Acute humoral rejection in renal allograft recipients: I. Incidence, serology and clinical characteristics

Early and Late Microvascular Inflammation Have Differing Etiological Causes and Clinical Expression

BACKGROUND

Microvascular inflammation (MVI) is an important pathological feature of antibody-mediated rejection (AMR). How posttransplant time affects its clinicopathological expression is little understood.

METHODS

This retrospective, single-center study screened 3398 kidney transplant biopsies and dichotomized 202 MVI ≥ 2 (Banff glomerulitis + peritubular capillaritis ≥ 2) samples by 9-mo median incidence time for comparison.

RESULTS

The prevalence of MVI ≥ 2 was 12.4% in transplant kidneys, which failed more frequently than propensity-matched normal controls (n = 202; P  < 0.001). Epidemiological risk factors for early MVI ≥ 2 were delayed graft function, prior AMR, and circulating donor-specific antibodies (DSAs+). Prior recipient sensitization occurred in 72.3%. Early MVI ≥ 2 was classified AMR in 65.3% and cellular rejection in 34.7%, and demonstrated excellent functional recovery and graft survival comparable to normal control kidneys. Late MVI ≥ 2 was predicted by younger (18 = 29 y) age, female recipient, living-donation, prior methylprednisolone, cyclosporine (versus tacrolimus, levels <5 ng/mL), absent antiproliferative therapy, and DSA+ using multivariable epidemiological modeling. Nonadherence caused 49.5%, with iatrogenic minimization responsible for 47.5%, usually for recipient infection. Late MVI ≥ 2 was because of AMR in 93.1%, and characterized by greater interstitial fibrosis, tubular atrophy, complement degradation split-product 4d (C4d) staining of peritubular capillaries+, endothelial C4d staining of glomerular capillaries+, transplant glomerulopathy and vasculopathy scores, DSA strength, and graft failure than early MVI ≥ 2 or normal transplant kidneys. Death-censored graft survival in 149 unique MVI ≥ 2 kidneys was independently determined by nonadherence, serum creatinine, proteinuria, DSA+, Banff C4d staining of peritubular capillaries+, and chronic interstitial fibrosis scores. MVI score and time lost significance using multivariable Cox regression.

CONCLUSIONS

The changing expression of MVI ≥ 2 over time is best explained by differences in underimmunosuppression and microvascular injury from AMR impacting allograft function and survival.

The relationship of microvascular inflammation with antibody-mediated rejection in kidney transplantation

Microvascular inflammation (MVI) is a key diagnostic feature of antibody-mediated rejection (AMR); however, recipients without donor-specific antibodies (DSA) defy etiologic classification using C4d staining of peritubular capillaries (C4dptc) and conventional DSA assignment. We evaluated MVI ≥ 2 (Banff g + ptc ≥ 2) using Banff 2019 AMR (independent of MVI ≥ 2 but including C4dptc) with unconventional endothelial C4d staining of glomerular capillaries (C4dglom) and - arterial endothelium and/or intima (C4dart) using tissue immunoperoxidase, shared-eplet and subthreshold DSA (median fluorescence intensity, [MFI] 100-499), and capillary ultrastructure from 3398 kidney transplant samples for evidence of AMR. MVI ≥ 2 (n = 202 biopsies) from 149 kidneys (12.4% prevalence) correlated with DSA+, C4dptc+, C4dglom+, Banff cg, i, t, ti scores, serum creatinine, proteinuria, and graft failure compared with 202 propensity score matched normal controls. The laboratory reported DSA- MVI ≥ 2 (MFI ≥500) occurred in 34.7%; however, subthreshold (28.6%), eplet-directed (51.4%), and/or misclassified anti-Human leukocyte antigen (HLA) DSA (12.9%) were identified in 67.1% by forensic reanalysis, with vascular C4d+ staining in 67.1%, and endothelial abnormalities in 57.1%, totaling 87.1%. Etiologic analysis attributed 62.9% to AMR (77.8% for MVI with negative reported DSA [DSA- MVI ≥2] with glomerulitis) and pure T cellular rejection in 37.1%. C4dptc-DSA- MVI ≥ 2 was unrecognized AMR in 48.0%. Functional outcomes and graft survival were comparable to normal controls. We concluded that DSA- MVI ≥ 2 frequently signified a mild "borderline" phenotype of AMR which was recognizable using novel serologic and pathological techniques.

The medical cost and outcome of desensitization protocol in kidney transplantation recipients with high immunological risks

BACKGROUND

Kidney transplantation is a well-established alternative in renal replacement therapy. Compared with hemodialysis, low-immunological-risk kidney transplantation can reduce the medical treatment costs associated with end-stage renal disease. However, there are few reports on whether high-immunological-risk kidney transplantation reduces the financial burden on governments. We investigated the medical costs of high-immunological-risk kidney transplantation in comparison with the cost of hemodialysis in Japan.

METHODS

We compared the medical costs of high-immunological-risk kidney transplantation with those of hemodialysis. 15 patients who underwent crossmatch-positive and/or donor-specific antibody-positive kidney transplantations between 2020 and 2021 were enrolled in this study. The patients received intravenous immunoglobulin, plasmapheresis, and rituximab as desensitizing therapy.

RESULTS

Acute antibody-mediated rejection was detected in nine (60%) recipients, while there were no indications of graft function deterioration during the follow-up. For each patient, the transplant hospitalization cost was 38 428 ± 8789 USD. However, the cumulative costs were 59 758 ± 10 006 USD and 79 781 ± 16 366 USD, at 12 and 24 months, respectively. Compared with hemodialysis (34 286 USD per year), high-immunological-risk kidney transplantation tends to be expensive in the first year, but the cost is likely to be lower than that of hemodialysis after 3 years.

CONCLUSIONS

Although kidney transplantation is initially expensive compared with hemodialysis, the medical cost becomes advantageous after 3 years even in kidney transplant recipients with high immunological risk.

Alloimmune risk assessment for antibody-mediated rejection in kidney transplantation: A practical proposal

Kidney transplantation is the treatment of choice for patients with end-stage renal disease. Although an improvement in graft survival has been observed in the last decades with the use of different immunosuppressive drugs, this is still limited in time with antibody-mediated rejection being a main cause of graft-loss. Immune monitoring and risk assessment of antibody-mediated rejection before and after kidney transplantation with useful biomarkers is key to tailoring treatments to achieve the best outcomes. Here, we provide a review of the rationale and several accessible tools for immune monitoring, from the most classic to the modern ones. Finally, we end up discussing a practical proposal for alloimmune risk assessment in kidney transplantation, including histocompatibility leukocyte antigen (HLA) and non-HLA antibodies, HLA molecular mismatch analysis and characterization of peripheral blood immune cells.

Accommodation in allogeneic and xenogeneic organ transplantation: Prevalence, impact, and implications for monitoring and for therapeutics

Accommodation refers to acquired resistance of organs or tissues to immune or inflammatory reactions that might otherwise cause severe injury or rejection. As first observed in ABO-incompatible kidney transplants and heterotopic cardiac xenografts, accommodation was identified when organ transplants continued to function despite the presence of anti-graft antibodies and/or other reactants in the blood of recipients. Recent evidence suggests many and perhaps most organ transplants have accommodation, as most recipients mount B cell responses specific for the graft. Wide interest in the impact of graft-specific antibodies on the outcomes of transplants prompts questions about which mechanisms confer protection against such antibodies, how accommodation might be detected and whether and how rejection could be superimposed on accommodation. Xenotransplantation offers a unique opportunity to address these questions because immune responses to xenografts are easily detected and the pathogenic impact of immune responses is so severe. Xenotransplantation also provides a compelling need to apply these and other insights to decrease the intensity and toxicity of immunosuppression that otherwise could limit clinical application.

