CpG-ODN-induced sustained expression of BTLA mediating selective inhibition of human B cells

Single-cell BCR and transcriptome analysis reveals peripheral immune signatures in patients with thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is the most prevalent orbital disease in adults caused by an autoimmune disorder, which can lead to disfigurement and vision impairment. Developing effective treatments for this condition presents challenges due to our limited understanding of its underlying immune aberrations. In this study, we profiled the immune components in the peripheral blood of patients with TAO as well as healthy individuals, utilizing single-cell RNA sequencing and B-cell receptor repertoires (BCR) analysis. We observed a significant reduction in the proportions of regulatory B cells (Bregs) and type 2 conventional dendritic cells (DCs) in patients with TAO during the active phase. Conversely, there was a significant increase in the proportion of type 1 DCs. Further analysis of cell differentiation trajectory revealed potential impairment in the transition of B cells towards Breg phenotype during the active phase of TAO. Besides, the activation process of TAO appeared to involve inflammation and immune dysfunction, as indicated by the dynamic changes in the activities of key regulators. The abnormalities in the peripheral immune system, such as the reduced capacity of Bregs to suppress inflammation, were primarily driven by the enhanced interaction among Breg, DCs, and monocytes (i.e., CD22-PTPRC and BTLA-TNFRSF14). Collectively, our findings offer a comprehensive insight into the molecular regulation and cellular reconfiguration during the active phase of TAO at the single-cell level, in order to explore the pathogenesis of TAO and provide new ideas for the future treatment of TAO.

BTLA biology in cancer: from bench discoveries to clinical potentials

Immune checkpoints play a critical role in maintaining the delicate balance of immune activation in order to prevent potential harm caused by excessive activation, autoimmunity, or tissue damage. B and T lymphocyte attenuator (BTLA) is one of crucial checkpoint, regulating stimulatory and inhibitory signals in immune responses. Its interaction with the herpes virus entry mediator (HVEM) plays an essential role in negatively regulating immune responses, thereby preserving immune homeostasis. In cancer, abnormal cells evade immune surveillance by exploiting checkpoints like BTLA. Upregulated BTLA expression is linked to impaired anti-tumor immunity and unfavorable disease outcomes. In preclinical studies, BTLA-targeted therapies have shown improved treatment outcomes and enhanced antitumor immunity. This review aims to provide an in-depth understanding of BTLA's biology, its role in various cancers, and its potential as a prognostic factor. Additionally, it explores the latest research on BTLA blockade in cancer immunotherapy, offering hope for more effective cancer treatments.

Immune Checkpoint Receptors Signaling in T Cells

The characterization of the receptors negatively modulating lymphocyte function is rapidly advancing, driven by success in tumor immunotherapy. As a result, the number of immune checkpoint receptors characterized from a functional perspective and targeted by innovative drugs continues to expand. This review focuses on the less explored area of the signaling mechanisms of these receptors, of those expressed in T cells. Studies conducted mainly on PD-1, CTLA-4, and BTLA have evidenced that the extracellular parts of some of the receptors act as decoy receptors for activating ligands, but in all instances, the tyrosine phosphorylation of their cytoplasmatic tail drives a crucial inhibitory signal. This negative signal is mediated by a few key signal transducers, such as tyrosine phosphatase, inositol phosphatase, and diacylglycerol kinase, which allows them to counteract TCR-mediated activation. The characterization of these signaling pathways is of great interest in the development of therapies for counteracting tumor-infiltrating lymphocyte exhaustion/anergy independently from the receptors involved.

