Follicular Helper T (Tfh) Cells in Autoimmune Diseases and Allograft Rejection

Epigenetic reprogramming of T cells: unlocking new avenues for cancer immunotherapy

T cells, a key component of cancer immunotherapy, undergo a variety of histone modifications and DNA methylation changes since their bone marrow progenitor stages before developing into CD8+ and CD4+ T cells. These T cell types can be categorized into distinct subtypes based on their functionality and properties, such as cytotoxic T cells (Tc), helper T cells (Th), and regulatory T cells (Treg) as subtypes for CD8+ and CD4+ T cells. Among these, the CD4+ CD25+ Tregs potentially contribute to cancer development and progression by lowering T effector (Teff) cell activity under the influence of the tumor microenvironment (TME). This contributes to the development of therapeutic resistance in patients with cancer. Subsequently, these individuals become resistant to monoclonal antibody therapy as well as clinically established immunotherapies. In this review, we delineate the different epigenetic mechanisms in cancer immune response and its involvement in therapeutic resistance. Furthermore, the possibility of epi-immunotherapeutic methods based on histone deacetylase inhibitors and histone methyltransferase inhibitors are under investigation. In this review we highlight EZH2 as the principal driver of cancer cell immunoediting and an immune escape regulator. We have addressed in detail how understanding T cell epigenetic regulation might bring unique inventive strategies to overcome drug resistance and increase the efficacy of cancer immunotherapy.

Single-Cell Genomics for Investigating Pathogenesis of Inflammatory Diseases

Recent technical advances have enabled unbiased transcriptomic and epigenetic analysis of each cell, known as "single-cell analysis". Single-cell analysis has a variety of technical approaches to investigate the state of each cell, including mRNA levels (transcriptome), the immune repertoire (immune repertoire analysis), cell surface proteins (surface proteome analysis), chromatin accessibility (epigenome), and accordance with genome variants (eQTLs; expression quantitative trait loci). As an effective tool for investigating robust immune responses in coronavirus disease 2019 (COVID-19), many researchers performed single-cell analysis to capture the diverse, unbiased immune cell activation and differentiation. Despite challenges elucidating the complicated immune microenvironments of chronic inflammatory diseases using existing experimental methods, it is now possible to capture the simultaneous immune features of different cell types across inflamed tissues using various single-cell tools. In this review, we introduce patient-based and experimental mouse model research utilizing single-cell analyses in the field of chronic inflammatory diseases, as well as multi-organ atlas targeting immune cells.

Transcriptional and Epigenetic Regulation of Context-Dependent Plasticity in T-Helper Lineages

Th cell lineage determination and functional specialization are tightly linked to the activation of lineage-determining transcription factors (TFs) that bind cis-regulatory elements. These lineage-determining TFs act in concert with multiple layers of transcriptional regulators to alter the epigenetic landscape, including DNA methylation, histone modification and three-dimensional chromosome architecture, in order to facilitate the specific Th gene expression programs that allow for phenotypic diversification. Accumulating evidence indicates that Th cell differentiation is not as rigid as classically held; rather, extensive phenotypic plasticity is an inherent feature of T cell lineages. Recent studies have begun to uncover the epigenetic programs that mechanistically govern T cell subset specification and immunological memory. Advances in next generation sequencing technologies have allowed global transcriptomic and epigenomic interrogation of CD4+ Th cells that extends previous findings focusing on individual loci. In this review, we provide an overview of recent genome-wide insights into the transcriptional and epigenetic regulation of CD4+ T cell-mediated adaptive immunity and discuss the implications for disease as well as immunotherapies.

Lactobacillus improves the effects of prednisone on autoimmune hepatitis via gut microbiota-mediated follicular helper T cells

Background

Autoimmune hepatitis (AIH) is a chronic, immune-mediated liver dysfunction. The gut microbiota and T follicular helper (Tfh) cells play critical roles in the immunopathogenesis and progression of AIH. We aimed to investigate the effect of gut microbiota combined with prednisone therapy on Tfh cell response in AIH.

Methods

Samples from AIH patients and mouse model of experimental autoimmune hepatitis (EAH) were analyzed using real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, flow cytometry, and hematoxylin–eosin staining to determine the role of gut microbiota on AIH.