The Presence of Donor-specific Antibodies Around the Time of Pancreas Graft Biopsy With Rejection Is Associated With an Increased Risk of Graft Failure

BACKGROUND

Donor-specific antibodies (DSA) against HLA are an important biomarker predicting graft injury, rejection (Rej), and failure in various solid-organ transplant recipients. However, the impact of DSA with or without histopathological evidence of rejection among pancreas transplant recipients (PTRs) is unknown.

METHODS

In this study, we included all PTRs at our center between 2005 and 2020, with pancreas allograft biopsy before March 31, 2021, and with DSA checked within 15 d of the biopsy. PTRs were divided into 4 groups based on the biopsy findings on the index biopsy and DSA status as Rej-/DSA-, Rej+/DSA-, Rej-/DSA+, and Rej+/DSA+.

RESULTS

Two hundred two PTRs had a pancreas allograft biopsy during the study period. Thirty-nine were in Rej-/DSA-, 84 Rej+/DSA-, 24 Rej-/DSA+, and 55 Rej+/DSA+. The mean interval from transplant to index biopsy was not statistically different between the 4 groups. The most common type of rejection was T cell-mediated rejection; however, antibody-mediated rejection was more prevalent in the Rej+/DSA+ group. At 5 y postbiopsy, the rate of death-censored graft failure (DCGF) for Rej-/DSA- was 18%, 24% in Rej+/DSA-; 17% in Rej-/DSA+ and 36% in Rej+/DSA+ (P = 0.14). In univariate analysis, mixed rejection (hazard ratio [HR], 3.0; 95% confidence intervals [CI], 1.22-7.39; P = 0.02) along with solitary pancreas transplantation and Rej+/DSA+ were associated with DCGF. In multivariate analysis, compared with Rej-/DSA-, Rej+/DSA+ was significantly associated with DCGF (HR, 2.32; 95% CI, 1.03-5.20; P = 0.04); however, Rej+/DSA- was not (HR, 1.06; 95% CI, 0.32-3.56; P = 0.92).

CONCLUSIONS

PTRs with pancreas allograft rejection and concomitant DSA have an increased risk of DCGF.

Clinical characteristics of renal transplant recipients who developed de novo donor-specific antigen in Kyoto University Hospital: a case series

Background

The clinical significance of de novo donor-specific antigen (DSA) in renal transplant recipients is not yet fully understood. This study aimed to report the prevalence of de novo DSA detected in antihuman leukocyte antigen (HLA) antibody testing and to evaluate the association between de novo DSA and renal transplant prognosis in living-donor renal transplant recipients at our hospital.

Methods

Of the 110 patients who underwent living-donor renal transplantation from 1980 to 2019, 80 patients who underwent anti-HLA antibody screening tests were retrospectively reviewed for the development of de novo DSA and outcomes regarding graft function.

Results

The mean age at transplantation was 43.2 ± 14.6 years. Of the 80 patients, 43 (53.8%) were men and 68 (85.0%) underwent ABO-compatible transplantation. Anti-HLA antibody was detected in 14 patients (17.5%), including eight (10.0%) with de novo DSA. Graft loss occurred in two (25%) of the eight patients with de novo DSA, none of the six patients with non-DSA anti-HLA antibody and no anti-HLA antibody (P = 0.0419, log-rank test). The mean estimated glomerular filtration rate at the time of the anti-HLA antibody test was 45.1 ± 14.4 mL/min/1.73m2 in the 66 patients with no anti-HLA antibody, while it was 35.0 ± 11.5 mL/min/1.73m2 in the eight patients with de novo DSA (P = 0.0702) and 39.3 ± 15.3 mL/min/1.73m2 in the six patients with non-DSA anti-HLA antibody (P = 0.3921). The mean monthly cyclosporin A trough concentration for the past year from the anti-HLA antibody test was 59.2 ± 24.8 ng/ml in the seven patients with no anti-HLA antibody, while it was 61.9 ± 12.5 ng/ml in the five patients with de novo DSA (P = 0.5670) and 36.3 ± 9.0 ng/ml in a patient with non-DSA anti-HLA antibody (P = 0.3921). The mean monthly tacrolimus trough concentration for the past year from the anti-HLA antibody test was 4.62 ± 1.20 ng/ml in the 55 patients with no anti-HLA antibody, while it was 4.09 ± 1.10 ng/ml in the three patients with de novo DSA (P = 0.0027) and 4.21 ± 1.14 ng/ml in the four patients with non-DSA anti-HLA antibody (P = 0.0722).

Conclusions

The optimal treatment for patients with de novo DSA has not been established, and immunosuppressive management that suppresses the development of de novo DSA is essential.

Banff classification from 1991 to 2019. A significant contribution to our understanding and reporting of allograft renal biopsies

The Banff schema of classification of renal allograft biopsies, first proposed at the meeting in Banff, Canada in 1991 has evolved through subsequent meetings held once in two years and is the internationally accepted scheme of classification which is consensual, current, validated and in clinical use. This review traces the evolution of the classification and our understanding of renal transplant pathology, with emphasis on alloimmune reactions. The proceedings of the meetings and the important studies which have shaped the classification are covered.

Histopathologic Features of Antibody Mediated Rejection: The Banff Classification and Beyond

Antibody mediated rejection (ABMR) in the kidney can show a wide range of clinical presentations and histopathologic patterns. The Banff 2019 classification currently recognizes four diagnostic categories: 1. Active ABMR, 2. Chronic active ABMR, 3. Chronic (inactive) ABMR, and 4. C4d staining without evidence of rejection. This categorization is limited in that it does not adequately represent the spectrum of antibody associated injury in allograft, it is based on biopsy findings without incorporating clinical features (e.g., time post-transplant, de novo versus preformed DSA, protocol versus indication biopsy, complement inhibitor drugs), the scoring is not adequately reproducible, and the terminology is confusing. These limitations are particularly relevant in patients undergoing desensitization or positive crossmatch kidney transplantation. In this article, I discuss Banff criteria for these ABMR categories, with a focus on patients with pre-transplant DSA, and offer a framework for considering the continuum of allograft injury associated with donor specific antibody in these patients.

Non-HLA Antibodies and Epitope Mismatches in Kidney Transplant Recipients With Histological Antibody-Mediated Rejection

Background

Correlation between antibody-mediated rejection (ABMR) and circulating HLA donor-specific antibodies (HLA-DSA) is strong but imperfect in kidney transplant (KT) recipients, raising the possibility of undetected HLA-DSA or non-HLA antibodies contributing to ABMR. Detailed evaluation of the degree of HLA matching together with the identification of non-HLA antibodies in KT may help to decipher the antibody involved.

Methods

We retrospectively assessed patients with transplant biopsies scored following Banff'15 classification. Pre- and post-transplant serum samples were checked for HLA and non-HLA antibodies [MICA-Ab, angiotensin-II type-1-receptor (AT1R)-Ab, endothelin-1 type-A-receptor (ETAR)-Ab and crossmatches with primary aortic endothelial cells (EC-XM)]. We also analyzed HLA epitope mismatches (HLA-EM) between donors and recipients to explore their role in ABMR histology (ABMRh) with and without HLA-DSA.

