BAFFR activates PI3K/AKT signaling in human naive but not in switched memory B cells through direct interactions with B cell antigen receptors

B Cell Activating Factor Induces Drug Resistance in Hairy Cell Leukemia Variant

Background: Chemoresistance is an existing challenge faced in the treatment of the hairy cell leukemia variant (HCL-v). Classical hairy cell leukemia (HCL-c) is very sensitive to the standard of care with purine nucleoside analogs (PNAs) cladribine (cDa) and pentostatin. However, almost half of these patients eventually become less sensitive to chemotherapy and relapse. HCL-variant (HCL-v) is a biologically distinct entity from HCL-c that is not sensitive to frontline PNA therapy, and this treatment is not recommended for these patients. To address these treatment challenges, we investigated the role of B-cell activating factor (BAFF) in promoting HCL-v cell chemoresistance. Methods: Flow cytometry and quantitative PCR were used to measure the levels of BAFF and its receptors. To determine BAFF activated pathways in HCL-c and HCL-v, the Bonna-12 HCL-c cell line or HCL-v patient-derived cancer cells were stimulated with recombinat BAFF and activation of common BAFF-activated pathways, including the nonclassical nuclear factor kappa B (NF-κB) pathway, the Extracellular Signal-Regulated Kinase (Erk) and phosphatidylinositol-3 (PI-3) kinase (PI3K)/AKT serine/threonine kinase (AKT) pathways were measured by western blotting. To test whether BAFF signaling promotes chemoresistance in HCL-v, we stimulated patient-derived HCL-v cells with BAFF and performed RNA sequencing. Lastly, to confirm the functional implications of BAFF signaling in HCL-v, we treated patient-derived HCL-v cells with exogenous BAFF before treatment with cladribine. Results: We found that HCL-v patient-derived cancer cells express receptors of BAFF at varying degrees and express relatively lower levels of membrane-bound BAFF ligand expression. BAFF stimulation of these cells resulted in substantial activation of the nonclassical NF-κB pathway, which is known to promote anti-apoptotic and pro-survival effects in B-cell cancers. Conversely, in the Bonna-12 cell line, we observed constitutive activation of the nonclassical NF-κB pathway. Through RNA sequencing, we found that BAFF upregulates a myriad of genes that are known to promote chemoresistance in various cancers, including IL1, CXCL1/2, CXCL5, CXCL8, TRAF3, and PTGS2. Lastly, we found that BAFF protects these cells from cladribine-induced cell death in vitro. Conclusions: We conclude that BAFF provides chemo-protection in HCL-v cells by activating nonclassical NF-κB signaling, which results in the upregulation of multiple pro-survival or anti-apoptotic genes. Our results highlight an important role of BAFF in HCL-v resistance to chemotherapy and suggest that the BAFF blockade may enhance the chemosensitivity to PNAs in drug-resistant HCL-v patients.

Early decrease of T-bet+ B cells during subcutaneous belimumab predicts response to therapy in systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is characterized by B cell dysregulation and expansion of atypical B cells that may correlate with disease manifestations and activity. This study investigated the impact of subcutaneous (sc) Belimumab (BLM) on the peripheral B cell compartment and on the functional properties of CD21low, T-bet+ and CD11c+ atypical B cells, in 21 active SLE patients over a 12-month period. At baseline, active SLE patients displayed reduced unswitched IgM memory B cells and expansion of atypical B cells, compared to healthy donors and to SLE patients in remission. sc BLM therapy promptly restored B cell homeostasis with a reduction of T-bet+ B cells, observed early in patients responsive to therapy. These findings highlight the pathogenic role of T-bet+ B cells in SLE disease and suggest their potential utility as biomarker of clinical response.

