Donor-Specific Antibodies in Kidney Transplant Recipients

Crossmatch, Donor-specific Antibody Testing, and Immunosuppression in Simultaneous Liver and Kidney Transplantation: A Review

Since the introduction of simultaneous liver-kidney transplantation (SLKT) in the 1960s, the potential for immunological protection from the liver allograft to a simultaneously transplanted kidney has been recognized. Due to expanded indications and changes in allocation policies, there has been increased utilization of SLKT. Despite growing experience, a lack of consensus exists regarding the extent of the immunological privilege of the liver the role for donor-specific HLA antibody (DSA) and crossmatch testing, and appropriateness of modern immunosuppression protocols in SLKT recipients. This review provides a detailed analysis of SLKT outcomes in the context of these factors, suggesting that although the liver can reduce the incidence of antibody-mediated rejection, attention should be given to liver allograft function, previous failed transplants, and other risk factors in pretransplant risk assessment. Current methods of DSA and crossmatch testing in SLKT are also discussed, and the role of specific DSA (high mean fluorescence intensity antibody, C1q+ binding) and their potential importance in posttransplant risk assessment are examined. Finally, trends in SLKT immunosuppression are discussed, including the use of nondepleting agents for induction and de-escalating use of steroids for maintenance immunosuppression. Ongoing research, including multicenter or randomized trials, will be necessary to optimize immune-related outcomes in SLKT recipients.

Use of Rituximab for persistent EBV DNAemia, and Its effect on donor-specific antibody development in pediatric renal transplant recipients: A case series

INTRODUCTION

Persistent EBV DNAemia (PEBV) is associated with late-onset PTLD. The efficacy of rituximab in PEBV is not conclusive. We monitored PEBV and DSA in pediatric kidney transplant patients with or without rituximab.

METHODS

13 PEBV patients received standard treatment with immunosuppression reduction and valganciclovir, with or without IVIG; 5/13 were further treated with rituximab.

RESULTS

All Rituximab-treated and 6/7 No-Rituximab patients were EBV seronegative at transplant and seroconverted post-transplant. Peak EBV PCR levels were lower in No-Rituximab than Rituximab patients and all No-Rituximab patients cleared PEBV after standard treatment. Additional 1-2 doses of rituximab reduced EBV PCR levels in all 5 Rituximab patients, 3 cleared PEBV. One No-Rituximab patient developed localized PLTD. None of Rituximab patients developed de novo DSA, while 4/8 No-Rituximab patients did: 2/4 had ABMR. 1/5 Rituximab and 5/8 No-Rituximab patients had acute rejection. There was no change in eGFR between pre-EBV DNAemia and follow-up in Rituximab patients, while reduction in No-Rituximab patients was found. There was no difference in graft and patient survival.

CONCLUSIONS

While early intervention with rituximab in pediatric patients with PEBV may reduce viral load and PTLD, we observed a slower development of de novo DSA, and rejection and maintenance of eGFR.

Eplet mismatches associated with de novo donor-specific HLA antibody in pediatric kidney transplant recipients

BACKGROUND

Optimizing amino acid (eplet) histocompatibility at first transplant decreases the risk of de novo donor-specific antibody (dnDSA) development and may improve long-term graft survival in pediatric kidney transplant recipients (KTR). We performed a retrospective analysis of pediatric KTR and their respective donors to identify eplets most commonly associated with dnDSA formation.

METHODS

Eplet mismatch analysis was performed in a cohort of 125 pediatric KTR-donor pairs (2006-2018). We determined the prevalence of each eplet mismatch and quantified the percentage of exposed patients who developed dnDSA for each mismatched eplet.

RESULTS

Recipient median age was 14 (IQR 8-17) years with a racial distribution of 42% Black, 48% Caucasian, and 5.6% Middle-Eastern. Median eplet load varied significantly by recipient race, Black 82 (IQR 58-98), White 60 (IQR 44-81) and Other 66 (IQR 61-76), p = 0.002. Forty-four percent of patients developed dnDSA after median 37.1 months. Compared to dnDSA- patients, dnDSA+ patients had higher median eplet load, 64 (IQR 46-83) vs. 77 (IQR 56-98), p = 0.012. The most common target of dnDSA were eplets expressed in HLA-A*11 and A2 in Class I, and HLA-DQ6 and DQA5 in Class II. The most commonly mismatched eplets were not the most likely to result in dnDSA formation.

CONCLUSIONS

In a racially diverse population, only a subset of eplets was linked to antibody formation. Eplet load alone is not a sufficient surrogate for eplet immunogenicity. These findings illustrate the need to optimize precision in donor selection and allocation to improve long-term graft outcomes. Graphical Abstract A higher resolution version of the Graphical abstract is available as Supplementary information.

Not all eplet mismatches are created equal - A cohort study illustrating implications to long-term graft outcomes

We assessed implications of various eplet-compatibility strategies to death-censored graft failure (DCGF), defined as return to dialysis or re-transplantation, in a base-case scenario from the Scientific Registry of Transplant Recipients. To inform personalized care, we evaluated how recipient, donor, and transplant characteristics affect DCGF by ascending categories of eplet mismatches (EMM), and derived adjusted hazard ratios (HR). The base-case analysis demonstrated 15-year estimated survival probabilities of 77.1%, 75.4%, 73.6%, 72.2%, 74.9%, and 73.5% for the lowest EMM categories (complete epitype: 0-19, antibody-verified (AbVer) epitype and class II eplets: 0-9, class II AbVer eplets: 0-4, 55 high-risk eplets associated with DCGF: 0-3, and subset of 15 high-risk eplets validated in an independent subcohort: 0 EMM, respectively). Beyond the lowest EMM categories, the Epi15 strategy allowed better differentiation of change in DCGF risk per EMM, with additional 5.2%, 3.9% and 4.1% decrease in estimated graft survival for each additional EMM (1, 2, and ≥ 3, respectively). Recipients < 25 years, donors > 55 years, and immunosuppression regimens excluding calcineurin inhibitors and steroids, demonstrated higher HR for DCGF. High-risk EMM allowed better differentiation between DCGF probabilities per EMM, suggesting that recipients at higher risk for graft failure could benefit most from allocation schemes ensuring compatibility on these eplets.

Impact of Anti-HLA De Novo Donor Specific Antibody on Graft Outcomes in Pancreas Transplantation: A Meta-Analysis

BACKGROUND

The aim of this review is to provide consensus on the impact of antihuman leukocyte antigen (anti-HLA) de novo donor-specific antibodies (dnDSA) on pancreatic allograft loss.

METHODS

We systematically searched electronic databases through August 2020 using Preferred Reporting Items for Systematic Reviews and Meta-Analyses methodology. Articles that provided or allowed estimation of the odds ratio (OR) and 95% confidence interval (CI) for pancreatic allograft loss in patients with and without anti-HLA dnDSA were included.

RESULTS

Eight studies with a total of 1434 patients were included. Patients with anti-HLA dnDSA had significantly higher odds of graft failure (OR = 4.42, 95% CI [3.15-6.22], I² = 38%). Pooled data on graft rejection showed that patients with anti-HLA dnDSA have significantly higher odds of rejection than patients without anti-HLA (OR = 3.35, 95% CI [2.28-4.91], I² = 38%).

CONCLUSION

The results of our meta-analysis show that anti-HLA dnDSA is strongly associated with pancreas graft failure and rejection. Surveillance for anti-HLA dnDSA is an important component of post-transplant immune monitoring.

Humoral Response of Renal Transplant Recipients to the BNT162b2 SARS-CoV-2 mRNA Vaccine Using Both RBD IgG and Neutralizing Antibodies

BACKGROUND

Data about SARS-CoV-2 vaccines efficacy in renal transplant recipients (RTR) are lacking.

METHODS

To reveal predictors for humoral response to BNT162b2 vaccine among RTR, patients were divided into positive (N = 42) and negative (N = 78) response groups based on receptor-binding domain (RBD) immunoglobulin G (IgG) ≥1.1 and neutralizing antibodies (NA) ≥16 dilution versus RBD IgG <1.1 or NA <16, respectively. NA were detected using a SARS-CoV-2 pseudo-virus.

