Peripheral B-cell phenotype and BAFF levels are associated with HLA immunization in patients awaiting kidney transplantation. Transplantation. 2014;97:917-924. [PMID: 24827764 DOI: 10.1097/01.tp.0000438211.34842.5e]

Past and present discovery of the BAFF/APRIL system - A bibliometric study from 1999 to 2023

Cytokines from the Tumour Necrosis Factor (TNF) family are important regulators of both physiological and pathological processes. The discovery of novel TNF ligands and receptors, BAFF and APRIL, have opened up new possibilities for scientists to explore the effect of these cytokines on the human immune system. The role of BAFF/APRIL system in B lymphocytes is particularly important for survival and maintenance of homeostasis. Aberrant expression of the system is associated with various immunological disorders. Hence, this study provides a comprehensive overview of the past and present BAFF/APRIL system research development in a bibliometric perspective. To our best knowledge, this is the first ever bibliometric analysis conducted focusing on the BAFF/APRIL system. A total of 1055 relevant documents were retrieved from WoSCC. Microsoft Excel, VOSviewer, and Biblioshiny of R studio were bibliometric tools used to analyse the scientific literature. From 1999, the annual publications showed an upward trend, with Journal of Immunology being the most productive journal. USA leads the race for BAFF/APRIL system research developments. Pascal Schneider, a senior researcher affiliated with University of Lausanne, Switzerland was recognised as the most productive author and institution in the BAFF/APRIL system research field. The research focus transitioned from focusing on the role of the system in B cell biology, to immunological disorders and finally to development of BAFF/APRIL targeting drugs. Despite several studies elucidating briefly the pathway mechanism of BAFF/APRIL system in B-cell selection, substantial research on the mechanism of action in disease models and T cell activation and development of immunomodulating drugs from natural origins remains largely unexplored. Therefore, future research focusing on these areas are crucial for the deeper understanding of the system in disease manifestations and progression allowing a better treatment management for various immunological disorders.

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.

High B-cell activating factor levels in multi-transfused thalassemia patients

OBJECTIVES

To assess the associations between B-cell activating factor (BAFF) and alloimmunisation in multi-transfused thalassemia.

BACKGROUND

Red blood cell (RBC) alloimmunisation is a complication of multi-transfused thalassemia. BAFF is promoting B cells that produce alloantibodies.

METHODS/MATERIALS

Multi-transfused thalassemia, 15 years or older, were recruited in the cohort study. Alloantibodies and BAFF levels were analysed.

RESULTS

Of 114 patients, the overall prevalence of RBC alloimmunisation was 29.8%. The most common alloantibodies were anti-E, anti-Mi^a and anti-c. BAFF levels were different among the three groups; the patients with baseline alloantibodies (median ± interquartile range 1251 ± 474 pg/ml), without alloantibodies (1098 ± 453) and healthy controls (719 ± 306), p < 0.001. The BAFF level was elevated in the >25 years old patients (vs. the <25, p = 0.011) and the buffy-coat-reduced blood recipients (vs. the pre-storage leukocyte-depletion, p = 0.005). Absolute lymphocyte count was higher in the patients without baseline alloantibodies (vs. with baseline alloantibodies, p = 0.049) and the splenectomised patients (vs. the non-splenectomised patients, p < 0.001). Of the 72 patients without baseline antibodies, four who developed new antibodies showed no statistically different BAFF levels compared with those without new antibodies after 40-month follow-up (1296 ± 734 vs. 1062 ± 460, p = 0.491). In multivariate analysis, BAFF to absolute lymphocyte ratio was independently associated with RBC alloimmunisation (odds ratio 3.07, 95% confidence interval 1.124-8.369, p = 0.029).

CONCLUSION

B-cell activating factor (BAFF) levels were elevated in multi-transfused thalassemia and the BAFF to absolute lymphocyte ratio was associated with red blood cell (RBC) alloimmunisation.

