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

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.

Seeking Standardized Definitions for HLA-incompatible Kidney Transplants: A Systematic Review

BACKGROUND

There is no standard definition for "HLA incompatible" transplants. For the first time, we systematically assessed how HLA incompatibility was defined in contemporary peer-reviewed publications and its prognostic implication to transplant outcomes.

METHODS

We combined 2 independent searches of MEDLINE, EMBASE, and the Cochrane Library from 2015 to 2019. Content-expert reviewers screened for original research on outcomes of HLA-incompatible transplants (defined as allele or molecular mismatch and solid-phase or cell-based assays). We ascertained the completeness of reporting on a predefined set of variables assessing HLA incompatibility, therapies, and outcomes. Given significant heterogeneity, we conducted narrative synthesis and assessed risk of bias in studies examining the association between death-censored graft failure and HLA incompatibility.

RESULTS

Of 6656 screened articles, 163 evaluated transplant outcomes by HLA incompatibility. Most articles reported on cytotoxic/flow T-cell crossmatches (n = 98). Molecular genotypes were reported for selected loci at the allele-group level. Sixteen articles reported on epitope compatibility. Pretransplant donor-specific HLA antibodies were often considered (n = 143); yet there was heterogeneity in sample handling, assay procedure, and incomplete reporting on donor-specific HLA antibodies assignment. Induction (n = 129) and maintenance immunosuppression (n = 140) were frequently mentioned but less so rejection treatment (n = 72) and desensitization (n = 70). Studies assessing death-censored graft failure risk by HLA incompatibility were vulnerable to bias in the participant, predictor, and analysis domains.

CONCLUSIONS

Optimization of transplant outcomes and personalized care depends on accurate HLA compatibility assessment. Reporting on a standard set of variables will help assess generalizability of research, allow knowledge synthesis, and facilitate international collaboration in clinical trials.

Monitoring of Soluble Forms of BAFF System (BAFF, APRIL, sR-BAFF, sTACI and sBCMA) in Kidney Transplantation

BAFF system plays an essential role in B cells homeostasis and tolerance, although it has widely not been tested in transplantation with doubtful results. The main purpose was to study the BAFF soluble forms and their correlation with acute rejection (AR) and donor-specific antibodies production. Serum levels of BAFF, APRIL, and soluble forms of their receptors were analyzed in renal recipients with and without acute rejection (AR/NAR) appearance. All molecules were evaluated at pre- and post-transplantation. sTACI showed a significant correlation with BAFF and sR-BAFF levels, and sBCMA also showed a positive correlation with sAPRIL levels. A significant increase in sAPRIL levels in patients suffering AR was also found, and ROC curves analysis showed an AUC = 0.724, a concentration of 6.05 ng/ml (sensitivity: 66.7%; specificity: 73.3%), the best cutoff point for predicting AR. In the post-transplant dynamics of sAPRIL levels in the longitudinal cohort, we observed a significant decrease at 3 and 6 month post-transplantation compared to pretransplantation status. We also observed that recipients with high pre-transplant levels of sAPRIL generated antibodies earlier than those with lower sAPRIL levels, although their long-term post-transplantation was not different. Our results show that elevated serum levels of APRIL may be helpful as a biomarker for the diagnosis of AR, although the longitudinal study shows that it is not helpful as a prognostic biomarker.

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.

BAFF signaling drives interstitial transformation of mouse renal tubular epithelial cells in a Pin1-dependent manner