RESULTS

NA were detected in only 42 of 120 (35%) of RTR versus 197 of 202 (97.5%) immunocompetent controls (P < 0.001). NA geometric mean titers in RTR were significantly lower versus the control group {83.7 (95% confidence interval [CI], 50.5-138.8) versus 482 (95% CI, 411-566), P < 0.001}. In a multivariable analysis, mycophenolic acid (MPA) dose and hemoglobin level were found to be independent predictors for antibody response in RTR. A positive response rate of 27% versus 63% was observed in patients on and off MPA, respectively. An increase in MPA dose by 1 mg/kg weight reduced the odds for a positive response by 17% (odds ratio = 0.83; 95% CI, 0.75-0.92; P < 0.001). Geometric mean titers for RBD IgG were significantly reduced as MPA daily dose increased. Hemoglobin blood level <13 g/dL reduced the antibody response by 63% (P = 0.04). Pain at the injection site after the second vaccine dose was significantly higher in the responders versus nonresponders (20.5% versus 5.5%, P = 0.01).

CONCLUSIONS

Only 35% of RTR develop NA to the BNT162b2 mRNA vaccine. MPA is a major suppressor of antibody response in RTR.

Prospective multi-centric study to analyze pre-transplant compatibility algorithm for live-related donor kidney transplant in Indian setting: the "Delhi approach"!

BACKGROUND

Since no single test is always accurate and sensitive, two or more tests are used to increase the precision of evaluation. Different algorithms have been proposed by centers in Leiden, Basel, Vienna and Minnesota, etc. With an intention to develop an optimal algorithm for India, we evaluated pre-transplant compatibility tests for live-donor kidney transplants. Three tests complement dependent cyto-toxicity cross-match (CDCXM), flow-cytometry cross-match (FCXM) and anti-HLA antibody screening (HAS) were performed and confirmed by the anti-HLA antibody identification (HAI) assay in a multi-centric trial (three transplant centers) in India.

MATERIALS AND METHODS

All prospective recipients (and their potential donors) underwent low-resolution HLA typing as well as CDCXM, FCXM and HAS assays. In addition, HAI {single antigen bead assay; (SAB)} was done for all recipients to identify possible anti-HLA antibodies. In a virtual cross-match (VXM), antibody specificity was mapped to donor HLA type to determine donor-specific antibodies (DSA). Only patients without DSA were cleared for the transplant. Alternatively, patients with DSA were offered an exchange in the kidney paired donation (KPD) program. The screening results (CDCXM, FCXM, and HAS) were analyzed, individually as well as in combination of screening assays (CDCXM+HAS, CDCXM+FCXM, and FCXM+HAS) and the results were compared with those from the HAI test.

RESULTS

Out of 100 patients, 69 were males and 31 were females; 85 recipients (85%) underwent a kidney transplant. The sensitivity of CDCXM was only 12.1% and the specificity of CDCXM was 100%; whereas the sensitivity of FCXM was 84.8% and the specificity of FCXM was 89.6%. The sensitivity and specificity of class I HAS was 88.2% and 84.3%, respectively. The sensitivity and specificity class II HAS was 88.0% and 80.0%, respectively. However, when both class I/II HAS were tested together the sensitivity increased to 97.0% and the specificity to 82.1%. Similarly, the sensitivity of combined FCXM+HAS had the sensitivity of 100% and the specificity of 76.1%; CDCXM+FCXM had the sensitivity of 84.8% and the specificity of 89.6% and CDCXM+HAS assays reached 97% with the specificity of 82.1%.

CONCLUSIONS

Our results showed that the algorithm of FCXM with HAS produced the best sensitivity of 100%. The specificity of 76.1% indicate that the combined FCXM+HAS assays may detect up to 24.9% false positive results. We suggest that these false-positives may be easily resolved by performing the virtual crossmatch based on HAI (SAB) results. In our reflex testing algorithmic approach only 49% patients needed HAI (SAB). Finally, our results suggested that the CDCXM assay may be discontinued in pre-transplant workup owing to its very low sensitivity (12.1%).

Immortal Time-Bias-Corrected Survival of Highly Sensitized Patients and HLA-desensitized Kidney Transplant Recipients

Introduction

In the setting of kidney transplantation (KT), we assessed the efficacy of desensitization and compared the survival of desensitized patients (HLA-incompatible KT) with similarly sensitized patients receiving HLA-compatible KT or sensitized patients still on a waiting list after adjusting for the usually unaccounted immortal time bias.

Methods

All patients in a French KT center on the waiting list between August 1994 and December 2019 with a high level of sensitization (panel-reactive antibodies [PRAs] ≥80%) were included. The primary outcome was all-cause mortality. A time-varying covariate Cox survival model was used to account for the immortal time bias. A landmark analysis was used as a sensitivity analysis.

Results

During the study period, 326 patients with high PRAs were followed, among which 147 (45%) remained on the waiting list at the time of last follow-up and 179 benefited from a KT. Thirty-six patients were desensitized, of which 30 received a kidney transplant, including eight deceased kidney donors. There were no differences in mortality rates between desensitized KT patients, nondesensitized KT patients, and waitlisted patients after adjusting for immortal time bias (hazard ratio [HR] = 0.48, P = 0.22). Death-censored graft survival was similar between desensitized and nondesensitized KT patients (HR = 0.92, P = 0.88 adjusting for donor age >65 years, donor status, and time on the waiting list). Mean estimated glomerular filtration rate at 1 year post-KT was similar for desensitized KT patients (53.3 ± 21 vs. 53.6 ± 21 ml/min per 1.73 m² for nondesensitized patients; P = 0.95).

Conclusions

HLA-desensitization was effective for highly sensitized patients and gave access to KT without detrimental effects on patient or graft survival rates.

Caveolin-1 in Kidney Chronic Antibody-Mediated Rejection: An Integrated Immunohistochemical and Transcriptomic Analysis Based on the Banff Human Organ Transplant (B-HOT) Gene Panel

Caveolin-1 overexpression has previously been reported as a marker of endothelial injury in kidney chronic antibody-mediated rejection (c-ABMR), but conclusive evidence supporting its use for daily diagnostic practice is missing. This study aims to evaluate if Caveolin-1 can be considered an immunohistochemical surrogate marker of c-ABMR. Caveolin-1 expression was analyzed in a selected series of 22 c-ABMR samples and 11 controls. Caveolin-1 immunohistochemistry proved positive in peritubular and glomerular capillaries of c-ABMR specimens, irrespective of C4d status whereas all controls were negative. Multiplex gene expression profiling in c-ABMR cases confirmed Caveolin-1 overexpression and identified additional genes (n = 220) and pathways, including MHC Class II antigen presentation and Type II interferon signaling. No differences in terms of gene expression (including Caveolin-1 gene) were observed according to C4d status. Conversely, immune cell signatures showed a NK-cell prevalence in C4d-negative samples compared with a B-cell predominance in C4d-positive cases, a finding confirmed by immunohistochemical assessment. Finally, differentially expressed genes were observed between c-ABMR and controls in pathways associated with Caveolin-1 functions (angiogenesis, cell metabolism and cell–ECM interaction). Based on our findings, Caveolin-1 resulted as a key player in c-ABMR, supporting its role as a marker of this condition irrespective of C4d status.

The role of circulating T follicular helper cells in kidney transplantation

Humoral rejection plays a crucial role in the chronic deterioration of kidney allografts, but there is no effective therapeutic strategy to prevent or treat it. T follicular helper (Tfh) cells provide help to B cells, subsequently contributing to humoral rejection. Investigation of Tfh cells may be a useful strategy for assessing the risk and level of humoral rejection. However, it is difficult to investigate Tfh cells from patient-derived lymphoid tissue. Recent studies have shown that circulating Tfh (cTfh) cells, working in parallel to Tfh cells, have the capacity to promote antibody-secreting B cell differentiation and antibody secretion. Here, we review recent studies of cTfh cells in kidney transplantation and discuss the characteristics and functions of cTfh cells in kidney transplant recipients.

Optimal Immunosuppression Strategy in the Sensitized Kidney Transplant Recipient

Patients with previous sensitization events against anti-human leukocyte antigens (HLA) often have circulating anti-HLA antibodies. Following organ transplantation, sensitized patients have higher rates of antibody-mediated rejection (AMR) compared to those who are non-sensitized. More stringent donor matching is required for these patients, which results in a reduced donor pool and increased time on the waitlist. Current approaches for sensitized patients focus on reducing preformed antibodies that preclude transplantation; however, this type of desensitization does not modulate the primed immune response in sensitized patients. Thus, an optimized maintenance immunosuppressive regimen is necessary for highly sensitized patients, which may be distinct from non-sensitized patients. In this review, we will discuss the currently available therapeutic options for induction, maintenance, and adjuvant immunosuppression for sensitized patients.

