Transplantation

BackgroundOrgan availability limits kidney transplantation, the best treatment for end-stage kidney disease. Globally, deceased donor acceptance criteria have been relaxed to include older donors, which comes with a higher risk of inferior posttransplant outcomes. Donor age, although negatively impacts transplant outcomes, lacks granularity in predicting graft dysfunction. Better donor kidney assessment and characterization of the biological mechanisms underlying age-associated donor organ damage and transplant outcomes is key to improving donor kidney utilisation and transplant longevity. Methods185 deceased pretransplant biopsies (from brain and circulatory death donors aged 18-78 years) were obtained from the Quality in Organ Donation (QUOD) biobank and proteomic profiles were acquired by mass spectrometry. Machine learning exploration using prediction rule ensembles guided LASSO regression modeling of kidney proteomes that identified protein signatures and biological mechanisms associated with 12-m posttransplant outcome. Data modeling was validated on held-out data and contextualised against published spatially resolved kidney injury related transcriptomes. ResultsOur analysis highlighted that outcomes were best modeled using combination of donor age and protein abundance signatures, revealing 539 proteins with these characteristics. Modeled age:protein interactions demonstrated stronger associations with transplant outcomes than age and protein alone and revealed mechanisms of kidney injury including metabolic changes and innate immune responses correlated with poor outcome. Comparison to single-cell transcriptome data suggests protein-outcome associations to specific cell types. ConclusionsMolecular signatures resulted from integration of donor age and proteomic profiles in deceased donor kidney biopsies offer the potential to develop improved pretransplant organ assessment and aid decisions on perfusion interventions.

The long-term impact of SARS-CoV-2 infection on kidney allograft survival remains incompletely understood, particularly regarding the influence of vaccination, acute kidney injury (AKI), and post-infection immunosuppression. We conducted a retrospective analysis of 129 kidney transplant recipients with confirmed SARS-CoV-2 infection between March 2020 and March 2022 with a median follow-up of 50 months. Among 129 recipients, 106 (82%) received vaccination at any time before or after SARS-CoV-2 infection (82%) while 23 (18%) remained unvaccinated. Unvaccinated patients experienced significantly lower long-term graft survival (52% vs. 85%; p = 0.0004) and patient survival (83% vs. 99%; p = 0.0003) compared with vaccinated recipients. AKI occurred in 15% of recipients and independently predicted graft failure (aHR 2.88; p = 0.0341). Post-SARS-CoV-2 serum creatinine and albuminuria were strong prognostic markers of graft loss. Unvaccinated status independently predicted graft failure in both transplantation-anchored (aHR 2.80; p = 0.0342) and SARS-CoV-2-anchored models (aHR 5.31; p = 0.0004). Continuation of mycophenolate mofetil at post-infection assessment was associated with reduced graft-failure risk (aHR 0.99; p = 0.0193). These findings underscore the importance of sustained vaccination in preserving long-term allograft function.

BackgroundKidney transplant recipients (KTR) have a diminished response to SARS-CoV-2 vaccination in comparison to immunocompetent individuals. Deeper understanding of the antibody response in KTRs following third-dose vaccination would enable identification of those who remain unprotected against Omicron and require additional treatment strategies. MethodsWe profiled antibody responses in KTRs pre- and at one and three months post-third-dose SARS-CoV2 mRNA-based vaccine. Anti-spike and anti-RBD IgG levels were determined by ELISA. Neutralization against wild-type, Beta, Delta and Omicron (BA.1) variants was determined using a SARS-CoV-2 spike pseudotyped lentivirus assay. Results44 KTRs were analysed at 1 and 3 months (n=26) post-third-dose. At one month, the proportion of participants with a robust antibody response had increased significantly from baseline, but Omicron-specific neutralizing antibodies were detected in just 45% of KTRs. Median binding antibody levels declined at 3 months, but the proportion of KTRs with a robust antibody response was unchanged. 38.5% KTRs maintained Omicron-specific neutralization at 3 months. No clinical variables were significantly associated with detectable Omicron neutralizing antibodies, but anti-RBD titres appeared to identify those with Omicron-specific neutralizing capacity. ConclusionOver 50% of KTRs lack an Omicron-specific neutralization response 1 month following a third mRNA-vaccine dose. Among responders, binding and neutralizing antibody responses were well preserved at 3 months. Anti-RBD antibody titres may be a useful identifier of patients with detectable Omicron neutralizing antibody response. Trial registrationClinical Trials Ontario: ID 3604 FundingFunded by the St. Michaels Hospital Foundation (CMM, DAY) and the Public Health Agency of Canada, through the COVID-19 Immunity Task Force (MAH, MJO, AL).