B-cell activating factor BAFF as a novel alert marker for the immunological risk stratification after kidney transplantation

The B cell activating factor BAFF has gained importance in the context of kidney transplantation due to its role in B cell survival. Studies have shown that BAFF correlates with an increased incidence of antibody-mediated rejection and the development of donor-specific antibodies. In this study, we analyzed a defined cohort of kidney transplant recipients who were treated with standardized immunosuppressive regimens according to their immunological risk profile. The aim was to add BAFF as an awareness marker in the course after transplantation to consider patient’s individual immunological risk profile. Included patients were transplanted between 2016 and 2018. Baseline data, graft function, the occurrence of rejection episodes, signs of microvascular infiltration, and DSA kinetics were recorded over 3 years. BAFF levels were determined 14 d, 3 and 12 months post transplantation. Although no difference in graft function could be observed, medium-risk patients showed a clear dynamic in their BAFF levels with low levels shortly after transplantation and an increase in values of 123% over the course of 1 year. Patients with high BAFF values were more susceptible to rejection, especially antibody-mediated rejection and displayed intensified microvascular inflammation; the combination of high BAFF + DSA puts patients at risk. The changing BAFF kinetics of the medium risk group as well as the increased occurrence of rejections at high BAFF values enables BAFF to be seen as an awareness factor. To compensate the changing immunological risk, a switch from a weaker induction therapy to an intensified maintenance therapy is required.

Harnessing Mechanisms of Immune Tolerance to Improve Outcomes in Solid Organ Transplantation: A Review

Survival after solid organ transplantation (SOT) is limited by chronic rejection as well as the need for lifelong immunosuppression and its associated toxicities. Several preclinical and clinical studies have tested methods designed to induce transplantation tolerance without lifelong immune suppression. The limited success of these strategies has led to the development of clinical protocols that combine SOT with other approaches, such as allogeneic hematopoietic stem cell transplantation (HSCT). HSCT prior to SOT facilitates engraftment of donor cells that can drive immune tolerance. Recent innovations in graft manipulation strategies and post-HSCT immune therapy provide further advances in promoting tolerance and improving clinical outcomes. In this review, we discuss conventional and unconventional immunological mechanisms underlying the development of immune tolerance in SOT recipients and how they can inform clinical advances. Specifically, we review the most recent mechanistic studies elucidating which immune regulatory cells dampen cytotoxic immune reactivity while fostering a tolerogenic environment. We further discuss how this understanding of regulatory cells can shape graft engineering and other therapeutic strategies to improve long-term outcomes for patients receiving HSCT and SOT.

Investigating the Role of BAFF and Its Receptors in Renal Transplant Recipients with Chronic Antibody-Mediated Rejection

Background

Kidney transplantation is the best treatment option for end stage renal disease (ESRD), but graft rejection is still a big obstacle that occurs in spite of immunosuppressive therapy. B cells are considered as the major reason for renal graft rejection because of antibody production. Due to their roles in B cell function, we intended to evaluate the B cell activating factor (BAFF) and its receptors including BAFF receptor (BAFF-R), B cell maturation antigen (BCMA), and transmembrane activator and cyclophilin ligand interactor (TACI) in renal transplant patients.

Method

The study included 40 kidney allograft patients with cAMR, 40 stable kidney allograft patients, and 8 healthy volunteers with normal kidney function. The percentage and absolute number of CD19⁺ B cells were analyzed by flow cytometry, the serum level of BAFF was analyzed by ELISA, and mRNA expressions of BAFF and BAFF receptors (BAFF-R, BCMA, and TACI) were measured using quantitative real-time PCR.

Results

The percentage and the absolute number of B cells decreased significantly in stable and cAMR patients compared to healthy individuals. The serum level and gene expression of BAFF, as well as the mRNA level of BCMA, were increased significantly in both cAMR and stable patients compared to healthy volunteers. There was an overexpression of TACI mRNA in cAMR patients compared to stable patients.