The causes and frequency of kidney allograft failure in a low-resource setting: observational data from Iraqi Kurdistan

Background

In the developing world, transplantation is the most common long-term treatment for patients with end-stage renal disease, but rates and causes of graft failure are uncertain.

Methods

This was a retrospective outcomes study of renal transplant patients seen in Iraqi Kurdistan nephrology clinics in the year 2019. In 2019, 871 renal transplant patients were registered and outcomes followed through 12/31/2020. Indicated renal biopsies were obtained on 431 patients at 1 day to 18 years post-transplantation. Outcomes were compared with United States Renal Data System (USRDS) living donor reports.

Results

All donors were living. The recipient age was 38.5 ± 13.3 years, 98.2% were < 65 years old, 3.7% had previous transplants, and 2.8% had pretransplant donor-specific antibodies (DSA). Gehan-Breslow estimated failure rates for all-cause, return to HD, and death with functional graft were 6.0, 4.2, and 1.9% at 1 year and 18.1, 13.7, and 5.1% at 5 years post-engraftment (USRDS 2000; 1 year: 7.0, 5.0, 2.6%; 5 year: 22.3, 15.2, 10.6%. USRDS 2010; 1 year: 3.7, 2.4, 1.4%; 5 year: 15.3, 9.6, 7.3%). The median graft survival was 15 years. Acute tubular injury (ATI), infarction, and acute T cell-mediated rejection accounted for 22.2% of graft loss, with > 75% of these failures taking place in the first year. Most graft failures occurred late, at a median post-transplant time of 1125 (interquartile range, 365–2555) days, and consisted of interstitial fibrosis and tubular atrophy (IF/TA) (23.8%), transplant glomerulopathy (13.7%), and acquired active antibody-mediated rejection (12.0%). The significant predictors of graft loss were C4d + biopsies (P < 0.01) and advanced IF/TA (P < 0.001).

Conclusions

Kurdistan transplant patients had graft failure rates similar to living donors reported by the USRDS for the year 2000 but higher than reported for 2010. Compared to USRDS 2010, Kurdistan patients had a moderate excess of HD failures at one and 5 years post-engraftment. Nevertheless, prolonged survival is the norm, with chronic disorders and acquired DSA being the leading causes of graft loss.

Beyond the Biopsy: Monitoring Immune Status in Kidney Recipients

Improved long-term kidney allograft survival is largely related to better outcomes at 12 months, in association with declining acute rejection rates and more efficacious immunosuppression. Finding the right balance between under- and overimmunosuppression or rejection versus immunosuppression toxicity remains one of transplant's holy grails. In the absence of precise measures of immunosuppression burden, transplant clinicians rely on nonspecific, noninvasive tests and kidney allograft biopsy generally performed for cause. This review appraises recent advances of conventional monitoring strategies and critically examines the plethora of emerging tests utilizing tissue, urine, and blood samples to improve upon the diagnostic precision of allograft surveillance.

The Problem of Subclinical Antibody-mediated Rejection in Kidney Transplantation

Defined as histologic evidence of rejection on a protocol biopsy in the absence of kidney dysfunction, subclinical rejection has garnered attention since the 1990s. The major focus of much of this research, however, has been subclinical T cell-mediated rejection (TCMR). Herein, we review the literature on subclinical antibody-mediated rejection (AMR), which may occur with either preexisting donor-specific antibodies (DSA) or upon the development of de novo DSA (dnDSA). In both situations, subsequent kidney function and graft survival are compromised. Thus, we recommend protocol biopsy routinely within the first year with preexisting DSA and at the initial detection of dnDSA. In those with positive biopsies, baseline immunosuppression should be maximized, any associated TCMR treated, and adherence stressed, but it remains uncertain if antibody-reduction treatment should be initiated. Less invasive testing of blood for donor DNA or gene profiling may have a role in follow-up of those with negative initial biopsies. If a protocol biopsy is positive in the absence of detectable HLA-DSA, it also remains to be determined whether non-HLA-DSA should be screened for either in particular or on a genome-wide basis and how these patients should be treated. Randomized controlled trials are clearly needed.

Innate-like self-reactive B cells infiltrate human renal allografts during transplant rejection

Intrarenal B cells in human renal allografts indicate transplant recipients with a poor prognosis, but how these cells contribute to rejection is unclear. Here we show using single-cell RNA sequencing that intrarenal class-switched B cells have an innate cell transcriptional state resembling mouse peritoneal B1 or B-innate (Bin) cells. Antibodies generated by Bin cells do not bind donor-specific antigens nor are they enriched for reactivity to ubiquitously expressed self-antigens. Rather, Bin cells frequently express antibodies reactive with either renal-specific or inflammation-associated antigens. Furthermore, local antigens can drive Bin cell proliferation and differentiation into plasma cells expressing self-reactive antibodies. These data show a mechanism of human inflammation in which a breach in organ-restricted tolerance by infiltrating innate-like B cells drives local tissue destruction.

Intrarenal B cells are indicative of poor prognosis in human renal allografts. Here the authors use single cell RNA sequencing to examine how intrarenal B cells contribute to renal rejection and find a population of innate B cells reactive to renal-specific or inflammation-associated antigens.

Impact of Sex in the Efficacy of Perioperative Desensitization Procedures in Heart Transplantation: A Retrospective Cohort Study

Background

Sensitized patients, i.e. recipients with preformed donor-specific HLA antibodies (pfDSA), are at high-risk of developing antibody-mediated rejections (AMR) and dying after heart transplantation (HTx). Perioperative desensitization procedures are associated with better outcomes but can cause sensitization, which may influence their efficacy.

Methods

In sensitized patients (pfDSA>1000 mean immunofluorescence (MFI) units), we assessed the effect of perioperative desensitization by comparing treated patients to a historical control cohort. Multivariable survival analyses were performed on the time to main outcome, a composite of death and biopsy-proven AMR with 5-year follow-up.

Results

The study included 68 patients: 31 control and 37 treated patients. There was no difference in preoperative variables between the two groups, including cumulative pfDSA [4026 (1788;8725) vs 4560 (3162;13392) MFI units, p=0.28]. The cause of sensitization was pregnancy in 24/68, 35.3%, transfusion in 61/68, 89.7%, and previous HTx in 4/68, 5.9% patients. Multivariable analysis yielded significant protective association between desensitization and events (adjusted (adj.) hazard ratio (HR)=0.44 (95% confidence interval (95CI)=0.25-0.79), p=0.006) and deleterious association between cumulative pfDSA and events [per 1000-MFI increase, adj.HR=1.028 (1.002-1.053), p=0.031]. There was a sex-difference in the efficacy of desensitization: in men (n=35), the benefit was significant [unadj.HR=0.33 (95CI=0.14-0.78); p=0.01], but not in women (n=33) [unadj.HR=0.52 (0.23-1.17), p=0.11]. In terms of the number of patients treated, in men, 2.1 of patients that were treated prevented 1 event, while in women, 3.1 required treatment to prevent 1 event.

Conclusion

Perioperative desensitization was associated with fewer AMR and deaths after HTx, and efficacy was more pronounced in men than women.

The evolution of histological changes suggestive of antibody-mediated injury, in the presence and absence of donor-specific anti-HLA antibodies

The interplay between donor-specific anti-HLA antibodies (HLA-DSA), histology of active antibody-mediated rejection (aABMR_h ), transplant glomerulopathy (cg) and graft failure in kidney transplantation remains insufficiently understood. We performed a single-center cohort study (n=1000) including 2761 protocol and 833 indication biopsies. Patients with pre-transplant HLA-DSA were more prone to develop aABMRh (OR 22.7, 95% CI, 11.8 - 43.7, p<0.001), cg (OR 5.76, 95% CI, 1.67 - 19.8, p=0.006) and aABMRh/cg (OR 19.5, 95% CI, 10.6 - 35.9, p<0.001). The negative impact of pre-transplant HLA-DSA on graft survival (HR 2.12, 95% CI, 1.41 - 3.20, p<0.001) was partially mediated through aABMRh and cg occurrence. When adjusted for time-dependent HLA-DSA (HR 4.03, 95% CI, 2.21 - 7.15, p=0.002), graft failure was only affected by aABMR_h when cg was evident. In HLA-DSA negative patients, aABMR_h was associated with impaired graft outcome only when evolving to cg (HR 1.32, 95% CI, 1.07 - 1.61, p=0.008). We conclude that the kinetics of HLA-DSA are important to estimate the rate of graft failure, and that histological follow-up is necessary to discover, often subclinical, ABMR and cg. In the absence of HLA-DSA, patients experience similar histological lesions and the evolution to transplant glomerulopathy associates with impaired graft outcome.

