself (referred to here as 'needle trauma') triggers a profound host response that is characterized by acute neuroinflammation, robust infiltration of peripheral immune cells and brain cell death. When midbrain dopamine (mDA) cells derived from human induced pluripotent stem (iPS) cells were transplanted into the rodent striatum, less than 10% of implanted tyrosine hydroxylase (TH)+ mDANs survived at two weeks after transplantation. By contrast, TH- grafted cells mostly survived. Notably, transplantation of autologous regulatory T (Treg) cells greatly modified the response to needle trauma, suppressing acute neuroinflammation and immune cell infiltration. Furthermore, intra-striatal co-transplantation of Treg cells and human-iPS-cell-derived mDA cells significantly protected grafted mDANs from needle-trauma-associated death and improved therapeutic outcomes in rodent models of Parkinson's disease with 6-hydroxydopamine lesions. Co-transplantation with Treg cells also suppressed the undesirable proliferation of TH- grafted cells, resulting in more compact grafts with a higher proportion and higher absolute numbers of TH+ neurons. Together, these data emphasize the importance of the initial inflammatory response to surgical injury in the differential survival of cellular components of the graft, and suggest that co-transplanting autologous Treg cells effectively reduces the needle-trauma-induced death of mDANs, providing a potential strategy to achieve better clinical outcomes for cell therapy in Parkinson's disease.

Rejection and graft outcomes in kidney transplant recipients with and without angiotensin II receptor type 1 antibodies.

AIM: Angiotensin II type 1 receptor antibody (AT1R Ab) is a non-Human Leucocyte Antigen (HLA) antibody that is maybe associated with early severe kidney transplant rejection and worse graft outcomes. This study aimed to assess the association between AT1R Ab and kidney transplant rejection and graft outcomes. METHODS: We performed a retrospective analysis of all adult kidney transplant recipients in an Australian centre who had an AT1R Ab test between 1 January 2015 to 30 June 2020. AT1R Ab positive patients were compared to AT1R Ab negative patients. Primary outcomes were rejection risk, type and histopathological severity scores. Secondary outcomes were 8-week graft function and graft loss. RESULTS: Of 965 kidney transplants that were performed during the study period, 73 patients had AT1R Ab tested; 16 (22%) were positive and 57(78%) were negative. Positive patients were on average younger and had higher level of donor-specific HLA antibodies. Rejection occurred in 13 (81%) positive patients and 41 (72%) negative patients (P = 0.45). No significant differences in rejection type or severity were found. HLA mismatch and peak panel reactive antibody ≥80%, but not AT1R Ab, independently predicted rejection. Average (132 vs. 177 mmol/L, P = 0.302) and graft loss were not significantly different between groups. CONCLUSION: The study found no evidence that AT1R Ab is associated with rejection type, severity or worse graft function. Future studies should assess its relationship with graft outcomes to help complement immunological risk assessment and potentially provide therapeutic options to alter outcomes.

Reduced Satb1 expression predisposes CD4+ T conventional cells to Treg suppression and promotes transplant survival.

Limiting CD4+ T cell responses is important to prevent solid organ transplant rejection. In a mouse model of costimulation blockade-dependent cardiac allograft tolerance, we previously reported that alloreactive CD4+ conventional T cells (Tconvs) develop dysfunction, losing proliferative capacity. In parallel, induction of transplantation tolerance is dependent on the presence of regulatory T cells (Tregs). Whether susceptibility of CD4+ Tconvs to Treg suppression is modulated during tolerance induction is unknown. We found that alloreactive Tconvs from transplant tolerant mice had augmented sensitivity to Treg suppression when compared with memory T cells from rejector mice and expressed a transcriptional profile distinct from these memory T cells, including down-regulated expression of the transcription factor Special AT-rich sequence-binding protein 1 (Satb1). Mechanistically, Satb1 deficiency in CD4+ T cells limited their expression of CD25 and IL-2, and addition of Tregs, which express higher levels of CD25 than Satb1-deficient Tconvs and successfully competed for IL-2, resulted in greater suppression of Satb1-deficient than wild-type Tconvs in vitro. In vivo, Satb1-deficient Tconvs were more susceptible to Treg suppression, resulting in significantly prolonged skin allograft survival. Overall, our study reveals that transplantation tolerance is associated with Tconvs' susceptibility to Treg suppression, via modulated expression of Tconv-intrinsic Satb1. Targeting Satb1 in the context of Treg-sparing immunosuppressive therapies might be exploited to improve transplant outcomes.