BackgroundDespite current matching efforts to identify optimal donor-recipient pairs in kidney transplantation, alloimmunity remains a major proponent of late transplant failure. While kidney allocation based on human leukocyte antigen (HLA) matching has markedly prolonged short-term graft survival, new data suggests that additional genetic parameters in donor-recipient matching could help improve the long-term outcomes. Here, we studied the impact of a recently discovered non-muscle myosin heavy chain 9 gene (MYH9) polymorphism on kidney allograft failure. MethodsWe conducted a prospective observational cohort study, analyzing the DNA of 1,271 kidney donor-recipient transplant pairs from a single academic hospital for the MYH9 rs11089788 C>A polymorphism. The association of the MYH9 genotype with the risk of graft failure (primary outcome), biopsy-proven acute rejection (BPAR), and delayed graft function (DGF) (secondary outcomes) were determined. ResultsThe MYH9 polymorphism in the donor was not associated with 15-year death-censored kidney graft survival, whereas a trend was seen for the association between the MYH9 polymorphism in the recipient and graft failure (recessive model, P=0.056). Having the AA-genotype of the MYH9 polymorphism in recipients was associated with a higher risk of DGF (P=0.031) and BPAR (P=0.021), although the significance was lost after adjustment for potential confounders (P=0.15 and P=0.10, respectively). The combined presence of the MYH9 polymorphism in donor-recipient pairs was significantly associated with long-term kidney allograft survival (P=0.036), in which recipients with an AA-genotype receiving a graft with an AA-genotype had the worst outcome. After adjustment for covariates, this combined genotype remained significantly associated with 15-year death-censored kidney graft survival (HR 1.68, 95%-CI: 1.05 - 2.70, P=0.031). ConclusionsOur results reveal that recipients with an AA-genotype MYH9 polymorphism receiving a donor kidney with an AA-genotype, have a significantly elevated risk of graft failure after kidney transplantation. Key pointsO_LIIn recipients, the MYH9 SNP was associated with delayed graft function and biopsy-proven acute rejection after kidney transplantation, although the significance was lost in multivariable analysis. C_LIO_LIPresence of the MYH9 variant in both the donor and recipient significantly associated with long-term kidney allograft survival in multivariable analysis. C_LIO_LIOur present findings suggests that matching donor-recipient transplant pairs based on the MYH9 polymorphism may attenuate the risk of graft loss. C_LI

AimAllograft survival post-kidney transplantation (KT) are in large part attributed to genetics, which render the recipient susceptible or protected from allograft rejection. KT studies involving single nucleotide polymorphisms (SNPs) have reported the association of interleukin-18 (IL-18) with KT and its role in allograft rejection. However, the reported outcomes been inconsistent, prompting a meta-analysis to obtain more precise estimates. MethodsWe posed two hypotheses about the IL-18 SNPs: their association with KT (H1), and increase or decrease in the risks of allograft rejection (H2). Using standard genetic models, we estimated odds ratios [ORs] and 95% confidence intervals by comparing the IL-18 genotypes between two groups: (i) patients and controls for H1 (GD: genotype distribution analysis); (ii) rejectors and non-rejectors for H2 (allograft analysis). Multiple comparisons were corrected with the Holm-Bonferroni (HB) test. Subgrouping was ethnicity-based (Asians and Caucasians). Heterogeneity was outlier-treated and robustness of outcomes was sensitivity-treated. ResultsThis metaanalysis generated eight significant outcomes, which HB filtered into four core outcomes, found in the dominant/codominant models. Two of the four were in GD, indicating associations of the IL-18 SNPs with KT (ORs 1.34 to 1.39, 95% CIs 1.13-1.70, PHB = .0007-.004). The other two were in allograft analysis indicating reduced risk with HB P-values of .03 for overall (OR 0.74, 95% CI 0.56-0.93) and Asian (OR 0.70, 95% CI 0.53-0.92). In contrast to the protected Asian subgroup, Caucasians showed non-significant increased risk (OR 1.20. 95% CI .82-1.75, Pa = .35). Sensitivity treatment conferred robustness to all the core outcomes. ConclusionsOverall association of IL-18 SNPs with KT was significant (up to 1.4-fold) and Asians KT recipients were protected (up to 30%). Enabled by outlier treatment, these findings were supported by non-heterogeneity and robustness. More studies may confirm or modify our findings.