Association between dd-cfDNA levels, de novo donor specific antibodies, and eGFR decline: An analysis of the DART cohort

BACKGROUND

Donor-derived cell-free DNA (dd-cfDNA) is a marker of allograft injury in transplant recipients; however, the relationship between dd-cfDNA and other clinical parameters associated with adverse allograft outcomes is not well-characterized.

METHODS

We performed a retrospective analysis of kidney transplant recipients from the DART cohort (ClinicalTrials.gov Identifier: NCT02424227) to evaluate the associations between eGFR decline, de novo donor-specific antibodies (dnDSA), and dd-cfDNA.

RESULTS

Both elevated dd-cfDNA (≥1%) and dd-cfDNA variability (≥.34%) in the first post-transplant year were associated with decline in eGFR ≥25% in the second year (21.4% vs. 4.1%, P = .005; 25% vs. 3.6%, P = .002, respectively). Compared to samples from DSA negative patients, samples from patients with concurrent de novo HLA DSAs had higher dd-cfDNA levels (P < .0001).

DISCUSSION

Abnormalities in dd-cfDNA levels are associated with clinical parameters commonly used as surrogate endpoints for adverse allograft outcomes, raising the possibility that molecular injury as characterized by dd-cfDNA could help identify patients at risk of these outcomes.

De novo donor-specific HLA antibodies reduce graft survival rates and increase the risk of kidney transplant rejection: A single-center retrospective study

BACKGROUND

We investigated the impact of de novo donor-specific anti-human leukocyte antigen antibodies (dnDSAs) on long-term death-censored graft survival and renal allograft rejection in kidney transplant recipients.

METHODS

The sample for this retrospective cohort study comprised 121 recipients of kidney transplants with negative complement-dependent cytotoxicity crossmatches to their deceased donors. Recipients were divided into two groups: dnDSAs+ (n = 31) and dnDSAs- (n = 90). We evaluated rejection and long-term graft survival rates in the recipients along with pathologic changes in the transplanted kidneys.

RESULTS

DnDSAs were identified in 31/121 patients (25.6%). The graft survival rate in the dnDSAs+ group was 87.1% (27/31) and that of the dnDSAs- group was 97.8% (88/90). The dnDSAs+ group had lower graft survival rates than patients without dnDSAs (p = 0.007). There was no difference in the graft survival rates between patients with high DSA mean fluorescence intensity (≥4000) and those with low intensity (<4000) (p = 0.669). There was also no difference in the graft survival rates of patients with HLA class I, II, and I + II dnDSAs (p = 0.571). The presence of dnDSA in serum was associated with a higher incidence of antibody- and T-cell-mediated rejection (p < 0.0001). Banff scores for arterial fibrointimal and arteriolar hyalin, thickening as well as C4d deposition differed for the dnDSAs+ and dnDSAs- groups (p < 0.05).

CONCLUSION

DnDSAs were found to be associated with decreased long-term graft survival rates and increased rejection rates, often accompanied by C4d deposition.

Current Evidence on the Clinical Relevance of Donor-specific Antibodies in Paediatric Liver Transplantation

ABSTRACT

The clinical impact of donor-specific antibodies (DSA) occurring before or after liver transplantation (LT) against donor-human leucocyte antigen (HLA) on graft outcome is still unclear. We aim to present the current consensus based on recent paediatric LT case series. Compared to kidney transplantation, the liver seems to be less susceptible to antibody-mediated graft damage, which is likely due to protective Kupffer cell activity. The incidence of DSA after liver transplantation is higher in children than in adults. DSA directed against HLA class II molecules, mainly DQ, occur more often. The presence of such anti-class II DSA (DQ/DR), especially of the complement-binding IgG3 subclass, may be associated with endothelial injury, T-cell-mediated rejection (TCMR), inflammation, and fibrosis. Regular DSA-posttransplant monitoring cannot as yet be recommended in routine practice but may be useful in selected cases.

B cells in transplant tolerance and rejection: friends or foes?

Our understanding of the role of B cells in organ transplantation remains incomplete and continues to grow. The majority of research has focused on the detrimental role of antibodies that drive the development of pathogenesis of the transplanted organ. However, it has been shown that not all donor-specific antibodies are harmful and in some circumstances can even promote tolerance through the mechanism of accommodation. Furthermore, B cells can have effects on transplanted organs through their interaction with T cells, namely antigen presentation, cytokine production, and costimulation. More recently, the role and importance of Bregs was introduced to the field of transplantation. Due to this functional and ontogenetic heterogeneity, targeting B cells in transplantation may bring undesired immunologic side effects including increased rejection. Therefore, the selective control of B cells that contribute to the humoral response against donor antigens will continue to be an important and challenging area of research and potentially lead to improved long-term transplant outcomes.

HLA Desensitization in Solid Organ Transplantation: Anti-CD38 to Across the Immunological Barriers

The presence of anti-human leucocyte antigen (HLA) antibodies in the potential solid organ transplant recipient's blood is one of the main barriers to access to a transplantation. The HLA sensitization is associated with longer waitlist time, antibody mediated rejection and transplant lost leading to increased recipient's morbidity and mortality. However, solid organ transplantation across the HLA immunological barriers have been reported in recipients who were highly sensitized to HLA using desensitization protocols. These desensitization regimens are focused on the reduction of circulating HLA antibodies. Despite those strategies improve rates of transplantation, it remains several limitations including persistent high rejection rate and worse long-term outcomes when compare with non-sensitized recipient population. Currently, interest is growing in the development of new desensitization approaches which, beyond targeting antibodies, would be based on the modulation of alloimmune pathways. Plasma cells appears as an interesting target given their critical role in antibody production. In the last decade, CD38-targeting immunotherapies, such as daratumumab, have been recognized as a key component in the treatment of myeloma by inducing an important plasma cell depletion. This review focuses on an emerging concept based on targeting CD38 to desensitize in the field of transplantation.

Tackling Chronic Kidney Transplant Rejection: Challenges and Promises

Despite advances in post-transplant management, the long-term survival rate of kidney grafts and patients has not improved as approximately forty percent of transplants fails within ten years after transplantation. Both immunologic and non-immunologic factors contribute to late allograft loss. Chronic kidney transplant rejection (CKTR) is often clinically silent yet progressive allogeneic immune process that leads to cumulative graft injury, deterioration of graft function. Chronic active T cell mediated rejection (TCMR) and chronic active antibody-mediated rejection (ABMR) are classified as two principal subtypes of CKTR. While significant improvements have been made towards a better understanding of cellular and molecular mechanisms and diagnostic classifications of CKTR, lack of early detection, differential diagnosis and effective therapies continue to pose major challenges for long-term management. Recent development of high throughput cellular and molecular biotechnologies has allowed rapid development of new biomarkers associated with chronic renal injury, which not only provide insight into pathogenesis of chronic rejection but also allow for early detection. In parallel, several novel therapeutic strategies have emerged which may hold great promise for improvement of long-term graft and patient survival. With a brief overview of current understanding of pathogenesis, standard diagnosis and challenges in the context of CKTR, this mini-review aims to provide updates and insights into the latest development of promising novel biomarkers for diagnosis and novel therapeutic interventions to prevent and treat CKTR.

The influence of the antithymocyte globulin dose on clinical outcomes of patients undergoing kidney retransplantation

Optimizing antithymocyte globulin (rATG) dosage is critical for high immunological risk patients undergoing a repeat kidney transplant. This natural retrospective cohort study compared clinical outcomes of two successive cohorts of consecutive recipients of retransplants receiving 5 x 1 mg/kg (rATG-5, n = 100) or a single 3 mg/kg (rATG-3, n = 110) dose of rATG induction therapy. All patients had negative complement-dependent cytotoxicity crossmatch and no anti-HLA A, B, DR donor-specific antibodies (DSA). The primary endpoint was efficacy failure (first biopsy-proven acute rejection, graft loss, or death) at 12 months. There was no difference in the cumulative incidence of efficacy failure (18.0% vs. 21.8%, HR = 1.22, 95% CI 0.66–2.25), respectively. There were no differences in 3-years freedom from biopsy proven acute rejection, and patient, graft, and death-censored graft survivals. There were no differences in the incidence of surgical complications (25.0% vs. 18.2%; p 0.151), early hospital readmission (27.8% vs. 29.5%; p = 0.877) and CMV infections (49% vs. 40%; p = 0.190). There were also no differences in the incidence (59.6% vs. 58.7%, p = 0.897) and duration of delayed graft function but a stable difference in estimate glomerular filtration rate was observed from month 1 (54.7±28.8 vs. 44.1±25.3 ml/min/1.73 m², p = 0.005) to month 36 (51.1±27.7 vs. 42.5±24.5, p = 0.019). Mean urinary protein concentration (month 36: 0.38±0.81 vs. 0.70±2.40 g/ml, p = 0.008) and mean chronic glomerular Banff score in for cause biopsies (months 4–36: 0.0±0.0 vs. 0.04±0.26, p = 0.044) were higher in the rATG-3 group. This cohort analysis did not detect differences in the incidence of efficacy failure and in safety outcomes at 12 months among recipients of kidney retransplants without A, B, and DR DSA, receiving induction therapy with a single 3 mg/kg rATG dose or the traditional 5 mg/kg rATG.