Signaling Activation and Modulation in Extrafollicular B Cell Responses

The differentiation of naive follicular B cells into either the germinal center (GC) or extrafollicular (EF) pathway plays a critical role in shaping the type, affinity, and longevity of effector B cells. This choice also governs the selection and survival of autoreactive B cells, influencing their potential to enter the memory compartment. During the first 2-3 days following antigen encounter, initially activated B cells integrate activating signals from T cells, Toll-like receptors (TLRs), and cytokines, alongside inhibitory signals mediated by inhibitory receptors. This integration modulates the intensity of signaling, particularly of the PI3K/AKT/mTOR pathway, which plays a central role in guiding developmental decisions. These early signaling events determine whether B cells undergo GC maturation or differentiate rapidly into antibody-secreting cells (ASCs) via the EF pathway. Dysregulation of these signaling pathways-whether through excessive activation or defective regulatory mechanisms-can disrupt the balance between GC and EF fates, predisposing individuals to autoimmunity. Accordingly, aberrant PI3K/AKT/mTOR signaling has been implicated in the defective selection of autoreactive B cells, increasing the risk of autoimmune disease. This review focuses on the signaling events in newly activated B cells, with an emphasis on the induction and regulation of the PI3K/AKT/mTOR pathway. It also highlights gaps in our understanding of how alternative B cell fates are regulated. Both the physiological context and the implications of inborn errors of immunity (IEIs) and complex autoimmune conditions will be discussed in this regard.

TCL1A in naïve B cells as a therapeutic target for type 1 diabetes

BACKGROUND

Type 1 diabetes (T1D) is an autoimmune disease characterised by the attack of pancreatic β cells by "self" immune cells. Although previous studies demonstrated that B cells contribute to T1D through antigen presentation and autoantibody production, the involvement of different populations of B cells, particularly in the early stages of T1D, has not been fully elucidated.

METHODS

In this study, we employed single-cell RNA sequencing (scRNA-seq) and flow cytometry to investigate immune cell populations in patients with newly diagnosed T1D, their relative controls and age-matched healthy controls. Phosphoprotein microarray analysis was employed to investigate changes in protein phosphorylation in B cells. Furthermore, we developed a siRNA-based nanomedicine and evaluated its therapeutic potential in the NOD mouse. The integration of scRNA-seq, flow cytometry, phosphoprotein microarrays, and functional assays established a robust framework for understanding and targeting B cell-mediated autoimmunity in T1D.

FINDINGS

Using single-cell RNA sequencing, we discovered that patients with T1D exhibited increased humoural immunity in the early stage of T1D. Specifically, the population of naïve B cells increased in patients with newly diagnosed T1D who expressed elevated levels of the AKT kinase coactivator TCL1A. Using a protein phosphorylation microarray, we confirmed that TCL1A knockdown specifically impaired AKT2 phosphorylation and affected B cell survival and proliferation. Notably, we discovered that the naïve B cell population increased and TCL1A expression was upregulated in NOD mice that developed T1D. Both the levels of naïve B cells and TCL1A were strongly associated with glucose intolerance in T1D mice. Importantly, treatment with a siRNA-based nanomedicine targeting Tcl1a mRNA effectively reduced the number of naïve B cells, prevented the loss of pancreatic β cells, and improved glucose intolerance in T1D mice.

INTERPRETATION

Using single-cell RNA-seq, we have not only uncovered a naïve B cell specific gene that may contribute to the pathogenesis of T1D but also highlighted the potential of siRNA-based nanomedicine for treating T1D. The clinical translation of these findings offers a new approach for the treatment of T1D.

FUNDING

See Acknowledgements.

Increased Phosphorylation of Intracellular Signaling Molecules Indicates Continuous Activation of Human Autoreactive B-Cells