The development of de novo donor-specific antibodies (DSAs) against HLA is associated with premature graft failure in kidney transplantation. However, rates and factors influencing de novo DSA formation vary widely across the literature. We aimed to identify pre-transplant factors influencing the development of de novo HLA-specific antibodies following kidney transplantation using machine learning. Data from 460 kidney transplant recipients at a single centre between 2009-2014 were analysed. Pre-transplant variables were collected, and post-transplant sera were screened for HLA antibodies. Positive samples were investigated using Single Antigen Bead (SAB) testing. Machine learning models (Classification and Regression Trees, Random Forest, XGBoost, CatBoost) were trained on a training set of pre-transplant data to predict de novo DSA formation, with and without SMOTE oversampling. Model performance was evaluated on an independent testing set using F1 scores, and feature importance was assessed using SHAP. In the full cohort analysis, XGBoost models performed the best, with F1 scores of 0.54-0.59 without SMOTE and 0.72-0.79 with SMOTE. The strongest predictors were pre-transplant HLA antibodies, number of kidney transplants, cold ischemia time (CIT), recipient age and female gender. SHAP dependence plots showed that pre-existing HLA antibodies and past transplants increased the risk of de novo DSA development. In the unsensitised subgroup analysis, model performance was poor. Machine learning models can be used to identify pre-transplant risk factors for de novo HLA-specific antibody development in kidney transplantation. Monitoring and risk-stratifying patients based on these factors may help guide preventive immunological strategies and recipient selection to improve long-term allograft outcomes. Translational statementThis study identified pre-transplant risk factors for the development of de novo HLA-specific antibody in kidney transplantation. Monitoring and risk-stratifying patients based on these factors may help guide preventive immunological strategies and recipient selection to improve long-term allograft outcomes.

BACKGROUNDDespite a sharp rise in kidney graft short-term survival rates and better donor-recipient HLA matching, mid- and long-term survival have not sufficiently improved over the past decades. Several studies suggest that non-HLA factors could be involved in kidney allograft injury, but no validated marker has yet been identified. Here, we aimed at finding genetic variations and mismatches associated with graft function and survival. METHODSUsing genome-wide strategies, we tested the recipients and donors common variations (SNPs and CNVs), and the donor-recipient genetic mismatches for association with 1-year kidney graft function and with time-to-death-censored kidney graft failure in a monocentric European cohort of 1,482 complete donor-recipient pairs. We validated our findings through a meta-analysis in two independent European cohorts gathering a total of 1,842 additional complete pairs. RESULTSWe did not identify any significant association with 1-year graft function. However, we discovered four non-HLA mismatches (3 SNPs and 1 CNV) associated with time-to-kidney graft failure. One signal in a regulatory region upstream the TOM1L1 gene (p=6.3x10-9, HR=4.1) was successfully replicated in the validation cohorts (pmeta-analysis=6.7x10-9, HR=2.9) and ranked among the top 50 rejection-specific genes in a pan-organ transcriptomics study. This locus was also associated with time-to-cellular and humoral rejection (p=0.02) in the discovery cohort in patients achieving primary graft function. CONCLUSIONSBy running one of the largest ever performed kidney transplantation genomic analyses, we identified and confirmed a novel donor-recipient genetic mismatch in a biologically relevant non-HLA locus associated with kidney allograft failure. Lay SummaryDespite significant advances in immunosuppression, kidney transplant recipients remain at risk of graft rejection and, in more severe cases, graft failure, which can lead to retransplantation, return to dialysis, or even patient death. Donor-recipient HLA compatibility is integrated into kidney transplant clinical care, as this genetic region is key for immunity and graft tolerance. However, several studies suggest that compatibility outside of the HLA region could also influence graft survival. We aimed at investigating this hypothesis in a cohort of 1,482 donor-recipient pairs and found a novel genetic region involved in kidney graft dysfunction that was validated after meta-analysis of two independent cohorts. These findings contribute to a better understanding of the impact of donor-recipient genetic compatibility on kidney transplant outcomes.