Attenuation of the BTLA/HVEM Regulatory Network in the Circulation in Primary Sjögren's Syndrome

Primary Sjögren’s syndrome (SjS) is an inflammatory autoimmune disorder which targets the lacrimal and salivary glands, resulting in glandular dysfunction. Currently, the immune drivers of SjS remain poorly understood and peripheral biomarkers of disease are lacking. The present study therefore sought to investigate the immune cell constituents of the SjS peripheral blood, and to assess the role of the BTLA/HVEM/CD160 co-stimulatory network by characterizing expression within the periphery. Peripheral blood mononuclear cells (PBMCs) were isolated from whole blood of n = 10 patients with SjS and n = 10 age- and sex-matched healthy control donors. Cells were divided and stained with three panels of antibodies, allowing assessment of T, B, and myeloid cell subsets, and measurement of BTLA, HVEM, and CD160 surface expression by flow cytometry. We identified distinct alterations in proportions of peripheral T, B, and myeloid cell types in SjS compared with healthy controls. Expression of BTLA/CD160/HVEM and frequency of BTLA/CD160/HVEM-expressing cells were significantly altered in peripheral SjS lymphocytes. The proportion of T cells co-expressing BTLA/HVEM and CD160/HVEM were significantly reduced in SjS. We found decreased BTLA and HVEM levels on peripheral B and T cells of SjS patients, and decreased BTLA/HVEM and CD160/HVEM co-expression, demonstrating dysregulation of the BTLA/HVEM axis in the peripheral blood of SjS patients. These results indicate the potential of targeting the BTLA-HVEM axis for the treatment of SjS.

BTLA Expression in CLL: Epigenetic Regulation and Impact on CLL B Cell Proliferation and Ability to IL-4 Production

In our previous study, while chronic lymphocytic leukemia (CLL) cases showed higher levels of B and T lymphocyte attenuator (BTLA) mRNA compared to controls, lower BTLA protein expression was observed in cases compared to controls. Hence we hypothesize that micro RNA (miR) 155-5p regulates BTLA expression in CLL. In line with earlier data, expression of BTLA mRNA and miR-155-5p is elevated in CLL (p = 0.034 and p = 0.0006, respectively) as well as in MEC-1 cell line (p = 0.009 and 0.016, respectively). Inhibition of miR-155-5p partially restored BTLA protein expression in CLL patients (p = 0.01) and in MEC-1 cell lines (p = 0.058). Additionally, we aimed to evaluate the significance of BTLA deficiency in CLL cells on proliferation and IL-4 production of B cells. We found that secretion of IL-4 is not dependent on BTLA expression, since fractions of BTLA positive and BTLA negative B cells expressing intracellular IL-4 were similar in CLL patients and controls. We demonstrated that in controls the fraction of proliferating cells is lower in BTLA positive than in BTLA negative B cells (p = 0.059), which was not observed in CLL. However, the frequency of BTLA positive Ki67+ B cells in CLL was higher compared to corresponding cells from controls (p = 0.055) while there were no differences between the examined groups regarding frequency of BTLA negative Ki67+ B cells. Our studies suggest that miR-155-5p is involved in BTLA deficiency, affecting proliferation of CLL B cells, which may be one of the mechanisms responsible for CLL pathogenesis.

Immune checkpoints and the multiple faces of B cells in systemic lupus erythematosus

PURPOSE OF REVIEW

B-lymphocytes are crucial in the pathogenesis of systemic lupus erythematosus (SLE), including autoantibody production, antigen presentation, co-stimulation, and cytokine secretion. Co-stimulatory and co-inhibitory molecules control interactions between B and T cells during an inflammatory response, which is essential for an appropriate host protection and maintenance of self-tolerance. Here, we review recent findings about checkpoint molecules and SLE B cells including their potential therapeutic implications and experiences from clinical trials.

RECENT FINDINGS

Most prominent checkpoint molecules involved in pathologic B and T cell interaction in SLE are CD40/CD40L and inducible co-stimulator/ICOSL, both also intimately involved in the formation of germinal centers and ectopic lymphoid tissue. Dysregulations of inhibitory checkpoint molecules, like programmed death-1/programmed death-ligand 1 and B- and T-lymphocyte attenuator have been suggested to impair B cell functions in SLE recently.

SUMMARY

Accumulating evidence indicates that dampening immune responses by either blocking co-activating signals or enhancing co-inhibitory signals in different cell types is a promising approach to treat autoimmune diseases to better control active disease but may also allow resolution of chronic autoimmunity.