Results

One-hundred eighteen patients with normal histology (n = 19), ABMRh (n = 52) or IFTA (n = 47) were studied. ABMRh patients were HLA-DSApos (n = 38, 73%) or HLA-DSAneg (n = 14, 27%). Pre-transplant HLA-DSA and AT1R-Ab were more frequent in ABMRh compared with IFTA and normal histology cases (p = 0.006 and 0.003), without differences in other non-HLA antibodies. Only three ABMRhDSAneg cases showed non-HLA antibodies. ABMRhDSAneg and ABMRhDSApos cases showed similar biopsy changes and graft-survival. Both total class II and DRB1 HLA-EM were associated with ABMRhDSApos but not with ABMRhDSAneg. Multivariate analysis showed that pre-transplant HLA-DSA (OR: 3.69 [1.31-10.37], p = 0.013) and AT1R-Ab (OR: 5.47 [1.78-16.76], p = 0.003) were independent predictors of ABMRhDSApos.

Conclusions

In conclusion, pre-transplant AT1R-Ab is frequently found in ABMRhDSApos patients. However, AT1R-Ab, MICA-Ab, ETAR-Ab or EC-XM+ are rarely found among ABMRhDSAneg patients. Pre-transplant AT1R-Ab may act synergistically with preformed or de novo HLA-DSA to produce ABMRhDSApos but not ABMRhDSAneg. HLA epitope mismatch associates with ABMRhDSApos compared with ABMRhDSAneg, suggesting factors other than HLA are responsible for the damage.

Desensitization and management of allograft rejection

PURPOSE OF REVIEW

Chronic lung allograft dysfunction (CLAD) limits the success of lung transplantation. Among the risk factors associated with CLAD, we recognize pretransplant circulating antibodies against the human leukocyte antigens (HLA), acute cellular rejection (ACR) and antibody-mediated rejection (AMR). This review will summarize current data surrounding management of desensitization, ACR, AMR, and CLAD.

RECENT FINDINGS

Strategies in managing in highly sensitized patients waiting for lung transplant include avoidance of specific HLA antigens and reduction of circulating anti-HLA antibodies at time of transplant. Several multimodal approaches have been studied in the treatment of AMR with a goal to clear circulating donor-specific antibodies (DSAs) and to halt the production of new antibodies. Different immunosuppressive strategies focus on influence of the host immune system, particularly T-cell responses, in order to prevent ACR and the progression of CLAD.

SUMMARY

The lack of significant evidence and consensus limits to draw conclusion regarding the impact of specific immunosuppressive regimens in the management of HLA antibodies, ACR, and CLAD. Development of novel therapeutic agents and use of multicenter randomized clinical trials will allow to better define patient-specific treatments and improve the length and quality of life of lung transplant recipients.

Recent progress and remaining hurdles toward clinical xenotransplantation

BACKGROUND

Xenotransplantation has made tremendous progress over the last decade.

METHODS

We discuss kidney and heart xenotransplantation, which are nearing initial clinical trials.

RESULTS

Life sustaining genetically modified kidney xenografts can now last for approximately 500 days and orthotopic heart xenografts for 200 days in non-human primates. Anti-swine specific antibody screening, preemptive desensitization protocols, complement inhibition and targeted immunosuppression are currently being adapted to xenotransplantation with the hope to achieve better control of antibody-mediated rejection (AMR) and improve xenograft longevity. These newest advances could probably facilitate future clinical trials, a significant step for the medical community, given that dialysis remains difficult for many patients and can have prohibitive costs. Performing a successful pig-to-human clinical kidney xenograft, that could last for more than a year after transplant, seems feasible but it still has significant potential hurdles to overcome. The risk/benefit balance is progressively reaching an acceptable equilibrium for future human recipients, e.g. those with a life expectancy inferior to two years. The ultimate question at this stage would be to determine if a "proof of concept" in humans is desirable, or whether further experimental/pre-clinical advances are still needed to demonstrate longer xenograft survival in non-human primates.

CONCLUSION

In this review, we discuss the most recent advances in kidney and heart xenotransplantation, with a focus on the prevention and treatment of AMR and on the recipient's selection, two aspects that will likely be the major points of discussion in the first pig organ xenotransplantation clinical trials.

Immunomodulatory effects of mesenchymal stem cells for the treatment of cardiac allograft rejection

Heart transplantation continues to be the gold standard clinical intervention to treat patients with end-stage heart failure. However, there are major complications associated with this surgical procedure that reduce the survival prognosis of heart transplant patients, including allograft rejection, malignancies, infections, and other complications that arise from the use of broad-spectrum immunosuppression drugs. Recent studies have demonstrated the use of mesenchymal stem cells (MSCs) against allotransplantation rejection in both in vitro and in vivo settings due to their immunomodulatory properties. Therefore, utilization of MSCs provides new and exciting strategies to improve heart transplantation and potentially reduce the use of broad-spectrum immunosuppression drugs while alleviating allograft rejection. In this review, we will discuss the current research on the mechanisms of cardiac allograft rejection, the physiological and immunological characteristics of MSCs, the effects of MSCs on the immune system, and immunomodulation of heart transplantation by MSCs.

Successful Treatment of Antibody-Mediated Rejection by De Novo Donor Specific Antibody After Primary Renal Transplantation in a Recipient From a Cadaveric Donor: A Case Report

A 19-year-old Japanese male recipient, who received a living related kidney transplantation from his father at 5 years old, was hospitalized for second renal transplantation from a cadaveric donor. The recipient had had an antibody-mediated rejection (AMR) to the first transplanted kidney. HLA typing of A, B, and DRB showed 2 of 6 mismatches. Lymphocyte cytotoxicity test (LCT) and flow cytometry crossmatches (FCXM) were negative on T cells. Tacrolimus, mycophenolate mofetil, methylprednisolone, and basiliximab induction were used as the standard immunosuppressive therapy. After second renal transplantation, his serum creatinine level favorably decreased until postoperative day (POD) 7, but his serum creatinine level raised from POD 8. We performed steroid pulse and intravenous immunoglobulin (IVIG). The episode biopsy showed AMR although FCXM and LCT were still negative on T cell. To determine the cause of AMR, we examined LABScreen single antigen test (One Lambda, Canoga Park, Calif., United States), and there was a donor-specific antibody (DSA) that is DQB8 in pre- and post-second renal transplantation. The DSA was suspected de novo DSA for the first transplanted kidney. AMR was successfully treated with plasma exchange, IVIG, and rituximab.

Use of Eculizumab for Active Antibody-mediated Rejection That Occurs Early Post-kidney Transplantation: A Consecutive Series of 15 Cases

BACKGROUND

Active antibody-mediated rejection (AMR) that occurs during the amnestic response within the first month posttransplant is a rare but devastating cause of early allograft loss after kidney transplant. Prior reports of eculizumab treatment for AMR have been in heterogeneous patient groups needing salvage therapy or presenting at varied time points. We investigated the role of eculizumab as primary therapy for active AMR early posttransplant.

METHODS

We performed a retrospective observational study of a consecutive cohort of solitary kidney transplant recipients who were transplanted between January 1, 2014, and January 31, 2018, and had AMR within the first 30 days posttransplant and treated with eculizumab ± plasmapheresis.

RESULTS

Fifteen patients had early active AMR at a median (interquartile range [IQR]) of 10 (7-11) days posttransplant and were treated with eculizumab ± plasmapheresis. Thirteen cases were biopsy proven, and 2 cases were presumed on the basis of donor-specific antibody trends and allograft function. Within 1 week of treatment, the median estimated glomerular filtration rate increased from 21 to 34 mL/min (P = 0.001); and persistent active AMR was only found in 16.7% (2/12) of biopsied patients within 4-6 months. No graft losses occurred, and at last follow-up (median [IQR] of 13 [12-19] mo), the median IQR estimated glomerular filtration rate increased to 52 (46-60) mL/min.

