Frequent development of subclinical chronic antibody-mediated rejection within 1year after renal transplantation with pre-transplant positive donor-specific antibodies and negative CDC crossmatches

Chronic Rejection After Kidney Transplantation

In kidney transplantation, ongoing alloimmune processes-commonly triggered by HLA incompatibilities-can trigger chronic transplant rejection, affecting the microcirculation and the tubulointerstitium. Continuous inflammation may lead to progressive, irreversible graft injury, culminating in graft dysfunction and accelerated transplant failure. Numerous experimental and translational studies have delineated a complex interplay of different immune mechanisms driving rejection, with antibody-mediated rejection (AMR) being an extensively studied rejection variant. In microvascular inflammation, a hallmark lesion of AMR, natural killer (NK) cells have emerged as pivotal effector cells. Their essential role is supported by immunohistologic evidence, bulk and spatial transcriptomics, and functional genetics. Despite significant research efforts, a substantial unmet need for approved rejection therapies persists, with many trials yielding negative outcomes. However, several promising therapies are currently under investigation, including felzartamab, a monoclonal antibody targeting the surface molecule CD38, which is highly expressed in NK cells and antibody-producing plasma cells. In an exploratory phase 2 trial in late AMR, this compound has demonstrated potential in resolving molecular and morphologic rejection activity and injury, predominantly by targeting NK cell effector function. These findings inspire hope for effective treatments and emphasize the necessity of further pivotal trials focusing on chronic transplant rejection.

Short-term outcomes of second kidney transplantation compared with those of first transplantation in Japanese patients: a single-center, retrospective, observational study

BACKGROUND

Among patients who undergo kidney transplantation, a subsequent second kidney transplantation (TX2) is often necessary. The TX2 outcomes remain controversial, however, and only limited data are available on clinical outcomes of TX2 in Japanese patients. This study aimed to assess graft and patient survival rates of TX2 and compared these rates with those of first kidney transplantation (TX1) in Japanese patients.

METHODS

Of the 898 kidney transplantations performed between 2010 and 2019 at our institution, 33 were TX2. We performed survival analysis using weighted Kaplan-Meier analysis and Cox proportional hazards analysis with propensity score matching, specifically inverse probability of treatment weighting (IPTW).

RESULTS

Death-censored graft survival (DCGS) rates at 1, 3, and 5 years for the TX1 versus TX2 groups were 99.3, 97.9, and 95.0% versus 100, 96.0, and 91.2%, respectively. Overall survival (OS) rates at 1, 3, and 5 years for the TX1 versus TX2 groups were 99.4, 98.9, and 97.8% versus 100, 100, and 94.4%, respectively. Using the log-rank test, IPTW-weighted Kaplan-Meier curves showed no significant differences for TX1 versus TX2 in DCGS (p = 0.535) and OS (p = 0.302). On Cox proportional hazards analysis for TX2 versus TX1, the IPTW-adjusted hazard ratio (HR) for DCGS was 1.75 (95% CI, 0.28-10.9; p = 0.550) and for OS was 2.71 (95% CI, 0.40-18.55; p = 0.311).

CONCLUSIONS

For patients who require TX2, this treatment is an acceptable option based on the short-term outcomes data for DCGS and OS.

Assessment and management of allosensitization following heart transplant in adults

Immunological injury to the allograft, specifically by antibodies to de novo donor specific human leukocyte antigen (dnDSA) and antibody mediated injury and rejection are the major limitations to graft survival after heart transplantation (HT). As such, our approach to allosensitization remains limited by the inability of contemporaneous immunoassays to unravel pathogenic potential of dnDSA. Additionally, the role of dnDSA is continuously evaluated with emerging methods to detect rejection. Moreover, the timing and frequency of dnDSA monitoring for early detection and risk mitigation as well as management of dnDSA remain challenging. A strategic approach to dnDSA employs diagnostic assays to determine relevant antibodies in conjunction with clinical presentation and injury/rejection of allograft to tailor therapeutics. In this review, we aim to outline contemporary knowledge involving detection, monitoring and management of dnDSA after HT. Subsequently, we propose a diagnostic and therapeutic approach that may mitigate morbidity and mortality while balancing adverse reactions from pharmacotherapy.