Conclusions

Both soluble protein and mRNA transcript of BAFF increased in transplant recipients. However, BAFF neither at the serum level nor at the mRNA transcript level cannot be a good biomarker for the prediction of cAMR. In addition, expression of TACI, compared to other receptors of BAFF, confers a potential to be used in distinguishing cAMR and stable kidney transplant patients.

Regulatory B cells in transplantation: roadmaps to clinic

Over the last two decades, an additional and important role for B cells has been established in immune regulation. Preclinical studies demonstrate that regulatory B cells (Breg) can prolong allograft survival in animal models and induce regulatory T cells. Operationally tolerant human kidney transplant recipients demonstrate B-cell-associated gene signatures of immune tolerance, and novel therapeutic agents can induce Bregs in phase I clinical trials in transplantation. Our rapidly expanding appreciation of this novel B-cell subtype has made the road to clinical application a reality. Here, we outline several translational pathways by which Bregs could soon be introduced to the transplant clinic.

Anti-BAFF Treatment Interferes With Humoral Responses in a Model of Renal Transplantation in Rats

BACKGROUND

B-cell-activating factor (BAFF) is associated with donor-specific antibodies (DSA) and poorer outcomes after renal transplantation (RTx). We examined the effects of anti-BAFF treatment on B cells, expression of costimulatory molecules and cytokines, germinal centers (GCs), and DSA formation in an RTx model in rats.

METHODS

Anti-BAFF antibody was injected on days 3, 17, 31, and 45 after allogeneic RTx. Rats received reduced dose cyclosporine A for 28 or 56 days to allow chronic rejection and DSA formation. Leukocytes, B-cell subsets, and DSA were measured using flow cytometry; expression of cytokines and costimulatory molecules was measured by quantitative polymerase chain reaction, and GCs and T follicular helper were assessed using immunohistochemistry. Rejection was evaluated by a nephropathologist.

RESULTS

Anti-BAFF treatment reduced the frequency of B cells in allografts and spleen. Naive B cells were strongly reduced by anti-BAFF treatment in all compartments. Messenger RNA expression of interleukin-6 and the costimulatory molecules CD40 and inducible T cell costimulator ligand was significantly reduced in anti-BAFF-treated rats. GC area was smaller and plasmablasts/plasma cell numbers lower in anti-BAFF-treated rats, which was reflected by less DSA in certain IgG subclasses.

CONCLUSIONS

Anti-BAFF treatment interferes with humoral responses at multiple levels in this model of allogeneic RTx.

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.

Phenotypic and Transcriptomic Lymphocytes Changes in Allograft Recipients After Intravenous Immunoglobulin Therapy in Kidney Transplant Recipients

High dose intravenous immunoglobulin (IVIG) are widely used after kidney transplantation and its biological effect on T and B cell phenotype in the context of maintenance immunosuppression was not documented yet. We designed a monocentric prospective cohort study of kidney allograft recipients with anti-HLA donor specific antibodies (DSA) without acute rejection on screening biopsies treated with prophylactic high-dose IVIG (2 g/kg) monthly for 2 months. Any previous treatment with Rituximab was an exclusion criterion. We performed an extensive analysis of phenotypic and transcriptomic T and B lymphocytes changes and serum cytokines after treatment (day 60). Twelve kidney transplant recipients who completed at least two courses of high-dose IVIG (2 g/kg) were included in a median time of 45 (12–132) months after transplant. Anti-HLA DSA characteristics were similar before and after treatment. At D60, PBMC population distribution was similar to the day before the first infusion. CD8⁺ CD45RA⁺ T cells and naïve B-cells (Bm2⁺) decreased (P = 0.03 and P = 0.012, respectively) whereas Bm1 (mature B-cells) increased (P = 0.004). RORγt serum mRNA transcription factor and CD3 serum mRNA increased 60 days after IVIG (P = 0.02 for both). Among the 25 cytokines tested, only IL-18 serum concentration significantly decreased at D60 (P = 0.03). In conclusion, high dose IVIG induced limited B cell and T cell phenotype modifications that could lead to anti-HLA DSA decrease. However, no clinical effect has been isolated and the real benefit of prophylactic use of IVIG after kidney transplantation merits to be questioned.