BackgroundThe effects of Banff histological diagnoses on kidney transplant outcome have been well characterized. However, repeated observation of such histological injury across multiple biopsies in kidney transplant recipients remains insufficiently explored. MethodsIn an observational cohort (N=1819 transplantations with 5736 post-transplant biopsies, recurrent event survival models quantified transitions between diagnoses of T-cell mediated rejection (TCMR), antibody-mediated rejection (AMR), DSA-negative C4d-negative microvascular inflammation (MVIDSA-/C4d-), BK polyomavirus nephropathy (BKPyVAN), borderline TCMR (bTCMR), and probable AMR (pAMR), revealing patterns in the disease trajectories. In two observational cohorts (N=1818 transplantations with 5732 biopsies, N=853 transplantations with 975 biopsies), time-dependent cumulative covariates were constructed for TCMR, AMR, MVIDSA-/C4d- and BKPyVAN, enabling estimation of associations of repeated diagnoses with graft failure using multivariable cause-specific Cox models. ResultsThe incidence rate of a diagnosis was most strongly associated with earlier diagnosis of the same type, but associations between different types of diagnoses also occurred. The hazard of kidney graft failure was significantly increased by repeated observation of TCMR in multiple biopsies (HR 7.97, 95% CI 4.94 - 12.86), as well as by repeated AMR (HR 6.19, 95% CI 3.15 - 12.17), repeated MVIDSA-/C4d- (HR 4.53, 95% CI 2.15-9.54) and repeated BKPyVAN (HR 10.90, 95% CI 5.83 - 20.35). The hazard of graft failure was increased more after repeated diagnoses in transplants than after first diagnoses. The effects of repeated TCMR and repeated AMR remained significant even when observed in protocol biopsies in the absence of graft dysfunction. Repeated observation of BKPyVAN was the most detrimental of all diagnoses when observed in indication biopsies, but it was the least harmful when observed in protocol biopsies. ConclusionIncidence of Banff histological diagnoses appears to be affected by earlier diagnoses, especially those of the same type. These repeated observations of a specific diagnosis have an additional effect on the hazard of graft failure, underscoring a critical unmet need for adequate treatment strategies for these recurrent or persistent injury processes. Lay summaryIn two observational cohorts of 1819 and 750 kidney transplant recipients, kidney transplant biopsies were taken at multiple time points after transplantation. Based on the Banff classification for transplant pathology, various post-transplant diseases were diagnosed, often at more than one time point during follow-up. We assessed patterns in the occurrence of diagnoses over time, and related these diagnoses to survival of the kidney grafts using survival models with time-dependent cumulative diagnoses. We found that repeated observation of the same diagnosis was much more common than consecutive observations of different diagnoses. Repeated diagnoses of tissue injury also decreased kidney graft survival more compared to single diagnoses. This indicates that treatment options for patients with repeated or persistent diagnoses are currently inadequate and novel strategies are needed.

BackgroundKidney transplantation is the preferred treatment for end-stage renal disease, but delayed graft function remains a significant complication. Cold ischemia during organ preservation can lead to the release of danger-associated molecular patterns (DAMPs), which may influence graft outcomes. This study aimed to quantify DAMPs in kidney preservation fluid and assess their correlation with delayed graft function (DGF). MethodsPreservation fluid samples from 88 deceased kidney donors were analyzed for various DAMPs, including mitochondrial DNA (mitDNA), cytochrome c, nucleosomes, hyaluronan, and inflammasome-related molecules (IL-18 and IL-1{beta}). The influence of donor type (DBD vs. DCD) and cold ischemia time (CIT) on DAMP concentrations was evaluated. Additionally, the correlation between DAMP levels and DGF was assessed. ResultsMultiple DAMPs were detected in preservation fluid, including mitDNA, cytochrome c, nucleosomes, and hyaluronan. The type of donation (DBD vs. DCD) had minimal impact on DAMP concentrations, except for HSP70, which was significantly higher in DCD donors. CIT positively correlated with hyaluronan and nucleosome levels. Cytochrome c emerged as a potential biomarker for DGF, showing a significant increase in patients with early dysfunction and correlating with post-transplant creatinine levels. ConclusionsQuantifying DAMPs in kidney preservation fluid is feasible and may provide valuable insights into graft quality and early post-transplant outcomes. Cytochrome c, in particular, shows promise as a biomarker for predicting delayed graft dysfunction. These findings highlight the importance of minimizing cold ischemia time and suggest that DAMP analysis could improve graft assessment prior to transplantation.

Background and objectivesT cell mediated rejection (TCMR) is the most frequent type of acute rejection and is associated with kidney allograft failure. Almost 40% of TCMR episodes fail to respond to anti-rejection therapy. FOXP3 is a specification factor for regulatory T cells and our single center study of 83 kidney allograft recipients showed that urinary cell FOXP3 mRNA level is diagnostic of TCMR and predicts TCMR reversibility and allograft survival. The objective of the current study is to determine whether our original findings could be replicated in an independent cohort of 480 kidney allograft recipients enrolled in the multicenter Clinical Trials of Organ Transplantation (CTOT)-04. Design, setting, participants, and measurementsWe measured levels of FOXP3 mRNA and levels of mRNA for CD25, CD3E, and perforin, and 18S rRNA in 3559 urines from 480 kidney allograft recipients prospectively enrolled in CTOT-04. RNA was isolated from the urinary cells and preamplification-enhanced real-time quantitative PCR assays were used to measure mRNAs. Results18S rRNA normalized levels of mRNA for FOXP3 (P=0.01, Kruskal-Wallis test), CD25 (P=0.01), CD3E (P<0.0001), and perforin (P<0.0001) distinguished patients with TCMR biopsies from those with No Rejection biopsies and those with stable graft function. FOXP3 mRNA level, but not the levels of mRNA for CD25, CD3E, or perforin, predicted TCMR reversal (AUC=0.764; 95% confidence interval, 0.611 to 0.917; P=0.008). Multivariable logistic regression analysis showed that FOXP3 mRNA level remains predictive after adjustment for potential cofounders. Kaplan-Meier survival curve analysis showed that FOXP3 mRNA level (P=0.0306) but not the levels of mRNA for CD25, CD3E, or perforin, is associated with kidney allograft survival. ConclusionIn the independent CTOT-04 cohort, we demonstrate that urinary cell level of FOXP3 mRNA is diagnostic of TCMR, predicts its reversibility, and is prognostic of kidney allograft survival following an episode of TCMR.