Influence of Graft Ureter Length, a Donor-Related Factor, on Urinary Tract Infections After Living-Donor Kidney Transplantation: A Single-Center Analysis of 211 Cases

Urinary tract infection (UTI) occurs in 25% of recipients of living-donor kidney transplantation (LDKT). Female sex, age, and anatomical abnormalities have been reported as recipient-related risk factors for UTI after LDKT; few studies have reported donor-related factors. We retrospectively examined UTI occurrence within 5 years of transplantation in recipients (n = 211) who underwent LDKT at our hospital between April 2011 and April 2021. All nephrectomies were performed using a retroperitoneal pure laparoscopic approach. The ureter was dissected at the lower level of the common iliac artery and trimmed to the shortest length, enough to reach the bladder using extra vesicular ureterocystoneostomy with a 3 cm submucosal tunnel. Twenty-nine recipients (13.7%) developed UTI within 5 years, and the median time to onset was 40.0 days. After adjusting for the well-known factors, including recipient sex, graft ureter length was an independent factor for UTI occurrence (HR 1.25, 95% CI 1.02∼1.53, p = 0.028) in the multivariate Cox regression analysis. The long ureter is usually trimmed, and the widest part is used for anastomosis, which may increase the possibility of reflux from the bladder to the ureter in the standard technique. The ureter length may be associated with the incidence of UTI after LDKT.

Pre-transplant donor-reactive IL-21 producing T cells as a tool to identify an increased risk for acute rejection

Pre-transplant screening focuses on the detection of anti-HLA alloantibodies. Previous studies have shown that IFN-γ and IL-21 producing T cells are associated with the development of acute rejection (AR). The aim of this study, was to assess whether pre-transplant donor-reactive T cells and/or B cells are associated with increased rejection risk. Samples from 114 kidney transplant recipients (transplanted between 2010 and 2013) were obtained pre-transplantation. The number of donor-reactive IFN-γ and IL-21 producing cells was analyzed by ELISPOT assay. The presence of donor specific antibodies (DSA) was also determined before transplantation. Numbers of donor-reactive IFN-γ producing cells were similar in patients with or without AR whereas those of IL-21 producing cells were higher in patients with AR (p = 0.03). Significantly more patients with AR [6/30(20%)] had detectable DSA compared to patients without AR [5/84(5.9%), p = 0.03]. Multivariate logistic regression showed that donor age (OR 1.06), pre-transplant DSA (OR 5.61) and positive IL-21 ELISPOT assay (OR 2.77) were independent predictors of an increased risk for the development of AR. Aside from an advanced donor-age and pre-transplant DSA, also pre-transplant donor-reactive IL-21 producing cells are associated with the development of AR after transplantation.

Chronic Active Antibody-Mediated Rejection With Donor-Specific Anti-HLA-DP Antibodies Following Living Donor Kidney Transplantation: A Case Report

Posttransplant donor-specific anti-HLA antibodies (DSA) cause chronic antibody-mediated rejection. Anti-DR and anti-DQ DSAs have especially been shown to be associated with negative graft function. In contrast, the prevalence and significance of anti-DP DSA have not been well established and remain unclear. We report a case of living donor kidney transplantation. The level of serum creatinine gradually became elevated because of chronic active antibody-mediated rejection, which was considered to be caused by anti-DP DSA. In this report, we indicate the significance of pretransplant screening for HLA-DP in donors to evaluate more comprehensively the donor specificity of posttransplant HLA antibodies.

Lower incidence of de novo donor-specific antibodies against HLA-DR in ABO-incompatible renal transplantation

Recently, in vitro experiments have demonstrated that anti-blood group A/B antibody binding to endothelial cells induce a protective effect against antibody-mediated injury. This study aimed to clarify the potential clinical benefit of ABO incompatibility in donor-specific HLA antibody (DSA)-induced chronic antibody-mediated rejection (ABMR). We enrolled 215 ABO-incompatible renal transplant (ABO-I) and 467 ABO-identical/compatible renal transplant recipients (ABO-Id/C). The prevalence of de novo DSA production and incidence of biopsy-proven chronic ABMR were compared between the two groups. The incidence of DR-associated de novo DSA was significantly lower in ABO-I than in ABO-Id/C (P = 0.028). Diagnostic biopsy for ABMR was conducted in 54 patients (11 ABO-I and 43 ABO-Id/C). Biopsy-proven chronic ABMR was lower in ABO-I than in ABO-Id/C (27.3% [3/11] vs. 44.2% [19/43]) patients. Our findings suggest that ABO incompatibility may cause low production of DR-associated de novo DSA, possibly resulting in a reduced incidence of chronic ABMR.