The role of soluble B cell-activating factor in further stratifying the risk of antibody-mediated rejection post-renal transplant: A meta-analysis

BACKGROUND

We conducted a meta-analysis to evaluate the predictive value of serum soluble B cell-activating factor (sBAFF) for antibody-mediated rejection (ABMR), which remains controversial.

METHODS

Systematic literature search was performed in PubMed, EMBASE, Scopus, Cochrane Library, Web of Science and three Chinese databases. Studies of any relevant design were included. Random and fixed-effects meta-analytical models were used. Study quality, publication bias, and heterogeneity were assessed. This study was registered with PROSPERO (CRD42019109198).

RESULTS

Nine observational studies were included in the meta-analysis, including 1302 cases (median NOS quality score = 8, range 6-8). The incidence of ABMR was significantly higher in the high sBAFF group than in the low sBAFF level group (Risk ratio [RR] 2.04 [95% CI 1.52-2.74], I² = 26%, P < 0.01, N = 1014). The subgroup analysis showed that regardless of pre-transplant donor-specific antibody (DSA) status, the high sBAFF level group still had a significantly higher incidence of ABMR. sBAFF was not associated with the risk of TCMR. The sBAFF level was significantly higher in the anti-HLA-antibody (+) group than in anti-HLA-antibody (-) patients before or after kidney transplantation (Standardized mean difference [SMD] 0.43 [0.29-0.56], P < 0.01, I² = 34%, N = 1001).

CONCLUSION

sBAFF is a promising biomarker to further stratify the risk of ABMR post-renal transplant.

B-Cell Activating Factor Predicts Acute Rejection Risk in Kidney Transplant Recipients: A 6-Month Follow-Up Study

B cell activating factor (BAFF) belonging to TNF family is a cytokine that enhances B-cell proliferation and differentiation. Recently, It has been suggested that BAFF might be a potential therapeutic target for treating autoimmune disease. However, the relationship between BAFF and allograft rejection is controversial, and the clinical significance of BAFF in predicting allograft rejection need to be further explored. We conducted 6-month follow-up study to confirm the hypothesis that BAFF might be a risk factor for predicting acute rejection in kidney transplant recipients. At the end of the study, a total of 155 kidney transplant recipients were recruited from October 2015 to October 2017, and classified into acute rejection group (n = 34) and stable renal function group (n = 121) according to their clinical course. We demonstrate that the serum BAFF levels when acute rejection occurred was significantly higher than that in the stable renal function group (2426.19 ± 892.19 vs. 988.17 ± 485.63 pg/mL, P < 0.05). BAFF expression was significantly enhanced in the membrane and cytoplasm of renal tubule epithelial cells in the transplant kidney tissue with acute rejection, and a positive correlation between BAFF and C4d expression was also observed (r = 0.880, P = 0.001). ROC analyses highlight the superiority of serum BAFF level before transplant over those on other post-transplant days in prediction of acute rejection episodes. The sensitivity, specificity and AUC (area under curve) were 83.3, 89.5, and 0.886%, respectively. Kaplan-Meier survival analysis showed that recipients with higher pretransplant BAFF levels had higher acute rejection incidence (P = 0.003). In conclusion, we have identified that BAFF levels are associated with the acute rejection and could be a promising biomarker to predict kidney transplant rejection risks.