Many human autoimmune diseases (AIDs) are hallmarked by the presence and persistence of autoreactive B-cells. While autoreactive B-cells may frequently encounter antigens, the signals required to balance and maintain their activation and survival are mostly unknown. Understanding such signals may be important for strategies aimed at eliminating human B-cell autoreactivity. Here, we assessed intracellular signaling pathways in B cells targeting citrullinated protein antigens isolated from patients with rheumatoid arthritis (RA), a common and well-characterized AID. Peripheral blood mononuclear cells of 15 RA patients positive for anti-citrullinated protein antibodies (ACPA) were analyzed directly ex vivo using spectral flow cytometry and B-cell differentiation markers, citrullinated antigen-biotin-streptavidin tetramers, and intracellular (phosphoflow) markers. Tetanus toxoid (TT)-specific B cells served as antigen-specific comparators. In absence of any in vitro BCR stimulation, ACPA-expressing memory B cells (MBCs) displayed enhanced expression of Ki-67 and increased SYK-, BTK-, AKT-, and S6-phosphorylation compared with TT-specific MBCs. We demonstrate the simultaneous detection of B cell antigen-specificity and intracellular protein phosphorylation on the single-cell level. The data reveal that autoreactive B-cells in RA, in contrast to B cells against recall antigens, display enhanced phosphorylation of signaling molecules that point toward continuous, presumably antigen-mediated activation of the autoreactive B-cell compartment.

Unveiling the Immune Landscape of Delirium through Single-Cell RNA Sequencing and Machine Learning: Towards Precision Diagnosis and Therapy

BACKGROUND

Postoperative delirium (POD) poses significant clinical challenges regarding its diagnosis and treatment. Identifying biomarkers that can predict and diagnose POD is crucial for improving patient outcomes.

METHODS

To explore potential biomarkers for POD, we conducted bulk RNA sequencing (bulk-seq) on peripheral blood samples from POD patients and healthy controls. The expression levels of genes downstream of the phosphatidylinositol 3-kinase/protein kinase B (PI3K-Akt) signalling pathway were analysed. We then validated the expression of these genes using quantitative real-time polymerase chain reaction (RT-qPCR) in an independent cohort of 30 healthy controls and 30 POD patients. Receiver operating characteristic (ROC) analysis and six machine learning models were used to evaluate the predictive and diagnostic value of these genes. Additionally, single-cell RNA sequencing (scRNA-seq) was performed to validate gene expression in specific subsets of peripheral blood mononuclear cells (PBMCs), including T-cells, B-cells, natural killer (NK) cells, dendritic cells (DCs), and monocytes.

RESULTS

Bulk-seq revealed increased expression of genes downstream of the PI3K-Akt signalling pathway, specifically CHRM2, IL6, NOS3, NGF, and IL6R, in the peripheral blood of POD patients compared to healthy controls. Conversely, the expression of IGF1 was significantly decreased. RT-qPCR validation confirmed these findings. ROC analysis and machine learning models indicated that these genes are useful for predicting and diagnosing POD. scRNA-seq further validated the expression of these genes in specific PBMC subsets, including T-cells, B-cells, NK cells, DCs, and monocytes, with results consistent with the bulk-seq and RT-qPCR data.

CONCLUSIONS

The abnormal activation of the PI3K-Akt signalling pathway in T-cells, B-cells, NK cells, DCs, and monocytes may serve as potential biomarkers for predicting and diagnosing POD. These findings could inform the development of novel therapeutic strategies for managing POD.

Efficacy of BAFF inhibition and B-cell depletion in non-obese diabetic mice as a spontaneous model for Sjögren's disease

INTRODUCTION

The therapeutic interest of targeting B-cell activating factor (BAFF) in Sjögren's disease (SjD) can be suspected from the results of two phase II clinical trials but has not been evaluated in an animal model of the disease. We aimed to evaluate the therapeutic efficacy of this strategy on dryness and salivary gland (SG) infiltrates in the NOD mouse model of SjD.

MATERIAL AND METHODS

Female NOD mice between ages 10 and 18 weeks were treated with a BAFF-blocking monoclonal antibody, Sandy-2 or an isotype control. Dryness was measured by the stimulated salivary flow. Salivary lymphocytic infiltrates were assessed by immunohistochemistry. Blood, SGs, spleen and lymph-node lymphocyte subpopulations were analysed by flow cytometry. SG mRNA expression was analysed by transcriptomic analysis.