ImportanceLower kidney allograft survival has been demonstrated in kidney transplant recipients (KTR) without HIV whose donors have two apolipoprotein L1 (APOL1) renal risk variants (RRV). The effects of APOL1 RRV on kidney transplant outcomes in people with HIV (PWH) have not been fully assessed. ObjectiveTo determine whether APOL1 renal risk variants (G1/G2) in donors or recipients are associated with outcomes of kidney transplantation in people with HIV (PWH)? DesignComparative analysis of kidney allograft outcomes in two of the largest longitudinal clinical studies examining transplantation outcomes in PWH. Setting and participantsTwo cohorts of HIV-positive KTR (R+) and their respective HIV-negative (D-) or HIV-positive (D+) kidney donors from the South African (SA) HIV+ to HIV+ transplantation clinical study and the United States of America (US) HOPE in Action Kidney transplantation clinical trial. All patients with genomic DNA available for APOL1 genotyping were included. APOL1 Genotype was determined using a probe-based assay. Main outcomes measuredTime to first rejection, HIV-associated nephropathy, graft failure or death were compared by both donor and recipient APOL1 RRV status. ResultsGenomic DNA was available for 21 donors with HIV and 38 HIV D+/R+ recipients in the SA cohort, and 57 donors (40 D+ and 17 D-) and 119 recipients (49 HIV D+/R+ and 70 D-/R+) in the US cohort. Recipient outcomes were not associated with recipient APOL1 genotype. However, recipients whose donor carried one versus zero APOL1 RRV were significantly more likely to experience a negative composite outcome (p<0.02 for both cohorts independently), which led to an adjusted hazard ratio of a poor composite outcome of 2.9 (95% CI 1.1-7.4) and 10.1 (95% CI 2.4-42.7) in the SA and US cohorts, respectively. Conclusions and relevanceIn two independent studies, the presence of one APOL1 RRV in a donor kidney led to significantly worse post-transplant outcomes while recipient APOL1 genotype was not associated with outcomes. Further research into the interaction between the allograft environment and donor APOL1 genotype in PWH is required. KEY POINTS QuestionDo APOL1 renal risk variants (G1/G2) influence the outcomes of kidney transplantation in people with HIV (PWH)? FindingsIn two of the largest cohorts of PWH who are also kidney transplant recipients, the presence of even one donor APOL1 renal risk variant was associated with an adjusted hazard ratio of a poor composite outcome of 10.1 (95%CI=2.4-42.7) and 2.9 (95%CI=1.1-7.4) in the US and SA cohorts, respectively. Recipient APOL1 genotype was not associated with graft outcomes. MeaningThis may have implications for allocation of allograft kidneys in PWH, as well as informing the need for therapies targeting APOL1 gene expression in kidney transplant recipients.

BackgroundMultiple factors affecting COVID19 vaccine induced antibody responses in SARS-CoV2 uninfected immunosuppressed solid organ transplant recipients have been reported; however, there is still a lack of information on non-ACE2 competing cross-CoV2 neutralizing functional antibodies induced in these cohorts, and similarly the vaccine efficacy in prior CoV2-infected immunosuppressed individuals is not well understood. MethodsCOVID19 vaccine efficacy was compared in a panel of kidney and heart transplant recipients who were either CoV2 uninfected (n=63) or CoV2 infected (n=13) prior to receiving two or three doses of mRNA vaccines using pseudoviral neutralization assays against eight CoV2 strains (the CoV2_D614G ancestral strain, alpha, beta, gamma, delta, kappa, lambda, and omicron-BA1 variants), while plasma antibody titers were determined by ELISA using recombinant CoV2-RBD-wt proteins. ResultsMinimally protective neutralizing plasma antibody titers (IC50 [&ge;] 1:50) against the variants were recorded 7-14% and 25-35% after the second and third doses respectively, with Omicron being the most resistant. In contrast, all previously infected vaccinees possessed minimal protective plasma titers against D614G after either two or three vaccine doses, with 11/13 exhibiting strong protection (IC50[&ge;] 1:500) and 10/13 exceeding the minimal protective titer against Omicron. Absorption of the selected plasma with immobilized parental RBD removed [&ge;] 90% of its neutralizing activity, indicating that the dominant neutralization targets were in the RBD. ConclusionsThis study showed that CoV2 infection followed by vaccination, but not vaccination alone, induces the presence of potent highly cross-reactive CoV2 neutralizing plasma antibodies that extend to Omicron variants, even in immunosuppressed SOTRs.