CONCLUSIONS

Prompt eculizumab treatment as primary therapy is safe and effective for early active AMR after kidney transplant or abrupt increases in donor-specific antibodies when biopsy cannot be performed for diagnosis confirmation.

A urinary Common Rejection Module (uCRM) score for non-invasive kidney transplant monitoring

A Common Rejection Module (CRM) consisting of 11 genes expressed in allograft biopsies was previously reported to serve as a biomarker for acute rejection (AR), correlate with the extent of graft injury, and predict future allograft damage. We investigated the use of this gene panel on the urine cell pellet of kidney transplant patients. Urinary cell sediments collected from patients with biopsy-confirmed acute rejection, borderline AR (bAR), BK virus nephropathy (BKVN), and stable kidney grafts with normal protocol biopsies (STA) were analyzed for expression of these 11 genes using quantitative polymerase chain reaction (qPCR). We assessed these 11 CRM genes for their abundance, autocorrelation, and individual expression levels. Expression of 10/11 genes were elevated in AR when compared to STA. Psmb9 and Cxcl10could classify AR versus STA as accurately as the 11-gene model (sensitivity = 93.6%, specificity = 97.6%). A uCRM score, based on the geometric mean of the expression levels, could distinguish AR from STA with high accuracy (AUC = 0.9886) and correlated specifically with histologic measures of tubulitis and interstitial inflammation rather than tubular atrophy, glomerulosclerosis, intimal proliferation, tubular vacuolization or acute glomerulitis. This urine gene expression-based score may enable the non-invasive and quantitative monitoring of AR.

Optimizing Detection of Kidney Transplant Injury by Assessment of Donor-Derived Cell-Free DNA via Massively Multiplex PCR

Standard noninvasive methods for detecting renal allograft rejection and injury have poor sensitivity and specificity. Plasma donor-derived cell-free DNA (dd-cfDNA) has been reported to accurately detect allograft rejection and injury in transplant recipients and shown to discriminate rejection from stable organ function in kidney transplant recipients. This study used a novel single nucleotide polymorphism (SNP)-based massively multiplexed PCR (mmPCR) methodology to measure dd-cfDNA in various types of renal transplant recipients for the detection of allograft rejection/injury without prior knowledge of donor genotypes. A total of 300 plasma samples (217 biopsy-matched: 38 with active rejection (AR), 72 borderline rejection (BL), 82 with stable allografts (STA), and 25 with other injury (OI)) were collected from 193 unique renal transplant patients; dd- cfDNA was processed by mmPCR targeting 13,392 SNPs. Median dd-cfDNA was significantly higher in samples with biopsy-proven AR (2.3%) versus BL (0.6%), OI (0.7%), and STA (0.4%) (p < 0.0001 all comparisons). The SNP-based dd-cfDNA assay discriminated active from non-rejection status with an area under the curve (AUC) of 0.87, 88.7% sensitivity (95% CI, 77.7⁻99.8%) and 72.6% specificity (95% CI, 65.4⁻79.8%) at a prespecified cutoff (>1% dd-cfDNA). Of 13 patients with AR findings at a routine protocol biopsy six-months post transplantation, 12 (92%) were detected positive by dd-cfDNA. This SNP-based dd-cfDNA assay detected allograft rejection with superior performance compared with the current standard of care. These data support the feasibility of using this assay to detect disease prior to renal failure and optimize patient management in the case of allograft injury.

Anti-CD20 Blocker Rituximab in Kidney Transplantation

Rituximab is a chimeric anti-CD20 monoclonal protein used in various clinical scenarios in kidney transplant recipients. However, its evidence-based use there remains limited due to lack of controlled studies, limited sample size, short follow-up and poorly defined endpoints. Rituximab is indicated for CD20+ posttransplant lymphoproliferative disorder. It may be beneficial for treating recurrent membranous nephropathy and recurrent allograft antineutrophilic cytoplasmic antibody vasculitis and possibly for recurrent focal segmental glomerulosclerosis. Rituximab, in combination with IVIg/plasmapheresis, appears to decrease antibody level and increase the odds of transplantation in sensitized recipients. The role of Rituximab in ABOi transplant remains unclear, as similar outcomes are achieved without its use. Rituximab is not efficacious in antibody-mediated rejection/chronic antibody-mediated rejection. Strict randomized control trials are necessary to elucidate its true role in these settings.

The Diagnostic Impact of C4d, CD68, and NF-κB Expression in the Differentiation Between Recurrent Hepatitis C and Acute Cellular Rejection After Liver Transplantation

Liver transplantation is the selected treatment for patients with advanced liver disease and cirrhosis, mostly as a complication of hepatitis C virus (HCV). Recurrent HCV and acute cellular rejection (ACR) of the graft are the most common causes of graft failure. The distinction between the 2 conditions is essential because they are managed differently. In some cases, the clinical and histopathologic features may overlap between recurrent hepatitis C and ACR, making differentiation difficult. The aim of this study was to investigate the role of C4d, CD68, and nuclear factor kappa-B (NF-κB) in the differentiation between ACR and recurrent HCV in the post-liver-transplant biopsy using immunohistochemistry. C4d expression in endothelial cells of portal or central veins (P=0.001) and the number of macrophages highlighted by CD68 (P=0.02) were in favor of ACR, whereas NF-κB expression by hepatocytes was in favor of recurrent hepatitis C. Vascular injury demonstrated by endothelial expression of C4d and prominent macrophage infiltration identified by CD68 expression were the distinguishing criteria for ACR and representing humoral and cellular-mediated immunity as evoking factors for graft injury. The upregulation of NF-κB in the hepatocytes of recurrent hepatitis C could be an immune response to infection or it may be induced by HCV itself.

Assessment of Circulating Protein Signatures for Kidney Transplantation in Pediatric Recipients

Identification and use of non-invasive biomarkers for kidney transplantation monitoring is an unmet need. A total of 121 biobanked sera collected from 111 unique kidney transplant (KT) patients (children and adolescent) and 10 age-matched healthy normal controls were used to profile serum proteins using semi-quantitative proteomics. The proteomics data were analyzed to identify panels of serum proteins that were specific to various transplant injuries, which included acute rejection (AR), BK virus nephropathy (BKVN), and chronic allograft nephropathy (CAN). Gene expression data from matching peripheral blood mononuclear cells were interrogated to investigate the association between soluble serum proteins and altered gene expression of corresponding genes in different injury phenotypes. Analysis of the proteomics data identified from different patient phenotypes, with criteria of false discovery rate <0.05 and at least twofold changes in either direction, resulted in a list of 10 proteins that distinguished KT injury from no injury. Similar analyses to identify proteins specific to chronic injury, acute injury, and AR after kidney transplantation identified 22, 6, and 10 proteins, respectively. Elastic-Net logistic regression method was applied on the 137 serum proteins to classify different transplant injuries. This algorithm has identified panels of 10 serum proteins specific for AR, BKVN, and CAN with classification rates 93, 93, and 95%, respectively. The identified proteins could prove to be potential surrogate biomarkers for routine monitoring of the injury status of pediatric KT patients.

Quantification of Alloantibody-Mediated Cytotoxicity In Vivo

BACKGROUND

Preexisting, donor-specific antibodies (DSAs) are culprits of hyperacute rejection. Donor-specific antibodies are also formed de novo, and their role in acute and chronic rejection is increasingly appreciated. However, it is difficult to assess damage inflicted exclusively by DSAs when alloreactive T cell and B cell responses coincide. We reasoned that allosensitization with "costimulation-deficient" cells should induce DSA synthesis but not naive cytotoxic T lymphocyte (CTL) precursors' priming via direct allorecognition. Accordingly, we have developed a novel model to quantify DSA-mediated cytotoxicity in vivo.