BTLA Expression and Function Are Impaired on SLE B Cells

B- and T-lymphocyte attenuator (BTLA/CD272) is an inhibitory checkpoint molecule expressed on T and B cells. Prior studies reported defective function of BTLA by T cells in patients with systemic lupus erythematosus (SLE), whereas nothing is known about its role on B cells in SLE, a disease with various B cell abnormalities. Peripheral blood mononuclear cells (PBMCs) from 23 healthy donors (HD) and 34 SLE patients were stained for BTLA and its expression on B cells was assessed. PBMCs or CD27^-IgD⁺ naive B cells were stimulated together with an activating anti-BTLA antibody or an inhibitor of spleen tyrosine kinase (SYK) and differentiation as well as the expression of activation markers CD71, PD-1 and CD86 were analyzed. Our phenotypic and functional studies revealed reduced BTLA expression on CD27^-IgD⁺ naïve B cells from SLE patients (p=0.0017) related to anti-dsDNA antibody titers (p=0.0394) and SIGLEC-1/CD169 expression on monocytes (p=0.0196), a type I interferon marker related to disease activity. BTLA engagement was found to control CpG/TLR9 activation limiting plasmablast (p=0.0156) and B cell memory induction (p=0.0078) in normal B cells in contrast to other B cell activation pathways (CD40, BCR). These BTLA functions were impaired in SLE B cells. Inhibition of SYK was found to mimic the effects of BTLA activity in vitro. Thus, is it possible that reduced BTLA expression and function of CD27-IgD+ antigen- and T cell-inexperienced SLE B cells could be overcome by SYK inhibition which should be tested in future studies as potential therapeutic principle.

Roles of BTLA in Immunity and Immune Disorders

B and T lymphocyte attenuator (BTLA) is one of the most important cosignaling molecules. It belongs to the CD28 superfamily and is similar to programmed cell death-1 (PD-1) and cytotoxic T lymphocyte associated antigen-4 (CTLA-4) in terms of its structure and function. BTLA can be detected in most lymphocytes and induces immunosuppression by inhibiting B and T cell activation and proliferation. The BTLA ligand, herpesvirus entry mediator (HVEM), does not belong to the classic B7 family. Instead, it is a member of the tumor necrosis factor receptor (TNFR) superfamily. The association of BTLA with HVEM directly bridges the CD28 and TNFR families and mediates broad and powerful immune effects. Recently, a large number of studies have found that BTLA participates in numerous physiopathological processes, such as tumor, inflammatory diseases, autoimmune diseases, infectious diseases, and transplantation rejection. Therefore, the present work aimed to review the existing knowledge about BTLA in immunity and summarize the diverse functions of BTLA in various immune disorders.

Friend or Foe: Prognostic and Immunotherapy Roles of BTLA in Colorectal Cancer

Background

B and T lymphocyte attenuator (BTLA) is a co-signaling protein belonging to the CD28 immunoglobulin superfamily. However, the role of BTLA in prognosis and immunotherapy of colorectal cancer (CRC) remains unclear.

Methods

We evaluated the expression of BTLA via the Oncomine and the cancer genome atlas (TCGA) database. We research the outcome among different BTLA expression patients by Kaplan–Meier curve. We used the Chi-Squared test and Cox regression analysis to identify potential risk factors. Besides, the correlations between BTLA and cancer immune infiltration were investigated via CIBERSORT.

Results

Various cohorts showed that BTLA expression was lower in CRC compared to corresponding normal tissue. Moreover, low BTLA expression was correlated with poor overall survival in TCGA cohorts and Gene Expression Omnibus cohorts (GSE29623 and GSE17536). Low BTLA expression was associated with less lymph node metastasis (p = 0.0123). In the Cox proportional hazards model, BTLA was identified as a favorable prognostic factor. Naive B cells, memory B cells, CD8 T cells, CD4 memory resting T cells, follicular helper T (Tfh) cells, monocytes, resting natural killing (NK) cells, M0 macrophages, M1 macrophages, resting mast cells, and activated mast cells were affected by BTLA expression (all p < 0.01). Correlated immune markers and functional enrichment analysis revealed BTLA functioned in the T cell receptor signaling pathway, B cell receptor signaling pathway, and NK cell-mediated cytotoxicity pathway.

