T Follicular Regulatory Cells Research Articles

Id1 expression in CD4 T cells promotes differentiation and function of follicular helper T cells and upregulation of related functional molecules.

Although the roles of E proteins and inhibitors of DNA-binding (Id) in T follicular helper (TFH) and T follicular regulatory (TFR) cells have been previously reported, direct models demonstrating the impact of multiple E protein members have been lacking. To suppress all E proteins including E2A, HEB and E2-2, we overexpressed Id1 in CD4 cells using a CD4-Id1 mouse model, to observe any changes in TFH and TFR cell differentiation. Our objective was to gain better understanding of the roles that E proteins and Id molecules play in the differentiation of TFH and TFR cells. The CD4-Id1 transgenic (TG) mice that we constructed overexpressed Id1 in CD4 cells, inhibiting E protein function. Our results showed an increase in the proportion and absolute numbers of Treg, TFH and TFR cells in the spleen of TG mice. Additionally, the expression of surface characterisation molecules PD-1 and ICOS was significantly upregulated in TFH and TFR cells. The study also revealed a downregulation of the marginal zone B cell precursor and an increase in the activation and secretion of IgG1 in spleen B cells. Furthermore, the peripheral TFH cells of TG mice enhanced the function of assisting B cells. RNA sequencing results indicated that a variety of TFH-related functional molecules were upregulated in TFH cells of Id1 TG mice. In conclusion, E proteins play a crucial role in regulating TFH/TFR cell differentiation and function and suppressing E protein activity promotes germinal centre humoral immunity, which has important implications for immune regulation and treating related diseases.

Sarcoidosis-related autoimmune inflammation in COVID-19 convalescent patients.

Currently, there are a large number of reports about the development of autoimmune conditions after COVID-19. Also, there have been cases of sarcoid-like granulomas in convalescents as a part of the post-COVID-19 syndrome. Since one of the etiological theories of sarcoidosis considers it to be an autoimmune disease, we decided to study changes in the adaptive humoral immune response in sarcoidosis and SARS-CoV-2 infection and to find out whether COVID-19 can provoke the development of sarcoidosis. This review discusses histological changes in lymphoid organs in sarcoidosis and COVID-19, changes in B cell subpopulations, T-follicular helper cells (Tfh), and T-follicular regulatory cells (Tfr), and analyzes various autoantibodies detected in these pathologies. Based on the data studied, we concluded that SARS-CoV-2 infection may cause the development of autoimmune pathologies, in particular contributing to the onset of sarcoidosis in convalescents.

CARD11 gain-of-function mutation drives cell-autonomous accumulation of PD-1+ ICOShigh activated T cells, T-follicular, T-regulatory and T-follicular regulatory cells.

Germline CARD11 gain-of-function (GOF) mutations cause B cell Expansion with NF-κB and T cell Anergy (BENTA) disease, whilst somatic GOF CARD11 mutations recur in diffuse large B cell lymphoma (DLBCL) and in up to 30% of the peripheral T cell lymphomas (PTCL) adult T cell leukemia/lymphoma (ATL), cutaneous T cell lymphoma (CTCL) and Sezary Syndrome. Despite their frequent acquisition by PTCL, the T cell-intrinsic effects of CARD11 GOF mutations are poorly understood. Here, we studied B and T lymphocytes in mice with a germline Nethyl-N-nitrosourea (ENU)-induced Card11M365K mutation identical to a mutation identified in DLBCL and modifying a conserved region of the CARD11 coiled-coil domain recurrently mutated in DLBCL and PTCL. Our results demonstrate that CARD11.M365K is a GOF protein that increases B and T lymphocyte activation and proliferation following antigen receptor stimulation. Germline Card11M365K mutation was insufficient alone to cause B or T-lymphoma, but increased accumulation of germinal center (GC) B cells in unimmunized and immunized mice. Card11M365K mutation caused cell-intrinsic over-accumulation of activated T cells, T regulatory (TREG), T follicular (TFH) and T follicular regulatory (TFR) cells expressing increased levels of ICOS, CTLA-4 and PD-1 checkpoint molecules. Our results reveal CARD11 as an important, cell-autonomous positive regulator of TFH, TREG and TFR cells. They highlight T cell-intrinsic effects of a GOF mutation in the CARD11 gene, which is recurrently mutated in T cell malignancies that are often aggressive and associated with variable clinical outcomes.