RESULTS

BAFF inhibition significantly decreased SG lymphocytic infiltrates, which was inversely correlated with salivary flow. The treatment markedly decreased B-cell number in SGs, blood, lymph nodes and spleen and increased Foxp3+ regulatory and CD3+CD4-CD8- double negative T-cell numbers in SGs.

CONCLUSION

A monoclonal antibody blocking BAFF and depleting B cells had therapeutic effectiveness in the NOD mouse model of SjD. The increase in regulatory T-lymphocyte populations might underlie the efficacy of this treatment.

The C5AR1/TNFSF13B axis alleviates osteoarthritis by activating the PI3K/Akt/GSK3β/Nrf2/HO-1 pathway to inhibit ferroptosis

Chondrocyte ferroptosis induces the occurrence of osteoarthritis (OA). As a key gene of OA, C5a receptor 1 (C5AR1) is related to ferroptosis. Here, we investigated whether C5AR1 interferes with chondrocyte ferroptosis during OA occurrence. C5AR1 was downregulated in PA-treated chondrocytes. Overexpression of C5AR1 increased the cell viability and decreased ferroptosis in chondrocytes. Moreover, Tumor necrosis factor superfamily member 13B (TNFSF13B) was downregulated in PA-treated chondrocytes, and knockdown of TNFSF13B eliminated the inhibitory effect of C5AR1 on ferroptosis in chondrocytes. More importantly, the PI3K/Akt/GSK3β/Nrf2/HO-1 pathway inhibitor LY294002 reversed the inhibition of C5AR1 or TNFSF13B on ferroptosis in chondrocytes. Finally, we found that C5AR1 alleviated joint tissue lesions and ferroptosis in rats and inhibited the progression of OA in the rat OA model constructed by anterior cruciate ligament transection (ACLT), which was reversed by interfering with TNFSF13B. This study shows that C5AR1 reduces the progression of OA by upregulating TNFSF13B to activate the PI3K/Akt/GSK3β/Nrf2/HO-1 pathway and thereby inhibiting chondrocyte sensitivity to ferroptosis, indicating that C5AR1 may be a potential therapeutic target for ferroptosis-related diseases.

Transcriptomic analysis identifies B-lymphocyte kinase as a therapeutic target for desmoplastic small round cell tumor cancer stem cell-like cells

Desmoplastic small round cell tumor (DSRCT) is an aggressive pediatric cancer caused by the EWSR1-WT1 fusion oncoprotein. The tumor is refractory to treatment with a 5-year survival rate of only 15-25%, necessitating the development of novel therapeutics, especially those able to target chemoresistant subpopulations. Novel in vitro cancer stem cell-like (CSC-like) culture conditions increase the expression of stemness markers (SOX2, NANOG) and reduce DSRCT cell line susceptibility to chemotherapy while maintaining the ability of DSRCT cells to form xenografts. To gain insights into this chemoresistant model, RNA-seq was performed to elucidate transcriptional alterations between DSRCT cells grown in CSC-like spheres and normal 2-dimensional adherent state. Commonly upregulated and downregulated genes were identified and utilized in pathway analysis revealing upregulation of pathways related to chromatin assembly and disassembly and downregulation of pathways including cell junction assembly and extracellular matrix organization. Alterations in chromatin assembly suggest a role for epigenetics in the DSRCT CSC-like state, which was further investigated with ATAC-seq, identifying over 10,000 differentially accessible peaks, including 4444 sphere accessible peaks and 6,120 adherent accessible peaks. Accessible regions were associated with higher gene expression, including increased accessibility of the CSC marker SOX2 in CSC-like culture conditions. These analyses were further utilized to identify potential CSC therapeutic targets, leading to the identification of B-lymphocyte kinase (BLK) as a CSC-enriched, EWSR1-WT1-regulated, druggable target. BLK inhibition and knockdown reduced CSC-like properties, including abrogation of tumorsphere formation and stemness marker expression. Importantly, BLK knockdown reduced DSRCT CSC-like cell chemoresistance, making its inhibition a promising target for future combination therapy.