The role of the gut microbiome in graft fibrosis after pediatric liver transplantation

Liver transplantation (LT) is a life-saving option for children with end-stage liver disease. However, about 50% of patients develop graft fibrosis in 1 year after LT, with normal liver function. Graft fibrosis may progress to cirrhosis, resulting in graft dysfunction and ultimately the need for re-transplantation. Previous studies have identified various risk factors for the post-LT fibrogenesis, however, to date, neither of the factors seems to fully explain the cause of graft fibrosis. Recently, evidence has accumulated on the important role of the gut microbiome in outcomes after solid organ transplantation. As an altered microbiome is present in pediatric patients with end-stage liver diseases, we hypothesize that the persisting alterations in microbial composition or function contribute to the development of graft fibrosis, for example by bacteria translocation due to increased intestinal permeability, imbalanced bile acids metabolism, and/or decreased production of short-chain fatty acids (SCFAs). Subsequently, an immune response can be activated in the graft, together with the stimulation of fibrogenesis. Here we review current knowledge about the potential mechanisms by which alterations in microbial composition or function may lead to graft fibrosis in pediatric LT and we provide prospective views on the efficacy of gut microbiome manipulation as a therapeutic target to alleviate the graft fibrosis and to improve long-term survival after LT.

CD45RA-CD25highCD127-CD4+ activated regulatory T cells are correlated with de novo donor-specific anti-HLA antibody formation after kidney transplantation in standard immunosuppression

Although de novo donor-specific anti-HLA antibodies (dnDSA) remain a barrier for human kidney transplantation (KTx), the role of regulatory T (Treg) cells in dnDSA formation remains unknown. To address this question, we evaluated Treg cell subsets in peripheral blood mononuclear cells in 15 healthy volunteers and 59 KTx recipients using flow cytometric analysis. The post-transplant CD25^highCD127^-CD4⁺ Treg cells in KTx recipients were down-regulated compared with those of healthy volunteers (P < .001). Among them, 11 KTx recipients showed dnDSA formation, which was associated with lower frequencies of CD25^highCD127^-CD4⁺ Treg cells (P = .040). Furthermore, of the total Treg cell population, CD45RA^-CD25^highCD127^-CD4⁺ activated Treg (aTreg) cells were significantly dominant in patients with dnDSA (P = .038), but not CD45RA⁺CD25^highCD127^-CD4⁺ resting Treg cells (P = .961). In contrast, non-donor-specific anti-HLA antibody formation was not associated with CD45RA^- aTreg cells (P = .772). Multivariate logistic regression analyses revealed that CD45RA^- aTreg cells were independently associated with dnDSA formation (Odds ratio = 6.69, P = .040). These findings indicate that CD45RA^- aTreg cells are strongly associated with dnDSA formation in KTx recipients and might be an important risk factor of antibody-mediated rejection before clinical diagnosis.

Therapies for Chronic Allograft Rejection

Remarkable advances have been made in the pathophysiology, diagnosis, and treatment of antibody-mediated rejection (ABMR) over the past decades, leading to improved graft outcomes. However, long-term failure is still high and effective treatment for chronic ABMR, an important cause of graft failure, has not yet been identified. Chronic ABMR has a relatively different phenotype from active ABMR and is a slowly progressive disease in which graft injury is mainly caused by de novo donor specific antibodies (DSA). Since most trials of current immunosuppressive therapies for rejection have focused on active ABMR, treatment strategies based on those data might be less effective in chronic ABMR. A better understanding of chronic ABMR may serve as a bridge in establishing treatment strategies to improve graft outcomes. In this in-depth review, we focus on the pathophysiology and characteristics of chronic ABMR along with the newly revised Banff criteria in 2017. In addition, in terms of chronic ABMR, we identify the reasons for the resistance of current immunosuppressive therapies and look at ongoing research that could play a role in setting better treatment strategies in the future. Finally, we review non-invasive biomarkers as tools to monitor for rejection.

Case Report: Splenic Irradiation for the Treatment of Chronic Active Antibody-Mediated Rejection in Kidney Allograft Recipients With De Novo Donor-Specific Antibodies

Chronic active antibody-mediated rejection (AMR) in renal transplantation is usually refractory to current conventional treatment with rituximab, plasmapheresis (PP), and intravenous immunoglobulins (IVIG). Splenic irradiation has been reported to be effective in the rescue of early severe acute AMR after kidney transplantation; however, its effect in chronic active AMR has not been reported to date. In order to reduce donor-specific antibody (DSA) and prevent the progression of chronic AMR, we used repetitive low-dose splenic irradiation, together with rituximab and PP/IVIG, in two living-related kidney transplant recipients with pathologically diagnosed chronic active AMR and the presence of long-term class II-de novo DSA. DSA monitoring and repeated renal biopsy revealed significantly reduced DSA levels as well as alleviated glomerulitis and peritubular capillaritis in both patients after treatment, and these therapies may have played a role in delaying the progression of chronic AMR. Although DSA levels in both patients eventually rebounded to some extent after treatment, serum creatinine increased slowly in one patient during the 16-month follow-up period and remained stable in the other during the 12-month follow-up period. Given the poor efficacy of conventional treatment at present, splenic irradiation may still be one of the treatment options for chronic active AMR.

Delayed graft function and acute rejection following HLA-incompatible living donor kidney transplantation

Incompatible living donor kidney transplant recipients (ILDKTr) have pre-existing donor-specific antibody (DSA) that, despite desensitization, may persist or reappear with resulting consequences, including delayed graft function (DGF) and acute rejection (AR). To quantify the risk of DGF and AR in ILDKT and downstream effects, we compared 1406 ILDKTr to 17 542 compatible LDKT recipients (CLDKTr) using a 25-center cohort with novel SRTR linkage. We characterized DSA strength as positive Luminex, negative flow crossmatch (PLNF); positive flow, negative cytotoxic crossmatch (PFNC); or positive cytotoxic crossmatch (PCC). DGF occurred in 3.1% of CLDKT, 3.5% of PLNF, 5.7% of PFNC, and 7.6% of PCC recipients, which translated to higher DGF for PCC recipients (aOR = _1.03 1.68_2.72 ). However, the impact of DGF on mortality and DCGF risk was no higher for ILDKT than CLDKT (p interaction > .1). AR developed in 8.4% of CLDKT, 18.2% of PLNF, 21.3% of PFNC, and 21.7% of PCC recipients, which translated to higher AR (aOR PLNF = _1.45 2.09_3.02 ; PFNC = _1.67 2.40_3.46 ; PCC = _1.48 2.24_3.37 ). Although the impact of AR on mortality was no higher for ILDKT than CLDKT (p interaction = .1), its impact on DCGF risk was less consequential for ILDKT (aHR = _1.34 1.62_1.95 ) than CLDKT (aHR = _1.96 2.29_2.67 ) (p interaction = .004). Providers should consider these risks during preoperative counseling, and strategies to mitigate them should be considered.

Donor-specific antibodies development in renal living-donor receptors: Effect of a single cohort

Minimization in immunosuppression could contribute to the appearance the donor-specific HLA antibodies (DSA) and graft failure. The objective was to compare the incidence of DSA in renal transplantation (RT) in recipients with immunosuppression with and without steroids. A prospective cohort from March 1st, 2013 to March 1st, 2014 and follow-up (1 year), ended in March 2015, was performed in living donor renal transplant (LDRT) recipients with immunosuppression and early steroid withdrawal (ESW) and compared with a control cohort (CC) of patients with steroid-sustained immunosuppression. All patients were negative cross-matched and for DSA pre-transplant. The regression model was used to associate the development of DSA antibodies and acute rejection (AR) in subjects with immunosuppressive regimens with and without steroids. Seventy-seven patients were included (30 ESW and 47 CC). The positivity of DSA class I (13% vs 2%; P < 0.05) and class II (17% vs 4%, P = 0.06) antibodies were higher in ESW versus CC. The ESW tended to predict DSA class II (RR 5.7; CI (0.93–34.5, P = 0.06). T-cell mediated rejection presented in 80% of patients with DSA class I (P = 0.07), and 86% with DSA II (P = 0.03), and was associated with DSA class II, (RR 7.23; CI (1.2–44), P = 0.03). ESW could favor the positivity of DSA. A most strictly monitoring the DSA is necessary for the early stages of the transplant to clarify the relationship between T-cell mediated rejection and DSA.