The integration of regenerative medicine into dynamic organ preservation may mitigate ischemia-reperfusion injury in kidney transplantation. This systematic review and meta-analysis evaluated the therapeutic potential of stem cell-based interventions during machine perfusion. Following PRISMA guidelines, PubMed, Embase, and Scopus were searched for experimental studies using stem cells or extracellular vesicles (EVs) during hypothermic or normothermic machine perfusion in animal or discarded human kidneys. Outcomes included renal function, injury biomarkers, inflammation, and histology. Nine studies were included, seven in meta-analysis. Despite heterogeneity in models and protocols, several reported reductions in inflammatory cytokines (e.g., IL-6, IL-1{beta}) and biomarkers (e.g., NGAL) following stem cell or EVs administration. However, meta-analysis showed no significant effects on creatinine clearance (Standardized Means (SMD): 0.00; 95% CI: -0.54 to 0.55), urine output (SMD: 0.54; 95% CI: -0.46 to 1.55), or NGAL (SMD: -1.68; 95% CI: -5.60 to 2.25). Histological protection varied, and stem cell retention was limited. Only one study assessed post-transplant function. While stem cell therapies during perfusion may have immunomodulatory and cytoprotective effects, consistent functional benefits were not observed. Further standardized studies, including transplant models and long-term outcomes, are needed to clarify therapeutic potential and optimize delivery strategies.

The main challenge of immunosuppressive therapy after solid organ transplantation is to create a new immunological balance that prevents organ rejection and does not promote opportunistic infection. Torque teno virus (TTV) a ubiquitous and non-pathogenic single-stranded DNA virus has been proposed as a marker of functional immunity in immunocompromised patients. Here investigate whether TTV loads predict the risk of common viral infection and allograft rejection in kidney transplantation recipients. In a retrospective cohort of 389 kidney transplantation recipients, individual TTV loads in were measured by qPCR in consecutive plasma samples during one year follow-up. The endpoints were allograft rejection, BK polyomavirus (BKPyV) viremia and cytomegalovirus (CMV) viremia. Repeated TTV measurements and rejection and infection survival data were analysed in a joint model. During follow-up, TTV DNA detection in the transplant recipients increased from 85 to 100%. The median viral load increased to 107 genome copies/ml within three months after transplantation. Rejection, BKPyV viremia and CMV viremia occurred in 23%, 27% and 17% of the patients, respectively. With every 10-fold TTV load-increase, the risk of rejection decreased considerably (HR: 0.74, CI 95%: 0.71-0.76), while the risk of BKPyV and CMV viremia remained the same (HR: 1.03, CI 95%: 1.03-1.04 and HR: 1.01, CI 95%: 1.01-1.01). In conclusion, TTV load kinetics predict allograft rejection in kidney transplantation recipients, but not the BKPyV and CMV infection. The potential use of TTV load levels as a guide for optimal immunosuppressive drug dosage to prevent allograft rejection deserves further validation.

HLA evolutionary divergence (HED), a continuous metric quantifying the differences between each amino acid of two homologous HLA alleles, reflects the importance of the immunopeptidome presented to T lymphocytes. It has been associated with rejection after liver transplantation. This retrospective cohort study aimed to analyze the potential effect of donor or recipient HED on liver transplant rejection in a new series of patients transplanted during childhood and followed in adulthood. The study included 120 children who had been transplanted between 1991 and 2010 and were followed by routine biopsies and histological evaluations with a median of 14.1 years post-LT. Liver biopsies were performed routinely 1, 5, 10 and 20 years after transplantation and in the event of liver dysfunction. HED was calculated using the physicochemical Grantham distance for donor and recipient class I (HLA-A, -B, -C) and class II (HLA-DRB1, -DQB1) alleles. The influence of HED on rejection was analyzed using IPW and target trial emulation using the g method. Based on the IPW score, donor HED class I was correlated with the occurrence of late (>90 days) rejection (HR, 1.19, 95% CI: 1.01-1.40) independently of HLA mismatches, donor age and initial induction. This emulated target trial confirmed that donor HED class I has a causal effect on liver graft rejection and this relationship was observed long-term.