METHODS

C57BL/6 (H-2b) mice were sensitized with H-2 kidney epithelial cells, and a cytofluorimetric killing assay was tailored to the measurement of allocytotoxicity. We took cell/complement depletion, costimulation blockade, and serum transfer approaches to reveal the mediators of cytotoxicity. "Third-party" controls and a skin allotransplantation model were used to confirm DSAs' specificity for allo-major histocompatibility complex. We validated our experimental approach in other mouse strains primed with different allogeneic cell types, including endothelial cells. To demonstrate the usefulness of our model/method for drug efficacy testing, we examined the effect of CTLA4-Ig and rapamycin on DSA-mediated cytolysis.

RESULTS

Allosensitization of MHC-disparate mouse strains with costimulation-deficient cells led to robust cytotoxicity mediated by complement-fixing DSAs and phagocytic cells. This response was independent of CTLs, natural killer or natural killer T cells. It required CD4 T cell help, CD40 signaling and CD28-based costimulation during allosensitization and could be reversed by sustained rapamycin treatment.

CONCLUSIONS

The unique model described herein should enable mechanistic studies on sensitization and effector phases of humoral alloreactivity as well as efficacy testing of future immunotherapies to prevent DSA-induced pathology.

Guidelines on the Use of Therapeutic Apheresis in Clinical Practice-Evidence-Based Approach from the Writing Committee of the American Society for Apheresis: The Seventh Special Issue

The American Society for Apheresis (ASFA) Journal of Clinical Apheresis (JCA) Special Issue Writing Committee is charged with reviewing, updating, and categorizing indications for the evidence-based use of therapeutic apheresis in human disease. Since the 2007 JCA Special Issue (Fourth Edition), the Committee has incorporated systematic review and evidence-based approaches in the grading and categorization of apheresis indications. This Seventh Edition of the JCA Special Issue continues to maintain this methodology and rigor to make recommendations on the use of apheresis in a wide variety of diseases/conditions. The JCA Seventh Edition, like its predecessor, has consistently applied the category and grading system definitions in the fact sheets. The general layout and concept of a fact sheet that was used since the fourth edition has largely been maintained in this edition. Each fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis in a specific disease entity. The Seventh Edition discusses 87 fact sheets (14 new fact sheets since the Sixth Edition) for therapeutic apheresis diseases and medical conditions, with 179 indications, which are separately graded and categorized within the listed fact sheets. Several diseases that are Category IV which have been described in detail in previous editions and do not have significant new evidence since the last publication are summarized in a separate table. The Seventh Edition of the JCA Special Issue serves as a key resource that guides the utilization of therapeutic apheresis in the treatment of human disease. J. Clin. Apheresis 31:149-162, 2016. © 2016 Wiley Periodicals, Inc.

The effect of histopathologic and clinical features on allograft survival in renal transplant patients with antibody-mediated rejection

Background: Antibody-mediated rejection is a frequent cause of graft failure; however, prognostic indications of this complication have not been well defined. The aim of this study was to evaluate the association of histopathological and clinical features and to determine the effect of these findings on allograft survival in patients with AMR.

Methods: Fifty-two patients suffered from AMR (30 male; mean age 39 ± 11 years) were included in the study. Data were investigated retrospectively and graft survival was analyzed. All transplant biopsies were evaluated according to Banff 2009 classification.

Results: Of the 52 cases, 45 were transplanted from living-donors. Twenty-one patients were diagnosed in the first 3-months after transplantation. Graft survival was 65% at 12 months and 54% at 36 months. Mean serum creatinine at time of biopsy was 3.8 ± 3.6 mg/dL. Thirty-five of the 52 cases showed diffuse C4d positivity, 12 cases showed focal and 5 remained C4d negative. One of the patients died, 13 experienced graft loss and 38 survived with functioning grafts. Serum creatinine levels at time of biopsy were correlated with graft survival (p = .021: OR = 1.10: 95 % CI = 1.015–1.199). In terms of the impact of pathological findings; tubulitis (p=.007: OR = 2.62: 95 % CI = 1.301–5.276), intimal arteritis (p=.017: OR = 2.85: 95% CI = 1.205–6.744) and interstitial infiltration (p=.004: OR = 3.37: 95% CI = 1.465–7.752) were associated with graft survival.

Conclusions: Serum creatinine at time of biopsy, tubulitis, intimal arteritis and interstitial infiltration were significantly associated with graft survival. Antibody-mediated rejection is associated with reduced long-term graft survival.

C1Q Assay Results in Complement-Dependent Cytotoxicity Crossmatch Negative Renal Transplant Candidates with Donor-Specific Antibodies: High Specificity but Low Sensitivity When Predicting Flow Crossmatch

The aim of the present study was to describe the association of positive flow cross match (FXM) and C1q-SAB. Methods. In this observational, cross-sectional, and comparative study, patients included had negative AHG-CDC-XM and donor specific antibodies (DSA) and were tested with FXM. All pretransplant sera were tested with C1q-SAB assay. Results. A total of 50 donor/recipient evaluations were conducted; half of them had at least one C1q+ Ab (n = 26, 52%). Ten patients (20.0%) had DSA C1q+ Ab. Twenty-five (50%) FXMs were positive. Factors associated with a positive FXM were the presence of C1q+ Ab (DSA C1q+ Ab: OR 27, 2.80–259.56, P = 0.004, and no DSA C1q+ Ab: OR 5, 1.27–19.68, P = 0.021) and the DSA LABScreen-SAB MFI (OR 1.26, 95% CI 1.06–1.49, P = 0.007). The cutoff point of immunodominant LABScreen SAB DSA-MFI with the greatest sensitivity and specificity to predict FXM was 2,300 (sensitivity: 72% and specificity: 75%). For FXM prediction, DSA C1q+ Ab was the most specific (95.8%, 85–100) and the combination of DSA-MFI > 2,300 and C1q+ Ab was the most sensitive (92.0%, 79.3–100). Conclusions. C1q+ Ab and LABScreen SAB DSA-MFI were significantly associated with FXM. DSA C1q+ Ab was highly specific but with low sensitivity.

The prognostic values of caveolin-1 immunoreactivity in peritubular capillaries in patients with kidney transplantation

The low sensitivity of C4d immunoreactivity in peritubular capillaries (PTCs) hinders its use in the diagnosis of chronic active antibody-mediated rejection (CAAMR). C4d-negative CAAMR was defined in the 2013 Banff classification, which included the expression of endothelial-associated transcripts (ENDATs). We previously showed that the ENDAT caveolin-1 (CAV-1) is a distinct feature of CAAMR. In this study, we investigated the prognostic value of CAV-1 immunoreactivity in PTCs in kidney transplant patients. Ninety-eight kidney transplant recipients were included in this study. The prognostic value of CAV-1 immunoreactivity in PTCs was evaluated by double immunostaining for CAV-1 and pathologische Anatomie Leiden endothelium (PAL-E, a PTC marker) in the PTCs of kidney allograft biopsy samples. The patients were divided into two groups: CAV-1/PAL-E<50% and CAV-1/PAL-E≥50%. Kaplan-Meier curves showed that CAV-1/PAL-E≥50% patients had a significantly worse prognosis than that of CAV-1/PAL-E<50% patients (log-rank; P<.001). C4d staining of PTCs was not associated with the development of graft failure (log-rank; P=.345), whereas in a multivariate Cox regression analysis, CAV-1 immunoreactivity in PTCs was independently associated with graft failure (hazard ratio: 11.1; P=.0324). CAV-1 immunoreactivity in PTCs may serve as a prognostic marker for kidney allograft survival.