Clinical significance of de novo donor-specific antibody in kidney transplant recipients with chronic antibody-mediated rejection

Background

Chronic antibody-mediated rejection (CABMR) is an important cause of late graft loss. De novo donor-specific antibody (dnDSA) is an important prognostic factor for long-term allograft outcomes. However, the prognosis of CABMR based on the presence of dnDSA is uncertain.

Methods

We retrospectively analyzed 35 kidney transplant recipients with CABMR between 2010 and 2018. Fourteen recipients had no detectable DSA, and 21 recipients had detectable DSA. We investigated the pathologic findings at diagnosis of CABMR, allograft function 12 months later, related factors for allograft failure, and allograft survival rate based on the presence of dnDSA.

Results

The pathologic findings showed that acute and chronic changes were more severe in the dnDSA (+) group than in the dnDSA (-) group. There was no significant difference in the allograft function 12 months after the diagnosis of CABMR and in the amount of proteinuria at diagnosis between the two groups. However, the death-censored graft survival rate was lower in the high-proteinuria group than in the low-proteinuria group in both groups. The treatment rate of recipients was higher in the dnDSA (+) group than in the dnDSA (-) group; however, there was no significant difference in the death-censored graft survival rate between the two groups.

Conclusions

Although the effect of dnDSA on the prognosis of CABMR is not clear, it would be important not to neglect treatment for CABMR with risk factors for allograft failure even without dnDSA. Continuous and rigorous surveillance of DSA and allograft function is needed in patients with CABMR.

G-CSF promotes alloregulatory function of MDSCs through a c-Kit dependent mechanism

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells that expand in inflammatory conditions including transplantation. MDSCs may be capable of controlling rejection. The critical mechanisms underlying MDSC mediated alloregulation remain unexplored. G-CSF potently stimulates MDSC expansion. We hypothesized that G-CSF-induced MDSCs use a novel mechanism to suppress T cell responses. G-CSF promoted expansion of MDSCs and enhanced their suppressive function against T cell proliferation. Gene expression analysis revealed MDSCs expanded with G-CSF upregulated immune-related genes, but downregulated proliferation-related genes when compared to naïve control MDSCs. The KIT oncogene, encoding the c-Kit (CD117) transmembrane tyrosine kinase receptor, was the most significantly increased in MDSCs expanded with G-CSF. c-Kit inhibition with both imatinib and monoclonal blocking antibody reduced expression of ARG-1, iNOS, PD-L1, and SAA3. Further, imatinib also reduced MDSC-mediated T cell suppression in vitro. Modulation of c-Kit activity may represent a therapeutic target for alloregulatory MDSCs.

C1q-binding DSA and allograft outcomes in pediatric kidney transplant recipients

Donor-specific antibody (DSA) is an independent risk factor for antibody-mediated rejection (ABMR) and graft loss. The C1q assay differentiates complement from non-complement-binding DSA and C1q-binding DSA may lead to poor allograft survival. Our aim was to characterize the type of DSA seen in pediatric kidney transplant recipients and to determine whether complement binding DSA was associated with inferior graft survival.This was a single-center retrospective study of 48 children who were transplanted between 2009 and 2016. DSA were monitored using Luminex single antigen beads. A negative crossmatch was required to proceed with transplantation. The median follow-up time was 4.9 (3.4, 7.9) years. The median age was 12 (5.7, 15.4) years. DSA developed in 27/48 (56.3%), while C1q-binding DSA developed in 17/27 (63%). There were no significant differences between DSA negative, C1q-binding DSA, and C1q negative DSA, with regard to the number of HLA-ABDR (P  =  .09) or HLA-DQ mismatches alone (P  =  .16). For both C1q negative and C1q-binding DSA, DQ was the most common target of the DSA (19/27; 70.4%). C1q-binding DSA was associated with a significantly higher frequency of biopsy proven rejection (76.5%) when compared to C1q negative (10%) and DSA negative (14.3%); P  =  .001. Graft loss was seen in 6 (12.5%), all of whom had C1q-binding DSA (P  =  .004). C1q-binding DSA was most commonly directed to DQ antigens. C1q-binding DSA was associated with increased rejection and graft loss. Monitoring for C1q-binding DSA may risk stratify recipients and guide physician management.

NK cells in antibody-mediated rejection - Key effector cells in microvascular graft damage

Antibody-mediated rejection (ABMR) stands as the major limitation to long-term transplant outcome. The immunologic understanding of ABMR continues to progress and has identified natural killer (NK) cells as key effector cells promoting and coordinating the immune attack on the graft microvascular endothelium. This review discusses the current concepts outlining the different ways that allow for NK cell recognition of graft endothelial cells which includes antibody-dependent as well as independent processes.

Safety and Efficacy of a Steroid Avoidance Immunosuppression Regimen in Renal Transplant Patients With De Novo or Preformed Donor-Specific Antibodies: A Single-Center Study

Although interest in the role of donor-specific antibodies (DSAs) in kidney transplant rejection, graft survival, and histopathological outcomes is increasing, their impact on steroid avoidance or minimization in renal transplant populations is poorly understood. Primary outcomes of graft survival, rejection, and histopathological findings were assessed in 188 patients who received transplants between 2012 and 2015 at the Scripps Center for Organ Transplantation, which follows a steroid avoidance protocol. Analyses were performed using data from the United Network for Organ Sharing. Cohorts included kidney transplant recipients with de novo DSAs (dnDSAs; n = 27), preformed DSAs (pfDSAs; n = 15), and no DSAs (nDSAs; n = 146). Median time to dnDSA development (classes I and II) was shorter (102 days) than in previous studies. Rejection of any type was associated with DSAs to class I HLA (P < .05) and class II HLA (P < .01) but not with graft loss. Although mean fluorescence intensity (MFI) independently showed no association with rejection, an MFI >5000 showed a trend toward more antibody-mediated rejection (P < .06), though graft loss was not independently associated. Banff chronic allograft nephropathy scores and a modified chronic injury score were increased in the dnDSA cohort at 6 months, but not at 2 years (P < .001 and P < .08, respectively). Our data suggest that dnDSAs and pfDSAs impact short-term rejection rates but do not negatively impact graft survival or histopathological outcomes at 2 years. Periodic protocol post-transplant DSA monitoring may preemptively identify patients who develop dnDSAs who are at a higher risk for rejection.

Impact of tacrolimus versus cyclosporine on one-year renal transplant outcomes: A single-centre retrospective cohort study

Background:

Calcineurin inhibitors are the cornerstone of maintenance immunosuppression after kidney transplant. While studies on predominantly Caucasian populations recommend tacrolimus over cyclosporine, the effects on Singapore’s local population remain unclear.

Objectives:

This study aimed to compare the impact of tacrolimus against cyclosporine on post-transplant outcomes in our local kidney transplant population.

Methods:

A single-centre retrospective chart review was conducted on ABO- and human leucocyte antigen (HLA)-compatible kidney transplantations between 1 January 2011 and 15 August 2018. Patients who received basiliximab induction, prednisolone, mycophenolate and either tacrolimus or cyclosporine were included and followed up for at least one year. Recipients of transplantations at other institutions or other immunosuppressive regimens were excluded. Patient and graft outcomes and adverse effects were collected.

Results:

Overall, 120 patients on tacrolimus and 49 on cyclosporine were included. Patients on tacrolimus were older. This group had more deceased donor transplants, a higher proportion with donor-specific antibodies (DSAs) present and more HLA mismatches. There were no differences in patient and graft survival, graft function and acute rejections at one year, despite adjusting for age, transplant type, presence of DSAs and total HLA mismatches. The tacrolimus group had more infectious admissions (odds ratio=0.27, 95% confidence interval 0.098–0.73, p=0.01) after adjusting for age, transplant type, HLA mismatches, presence of DSAs and acute rejections, with increased severity and more opportunistic infections. More patients on cyclosporine required a change to alternative immunosuppressants (p=0.003).