Results

Lactobacillus significantly increased the levels of Bacteroides fragilis, Clostridium, Clostridium leptum, Bifidobacterium, and Lactobacillus and significantly enhanced the suppressive effects of prednisone on the levels of AIH clinical indexes in AIH patients. Lactobacillus exerts the same prptective effects as prednisone in EAH mice and enhanced the effects of prednisone. Lactobacillus also reinforced the inhibitory effects of prednisone on the levels of serum IL-21 and the proportions of Tfh cells in peripheral blood mononuclear cells. Mechanistically, prednisone and Lactobacillus regulated Tfh cell response in EAH mice in an MyD88/NF-κB pathway-dependent manner.

Conclusion

Our results suggested a therapeutic potential of Lactobacillus in the prednisone-combined treatment of AIH.

Altered B cell compartment associated with Tfh cells in children with Henoch-Schonlein Purpura

AIM

IgA-producing B cells have been found to be associated with children diagnosed with Henoch-Schonlein purpura (HSP). The aim of the present study was to determine whether children with HSP possess altered B-cell subsets.

METHODS

A total of 14 children diagnosed with HSP and age- and sex-matched healthy controls (HCs) were enrolled in our study. Peripheral blood mononuclear cells were isolated, and the percentage and absolute number of B-cell subsets and Follicular helper T (Tfh) cells were determined by flow cytometry. Finally, Spearman's correlation coefficient was used to analyse the correlation between the percentage of Tfh cells and B-cell subsets.

RESULTS

We found that compared to HCs, the frequency and absolute number of total B cells were significantly higher in children with HSP, but the percentages of plasma cells and naïve B cells were significantly lower. A significantly increased percentage and absolute number of memory nonswitched B cells were found in children with HSP compared with HCs. We observed that the expression of C-X-C chemokine receptor type 5 (CXCR5) on total CD4⁺ T cells and the percentage of CD4⁺CXCR5⁺ cells were significantly increased in patients with HSP. Moreover, significantly correlations between Tfh cells and various B-cell subsets were observed.

CONCLUSIONS

Our study showed a Tfh-cell-associated altered B cell compartment in children with HSP.

Supraphysiological estradiol promotes human T follicular helper cell differentiation and favours humoural immunity during in vitro fertilization

During pregnancy, humoural immunity is essential for protection against many extracellular pathogens; however, autoimmune diseases may be induced or aggravated. T follicular helper (Tfh) cells contribute to humoural immunity. The aim of this study was to test whether Tfh cell function can be manipulated via hormones. Seventy‐four women who underwent in vitro fertilization were recruited and divided into four groups: menstrual period (MP), controlled ovarian hyperstimulation (COH), embryo transfer (ET) and pregnant after embryo transfer (P). A flow cytometry analysis was performed to identify Tfh cells in peripheral blood mononuclear cells (PBMCs). Bioinformatics analysis revealed a possible pathway between Tfh and B cells. Enzyme‐linked immunosorbent assays were used to detect interleukin (IL)‐21 and IL‐6. The quantitative polymerase chain reaction was performed to quantify BCL‐6, BACH2, XBP‐1, IRF‐4 and G protein‐coupled (GP)ER‐1 mRNA expression. Compared with the MP group, the COH, ET and P groups showed more Tfh and B cells, as well as higher IL‐21, IL‐6, BCL‐6 and BACH2 expression. Furthermore, Tfh cell frequency in PBMCs, as well as serum IL‐21 and IL‐6 levels, were all positively correlated with serum estradiol (E₂) levels; the B cell percentage also correlated positively with Tfh cells in PBMCs. Combined with the bioinformatics analysis, XBP‐1, IRF‐4 and GPER‐1 expression was related to E₂ levels, both in vivo and in vitro. We speculate that E₂ augments Tfh cells and favours humoural immunity. This study indicates that Tfh cell regulation may be a novel target in maintaining the maternal‐foetal immune balance.

HIF1α-Dependent Metabolic Signals Control the Differentiation of Follicular Helper T Cells