Prevention and treatment of liver allograft antibody-mediated rejection and the role of the 'two-hit hypothesis'

PURPOSE OF REVIEW

The review outlines the diagnosis, prevention strategies, and possible treatment options for acute and chronic antibody-mediated rejection (AMR).

RECENT FINDINGS

Although rare, severe acute AMR (aAMR) usually occurs in patients with high mean fluorescence intensity despite serial dilutions or high-titer preformed class I donor-specific alloantibodies (DSA). The diagnosis is suspected when allograft dysfunction occurs with DSA, diffuse C4d staining, and a microvascular injury, and may be aided by the aAMR score. However, the incidence of and treatment approach to combined T-cell-mediated rejection (TCMR) with DSA present and some but not all features of AMR is yet to be determined. Chronic liver allograft AMR is characterized by low-grade chronic inflammation and progressive fibrosis with DSA, the chronic AMR (cAMR) score may facilitate diagnosis. The 'two-hit' hypothesis, whereby a coexistent insult upregulates human leukocyte antigen class II target antigens on the microvascular endothelium, may explain why suboptimal donors with lower sensitization levels might suffer from acute AMR and those with chronic complications (e.g., recurrent original disease) might be more susceptible to chronic AMR. Although treatment algorithms are needed, prevention is preferable and at a minimum includes transfusion minimization, and medication adherence.

SUMMARY

Severe acute AMR is rare but diagnosable, and there is need to determine the incidence of and optimal therapy for less severe combined AMR and TCMR. Chronic AMR is likely more common and of significant relevance to long-term allograft survival improvement. The two-hit hypothesis may help to explain the rarity of both findings and shed insight onto future prevention and treatment strategies.

Impact of the Banff 2013 classification on the diagnosis of suspicious versus conclusive late antibody-mediated rejection in allografts without acute dysfunction

BACKGROUND

The Banff classification is used worldwide to characterize pathological findings in renal allograft biopsies. During the 11th Banff meeting, relevant changes were introduced in the diagnostic criteria for Category 2 antibody-mediated rejection (ABMR). Here, we assess the effect of these changes on the diagnosis of late chronic ABMR.

METHODS

Seventy-three indication renal graft biopsies (chronic dysfunction, proteinuria and/or the presence of de novo donor-specific antibodies) from 68 kidney transplant recipients initially classified following the Banff 2009 criteria were reviewed and reclassified as per the new Banff 2013 criteria.

RESULTS

The diagnostic category changed in 18% of the study biopsies with Banff 2013. The reclassification mainly involved Category 2 cases, from which 23.5% of the biopsies from older patients with worse graft function were overlooked by Banff 2009. ABMR was ruled out in 13% of cases under the Banff 2009 criteria. A significant number of the study samples were conclusively diagnosed as ABMR (40% as per Banff 2009 and 74% as per Banff 2013; P = 0.006), because of the inclusion of microvascular inflammation and the acceptance of some ultrastructural diagnostic criteria. However, when following the criteria of the new classification, samples with histological signs of chronic ABMR, in which human leucocyte antigen donor-specific antibodies are not detected or ultrastructural studies are not performed, may be inadequately characterized.

CONCLUSIONS

The Banff 2013 classification helps in making a diagnosis of late ABMR, identifying cases, decreasing the percentage of suspected ABMR and making more conclusive diagnoses.

Immune response and histology of humoral rejection in kidney transplantation

The adaptive immune response forms the basis of allograft rejection. Its weapons are direct cellular cytotoxicity, identified from the beginning of organ transplantation, and/or antibodies, limited to hyperacute rejection by preformed antibodies and not as an allogenic response. This resulted in allogenic response being thought for decades to have just a cellular origin. But the experimental studies by Gorer demonstrating tissue damage in allografts due to antibodies secreted by B lymphocytes activated against polymorphic molecules were disregarded. The special coexistence of binding and unbinding between antibodies and antigens of the endothelial cell membranes has been the cause of the delay in demonstrating the humoral allogenic response. The endothelium, the target tissue of antibodies, has a high turnover, and antigen-antibody binding is non-covalent. If endothelial cells are attacked by the humoral response, immunoglobulins are rapidly removed from their surface by shedding and/or internalization, as well as degrading the components of the complement system by the action of MCP, DAF and CD59. Thus, the presence of complement proteins in the membrane of endothelial cells is transient. In fact, the acute form of antibody-mediated rejection was not demonstrated until C4d complement fragment deposition was identified, which is the only component that binds covalently to endothelial cells. This review examines the relationship between humoral immune response and the types of acute and chronic histological lesion shown on biopsy of the transplanted organ.

Acute Antibody-Mediated Rejection in Kidney Transplant Based on the 2013 Banff Criteria: Single-Center Experience in Uruguay

BACKGROUND

Acute antibody-mediated rejection (AMR) diagnosis criteria have changed in recent consensus of Banff, with current evidence of C4d-negative AMR. Our objective was to evaluate incidence of AMR in renal transplantation according to Banff 2013 criteria and to examine the histological features and outcome.

METHODS

This retrospective study involved all kidney transplants with histological diagnosis of acute rejection (AR) at our center between 2000 and 2014. All the biopsies with AR were re-assessed by a nephro-pathologist and classified by use of the Banff 2013 criteria.

RESULTS

Of 205 kidney transplants, biopsy-proven AR was diagnosed in 25 cases (12%). Re-assessing them according to Banff 2013 criteria, AMR was diagnosed in 17 (8.3%) and represented 68% of the confirmed rejections. AMR diagnosis was performed on day 23 ± 26, with median of 11 days. From the 17 cases, 7 had concomitant T-cell-mediated rejection. All cases presented endothelial edema and acute tubular necrosis. Glomerulitis was found in 12 cases and capillaritis in 14. In 3, associated thrombotic micro-angiopathy (TMA) was found. Intimal and transmural arteritis was evidenced in 5 and 1 patient. In 2, transplant glomerulopathy was present. Seven of the 10 biopsies with C4d staining in the peri-tubular capillaries were positive. Twelve cases received plasmapheresis, 6 received gamma-globulin, and 6 received rituximab. After administration of anti-AMR therapy, 16 cases recovered renal function, reaching a serum creatinine level of 1.5 ± 0.6 mg %. Graft survival at 1 year was lower in the AMR group versus patients without AMR (81.9% vs 98.9%, log-rank test, P < .001). Risk factors for AMR were re-transplant (30% vs 7%, P = .02), HLA-DR mismatch (1.06 ± 0.65 vs 0.7 ± 0.6, P = .03), panel-reactive antibody (28% ± 33 vs 6.2 ± 13, P = .00), and delayed graft function (82% vs 30%, P = .00).

CONCLUSIONS

Adapting the new Banff 2013 criteria increased the sensitivity of the diagnosis of ARM. Regarding our data, despite an adequate response to the therapy, it resulted in a worse graft survival by the first year of renal transplant.

Four-Year Analyses of Renal Graft Biopsies: A Single-Center Pathology Experience

OBJECTIVES

Kidney transplant is the best treatment for patients with end-stage renal disease. Long-term graft survival depends on the protection of renal allograft function. Renal allograft biopsy is the most important method for examining an allograft function. Biopsy provides critical information, enabling diagnosis and grading of pathologic changes, prediction of response to therapy, and long-term graft prognosis.