Conclusion:

Our study demonstrated comparable short-term post-transplant outcomes between cyclosporine and tacrolimus. Tacrolimus appears more tolerable but may be associated with infection risks.

Preceding T-Cell-Mediated Rejection Is Associated with the Development of Chronic Active Antibody-Mediated Rejection by de Novo Donor-Specific Antibody

AIM

Chronic active antibody-mediated rejection (CAABMR) is an important cause of late-stage renal allograft loss. Early inflammatory events such as acute rejection and infection after transplantation are considered to be the risk factors of de novo donor-specific antibody (dnDSA) production. In this study, we investigated the relationship between pre-disposing T-cell-mediated rejection and dnDSA-positive CAABMR.

METHODS

We recruited 365 patients who underwent ABO-compatible renal transplantation at our hospital. Among them, 16 patients diagnosed as having dnDSA-positive CAABMR were designated as a CAABMR group, and 38 randomly selected patients were designated as a control group. All biopsies from 1 month after transplantation were included in the study. The presence or absence of borderline changes (BLCs), acute T-cell-mediated rejection (ATMR), microvascular inflammation (MVI), and C4d positive on peritubular capillaries (C4d-P) was examined.

RESULTS

In the CAABMR group, BLC/ATMR was found in 12 cases (75%), and the mean duration until appearance of BLC/ATMR was 282.7 ± 328.7 days. C4d-P was found in 11 cases (68.8%), and the mean duration until its appearance was 1,432 ± 1,307 days. MVI was found in all cases, and the mean duration until its appearance was 1,333 ± 1,126 days. The mean duration until diagnosis of CAABMR was 2,268 ± 1,191 days. In the control group, BLC/ATMR was found in 13 cases (34.2%), and the mean duration until the appearance of BLC/ATMR was 173.1 ± 170.4 days. C4d-P was found in 2 cases (5.3%), and the durations until its appearance were 748 and 1,881 days. No cases of MVI were found in the control group. The frequency of BLC/ATMR was significantly higher in the CAABMR group (p < 0.01).

CONCLUSION

Preceding BLC/ATMR is associated with the development of CAABMR with dnDSA.

Treatment of Antibody-Mediated Rejection After Kidney Transplantation: Immunological Effects, Clinical Response, and Histological Findings

Background

Antibody-mediated rejection (AMR) presents with diverse clinical manifestations and can have a potential negative impact on graft function and survival. If not treated successfully, AMR can lead to 20–30% graft loss after 1 year. Little is known about the efficacy of AMR treatment, and the most appropriate therapeutic strategy has not yet been determined. This study evaluated the effects of AMR treatment with plasmapheresis (PP) and intravenous immunoglobulin (IVIG) on renal function, intensity of anti-HLA antibodies, and graft biopsy morphology.

Material/Methods

This single-center retrospective cohort study included renal transplant recipients with biopsy-proven AMR who were treated with PP and/or IVIG. Clinical findings, mean fluorescence intensity of donor-specific anti-HLA antibodies (DSA), and graft histology findings, classified according to Banff score at the time of AMR and 6 and 12 months later, were evaluated.

Results

Of the 42 patients who met the inclusion criteria, 38 (90.5%) received IVIG and 26 (61.9%) underwent PP. At AMR diagnosis, 36 (85.7%) patients had proteinuria, with their estimated glomerular filtration rate remaining stable during follow-up. During the first year, 8 (19.0%) patients experienced graft failure, but none died with a functioning graft. Reductions in the class I panel of reactive antibodies were observed 6 and 12 months after AMR treatment, with significant reductions in DSA-A and -B fluorescence intensity, but no changes in DSA-DQ. Graft biopsy showed reductions in inflammation and C4d scores, without improvements in microvascular inflammation.

Conclusions

AMR treatment reduced biopsy-associated and serological markers of AMR, but did not affect DSA-DQ.

Implication of a positive virtual crossmatch with negative flow crossmatch: A mind-boggler

There are occasions when tests performed before considering a patient for transplant are ambiguous and require further workup. One such condition is the presence of a positive virtual crossmatch (VXm) (anti-human leukocyte antigen [HLA-A]*26: 01 antibody in this case) with a negative complement-dependent cytotoxicity, Luminex, and flow crossmatch. To ascertain the nature of the antibody, the beads used in single-antigen bead assay (SAB) were treated by acid to denature the antigens and retested with the control and test sample. The mean fluorescence intensities (MFIs) from the patient sera with acid-treated beads increased considerably as compared to the regularly untreated SAB indicating additional antigen epitopes become available by the denaturation process. The MFIs of the antibodies from that of the control sera were reduced to half on testing with the acid-treated SAB assay, indicating that HLA antigen HLA-A*26 was susceptible to acid treatment. Therefore, results of VXm should be interpreted with caution.

Donor apoptotic cell-based therapy for effective inhibition of donor-specific memory T and B cells to promote long-term allograft survival in allosensitized recipients

Allosensitization constitutes a major barrier in transplantation. Preexisting donor-reactive memory T and B cells and preformed donor-specific antibodies (DSAs) have all been implicated in accelerated allograft rejection in sensitized recipients. Here, we employ a sensitized murine model of islet transplantation to test strategies that promote long-term immunosuppression-free allograft survival. We demonstrate that donor-specific memory T and B cells can be effectively inhibited by peritransplant infusions of donor apoptotic cells in combination with anti-CD40L and rapamycin, and this treatment leads to significant prolongation of islet allograft survival in allosensitized recipients. We further demonstrate that late graft rejection in recipients treated with this regimen is associated with a breakthrough of B cells and their aggressive graft infiltration. Consequently, additional posttransplant B cell depletion effectively prevents late rejection and promotes permanent acceptance of islet allografts. In contrast, persistent low levels of DSAs do not seem to impair graft outcome in these recipients. We propose that B cells contribute to late rejection as antigen-presenting cells for intragraft memory T cell expansion but not to alloantibody production and that a therapeutic strategy combining donor apoptotic cells, anti-CD40L, and rapamycin effectively inhibits proinflammatory B cells and promotes long-term islet allograft survival in such recipients.

KidneyCare Guided Immuno-Optimization in Renal Allografts: The KIRA Protocol

Immunosuppressant agents are essential in every transplant recipient's care yet walking the fine line of over- or under-immunosuppression is a constant struggle for both patients and transplant providers alike. Optimization and personalization of immunosuppression has been limited by the need for non-invasive graft surveillance methods that are specific enough to identify organ injury in real time. With this in mind, we propose a pilot study protocol utilizing both donor derived cell free DNA (dd-cfDNA, gene expression profiling (GEP), and machine learning (iBox), called KidneyCare, to assess the feasibility and safety in reducing immunosuppressant exposure without increasing the risk of clinical rejection, graft injury, or allograft loss. Patients randomized to the immunominimization arm will be enrolled in one of two protocols designed to eliminate one immunosuppressant and optimize the dose of the Calcineurin Inhibitors (CNIs) using the KidneyCare platform. All patients will be maintained on dual therapy of either steroids and a low dose CNI, or mycophenolate mofetil (MMF) and low dose CNI. Their outcomes will be compared to patients who have their immunosuppressants managed using standard clinical assessment and treatment protocols to determine the impact of immuno-optimization on graft function, complications, and patient reported outcomes.

Preemptive HLA Antibody Screening Prior to Episodic Transplant Renal Biopsy Enables Early Diagnosis and Therapeutic Response in Asymptomatic Chronically Active Antibody-Related Rejection: A Case Report

Common management of renal transplant recipients includes episodic renal biopsy based on clinical findings such as an increase in proteinuria or serum creatinine. When antibody-related rejection is suspected from the renal biopsy, subsequent testing for donor-specific antibodies (DSAs) is performed. We instead performed preemptive screening of asymptomatic post-renal transplant recipients for DSAs prior to renal biopsy. In this case, a 30-year-old woman with a secondary transplant was positive for 61 anti-HLA antibodies of class I and class II, among which DQ2 was a DSA with a mean fluorescence index of 2039. The patient had a living kidney transplant 9 years earlier. She had never been diagnosed with rejection, her serum creatinine was around 1.0 mg/dL, and her proteinuria was negative. Following the positive DSA result, a renal biopsy was performed, and she was diagnosed as C4d-negative chronic-active antibody-mediated rejection (CAABMR) with a Banff score of cg1b, (g + ptc) ≥ 2, and C4d 0. Intravenous steroid pulse, deoxyspagarin, antithymocyte globulin, rituximab, and oral everolimus were administrated. The treatment resulted in a gradual decrease in the DSA, which became negative 1 year later. The patient's serum creatinine remains around 1.0 mg/dL, and proteinuria remains negative. Treatments for advanced CAABMR are often expensive and ineffective. Our present case suggests that early detection and treatment through preemptive HLA antibody screening could improve the prognosis of renal transplants.