Belimumab in kidney transplantation: an experimental medicine, randomised, placebo-controlled phase 2 trial

BACKGROUND

B cells produce alloantibodies and activate alloreactive T cells, negatively affecting kidney transplant survival. By contrast, regulatory B cells are associated with transplant tolerance. Immunotherapies are needed that inhibit B-cell effector function, including antibody secretion, while sparing regulators and minimising infection risk. B lymphocyte stimulator (BLyS) is a cytokine that promotes B-cell activation and has not previously been targeted in kidney transplant recipients. We aimed to determine the safety and activity of an anti-BLyS antibody, belimumab, in addition to standard-of-care immunosuppression in adult kidney transplant recipients. We used an experimental medicine study design with multiple secondary and exploratory endpoints to gain further insight into the effect of belimumab on the generation of de-novo IgG and on the regulatory B-cell compartment.

METHODS

We undertook a double-blind, randomised, placebo-controlled phase 2 trial of belimumab, in addition to standard-of-care immunosuppression (basiliximab, mycophenolate mofetil, tacrolimus, and prednisolone) at two centres, Addenbrooke's Hospital, Cambridge, UK, and Guy's and St Thomas' Hospital, London, UK. Participants were eligible if they were aged 18-75 years and receiving a kidney transplant and were planned to receive standard-of-care immunosuppression. Participants were randomly assigned (1:1) to receive either intravenous belimumab 10 mg per kg bodyweight or placebo, given at day 0, 14, and 28, and then every 4 weeks for a total of seven infusions. The co-primary endpoints were safety and change in the concentration of naive B cells from baseline to week 24, both of which were analysed in all patients who received a transplant and at least one dose of drug or placebo (the modified intention-to-treat [mITT] population). This trial has been completed and is registered with ClinicalTrials.gov, NCT01536379, and EudraCT, 2011-006215-56.

FINDINGS

Between Sept 13, 2013, and Feb 8, 2015, of 303 patients assessed for eligibility, 28 kidney transplant recipients were randomly assigned to receive belimumab (n=14) or placebo (n=14). 25 patients (12 [86%] patients assigned to the belimumab group and 13 [93%] patients assigned to the placebo group) received a transplant and were included in the mITT population. We observed similar proportions of adverse events in the belimumab and placebo groups, including serious infections (one [8%] of 12 in the belimumab group and five [38%] of 13 in the placebo group during the 6-month on-treatment phase; and none in the belimumab group and two [15%] in the placebo group during the 6-month follow-up). In the on-treatment phase, one patient in the placebo group died because of fatal myocardial infarction and acute cardiac failure. The co-primary endpoint of a reduction in naive B cells from baseline to week 24 was not met. Treatment with belimumab did not significantly reduce the number of naive B cells from baseline to week 24 (adjusted mean difference between the belimumab and placebo treatment groups -34·4 cells per μL, 95% CI -109·5 to 40·7).

INTERPRETATION

Belimumab might be a useful adjunct to standard-of-care immunosuppression in renal transplantation, with no major increased risk of infection and potential beneficial effects on humoral alloimmunity.

FUNDING

GlaxoSmithKline.

B Cell Activating Factor (BAFF) in Long-term Kidney Transplant Recipients Is Not a Prognostic Marker for Allograft Dysfunction or Survival

OBJECTIVE

B cell activating factor (BAFF) has been shown to play a role in B cell survival, maturation, and activation, and has been linked with renal transplant outcome. BAFF signaling has been associated with plasmablast survival, anti-HLA immunization, and loss of graft function. We aimed to analyze the interplay between BAFF, memory B cells, and plasmablasts in relation to allograft function in long-term kidney transplant (KTx) recipients and their anti-HLA sensitization.

MATERIALS AND METHODS

This study included 70 long-term KTx recipients on standard immunosuppression 15 ± 6 years post transplantation (44 stable, 26 chronic allograft dysfunction, CAD) and 25 healthy volunteers. CD19+ B cells, memory B cells (CD19+CD27+), and plasmablasts (CD19+CD24-CD27++CD38++) were enumerated with flow cytometry. BAFF serum level and anti-HLA antibodies were assessed by Luminex bead arrays.