MATERIALS AND METHODS

We reviewed the medical records of patients who underwent renal transplant from living and deceased donors at Baskent University Adana Teaching and Research Hospital between 2010 and 2014 and who had an indication for biopsy. Clinical characteristics and laboratory results of patients were recorded. Patient biopsy samples were examined according to the Banff 2009 classification.

RESULTS

Between 2010 and 2014, there were 175 renal transplants performed at our hospital, with 134 recipients (76.6%) having living-donor and 41 recipients (23.4%) having deceased-donor transplants. Fifty-one patients (29.1%) were children, and 124 patients (70.9%) were adults. We found that there were 123 biopsies made from 75 transplant patients over a 4-year period. When examined according to Banff 2009 criteria, the biopsy samples revealed acute T-cell-mediated rejection alone in 14.1% of the samples, acute antibody-mediated rejection in 4%, and a combination of the 2 rejections in 5.7%. Specific infections were detected in 12 patients. The graft nephrectomy rate was 5.1%.

CONCLUSIONS

This study investigated biopsy results, their relation with patient clinical status and 4-year survival rates, and our pathology experience and found that rejection and infection rates were similar to the literature. Our future studies with a longer follow-up and a larger sample size will likely provide more accurate information about graft survival and biopsy results.

Successful treatment of severe acute antibody-mediated rejection of renal allografts with bortezomib--a report of two pediatric cases

aAMR in renal allografts is uncommon and remains a challenge as it is often refractory to treatment modalities. Aggressive therapy is essential to reverse the rejection as it results in renal allograft loss in approximately 27-40% of cases. There are anecdotal case reports of use of bortezomib, a proteasome inhibitor in the treatment of resistant AMR cases in solid organ transplant recipients; however, the experience is limited. We herein report successful reversal of resistant aAMR in two pediatric patients with bortezomib. Patients were initially treated with IV methylprednisolone pulse therapy with IVIG and PP three times weekly for a total of 10 treatments. After the standard therapy used at our institution persistence of DSA associated with graft dysfunction prompted the use of bortezomib to further treat the rejection. We did not have any neurologic side effects, but one patient did experience significant infections after bortezomib infusions requiring prolonged antimicrobial therapy. The long-term outcome of both children was excellent with preservation of normal renal function and persistent reduction in DSA titers.

New insights in antibody-mediated rejection

PURPOSE OF REVIEW

In the present review, we aim to describe the state of knowledge concerning antibody-mediated rejection (ABMR) spectrum and diagnosis criteria before analyzing the present and future promising leads regarding ABMR prognosis markers and treatment.

RECENT FINDINGS

Recent studies regarding complement-binding donor-specific antibodies and the molecular approach highlighted the unmet need for stratification tools for prognosis and treatment inside ABMR disease.

SUMMARY

ABMR is the leading cause of kidney allograft failure. The recent expansion of its spectrum is related to the paradigm of a continuous process, leading insidiously to a chronic form of ABMR and to the progressive acknowledgement of new entities (such as vascular ABMR, subclinical ABMR, C4d-negative ABMR). Considering the global picture of ABMR, the Banff classification gradually refined the diagnosis criteria so that it now describes a clinically relevant and coherent entity. Nevertheless, if the diagnosis mainly relies on conventional assessment, such as histological findings and circulating donor-specific antibodies, these criteria face serious limitations in terms of stratification of patients at risk of graft loss inside ABMR disease. Recently, new promising tools have emerged in order to identify long-term outcomes at the time of the diagnosis of rejection. In this regard, donor-specific antibodies' complement-fixing ability and the molecular approach contributed significantly. Currently, however, no clinically relevant surrogate marker of treatment efficiency is currently available.

Acute Antibody-Mediated Rejection in Presence of MICA-DSA and Successful Renal Re-Transplant with Negative-MICA Virtual Crossmatch

The presence of donor-specific alloantibodies (DSAs) against the MICA antigen results in high risk for antibody-mediated rejection (AMR) of a transplanted kidney, especially in patients receiving a re-transplant. We describe the incidence of acute C4d+ AMR in a patient who had received a first kidney transplant with a zero HLA antigen mismatch. Retrospective analysis of post-transplant T and B cell crossmatches were negative, but a high level of MICA alloantibody was detected in sera collected both before and after transplant. The DSA against the first allograft mismatched MICA*018 was in the recipient. Flow cytometry and cytotoxicity tests with five samples of freshly isolated human umbilical vein endothelial cells demonstrated the alloantibody nature of patient’s MICA-DSA. Prior to the second transplant, a MICA virtual crossmatch and T and B cell crossmatches were used to identify a suitable donor. The patient received a second kidney transplant, and allograft was functioning well at one-year follow-up. Our study indicates that MICA virtual crossmatch is important in selection of a kidney donor if the recipient has been sensitized with MICA antigens.

Circulating NK-cell subsets in renal allograft recipients with anti-HLA donor-specific antibodies

Detection of posttransplant donor-specific anti-HLA antibodies (DSA) constitutes a risk factor for kidney allograft loss. Together with complement activation, NK-cell antibody-dependent cell mediated cytotoxicity (ADCC) has been proposed to contribute to the microvascular damage associated to humoral rejection. In the present observational exploratory study, we have tried to find a relationship of circulating donor-specific and non donor-specific anti-HLA antibodies (DSA and HLA non-DSA) with peripheral blood NK-cell subsets and clinical features in 393 renal allograft recipients. Multivariate analysis indicated that retransplantation and pretransplant sensitization were associated with detection of posttransplant DSA. Recipient female gender, DR mismatch and acute rejection were significantly associated with posttransplant DSA compared to HLA non-DSA. In contrast with patients without detectable anti-HLA antibodies, DSA and HLA non-DSA patients displayed lower proportions of NK-cells, associated with increased CD56(bright) and NKG2A(+) subsets, the latter being more marked in DSA cases. These differences appeared unrelated to retransplantation, previous acute rejection or immunosuppressive therapy. Although preliminary and observational in nature, our results suggest that the assessment of the NK-cell immunophenotype may contribute to define signatures of alloreactive humoral responses in renal allograft recipients.

Monitoring B cell subsets and alloreactivity in kidney transplantation

B cells are the precursors of antibody producing plasma cells that can give rise to the formation of donor-specific antibodies. However, recent data suggest that besides their role in antibody production, B cells participate in antibody-independent responses, potentially leading to allograft rejection or allograft tolerance. The presence of CD20(+) B cells in kidney graft biopsies has been shown during severe acute rejection episodes and during chronic rejection. Furthermore, operationally tolerant kidney transplant recipients showed a clear B cell dominated fingerprint of tolerance. Several techniques exist to study B cells on different levels. Numerous classification schemes allow for the distinction of many different B cell subsets using flow cytometry. Regardless, data on B cell subsets during stable graft function, rejection or tolerance remain scarce. To obtain a complete picture of the role of B cells during transplantation, antigen specific B cell assays may be required. Therefore, techniques have now been developed that allow for studying the specificity and frequency of HLA specific B cells. Here, we present an overview of the existent assays, panels and techniques intended to characterize peripheral B cells, and the currently available HLA specific B cell functional assays that may allow for monitoring the humoral alloimmune response in transplant recipients.