Conclusion

These analyses suggest BTLA is a potential factor for extended survival and closely related to CD8 T cells, Tfh cells, B cells, and NK cells in CRC. We summarize these results that BTLA can be used as a prognostic biomarker and might contribute to developing novel CRC immunological treatment strategies.

A combination of the activation marker CD86 and the immune checkpoint marker B and T lymphocyte attenuator (BTLA) indicates a putative permissive activation state of B cell subtypes in healthy blood donors independent of age and sex

Background

The use of anti-B cell based therapies in immune-mediated diseases targeting general B cell markers or molecules important for B cell function has increased the clinical needs of monitoring B cell subpopulations.

Results

We analyzed the expression profile of cell surface markers CD86 and B and T lymphocyte attenuator (BTLA) in B cell subtypes using flow cytometry, including naïve, transitional, switched memory, non-switched memory and double-negative memory B cells and plasmablasts, and investigated the dependence of age and sex in a healthy adult blood donor population. The switched memory B cell subtype displayed a divergent expression of the markers, with increased CD86 and decreased BTLA as compared to non-switched and double negative memory cells, as well as compared to naïve B cells. Plasmablasts expressed highly increased CD86 compared to all other subtypes and a decreased expression of BTLA compared to naïve cells, but still higher compared to the memory cell populations. Transitional B cells had CD86 and BTLA expression similar to the other naïve cells.

Conclusions

We show divergent expression of CD86 and BTLA in memory cells and plasmablasts compared to naïve B cells independent of age and sex. Furthermore, a similarly divergent difference of expression pattern was seen between the memory cell subtypes, altogether indicating that the combination of CD86 and BTLA might be markers for a permissive activation state. We suggest the combination of CD86 and BTLA expression on B cell subtypes as a potentially important tool in monitoring the status of B cell subtypes before and after treatments influencing the B cell compartment.

BTLA/HVEM Signaling: Milestones in Research and Role in Chronic Hepatitis B Virus Infection

B- and T-lymphocyte attenuator (BTLA) is an immune-regulatory receptor, similar to CTLA-4 and PD-1, and is mainly expressed on B-, T-, and all mature lymphocyte cells. Herpes virus entry mediator (HVEM)-BTLA plays a critical role in immune tolerance and immune responses which are areas of intense research. However, the mechanisms of the BTLA and the BTLA/HVEM signaling pathway in human diseases remain unclear. This review describes the research milestones of BTLA and HVEM in chronological order and their role in chronic HBV infection.

Defective BTLA functionality is rescued by restoring lipid metabolism in lupus CD4+ T cells

Coinhibitory receptors play an important role in the prevention of autoimmune diseases, such as systemic lupus erythematosus (SLE), by limiting T cell activation. B and T lymphocyte attenuator (BTLA) is an inhibitory receptor, similar to cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and programmed death 1 (PD1), that negatively regulates the immune response. The role of BTLA in the pathogenesis of autoimmune diseases in humans and, more specifically, in SLE is largely unknown. We investigated BTLA expression on various T cell subsets, and we did not observe significant variations of BTLA expression between lupus patients and healthy controls. However, the enhancement of BTLA expression after activation was significantly lower in SLE patients compared with that in healthy controls. Furthermore, we found an impaired capacity of BTLA to inhibit T cell activation in SLE due to a poor BTLA recruitment to the immunological synapse following T cell stimulation. Finally, we demonstrated that defective BTLA function can be corrected by restoring intracellular trafficking and by normalizing the lipid metabolism in lupus CD4+ T cells. Collectively, our results evidence that the BTLA signaling pathway is altered in SLE T cells and highlight the potential of targeting this pathway for the development of new therapeutic strategies in lupus.