CTLA4-Ig mediated immunosuppression favors immunotolerance and restores graft in mouse airway transplants.

CTLA4-Ig is a potent costimulatory blocker that inhibits T cell activation during alloimmune inflammation and increases graft survival and function. CTLA4-Ig-mediated immunosuppression has been demonstrated to support transplant function in various clinical trials and preclinical settings, but its effects on the balance between regulatory T cells (Tregs) and effector T cells (Teffs), as well as complement activation, are less well investigated. In the present study, we proposed to investigate the effects of CTLA4-Ig mediated immunosuppression on the phase of immunotolerance and the subsequent graft microvascular and epithelial repair during the progression of subepithelial fibrosis in a mouse model of orthotopic trachea transplantation. Briefly, CTLA4-Ig treated allografts (2 mg/kg, I.P.), untreated allografts, and syngrafts were serially monitored for peripheral FOXP3+ Tregs, antibody-mediated complement activation (C3d and C4d), tissue oxygenation, donor-recipient microvascular blood flow, and subsequent tissue remodeling following transplantation. Our data demonstrate that CTLA4-Ig mediated immunosuppression significantly results in late increases in both peripheral CD4+/CD8+ FOXP3+ Tregs and serum IL-10, but prevents the microvascular deposition of IgG, complement factor C3d, and epithelial C4d respectively, which proportionally improved blood flow and tissue oxygenation in the graft and, thus, promotes graft repair. Also, it restored the airway lumen, epithelium, and prevented the progression of subepithelial collagen deposition up to 90 days after transplantation. This study demonstrates that CTLA4-Ig-mediated immunosuppression potentially modulates both effector response and a late surge of regulatory activity to preserve graft microvasculature and rescue allograft from sustained hypoxia and ischemia and thereby limits subepithelial fibrosis.

Influence of Calcineurin Inhibitor Choice on Outcomes in Kidney Transplant Recipients Aged ≥60 Y: A Collaborative Transplant Study Report.

BACKGROUND: Patients aged ≥60 y represent the fastest growing population among kidney transplant recipients and waitlist patients. They show an elevated infection risk and are frequently transplanted with multiple human leukocyte antigen mismatches. Whether the choice of calcineurin inhibitor influences graft survival, mortality, or key secondary outcomes such as infections in this vulnerable recipient population is unknown. METHODS: A total of 31 177 kidney transplants from deceased donors performed between 2000 and 2019 at European centers and reported to the Collaborative Transplant Study were analyzed using multivariable Cox and logistic regression analyses. All recipients were ≥60 y old and received tacrolimus (Tac) or cyclosporine A on an intention-to-treat basis, combined with mycophenolic acid or azathioprine plus/minus steroids. RESULTS: The risk of 3-y death-censored graft loss and patient mortality did not differ significantly between Tac- and cyclosporine A-treated patients (hazard ratio 0.98 and 0.95, P = 0.74 and 0.20, respectively). No difference was found in the overall risk of hospitalization for infection (hazard ratio = 0.95, P = 0.19); however, a lower incidence of rejection treatment (hazard ratio = 0.81, P < 0.001) was observed in Tac-treated patients. Assessment of pathogen-specific hospitalizations revealed no difference in the risk of hospitalization due to bacterial infection (odds ratio = 1.00, P = 0.96), but a significantly higher risk of hospitalization due to human polyomavirus infection was found among Tac-treated patients (odds ratio = 2.45, P = 0.002). The incidence of de novo diabetes was higher for Tac-based immunosuppression (odds ratio = 1.79, P < 0.001). CONCLUSIONS: Calcineurin inhibitor selection has no significant influence on death-censored graft survival, mortality, and overall infection risk in ≥60-y-old kidney transplant recipients.

Human leukocyte antigen eplet mismatching is associated with increased risk of graft loss and rejection after pediatric heart transplant.