RESULTS

We found no difference in BAFF levels between KTx recipients and controls (median, interquartile range: 1.67, 1.40-1.97 vs 1.78, 1.63-1.93 ng/mL, P = .478) and no correlation between BAFF level and cell counts. Recipients presented lower plasmablast count than controls (22.5, 8-57 vs 79, 48-166 cells/mL, P < .001). There was a positive correlation between estimated glomerular filtration rate and plasmablasts (r_s = 0.30, P = .013) in recipients. Cell populations and BAFF were not related to the presence of anti-HLA antibodies. None of the parameters investigated was related to deterioration of allograft function during the 2-year follow-up.

CONCLUSION

BAFF serum level is not related to anti-HLA sensitization, circulating memory B cells, plasmablast count, or allograft function. Circulating plasmablasts are associated with current allograft function but are not prognostic for future course.

Pretransplant serum BAFF levels are associated with pretransplant HLA immunization and renal allograft survival

BACKGROUND

The essential function of B cell-activating factor (BAFF) is regulating the survival and differentiation of B cells. The link between pretransplant BAFF levels and pretransplant alloimmunization and its value to predict subsequent acute antibody-mediated rejection (AMR) and outcome after renal transplantation is not fully understood.

METHODS

Objective of our retrospective single-center study was to determine, by ELISA analysis of pretransplant serum BAFF levels in 249 patients undergoing renal transplantation, association between preformed anti-human leukocyte antigen (HLA) antibodies, occurrence of acute antibody mediated rejection (AMR) and renal allograft survival.

RESULTS

Pretransplant serum BAFF levels were significantly higher in presensitized recipients with anti-HLA antibodies (3262±2796pg/ml) than in recipients without occurrence of anti-HLA antibodies (2252±1425pg/ml; p<0.0001). In addition, pretransplant BAFF levels correlated with cumulative MFI values of anti-HLA antibodies (r=0.2966, p=0.0025). Patients with high pretransplant BAFF levels (≥2137pg/ml) experienced significantly lower allograft survival rates compared to low pretransplant BAFF levels (80% vs. 91%; p=0.01). Coexistence of high pretransplant BAFF levels and posttransplant AMR was associated with the worst allograft survival rates (56%). Relative risk (RR) for allograft loss was associated with high serum BAFF levels (RR 2.3; p=0.02), presence of anti-HLA antibodies (RR 2.5; p=0.007) or anti-HLA -donor-specific antibodies (DSAs) (RR 2.6; p=0.003) before transplant and AMR post transplant (RR 2.5; p=0.007). AMR was the strongest independent risk factor for allograft failure (RR 2.6; p=0.03).

CONCLUSION

Elevated pretransplant serum BAFF levels negatively affect renal allograft survival and represent a risk factor for allosensitization and subsequent AMR.

B-cell activating factor BAFF reflects patients' immunological risk profile after kidney transplantation

The B-cell activating factor BAFF plays an important role in the development and maturation of B-lymphocytes, which can contribute to the generation of donor-specific antibodies and thus may influence graft function and graft survival. Inconsistent data on the role of BAFF levels after renal transplantation for the formation of donor-specific antibodies and the contribution for allograft rejection exist. The aim of the current study was to determine to what extent the degree of pre-immunization is reflected by each patient's BAFF levels before transplantation and in the follow-up. Furthermore, the impact of BAFF on allograft rejection frequency as well as severity and resulting allograft function over time was analyzed. Additionally, the impact of viral infections on BAFF levels after transplantation - as a potential confounder - was examined. For this purpose, a group of pre-sensitized patients (PRA>0%, (52±24% on average), n=40) was compared with non-sensitized patients (PRA=0%, n=62) and in a subsequent analysis stratification in accordance to the detected BAFF level was performed. Pre-sensitized patients had significantly higher BAFF levels before transplantation and suffered significantly more often from early steroid-resistant, mainly antibody-mediated rejections. A result which was confirmed also in highly sensitized patients with PRA levels >50%. Additionally, in the follow-up patients with either rising BAFF levels over time or BAFF levels above the median also had significantly more often antibody mediated rejections. Additionally, patients with BAFF levels above detected median even displayed impaired creatinine values as well as an induced eGFR slope up to month 48 after transplantation. The occurrence of viral infections (CMV, BKV) was only an additional influencing factor in the absence of concomitant allograft rejections. Therefore, the B-cell proliferation factor BAFF appears not only to reflect the immunological risk profile of patients in the context of kidney transplantation, it may possibly be further developed as a predictor of patients with an increased risk profile for subsequent allograft rejection and impaired allograft function.