C4d immunoreactivity of intraoperative zero-hour biopsy in renal allograft

C4d deposition in the peritubular capillaries is known to be correlated with antibody-mediated rejection (AMR) in renal allografts. An intraoperative zero-hour biopsy during transplantation is considered an indicator to indirectly determine the status of the donor kidney. In this study, we investigated the relationship between C4d immunoreactivity of intraoperative zero-hour biopsy in renal allograft, thought to be due to donor condition, and acute rejection episodes during follow-up. We collected 147 renal transplantation cases examining intraoperative zero-hour biopsy with C4d immunohistochemical staining. All cases were from the Seoul National University Hospital between 2010 and 2011. Of the 147 cases, 24 (16.3%) showed strong C4d staining in the glomeruli, 38 (25.9%) showed weak staining, and the remainder (57.8%) showed negative staining. Nine cases (6.1%) showed positive C4d staining in the arterioles, and the remainder (93.9%) were negative. There were no significant differences between acute T-cell-mediated rejection and acute AMR episodes in the renal allograft specimens during follow-up according to the glomerular or arteriolar C4d immunoreactivity of the intraoperative zero-hour biopsy specimens.

Pretransplant IgG reactivity to apoptotic cells correlates with late kidney allograft loss

Preexisting serum antibodies have long been associated with graft loss in transplant recipients. While most studies have focused on HLA-specific antibodies, the contribution of non-HLA-reactive antibodies has been largely overlooked. We have recently characterized mAbs secreted by B cell clones derived from kidney allograft recipients with rejection that bind to apoptotic cells. Here, we assessed the presence of such antibodies in pretransplant serum from 300 kidney transplant recipients and examined their contribution to the graft outcomes. Kaplan-Meier survival analysis revealed that patients with high pretransplant IgG reactivity to apoptotic cells had a significantly increased rate of late graft loss. The effect was only apparent after approximately 1 year posttransplant. Moreover, the association between pretransplant IgG reactivity to apoptotic cells and graft loss was still significant after excluding patients with high reactivity to HLA. This reactivity was almost exclusively mediated by IgG1 and IgG3 with complement fixing and activating properties. Overall, our findings support the view that IgG reactive to apoptotic cells contribute to presensitization. Taking these antibodies into consideration alongside anti-HLA antibodies during candidate evaluation would likely improve the transplant risk assessment.

Clinical efficacy of rituximab for acute rejection in kidney transplantation: a meta-analysis

OBJECTIVES

This meta-analysis was undertaken to compare the efficacy and safety of pretransplant treatment with rituximab in sensitized patients receiving kidney transplantation.

METHODS

PubMed, EMBASE, and Cochrane databases were searched to identify studies that used pretransplantation rituximab in eligible patients. The major outcomes included antibody-mediated rejections (AMR) after kidney transplantation and one-year graft survival rate. The meta-analysis was performed using fixed-effects model.

RESULTS

Seven studies were identified including a total of 589 patients, of whom 312 were treated without rituximab, while 277 were treated with rituximab. In our meta-analysis, patients treated with rituximab had significantly fewer AMR after kidney transplantation [odds ratio (OR) 0.52, 95 % CI 0.28, 0.98, P = 0.04] and higher rate of one-year graft survival rates (OR 3.02, 95 % CI 1.14, 8.02, P = 0.03), indicating that rituximab is effective against acute rejection and enhances graft survival in kidney transplantation. No differences were noted in other efficacy and safety parameters in these two patient groups.

CONCLUSIONS

We demonstrated that preinduction with rituximab could significantly improve AMR and graft survival rates in sensitized patients undergoing kidney transplantation. Future prospective controlled studies are warranted to further understand rituximab's role in kidney transplantation.

A systematic review of the role of C4d in the diagnosis of acute antibody-mediated rejection

In this study, we conducted a systematic review of the literature to re-evaluate the role of C4d in the diagnosis of acute antibody-mediated rejection of kidney allografts. Electronic databases were searched until September 2013. Eligible studies allowed derivation of diagnostic tables for the performance of C4d by immunofluorescence or immunohistochemistry with comparison to histopathological features of acute antibody-mediated rejection and/or donor-specific antibody (DSA) assays. Of 3492 unique abstracts, 29 studies encompassing 3485 indication and 868 surveillance biopsies were identified. Assessment of C4d by immunofluorescence and immunohistochemistry exhibited slight to moderate agreement with glomerulitis, peritubular capillaritis, solid-phase DSA assays, DSA with glomerulitis, and DSA with peritubular capillaritis. The sensitivity and specificity of C4d varied as a function of C4d and comparator test thresholds. Prognostically, the presence of C4d was associated with inferior allograft survival compared with DSA or histopathology alone. Thus, our findings support the presence of complement-dependent and -independent phenotypes of acute antibody-mediated rejection. Whether the presence of C4d in combination with histopathology or DSA should be considered for the diagnosis of acute antibody-mediated rejection warrants further study.

The Maintenance Immunosuppression Scheme Influences Early C4d Urinary Excretion in Kidney Graft Recipients but Does Not Affect the Long-term Graft Survival

C4d urinary excretion varies according to the risk of graft rejection or progression of chronic allograft nephropathy. The most common maintenance immunosuppression (IS) schemes include cyclosporine (CSA) or tacrolimus (TAC) with azathiopryne (AZA) or mycophenolate mophetil (MMF). The chosen IS may influence kidney transplant outcomes and possibly modify urinary C4d. The aim of the study was to determine whether early C4d urinary excretion varies in patients after kidney allograft transplantation (KTx) regarding administered IS and if these factors may help to predict long-term KTx outcomes. The study involved 185 patients who underwent KTx. The urinary specimens were assessed by enzyme-linked immunosorbent assay test for C4d excretion. To increase the objectivity, C4d excretion was divided by urinary creatinine excretion (ng/mgCr). The study population was grouped according to the IS scheme, that is, CSA + AZA, CSA + MMF, and TAC + MMF. At baseline, the greatest C4d urinary excretion was noticed in patients treated with CSA + AZA, 199.5 ± 175.9 ng/mL (5.3 ± 7.1 ng/mgCr) and the lowest in those in whom tacrolimus and mycophenolate mophetil was administered, 166.6 ± 186.3 ng/mL (3.9 ± 6.2 ng/mgCr). In the CSA + MMF group, C4d excretion was 195.6 ± 200.3 ng/mL (5.0 ± 6.6 ng/mgCr). Statistically significant differences were seen only between the CSA + AZA and TAC + MMF groups, analysis of variance P < 0.05 (P < 0.01 for C4d/urinary creatinine ratio). No statistically significant differences were found in graft survival rates between different immunosuppressive regimens. Although early C4d measurements vary in patients after kidney allograft transplantation regarding administered IS, this IS dependant variation does not seem to affect the long-term graft survival.

Antibody-mediated rejection in kidney transplantation: a review of pathophysiology, diagnosis, and treatment options

Antibody-mediated rejection (AMR), also known as B-cell-mediated or humoral rejection, is a significant complication after kidney transplantation that carries a poor prognosis. Although fewer than 10% of kidney transplant patients experience AMR, as many as 30% of these patients experience graft loss as a consequence. Although AMR is mediated by antibodies against an allograft and results in histologic changes in allograft vasculature that differ from cellular rejection, it has not been recognized as a separate disease process until recently. With an improved understanding about the importance of the development of antibodies against allografts as well as complement activation, significant advances have occurred in the treatment of AMR. The standard of care for AMR includes plasmapheresis and intravenous immunoglobulin that remove and neutralize antibodies, respectively. Agents targeting B cells (rituximab and alemtuzumab), plasma cells (bortezomib), and the complement system (eculizumab) have also been used successfully to treat AMR in kidney transplant recipients. However, the high cost of these medications, their use for unlabeled indications, and a lack of prospective studies evaluating their efficacy and safety limit the routine use of these agents in the treatment of AMR in kidney transplant recipients.