The COVID-19 pandemic has reduced access to solid organ transplantation, compounding organ shortages and waitlist mortality. A continued area of uncertainty is the safety of transplanting organs recovered from SARS-CoV-2 infected donors, as autopsies of patients who died with COVID-19 show that the virus can be found in extra-pulmonary organs1. Case reports and series on transplantation of these organs have been published 2, 3, but population-level data is lacking. We queried a national transplant database for recipients of organs recovered from donors recently infected by SARS-CoV-2. For organs with more than 50 cases, these were then propensity-score matched at a ratio of 1:10 to similar recipients of organs recovered from donors who tested negative for SARS-CoV-2 (controls). Data were extracted from the Scientific Registry of Transplant Recipients (SRTR - v2203 - updated March 2022), which collects detailed information on all solid organ transplants in the United States since 1986. Cases were defined as adult ([&ge;] 18 years) recipients of organs recovered from deceased donors who tested positive for SARS-CoV-2 by nasopharyngeal or lower respiratory sample polymerase chain reaction or antigen assay within 7 days of organ transplantation. Multiple organ transplants were excluded. There were 775 kidney, 330 liver, 123 heart, 44 kidney-pancreas, 16 lung, 5 pancreas, and 3 small bowel transplants of organs recovered from 393 deceased donors recently infected by COVID-19. For kidney, liver, and heart transplants, Kaplan-Meier curves of both overall and graft survival at 90 days were similar between cases and controls. Our data shows that transplanting kidneys, livers, and hearts recovered from deceased donors recently infected by SARS-CoV-2 was not associated with increased recipient mortality or worse graft-survival. This should help transplant providers make decisions regarding acceptance of these organs, and counsel transplant candidates on the safety of receiving them. The limited number of kidney-pancreas, lung, pancreas, and intestinal cases precludes significant conclusions for these organs. Our data also strongly supports the notion that donors with recent COVID-19 infection should not be automatically excluded from the donor pool. The limited number of kidney-pancreas, lung, pancreas, and intestinal cases precludes significant conclusions for these organs. Limitations include lack of data on donor infection timeline and estimates of viral load (PCR cycle thresholds), description of donor COVID-19 symptomatology at organ procurement, donor or recipient vaccination or prior COVID-19 infection status, which are not tracked in the database. We did not have information regarding transmission of COVID-19 to transplant recipients. Future analysis of updated versions of the database should help address. Our data strongly support the notion that donors with recent COVID infection should not be automatically excluded from the donor pool. Prospective studies are needed to confirm our findings and provide insights on optimal post-transplant management of these recipients.

BackgroundSolid organ transplant recipients have attenuated immune responses to SARS-CoV-2 vaccines. In this study, we report on immune responses to 3rd- (V3) and 4th- (V4) doses of heterologous and homologous vaccines in a kidney transplant population. Methods724 kidney transplant recipients were prospectively screened for serological responses following 3 primary doses of a SARS-CoV2 vaccine. 322 patients were sampled post-V4 for anti-spike (anti-S), with 69 undergoing assessment of SARS-CoV-2 T-cell responses. All vaccine doses were received post-transplant, only mRNA vaccines were used for V3 and V4 dosing. All participants had serological testing performed post-V2 and at least once prior to their 1st dose of vaccine. Results586/724 (80.9%) patients were infection-naive post-V3; 141/2586 (24.1%) remained seronegative at 31 (21-51) days post-V3. Timing of vaccination in relation to transplantation, OR: 0.28 (0.15-0.54), p=0.0001; immunosuppression burden, OR: 0.22 (0.13-0.37), p<0.0001, and a diagnosis of diabetes, OR: 0.49 (0.32-0.75), p=0.001, remained independent risk factors for non-seroconversion. Seropositive patients post-V3 had greater anti-S if primed with BNT162b2 compared with ChAdOx1, p=0.001. Post-V4, 45/239 (18.8%) infection-naive patients remained seronegative. De novo seroconversion post-V4 occurred in 15/60 (25.0%) patients who were seronegative post-V3. There was no difference in anti-S post-V4 by vaccine combination, p=0.50. Anti-S post-V4 were sequentially greater in those seroconverting post V2- compared with V3-, and V3- compared with V4-, at 1561 (567-5211), 379 (101-851) and 19 (9.7-48) BAU/ml respectively. T-cell responses were poor, with only 11/54 (20.4%) infection-naive patients having detectable T-cell responses post-V4, with no difference seen by vaccine type. ConclusionA significant proportion of transplant recipients remain seronegative following 3- and 4- doses of SARS-CoV-2 vaccines, with poor T-cell responses, and are likely to have inadequate protection against infection.