Antibody-mediated rejection across solid organ transplants: manifestations, mechanisms, and therapies

Solid organ transplantation is a curative therapy for hundreds of thousands of patients with end-stage organ failure. However, long-term outcomes have not improved, and nearly half of transplant recipients will lose their allografts by 10 years after transplant. One of the major challenges facing clinical transplantation is antibody-mediated rejection (AMR) caused by anti-donor HLA antibodies. AMR is highly associated with graft loss, but unfortunately there are few efficacious therapies to prevent and reverse AMR. This Review describes the clinical and histological manifestations of AMR, and discusses the immunopathological mechanisms contributing to antibody-mediated allograft injury as well as current and emerging therapies.

Antibody response to HBV vaccination on dialysis does not correlate with the development of deNovo anti-HLA antibodies after renal transplantation

BACKGROUND

Response to Hepatitis B virus (HBV) vaccination can be diminished in some (50-80%) but not all dialysis patients. We hypothesized, that the response to vaccination on dialysis may correlate with the development of anti-HLA antibodies after renal transplantation and might therefore be a valuable parameter to predict alloresponses.

METHODS

The response to HBV vaccination on dialysis and the development of deNovo anti-HLA antibodies post-transplant was analyzed in 188 non-immunized renal transplant recipients. The response to HBV vaccination was evaluated by measuring the anti-HBs titer at time of transplantation. Anti-HLA antibodies post-transplant were monitored by serial measurements by means of Luminex. Acute rejection episodes, graft loss and renal dysfunction were assessed within a median follow-up of 5.5years.

RESULTS

One hundred and forty-one patients (75%) exhibited an adequate immune response to HBV vaccination on dialysis. Vaccine responder (R) and none responder (NR) did not differ with respect to age, gender and BMI, while R spend significantly more time on dialysis before transplantation (4.58±3.35 vs 3.23±2.55 years, p=0.033). More NR developed deNovo anti-HLA antibodies (27.7 vs 22.7%, p=0.554) and donor-specific anti-HLA antibodies (23.4 vs 14.2%, p=0.173) in comparison to R. Accordingly, the number of acute rejections was higher in NR as compared to R (36.1 vs 24.1%, p=0.130) while graft survival was similar in both groups.

CONCLUSION

Contrary to our hypothesis antibody response to HBV vaccination on dialysis does not predict the development of anti-HLA antibodies post transplant.

Soluble BAFF Cytokine Levels and Antibody-Mediated Rejection of the Kidney Allograft

The B-cell activating factor (BAFF) cytokine has important functions for the survival and maturation of B lymphocytes, which implies that this cytokine might play a role in the development of antibody-mediated rejection (AMR) after kidney transplantation. In our study, we compared the concentrations of the soluble BAFF cytokine in kidney graft recipients with AMR and patients without rejection with the goal of testing the hypothesis whether BAFF level measurement might be useful as a diagnostic marker of AMR. The study included a cohort of 19 high-risk patients with diagnosed AMR and 17 control patients free of rejection. BAFF was measured in all patients before transplantation, during the rejection episodes, and three months after transplantation in patients free of rejection using the Luminex technique. Before transplantation, the serum concentrations of BAFF in patients with AMR and kidney recipients without rejection did not significantly differ. After transplantation, however, BAFF levels were significantly lower in patients with AMR and also in patients with concurrent humoral and cellular rejection compared with patients without rejection (p < 0.05 and p < 0.01, respectively). No correlation was found between BAFF and the production of donor-specific antibodies (DSA) before and after transplantation. Patients experiencing AMR and simultaneous cellular and AMR had significantly lower concentrations of BAFF in comparison with patients free of rejection.