B-Cell Receptor Signaling and Beyond: The Role of Igα (CD79a)/Igβ (CD79b) in Normal and Malignant B Cells

B-cell receptor (BCR) is a B cell hallmark surface complex regulating multiple cellular processes in normal as well as malignant B cells. Igα (CD79a)/Igβ (CD79b) are essential components of BCR that are indispensable for its functionality, signal initiation, and signal transduction. CD79a/CD79b-mediated BCR signaling is required for the survival of normal as well as malignant B cells via a wide signaling network. Recent studies identified the great complexity of this signaling network and revealed the emerging role of CD79a/CD79b in signal integration. In this review, we have focused on functional features of CD79a/CD79b, summarized signaling consequences of CD79a/CD79b post-translational modifications, and highlighted specifics of CD79a/CD79b interactions within BCR and related signaling cascades. We have reviewed the complex role of CD79a/CD79b in multiple aspects of normal B cell biology and how is the normal BCR signaling affected by lymphoid neoplasms associated CD79A/CD79B mutations. We have also summarized important unresolved questions and highlighted issues that remain to be explored for better understanding of CD79a/CD79b-mediated signal transduction and the eventual identification of additional therapeutically targetable BCR signaling vulnerabilities.

A multimorphic mutation in IRF4 causes human autosomal dominant combined immunodeficiency

Interferon regulatory factor 4 (IRF4) is a transcription factor (TF) and key regulator of immune cell development and function. We report a recurrent heterozygous mutation in IRF4, p.T95R, causing an autosomal dominant combined immunodeficiency (CID) in seven patients from six unrelated families. The patients exhibited profound susceptibility to opportunistic infections, notably Pneumocystis jirovecii, and presented with agammaglobulinemia. Patients' B cells showed impaired maturation, decreased immunoglobulin isotype switching, and defective plasma cell differentiation, whereas their T cells contained reduced TH17 and TFH populations and exhibited decreased cytokine production. A knock-in mouse model of heterozygous T95R showed a severe defect in antibody production both at the steady state and after immunization with different types of antigens, consistent with the CID observed in these patients. The IRF4T95R variant maps to the TF's DNA binding domain, alters its canonical DNA binding specificities, and results in a simultaneous multimorphic combination of loss, gain, and new functions for IRF4. IRF4T95R behaved as a gain-of-function hypermorph by binding to DNA with higher affinity than IRF4WT. Despite this increased affinity for DNA, the transcriptional activity on IRF4 canonical genes was reduced, showcasing a hypomorphic activity of IRF4T95R. Simultaneously, IRF4T95R functions as a neomorph by binding to noncanonical DNA sites to alter the gene expression profile, including the transcription of genes exclusively induced by IRF4T95R but not by IRF4WT. This previously undescribed multimorphic IRF4 pathophysiology disrupts normal lymphocyte biology, causing human disease.

Aberrant B Cell Signaling in Autoimmune Diseases

Aberrant B cell signaling plays a critical in role in various systemic and organ-specific autoimmune diseases. This is supported by genetic evidence by many functional studies in B cells from patients or specific animal models and by the observed efficacy of small-molecule inhibitors. In this review, we first discuss key signal transduction pathways downstream of the B cell receptor (BCR) that ensure that autoreactive B cells are removed from the repertoire or functionally silenced. We provide an overview of aberrant BCR signaling that is associated with inappropriate B cell repertoire selection and activation or survival of peripheral B cell populations and plasma cells, finally leading to autoantibody formation. Next to BCR signaling, abnormalities in other signal transduction pathways have been implicated in autoimmune disease. These include reduced activity of several phosphates that are downstream of co-inhibitory receptors on B cells and increased levels of BAFF and APRIL, which support survival of B cells and plasma cells. Importantly, pathogenic synergy of the BCR and Toll-like receptors (TLR), which can be activated by endogenous ligands, such as self-nucleic acids, has been shown to enhance autoimmunity. Finally, we will briefly discuss therapeutic strategies for autoimmune disease based on interfering with signal transduction in B cells.