Mechanism of Graft Damage Caused by NTPDase1-activated Macrophages in Acute Antibody-Mediated Rejection

OBJECTIVES

To investigate the effect and mechanism of macrophage activation and graft damage caused by nucleoside triphosphate diphosphohydrolase 1 (NTPDase1) in acute antibody-mediated rejection (AMR).

METHODS

Acute AMR was induced in different skin-grafted nude mouse models with wild-type NTPDase1 expression, transgene-enhanced NTPDase1 expression, or NTPDase1 gene knockout. Several methods (eg, real-time fluorescence quantitative polymerase chain reaction, high-performance liquid chromatography [HPLC], immunofluorescence, flow cytometry, and luciferin/luciferase assays) were used to study (at the histologic and molecular levels) the extracellular adenosine diphosphate (ADP) concentration, macrophage proliferation, major histocompatibility complex (MHC) class II antigen expression on the surface of macrophages, B-cell activating factor (BAFF) expression in the peripheral blood serum, and the total number of SmIg-positive B cells during acute AMR. The relative activity of NTPDase1 in B cells and epithelial cells, pathologic changes, and the incidence of positive C4d deposition around the capillaries of skin grafts on the different nude mice were studied.

RESULTS

Macrophages proliferated significantly when acute AMR occurred. The higher the NTPDase1 expression level, the lower the extracellular ADP concentration, the expression of MHC class II antigens on the surface of macrophages, the expression of BAFF in the peripheral blood serum, and the total number of SmIg-positive B cells, indicating negative correlations. The relative activity of NTPDase1 in B cells and epithelial cells of the skin graft was different among the different mice. The higher the NTPDase1 expression level, the lower the degree of pathologic damage to the skin graft.

CONCLUSIONS

Imbalance in extracellular ADP degradation by NTPDase1 may promote macrophage activation, and activated macrophages may be an important cause of graft damage.

Novel therapeutic opportunities afforded by plasma cell biology in transplantation

Despite new immunotherapies aimed at B and T cells, plasma cells and their lifelong antibody secretion constitute a major immune barrier to long-term graft survival. In this mini-review, we survey the recent advances that have been made in the biology and immunometabolism of long-lived plasma cells, and outline aspects of plasma cell function that can be exploited for clinical benefit in recipients of solid organ transplants. A handful of ongoing studies are already targeting plasma cells to achieve desensitization and reduce the alloantibody burden in individuals posttransplant. In reviewing the recent strides made in our understanding of the molecular basis of plasma cell survival, we will place our discussions in the context of existing preclinical and clinical studies.

Understanding and using AlloSure donor derived cell-free DNA

Renal transplant is a lifesaving and cost-effective intervention for patients with End Stage Renal Failure. Yet it is often regarded as replacement therapy rather than a cure given the overall failure rate over time. With a shortage of organs, this global issue has been further compounded by increased incidences of obesity, hypertension and diabetes, such that the disease burden and need for transplantation continues to increase. Considering the lifetime of immunosupression in transplant patients, there will also be significant associated co-morbidities By leveraging the advances in innovation in Next Generation Sequencing, the field of transplant can now monitor patients with an optimized surveillance schedule, and change the care paradigm in the post-transplant landscape. Notably, low grade inflammation is an independent risk for mortality across different disease states. In transplantation, sub-clinical inflammation enhances acute and chronic rejection, as well as accelerates pathologies that leads to graft loss. Cell free DNA has been shown to be increased in inflammatory processes as we all as provide an independent predictor of all-cause mortality. This review considers the utility of AlloSure, a donor derived cell free DNA molecular surveillance tool, which has shown new clinical insights on how best to manage renal transplant patients, and how to improve patient outcomes.

Recent Advances on Biomarkers of Early and Late Kidney Graft Dysfunction

New biomarkers of early and late graft dysfunction are needed in renal transplant to improve management of complications and prolong graft survival. A wide range of potential diagnostic and prognostic biomarkers, measured in different biological fluids (serum, plasma, urine) and in renal tissues, have been proposed for post-transplant delayed graft function (DGF), acute rejection (AR), and chronic allograft dysfunction (CAD). This review investigates old and new potential biomarkers for each of these clinical domains, seeking to underline their limits and strengths. OMICs technology has allowed identifying many candidate biomarkers, providing diagnostic and prognostic information at very early stages of pathological processes, such as AR. Donor-derived cell-free DNA (ddcfDNA) and extracellular vesicles (EVs) are further promising tools. Although most of these biomarkers still need to be validated in multiple independent cohorts and standardized, they are paving the way for substantial advances, such as the possibility of accurately predicting risk of DGF before graft is implanted, of making a “molecular” diagnosis of subclinical rejection even before histological lesions develop, or of dissecting etiology of CAD. Identification of “immunoquiescent” or even tolerant patients to guide minimization of immunosuppressive therapy is another area of active research. The parallel progress in imaging techniques, bioinformatics, and artificial intelligence (AI) is helping to fully exploit the wealth of information provided by biomarkers, leading to improved disease nosology of old entities such as transplant glomerulopathy. Prospective studies are needed to assess whether introduction of these new sets of biomarkers into clinical practice could actually reduce the need for renal biopsy, integrate traditional tools, and ultimately improve graft survival compared to current management.

Alloimmunity in pancreas transplantation

PURPOSE OF REVIEW

Despite significant improvement in pancreas allograft survival, rejection continues to be a major clinical problem. This review will focus on emerging literature related to the impact of pretransplant and de-novo DSA (dnDSA) in pancreas transplant recipients, and the diagnosis and treatment of T-cell-medicated rejection (TCMR) and antibody-mediated rejection (ABMR) in this complex group of patients.

RECENT FINDINGS

Recent data suggest that pretransplant DSA and the emergence of dnDSA in pancreas transplant recipients are both associated with increased risk of ABMR. The pancreas allograft biopsy is essential for the specific diagnosis of TCMR and/or ABMR, distinguish rejection from other causes of graft dysfunction, and to guide-targeted therapy. This distinction is important especially in the setting of solitary pancreas transplants but also in simultaneous pancreas-kidney transplants where solid evidence has now emerged demonstrating discordant biopsy findings. Treatment of rejection in a functioning pancreas can prolong allograft survival.

SUMMARY

The accurate and timely diagnosis of active alloimmune destruction in pancreas transplant recipients is paramount to preserving graft function in the long term. This review will discuss new, rapidly evolving information that is valuable for the physician caring for these patients to achieve optimal immunological outcomes.

Complement-activated interferon-γ-primed human endothelium transpresents interleukin-15 to CD8+ T cells

Alloantibodies in presensitized transplant candidates deposit complement membrane attack complexes (MACs) on graft endothelial cells (ECs), increasing risk of CD8+ T cell-mediated acute rejection. We recently showed that human ECs endocytose MACs into Rab5+ endosomes, creating a signaling platform that stabilizes NF-κB-inducing kinase (NIK) protein. Endosomal NIK activates both noncanonical NF-κB signaling to synthesize pro-IL-1β and an NLRP3 inflammasome to process and secrete active IL-1β. IL-1β activates ECs, increasing recruitment and activation of alloreactive effector memory CD4+ T (Tem) cells. Here, we report that IFN-γ priming induced nuclear expression of IL-15/IL-15Rα complexes in cultured human ECs and that MAC-induced IL-1β stimulated translocation of IL-15/IL-15Rα complexes to the EC surface in a canonical NF-κB-dependent process in which IL-15/IL-15Rα transpresentation increased activation and maturation of alloreactive CD8+ Tem cells. Blocking NLRP3 inflammasome assembly, IL-1 receptor, or IL-15 on ECs inhibited the augmented CD8+ Tem cell responses, indicating that this pathway is not redundant. Adoptively transferred alloantibody and mouse complement deposition induced IL-15/IL-15Rα expression by human ECs lining human coronary artery grafts in immunodeficient mice, and enhanced intimal CD8+ T cell infiltration, which was markedly reduced by inflammasome inhibition, linking alloantibody to acute rejection. Inhibiting MAC signaling may similarly limit other complement-mediated pathologies.