BACKGROUND: While mismatching between donor and recipient human leukocyte antigen (HLA) alleles has been associated with increased graft loss in pediatric heart recipients, it is actually the surface amino acid structures, termed eplets, which determine the antigenicity of each HLA molecule. We hypothesized that HLA eplet mismatch analysis is a better predictor of adverse outcomes after pediatric heart transplant than conventional allele mismatch comparison. METHODS: A retrospective review of the Pediatric Heart Transplant Society database identified pediatric heart recipients (<18 years at listing) with complete donor and recipient HLA typing (A, B, and DR). Imputed high-resolution HLA genotypes were entered into HLAMatchmaker software which then calculated the number of eplet mismatches between each donor-recipient pair. Multivariable Cox regression analysis was used to examine associations between allele or eplet mismatching and adverse outcomes. RESULTS: Compared to those with <20 HLA class I eplet mismatches, recipients with 20 or more HLA class I eplet mismatches had an increased risk of graft loss (HR 1.46 [1.01-2.12], p = .049). HLA class I eplet mismatching was also associated with rejection (>20 mismatches: HR 1.30 [1.03-1.65], p = .030), while HLA class II eplet mismatching was associated with specified antibody-mediated rejection (10-20 mismatches: HR 1.57 [1.06-2.34], p = .025; >20 mismatches: HR 3.14 [1.72-5.71], p < .001). Neither HLA class I nor class II allele mismatching was significantly associated with graft loss or rejection. CONCLUSION: Eplet mismatch analysis was more predictive of adverse post-transplant outcomes (including graft loss and rejection) than allele mismatch comparison. Further study, including prospective high-resolution HLA typing, is warranted.

The Neuropeptide Alpha-Melanocyte-Stimulating Hormone Is Critical for Corneal Endothelial Cell Protection and Graft Survival after Transplantation.

Corneal transplantation is the most common form of tissue transplantation. The success of corneal transplantation mainly relies on the integrity of corneal endothelial cells (CEnCs), which maintain tissue transparency by pumping out excess water from the cornea. After transplantation, the rate of CEnC loss far exceeds that seen with normal aging, which can threaten sight. The underlying mechanisms are poorly understood. Alpha-melanocyte-stimulating hormone (α-MSH) is a neuropeptide that is constitutively found in the aqueous humor with both cytoprotective and immunomodulatory effects. The curent study found high expression of melanocortin 1 receptor (MC1R), the receptor for α-MSH, on CEnCs. The effect of α-MSH/MC1R signaling on endothelial function and allograft survival in vitro and in vivo was investigated using MC1R signaling-deficient mice (Mc1re/e mice with a nonfunctional MC1R). Herein, the results indicate that in addition to its well-known immunomodulatory effect, α-MSH has cytoprotective effects on CEnCs after corneal transplantation, and the loss of MC1R signaling significantly decreases long-term graft survival in vivo. In conclusion, α-MSH/MC1R signaling is critical for CEnC function and graft survival after corneal transplantation.

Maternal versus paternal living kidney transplant donation is associated with lower rejection in young pediatric recipients: A Collaborative Transplant Study report.

BACKGROUND: Approximately 1700 children per year with end-stage kidney disease undergo kidney transplantation in Europe and the United States of America; 30%-50% are living donor kidney transplantations. There may be immunological differences between paternal and maternal donors due to transplacental exchange of cells between the mother and fetus during pregnancy leading to microchimerism. We investigated whether the outcome of living-related kidney transplantation in young children is different after maternal compared with paternal organ donation. METHODS: Using the international Collaborative Transplant Study (CTS) database, we analyzed epidemiological data of 7247 children and adolescents aged <18 years who had received a kidney transplant from either mother or father. Risk of treated rejection episodes and death-censored graft failure were computed using the Kaplan-Meier method and multivariable Cox regression. RESULTS: In the recipient age group 1-4 years, the rate of treated rejection episodes in recipients of kidneys from maternal donors (N = 195) during the first 2 years post-transplant was significantly lower (hazard ratio HR = 0.47, p = .004) than in patients receiving kidneys from paternal donors (N = 179). This association between donor sex and risk of treated rejections was not observed in children aged 5-9 years. The 5-year death-censored graft survival in children aged 1-4 years with a maternal or paternal donor was comparable. CONCLUSIONS: Maternal kidney donation in young pediatric renal transplant recipients is associated with an approximately 50% lower rate of treated rejection than paternal kidney donation. Whether this phenomenon is due to maternal microchimerism-induced donor-specific hyporesponsiveness must be evaluated in prospective mechanistic studies.