B Cell Immunity in Solid Organ Transplantation

The contribution of B cells to alloimmune responses is gradually being understood in more detail. We now know that B cells can perpetuate alloimmune responses in multiple ways: (i) differentiation into antibody-producing plasma cells; (ii) sustaining long-term humoral immune memory; (iii) serving as antigen-presenting cells; (iv) organizing the formation of tertiary lymphoid organs; and (v) secreting pro- as well as anti-inflammatory cytokines. The cross-talk between B cells and T cells in the course of immune responses forms the basis of these diverse functions. In the setting of organ transplantation, focus has gradually shifted from T cells to B cells, with an increased notion that B cells are more than mere precursors of antibody-producing plasma cells. In this review, we discuss the various roles of B cells in the generation of alloimmune responses beyond antibody production, as well as possibilities to specifically interfere with B cell activation.

Effect of Treatment With Tabalumab, a B Cell-Activating Factor Inhibitor, on Highly Sensitized Patients With End-Stage Renal Disease Awaiting Transplantation

B cell-activation factor (BAFF) is critical for B cell maturation. Inhibition of BAFF represents an appealing target for desensitization of sensitized end-stage renal disease (ESRD) patients. We conducted a Phase 2a, single-arm, open-label exploratory study investigating the effect of tabalumab (BAFF inhibitor) in patients with ESRD and calculated panel reactive antibodies (cPRAs) >50%. The treatment period duration was 24 weeks. Eighteen patients received tabalumab, at doses of 240-mg subcutaneous (SC) at Week 0 followed by 120-mg SC monthly for 5 additional months. Patients were followed for an additional 52 weeks. Immunopharmacologic effects were characterized through analysis of blood for HLA antibodies, BAFF concentrations, immunoglobulins, T and B cell subsets, as well as pre- and posttreatment tonsil and bone marrow biopsies. Significant reductions in cPRAs were observed at Weeks 16 (p = 0.043) and 36 (p = 0.004); however, absolute reductions were small (<5%). Expected pharmacologic changes in B cell subsets and immunoglobulin reductions were observed. Two tabalumab-related serious adverse events occurred (pneumonia, worsening of peripheral neuropathy), while the most common other adverse events were injection-site pain and hypotension. Three patients received matched deceased donor transplants during follow-up. Treatment with a BAFF inhibitor resulted in statistically significant, but not clinically meaningful reduction in the cPRA from baseline (NCT01200290, Clinicaltrials.gov).

Biomarkers in kidney transplantation: From bench to bedside

Immunosuppressive drug level monitoring and serum creatinine are widely used for kidney transplantation (KT) monitoring. Monitoring of drug level is not the direct measurement of the immune response while the rising of creatinine is too late for detection of allograft injury. Kidney biopsy, the gold standard for KT monitoring, is invasive and may lead to complications. Many biomarkers have been discovered for direct monitoring of the immune system in KT and the benefit of some biomarkers has reached clinical level. In order to use biomarkers for KT monitoring, physicians have to understand the biology including kinetics of each marker. This can guide biomarker selection for specific condition. Herein, we summarize the recent findings of donor specific anti-human leukocyte antigen antibody, B lymphocyte stimulator, interferon-gamma induced protein of 10 kDa, and intracellular adenosine triphosphate monitoring, all of which have very strong evidence support for the clinical use in KT.