B Lymphocytes in Multiple Sclerosis: Bregs and BTLA/CD272 Expressing-CD19+ Lymphocytes Modulate Disease Severity

B lymphocytes contribute to the pathogenesis of Multiple Sclerosis (MS) by secreting antibodies and producing cytokines. This latter function was analyzed in myelin olygodendrocyte protein (MOG)-stimulated CD19+ B lymphocytes of 71 MS patients with different disease phenotypes and 40 age-and sex-matched healthy controls (HC). Results showed that: 1) CD19+/TNFα+, CD19+/IL-12+ and CD19+/IFNγ+ lymphocytes are significantly increased in primary progressive (PP) compared to secondary progressive (SP), relapsing-remitting (RR), benign (BE) MS and HC; 2) CD19+/IL-6+ lymphocytes are significantly increased in PP, SP and RR compared to BEMS and HC; and 3) CD19+/IL-13+, CD19+/IL-10+, and CD19+/IL-10+/TGFβ+ (Bregs) B lymphocytes are reduced overall in MS patients compared to HC. B cells expressing BTLA, a receptor whose binding to HVEM inhibits TcR-initiated cytokine production, as well as CD19+/BTLA+/IL-10+ cells were also significantly overall reduced in MS patients compared to HC. Analyses performed in RRMS showed that fingolimod-induced disease remission is associated with a significant increase in Bregs, CD19+/BTLA+, and CD19+/BTLA+/IL-10+ B lymphocytes. B lymphocytes participate to the pathogenesis of MS via the secretion of functionally-diverse cytokines that might play a role in determining disease phenotypes. The impairment of Bregs and CD19+/BTLA+ cells, in particular, could play an important pathogenic role in MS.

Loss of marginal zone B-cells in SHIVSF162P4 challenged rhesus macaques despite control of viremia to low or undetectable levels in chronic infection

Marginal zone (MZ) B cells generate T-independent antibody responses to pathogens before T-dependent antibodies arise in germinal centers. They have been identified in cynomolgus monkeys and monitored during acute SIV infection, yet have not been well-studied in rhesus macaques. Here we characterized rhesus macaque MZ B cells, present in secondary lymphoid tissue but not peripheral blood, as CD19(+), CD20(+), CD21(hi), IgM(+), CD22(+), CD38(+), BTLA(+), CD40(+), CCR6(+) and BCL-2(+). Compared to healthy macaques, SHIVSF162P4-infected animals showed decreased total B cells and MZ B cells and increased MZ B cell Ki-67 expression early in chronic infection. These changes persisted in late chronic infection, despite viremia reductions to low or undetectable levels. Expression levels of additional phenotypic markers and RNA PCR array analyses were in concert with continued low-level activation and diminished function of MZ B cells. We conclude that MZ B-cell dysregulation and dysfunction associated with SIV/HIV infection are not readily reversible.

Tertiary Lymphoid Structure-Associated B Cells are Key Players in Anti-Tumor Immunity

It is now admitted that the immune system plays a major role in tumor control. Besides the existence of tumor-specific T cells and B cells, many studies have demonstrated that high numbers of tumor-infiltrating lymphocytes are associated with good clinical outcome. In addition, not only the density but also the organization of tumor-infiltrating immune cells has been shown to determine patient survival. Indeed, more and more studies describe the development within the tumor microenvironment of tertiary lymphoid structures (TLS), whose presence has a positive impact on tumor prognosis. TLS are transient ectopic lymphoid aggregates displaying the same organization and functionality as canonical secondary lymphoid organs, with T-cell-rich and B-cell-rich areas that are sites for the differentiation of effector and memory T cells and B cells. However, factors favoring the emergence of such structures within tumors still need to be fully characterized. In this review, we survey the state of the art of what is known about the general organization, induction, and functionality of TLS during chronic inflammation, and more especially in cancer, with a particular focus on the B-cell compartment. We detail the role played by TLS B cells in anti-tumor immunity, both as antigen-presenting cells and tumor antigen-specific antibody-secreting cells, and raise the question of the capacity of chemotherapeutic and immunotherapeutic agents to induce the development of TLS within tumors. Finally, we explore how to take advantage of our knowledge on TLS B cells to develop new therapeutic tools.