Follicular helper T (T_FH) cells are critical for germinal center (GC) formation and are responsible for effective B cell-mediated immunity; metabolic signaling is an important regulatory mechanism for the differentiation of T_FH cells. However, the precise roles of hypoxia inducible factor (HIF) 1α-dependent glycolysis and oxidative phosphorylation (OXPHOS) metabolic signaling remain unclear in T_FH cell differentiation. Herein, we investigated the effects of glycolysis and OXPHOS on T_FH cell differentiation and GC responses using a pharmacological approach in mice under a steady immune status or an activated immune status, which can be caused by foreign antigen stimulation and viral infection. GC and T_FH cell responses are related to signals from glycolytic metabolism in mice of different ages. Foreign, specific antigen-induced GC, and T_FH cell responses and metabolic signals are essential upon PR8 infection. Glycolysis and succinate-mediated OXPHOS are required for the GC response and T_FH cell differentiation. Furthermore, HIF1α is responsible for glycolysis- and OXPHOS-induced alterations in the GC response and T_FH cell differentiation under steady or activated conditions in vivo. Blocking glycolysis and upregulating OXPHOS signaling significantly recovered T_FH cell differentiation upon PR8 infection and ameliorated inflammatory damage in mice. Thus, our data provide a comprehensive experimental basis for fully understanding the precise roles of HIF1α-mediated glycolysis and OXPHOS metabolic signaling in regulating the GC response and T_FH cell differentiation during stable physiological conditions or an antiviral immune response.

Curcumin Elevates TFH Cells and Germinal Center B Cell Response for Antibody Production in Mice

Curcumin is a natural product extracted from Curcuma longa. It has been reported as a potent antioxidant and anti-inflammatory compound. Previous studies have demonstrated that curcumin suppresses pro-inflammatory cytokine production via inhibition of NF-κB in macrophages. However, its role in adaptive immune cells such as T cells, in vivo, has not clearly been elucidated. Here, we examined the effects of curcumin in T follicular helper (T_FH) cells and on Ab production during NP-ovalbumin immunization in mice. The results revealed that curcumin administered daily significantly increased CXCR5⁺B-cell lymphoma 6⁺ T_FH cells and CD95⁺GL-7⁺ germinal center (GC) B cells in draining lymph nodes. In addition, curcumin treatment in mice induced total Ab production as well as high affinity IgG1 and IgG2b Ab production. Collectively, these results suggest that curcumin has positive regulatory roles in T_FH cell functions and GC responses. Thus, this could be an advantageous supplement to enhance humoral immunity against infectious diseases and cancer.

The Kinase Complex mTOR Complex 2 Promotes the Follicular Migration and Functional Maturation of Differentiated Follicular Helper CD4+ T Cells During Viral Infection

Follicular helper CD4⁺ T (T_FH) cells are critical for optimal B-cell-mediated humoral immunity by initiating, fueling, and sustaining germinal center reactions. The differentiation of T_FH cells relies on multiple intrinsic and extrinsic factors; however, the details by which these factors are integrated to coordinate T_FH differentiation are largely unknown. In this study, using a mouse model of acute lymphocytic choriomeningitis virus (LCMV) viral infection, we demonstrate that mTOR complex 2 (mTORC2) kinase integrates TCR signaling and ICOS-mediated co-stimulation to promote late differentiation and functional maturation of virus-specific T_FH cells. Specifically, mTORC2 functions to maintain T_FH lineage specifications, including phenotypes, migratory characteristics, and functional properties. Thus, our results highlight the importance of mTORC2 in guarding T_FH phenotypic and functional maturation.

CCL2 deficient mesenchymal stem cells fail to establish long-lasting contact with T cells and no longer ameliorate lupus symptoms

Systemic lupus erythematosus (SLE) is a multi-organ autoimmune disease characterized by autoantibody production. Mesenchymal stem cells (MSCs) ameliorate SLE symptoms by targeting T cells, whereas the mechanisms of their efficacy remain incompletely understood. In this study, we show that transfer of human MSCs increased MRL.Fas^lpr mouse survival, decreased T cell infiltration in the kidneys, and reduced T cell cytokine expression. In vitro, allogeneic mouse MSCs inhibited MRL.Fas^lpr T cell proliferation and cytokine production. Time-lapse imaging revealed that MSCs recruited MRL.Fas^lpr T cells establishing long-lasting cellular contacts by enhancing T cell VCAM-1 expression in a CCL2-dependent manner. In contrast, CCL2 deficient MSCs did not induce T cell migration and VCAM-1 expression, resulting in insufficient cell-cell contact. Consequently, CCL2 deficient MSCs did not inhibit IFN-γ production by T cells and upon transfer no longer prolonged survival of MRL.Fas^lpr mice. Taken together, our imaging study demonstrates that CCL2 enables the prolonged MSC-T cell interactions needed for sufficient suppression of autoreactive T cells and helps to understand how MSCs ameliorate symptoms in lupus-prone MRL.Fas^lpr mice.