Positive Luminex and negative flow cytometry in kidney transplantation: a systematic review and meta-analysis

The presence of pre-formed donor-specific antibodies (DSAs) in kidney transplantation is associated with worse overall outcomes compared with DSA-negative transplantation. A positive complement-dependant cytotoxic crossmatch presents a high immunological risk, while a negative flow cytometry crossmatch is at the lower end of the risk spectrum. Yet, the presence of low-level DSA detected by Luminex alone, that is, positive Luminex and negative flow (PLNF) cytometry crossmatch lacks robust scientific exploration. In this systematic review and pooled analysis, we investigate the glomerular filtration rate, acute rejection (AR), graft survival and patient survival of PLNF transplants compared with DSA-negative transplants. Our analysis identified seven retrospective studies consisting of 429 PLNF transplants and 10 677 DSA-negative transplants. Pooled analysis identified no significant difference in the incidence of AR at 1 year [relative risk (RR) = 1.35, 95% confidence interval (CI) 0.90–2.02, Z = 1.46, P = 0.14, I2 = 0%], graft failure at 1 year (RR = 1.66, 95% CI 0.94–2.94, Z = 1.75, P = 0.08, I2 = 23%), graft failure at 5 years (RR = 1.29, 95% CI 0.90–1.87, Z = 1.38, P = 0.17, I2 = 0%), patient mortality at 1 year (RR = 0.89, 95% CI 0.31–2.56, Z = 0.22, P = 0.82, I2 = 0%) and patient mortality at 5 years (RR = 1.76, 95% CI 0.48–6.48, Z = 0.85, P = 0.39, I2 = 61%). Pooled analysis of graft function was not possible due to insufficient data. Current evidence suggests that low-level DSA detected by Luminex alone does not pose significant risk at least in the short–medium term. Considering the shortage of kidney transplants and the ever-increasing waiting time, the avoidance of PLNF transplants may be unwarranted especially in patients who have been enlisted for a long time.

Reviewing the pathogenesis of antibody-mediated rejection and renal graft pathology after kidney transplantation

The clinicopathological context of rejection after kidney transplantation was well recognized. Banff conferences greatly contributed to elucidate the pathogenesis and to establish the pathologic criteria of rejection after kidney transplantation. The most important current problem of renal transplantation is de novo donor-specific antibody (DSA) production leading chronic rejection and graft loss. Microvascular inflammation is considered as a reliable pathological marker for antibody-mediated rejection (AMR) in the presence of DSA. Electron microscopic study allowed us to evaluate early changes in peritubular capillaries in T-lymphocyte mediated rejection and transition to antibody-mediated rejection. Severe endothelial injuries with edema and activated lymphocyte invaded into subendothelial space with early multi-layering of peritubular capillary basement membrane suggest T-lymphocyte mediated rejection induce an unbounded chain of antibody-mediated rejection. The risk factors of AMR after ABO-incompatible kidney transplantation are important issues. Anti-ABO blood type antibody titre of IgG excess 32-fold before transplant operation is the only predictable factor for acute AMR. Characteristics of chronic active antibody-mediated rejection (CAAMR) are one of the most important problems. Light microscopic findings and C4d stain of peritubular capillary and glomerular capillary are useful diagnostic criteria of CAAMR. Microvascular inflammation, double contour of glomerular capillary and thickening of peritubular capillary basement are good predictive factors of the presence of de novo DSA. C4d stain of linear glomerular capillary is a more sensitive marker for CAAMR than positive C4d of peritubular capillary. Early and sensitive diagnostic attempts of diagnosing CAAMR are pivotal to prevent chronic graft failure.

Minimizing the risk of allo-sensitization to optimize the benefit of allogeneic cardiac-derived stem/progenitor cells

Allogeneic human cardiac-derived stem/progenitor cells (hCPC) are currently under clinical investigation for cardiac repair. While cellular immune response against allogeneic hCPC could be part of their beneficial-paracrine effects, their humoral immune response remains largely unexplored. Donor-specific HLA antibodies (DSA-HLA-I/DSA-HLA-II), primary elements of antibody-mediated allograft injury, might present an unidentified risk to allogeneic hCPC therapy. Here we established that the binding strength of anti-HLA monoclonal antibodies delineates hCPC proneness to antibody-mediated injury. In vitro modeling of clinical setting demonstrated that specific DSA-HLA-I of high/intermediate binding strength are harmful for hCPC whereas DSA-HLA-II are benign. Furthermore, the Luminex-based solid-phase assays are suitable to predict the DSA-HLA risk to therapeutic hCPC. Our data indicate that screening patient sera for the presence of HLA antibodies is important to provide an immune-educated choice of allogeneic therapeutic cells, minimize the risk of precipitous elimination and promote the allogeneic reparative effects.