IntroductionPlasma carboxypeptidase B2 (CPB2) is an enzyme that cleaves C-terminal amino acids from proteins, thereby regulating their activities. CPB2 has anti-inflammatory and anti-fibrinolytic properties and can therefore be protective or harmful in disease. We explored the impact of functional carboxypeptidase B2 gene (CPB2) polymorphisms on graft survival following kidney transplantation. MethodsWe performed a longitudinal cohort study to evaluate the association of functional CPB2 polymorphisms (rs2146881, rs3742264, rs1926447, rs3818477) and complement polymorphisms (rs2230199, rs17611) with long-term allograft survival in 1,271 kidney transplant pairs from the University Medical Center Groningen in The Netherlands. ResultsThe high-producing CPB2 rs3742264 polymorphism in the donor was associated with a reduced risk of graft loss following kidney transplantation (hazard ratio, 0.71 for the A-allele; 95%-CI, 0.55-0.93; P=0.014). In fully adjusted models, the association between the CPB2 polymorphism in the donor and graft loss remained significant. The protective effect of the high-producing CPB2 variant in the donor could be mitigated by the hazardous effect of gain-of-function complement polymorphisms. Additionally, we compiled a genetic risk score of the four CPB2 variants in the recipients and donors, which was independently associated with long-term allograft survival. Furthermore, this genetic risk score substantially improved risk prediction for graft loss beyond currently used clinical predictors. ConclusionKidney allografts from deceased donors possessing a high-producing CPB2 polymorphism are at a lower risk of graft loss after kidney transplantation. Furthermore, our findings suggest that CPB2 might have a protective effect on graft loss through its ability to inactivate complement anaphylatoxins. EssentialsO_LICarboxypeptidase B2 (CPB2) is a metalloprotease with anti-fibrinolytic and anti-inflammatory properties. C_LIO_LIWe investigated the impact of CPB2 polymorphisms on graft loss after kidney transplantation. C_LIO_LIThe rs3742264-A SNP in the donor, linked to higher CPB2 levels, decreased the risk of graft loss. C_LIO_LICPB2 could have a protective effect on graft survival by inactivating complement anaphylatoxins. C_LI

BackgroundSolid organ transplant recipients have attenuated immune responses to SARS-CoV-2 vaccines. Emerging evidence suggests at least equivalent immunogenicity of heterologous compared with homologous vaccine regimens in the general population. In this study, we report on immune responses to 3rd dose BNT162b2 vaccines in transplant recipients either primed with ChAdOx1 or BNT162b2. Methods700 kidney transplant recipients were prospectively screened for serological responses (median time of 33 (21-52) days) following 3 primary doses of a SARS-CoV2 vaccine. All vaccine doses were received post-transplant, and all 3rd doses were BNT162b2. All participants had serological testing performed post-2nd vaccination at a median time of 34 (IQR 26-46) days following the 2nd inoculation, and at least once prior to their 1st dose of vaccine. Results366/700 (52.3%) participants were primed with BNT162b2, whilst 334/700 (47.7) had received ChAdOx1. Overall, 139/700 (19.9%) participants had evidence of prior infection. Of 561 infection naive participants, 263 (46.9%) had no detectable anti-S following 2-doses of vaccine (V2). 134 (23.9%) participants remained seronegative post 3rd vaccine (V3); 54/291 (18.6%) and 79/270 (29.3%) of participants receiving BNT162b2 and ChAdOx1 respectively, p=0.0029. Median anti-S concentrations were significantly higher post-V3 in patients who had received BNT162b2 compared with ChAdOx1, at 612 (27-234) versus 122 (7.1-1111) BAU/ml respectively, p<0.0001. Cellular responses were investigated in 30 infection naive participants at a median time of 35 (24-46) days post-V3. Eighteen of 30 (60.0%) participants had undetectable T-cell responses. There were neither qualitative or quantitative differences in T-cell responses between those patients who received BNT162b2 or ChAdOx1 as their first 2-doses, with 10/16 (62.5%) and 8/14 (57.1%) respectively having undetectable T-cell responses, p=0.77. ConclusionA significant proportion of transplant recipients remain seronegative following 3 doses of SARS-CoV-2 vaccines, with anti-S concentrations lower in patients receiving heterologous versus homologous vaccinations.

BackgroundGenetic analysis in transplantation offers potential for personalized medicine. Given the crucial role of the complement system in renal allograft injury, we investigated in kidney transplant pairs the impact of complement polymorphisms on long-term outcomes. MethodsIn this observational cohort study, we analyzed polymorphisms in C3 (C3R102G), factor B (CFBR32Q), and factor H (CFHV62I) genes of 1,271 donor-recipient kidney transplant pairs and assessed their association with 15-year death-censored allograft survival. ResultsIndividually, only the presence of the CFB32Q variant in the donor and the combined presence in donor-recipient pairs were associated with better graft survival (P=0.027 and P=0.045, respectively). In the combined analysis, the C3R102G, CFBR32Q, and CFHV62I variants in the donor independently associated with the risk of graft loss (HR 1.32; 95%-CI, 1.08- 1.58; P=0.005). Thus, donor kidneys carrying the genetic variants that promote the highest complement activity exhibited the worst graft survival, whereas those with the genetic variants causing the lowest complement activity showed the best graft survival (15-year death-censored allograft survival: 48.8% vs 87.8%, P=0.001). ConclusionOur study demonstrates that the combination of complement polymorphisms in the donor strongly associates with long-term allograft survival following kidney transplantation. These findings hold significance for therapeutic strategies involving complement inhibition in kidney transplantation.