Aberrant expression of B cell–activating factor belonging to TNF superfamily (BAFF) and its receptors results in abnormal biological activities in hematopoietic and non-hematopoietic cells and is closely associated with the occurrence and development of various diseases. However, the biological significance and potential mechanisms underlying BAFF signaling in renal tubular epithelial cells (RTECs) remain unknown. This study aimed to investigate the biological role of BAFF signaling in RTECs. Mice primary RTECs were applied. The proliferation status and apoptotic rates were examined by MTS assay and flow cytometry, respectively. The expression of BAFF and its receptors was analyzed via flow cytometry and sodium ion transport function, and cytokeratin-18 expression was detected through immunofluorescence staining. In addition, Pin1 was knocked down via siRNA and its expression was assessed through reverse transcription PCR. Lastly, western blotting was performed to analyze E-cadherin, ɑ-SMA, and Pin1 expression. Results suggested that BAFF-R was significantly upregulated upon IFN-γ stimulation, and enhancement of BAFF signaling promoted cell survival and reduced their apoptotic rate, while simultaneously reducing the epithelial phenotype and promoting the interstitial transformation of cells. Furthermore, Pin1 was significantly increased, along with the upregulation of BAFF signaling in the RTECs, and participated in interstitial transformation induced by BAFF signaling. Collectively, the present results elucidate the potential mechanism of loss of normal function of RTECs under long-term high dose of BAFF stimulation provides a potential therapeutic target for renal interstitial fibrosis, and underlining mechanisms of shortening of long-term outcomes of kidney allografts via augmenting of BAFF signaling.

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.

B Cell Activating Factor (BAFF) Is Required for the Development of Intra-Renal Tertiary Lymphoid Organs in Experimental Kidney Transplantation in Rats

Intra-renal tertiary lymphoid organs (TLOs) are associated with worsened outcome in kidney transplantation (Ktx). We used an anti-BAFF (B cell activating factor) intervention to investigate whether BAFF is required for TLO formation in a full MHC-mismatch Ktx model in rats. Rats received either therapeutic immunosuppression (no rejection, NR) or subtherapeutic immunosuppression (chronic rejection, CR) and were sacrificed on d56. One group additionally received an anti-BAFF antibody (CR + AB). Intra-renal T (CD3⁺) and B (CD20⁺) cells, their proliferation (Ki67⁺), and IgG⁺ plasma cells were analyzed by immunofluorescence microscopy. Formation of T and B cell zones and TLOs was assessed. Intra-renal expression of TLO-promoting factors, molecules of T:B crosstalk, and B cell differentiation was analyzed by qPCR. Intra-renal B and T cell zones and TLOs were detected in CR and were associated with elevated intra-renal mRNA expression of TLO-promoting factors, including CXCL13, CCL19, lymphotoxin-β, and BAFF. Intra-renal plasma cells were also elevated in CR. Anti-BAFF treatment significantly decreased intra-renal B cell zones and TLO, as well as intra-renal B cell-derived TLO-promoting factors and B cell differentiation markers. We conclude that BAFF-dependent intra-renal B cells promote TLO formation and advance local adaptive alloimmune responses in chronic rejection.

High Pretransplant BAFF Levels and B-cell Subset Polarized towards a Memory Phenotype as Predictive Biomarkers for Antibody-Mediated Rejection

Antibody-mediated rejection (AbMR) is one of the leading causes of graft loss in kidney transplantation and B cells play an important role in the development of it. A B-cell activating factor (BAFF) is a cytokine involved in B cell ontogeny. Here, we analyzed whether B cell maturation and the effect of B cell soluble factors, such as BAFF could be involved in AbMR. Serum BAFF levels and B and T cell subpopulations were analyzed 109 kidney transplant patients before transplantation and at 6 and 12 months after kidney transplantation. Pretransplant serum BAFF levels as well as memory B cell subpopulations were significantly higher in those patients who suffered clinical AbMR during the first 12 months after kidney transplantation. Similar results were observed in the prospective analysis of patients with subclinical antibody-mediated rejection detected in the surveillance biopsy performed at 12 months after kidney transplantation. A multivariate analysis confirmed the independent role of BAFF in the development of AbMR, irrespective of other classical variables. Pretransplant serum BAFF levels could be an important non-invasive biomarker for the prediction of the development of AbMR and posttransplant increased serum BAFF levels contribute to AbMR.

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.

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.