Determining donor-specific antibody C1q-binding ability improves the prediction of antibody-mediated rejection in human leucocyte antigen-incompatible kidney transplantation

Detrimental impact of preformed donor-specific antibodies (DSAs) against human leucocyte antigens on outcomes after kidney transplantation are well documented, however, the value of their capacity to bind complement for predicting antibody-mediated rejection (AMR) and graft survival still needs to be confirmed. We aimed to study DSA characteristics (strength and C1q binding) that might distinguish harmful DSA from clinically irrelevant ones. We retrospectively studied 60 kidney-transplanted patients with preformed DSA detected by single antigen bead (SAB) assays (IgG and C1q kits), from a cohort of 517 kidney graft recipients (124 with detectable anti-HLA antibodies). Patients were divided into DSA strength (MFI < vs. ≥ 15 000) and C1q-binding ability. AMR frequency was high (30%) and it increased with DSA strength (P = 0.002) and C1q+ DSA (P < 0.001). The performance of DSA C1q-binding ability as a predictor of AMR was better than DSA strength (diagnostic odds ratio 16.3 vs. 6.4, respectively). Furthermore, a multivariable logistic regression showed that C1q+ DSA was a risk factor for AMR (OR = 16.80, P = 0.001), while high MFI DSAs were not. Graft survival was lower in high MFI C1q+ DSA in comparison with patients with C1q- high or low MFI DSA (at 6 years, 38%, 83% and 80%, respectively; P = 0.001). Both DSA strength and C1q-binding ability assessment seem valuable for improving pretransplant risk assessment. Since DSA C1q-binding ability was a better predictor of AMR and correlated with graft survival, C1q-SAB may be a particularly useful tool.

Current outcomes of chronic active antibody mediated rejection - A large single center retrospective review using the updated BANFF 2013 criteria

BACKGROUND

The updated BANFF 2013 criteria has enabled a more standardized and complete serologic and histopathologic diagnosis of chronic active antibody mediated rejection (cAMR). Little data exists on the outcomes of cAMR since the initiation of this updated criteria.

METHODS

123 consecutive patients with biopsy proven cAMR (BANFF 2013) between 2006 and 2012 were identified.

RESULTS

Patients identified with cAMR were followed for a median of 9.5 (2.7-20.3) years after transplant and 4.3 (0-8.8) years after cAMR. Ninety-four (76%) recipients lost their grafts with a median survival of 1.9 years after diagnosis with cAMR. Mean C4d and allograft glomerulopathy scores were 2.6 ± 0.7 and 2.2 ± 0.8, respectively. 53.2% had class II DSA, 32.2% had both class I and II, and 14.5% had class I DSA only. Chronicity score >8 (HR 2.9, 95% CI 1-8.4, p=0.05), DSA >2500 MFI (HR 2.8, 95% CI 1.1-6.8, p=0.03), Scr >3mg/dL (HR 3.2, 95% CI 1.6-6.3, p=0.001) and UPC >1g/g (HR 2.5, 95% CI 1.4-4.5, p=0.003) were associated with a higher risk of graft loss.

CONCLUSIONS

cAMR was associated with poor graft survival after diagnosis. Improved therapies and earlier detection strategies are likely needed to improve outcomes of cAMR in kidney transplant recipients.

One-year protocol biopsies from ABO-incompatible renal allografts compared with a matched cohort of ABO-compatible allografts

Introduction

Early acute antibody-mediated rejection (ABMR) occurs more frequently in ABO-incompatible (ABOi) than in ABO-compatible (ABOc) kidney transplantation. This could lead to increased inflammation/scarring in the ABOi grafts. Protocol biopsy data in ABOi kidney recipients are scarce.

Methods

A single-center retrospective matched cohort study was conducted. Eighty adult living donor (LD) renal transplant recipients without HLA donor-specific antibodies (DSA) transplanted between 2009 and 2012 were included; 20 ABOi and 60 ABOc controls matched for donor age and transplantation year. Protocol biopsies at one yr were scored according to the Banff classification. Three sums of scores were constructed: tubulointerstitial inflammation (t + i = 0 vs. >0), microvascular inflammation (g + ptc = 0 vs. >0), scarring/hyalinosis (ci + ct + cv + ah ≤ 1 vs. >1. Scores and presence of subclinical rejection (SCR) at one yr were compared.

Results

Protocol biopsy findings at one yr in the ABOi vs. ABOc matched control group were not statistically different: (t + i) > 0, 30% vs. 20%; (g + ptc) > 0, 5% vs. 8%; (ci + ct + cv + ah) > 1, 85% vs. 60%, respectively. No transplant glomerulopathy occurred. SCR rate at one yr was 30% vs. 18%, subclinical ABMR 5% vs. 7% (all with de novo HLA DSA).

Conclusion

One-year protocol biopsies of ABOi and ABOc LD recipients do not differ in chronic changes, inflammation, or SCRs.

The use of novel diagnostics to individualize immunosuppression following transplantation

Despite major improvements in short-term survival of organ allografts, long-term graft survival has not changed significantly. It is also known that toxic side effects of current immunosuppressive drugs (IS) especially calcineurin inhibitors (CNI) contribute to the unsatisfactory graft and patient survival following transplantation. Thus, clinicians strive to reduce or wean IS in potentially eligible patients. Research in the last 10 years has focussed on identification of biomarkers suitable for patient stratification in minimization or weaning trials. Most of the described biomarkers have been run retrospectively on samples collected within single-centre trials. Thus, often their performance has not been validated in other potentially multicentre clinical trials. Ultimately, the utility of biomarkers to identify potential weaning candidates should be investigated in large randomized prospective trials. In particular, for testing in such trials, we need more information about the accuracy, reproducibility, stability and limitations of the described biomarkers. Also, data repositories summarizing crucial information on biomarker performance in age- and gender-matched healthy individuals of different ethnicity are missing. This together with improved bioinformatics tools might help in developing better scores for patient stratification. Here, we will summarize the current results, knowledge and limitations on biomarkers for drug minimization or weaning trials.

Differences in immunogenicity of HLA antigens and the impact of cross-reactivity on the humoral response

BACKGROUND

Information about differences in immunogenicity of various HLA antigens may help guide donor selection and identify mismatches to avoid for patients likely to need retransplantation. To date, antibody responses to a wide array of individual mismatched antigens have not been evaluated.

METHODS

Frequencies of antibodies to mismatched HLA-A, HLA-B, HLA-DR, and HLA-DQ antigens were determined for 703 renal transplant patients who had no detectable donor-specific antibody before transplantation. The impact of cross-reactive group matching and production of antibodies cross-reactive with mismatched antigens were also assessed. Antibodies were identified using multiplexed bead assays.

RESULTS

The overall mean frequencies were similar for HLA-A (53.2%), HLA-DR (52.6%), and HLA-DQ (59.0%) antibodies, but significantly lower for HLA-B antibodies (42.4%). However, the response to individual antigens ranged from 15.0% to 76.2%. Antibody frequencies were reduced significantly for 54 of 62 specificities when the patient possessed an antigen cross-reactive with the donor mismatch, but the magnitude of the effect was variable and ranged from 8% to 83%. Moreover, there was directionality in the protective effect of cross-reactive group matching. Overall mean donor-specific antibody frequencies were comparable for men and women except for a significantly higher frequency of antibodies to HLA-DR among men (56.6% vs. 47.8%, P=0.004). Overall mean frequencies in blacks were higher than, or comparable to those of, whites, but differences were not significant.

CONCLUSION

There is considerable variability in the immunogenicity of different HLA antigens that is impacted by the presence or absence of cross-reactive antigens in the patient's phenotype. This information can be used to augment the immunologic evaluation of donor-recipient pairs.

Desensitization for solid organ and hematopoietic stem cell transplantation

Desensitization protocols are being used worldwide to enable kidney transplantation across immunologic barriers, i.e. antibody to donor HLA or ABO antigens, which were once thought to be absolute contraindications to transplantation. Desensitization protocols are also being applied to permit transplantation of HLA mismatched hematopoietic stem cells to patients with antibody to donor HLA, to enhance the opportunity for transplantation of non-renal organs, and to treat antibody-mediated rejection. Although desensitization for organ transplantation carries an increased risk of antibody-mediated rejection, ultimately these transplants extend and enhance the quality of life for solid organ recipients, and desensitization that permits transplantation of hematopoietic stem cells is life saving for patients with limited donor options. Complex patient factors and variability in treatment protocols have made it difficult to identify, precisely, the mechanisms underlying the downregulation of donor-specific antibodies. The mechanisms underlying desensitization may differ among the various protocols in use, although there are likely to be some common features. However, it is likely that desensitization achieves a sort of immune detente by first reducing the immunologic barrier and then by creating an environment in which an autoregulatory process restricts the immune response to the allograft.