P-392 Peripheral blood naïve Treg (nTreg) cell subsets and implantation success in patients undergoing in vitro fertilization (IVF) treatment

Abstract Study question Which populations of circulating Treg cells, based on immunophenotyping with thirteen color flow cytometry and analysis with clustering algorithms play a role in implantation? Summary answer The phenotype of subpopulation within Treg cells that was most significantly increased in women who became pregnant was nTreg-like phenotype, which lacked CXCR5 expression. What is known already There are indications that Treg lymphocytes mediated immuno-regulatory mechanisms contribute to the occurrence of idiopathic infertility. Findings of studies indicate that higher nTreg cell subsets were associated with successful IVF treatment. These findings suggest that changes in the composition of the nTreg subset may allow increased tolerance induction during implantation. More detailed characterization of the Tregs in blood samples from women undergoing IVF/ICSI treatment has not been performed and the degree of heterogeneity of among these cells has not been studied to date. Using 13-color flow cytometry Tregs cells can be divided into multiple complex subsets based on different markers. Study design, size, duration This prospective observational study included 36 patients undergoing IVF/ICSI treatment. Blood samples for 13-color flow cytometry, UMAP and FlowSOM cell clustering analyses were obtained from 19 patients undergoing controlled ovarian hyperstimulation and 17 patients undergoing vitrified-warmed blastocysts transfer (FET) in the natural cycle on the day of optimal blastocysts transfer, for data analysis GraphPad Prism was used. The study was performed between March 2020 and October 2021. Participants/materials, setting, methods In this study peripheral blood Treg cells composition was determined. We analyzed the phenotype of populations over or under-represented in samples from women who became pregnant compared to the women who did not within Treg cells. Treg cells were analyzed by both standard gating flow cytometry analysis and clustered by algorithms according to their level of expression of cell surface markers: CD25 (IL-2Rα), CD127 (IL-7Rα), CCR7, CXCR5, CD28, CD38, CD161, CD31, CD45RA, HLA-DR and CD15s. Main results and the role of chance Thirteen color flow cytometry and dimensionality reduction analyses were carried out, using the UMAP and FlowSOM cell clustering algorithms. Combining these tools, we were able to analyze the phenotype of populations in samples from women who became pregnant ( n = 23) compared to the women who did not (n = 13) within Treg cells. FlowSOM identified 15 phenotypically distinct populations within Treg cells. The most prevalent population that was increased in women who became pregnant was nTreg-like phenotype, which lacked CXCR5 expression. This related to our results by standard gating, where we observed that the percentage of CXCR5-nTreg cells and CD31+RTEnTreg cells within CD25+CD127low Treg cells was significantly higher in pregnant women (p = 0.003; p = 0.0162, respectively). Pregnant females had significantly higher percentage of CD45RA+nTreg cells within CD25hiCD127low Treg cells (p = 0.0162) which was in good correlation with the percentage of CD45RA+FOXP3low nTreg cells within CD25+FOXP3+ Treg cells (p < 0.0001). Furthermore, the percentage of CD45RA+FOXP3+low nTreg cells within CD25+FOXP3+ Treg cells was significantly higher in pregnant women (p = 0.045). Meanwhile, the percentage of CD45RA-FOXP3hi effector (eTreg) Treg cells within CD25+FOXP3 Treg cells was lower in pregnant women (p = 0.0238). Finally, women who achieve a pregnancy had significantly lower percentage of CD45RA-FOXP3hiCD15s+eTreg cells within CD25+FOXP3+ Treg cells (p = 0.0233). Limitations, reasons for caution This study has some limitations. The sample size is too small. Standard gating in flow cytometry has the limitation of analysing only few markers at a time in a flow plot, the levels of expression of the markers are not considered, as an alternative, dimensionality reduction analyses were carried out. Wider implications of the findings Our findings imply that the composition of distinct populations within nTreg cells can influence the women’s chance of becoming pregnant, especially nTreg cells, lacking CXCR5 expression, which distingushes T-follicular regulatory cells. Findings help us to understand the role of nTreg subpopulations in process of implantation in women undergoing IVF/ICSI treatment. Trial registration number not applicable

TFR Cells Express Functional CCR6 But It Is Dispensable for Their Development and Localization During Splenic Humoral Immune Responses.

Follicular T cells including T follicular helper (TFH) and T follicular regulatory (TFR) cells are essential in supporting and regulating the quality of antibody responses that develop in the germinal centre (GC). Follicular T cell migration during the propagation of antibody responses is largely attributed to the chemokine receptor CXCR5, however CXCR5 is reportedly redundant in migratory events prior to formation of the GC, and CXCR5-deficient TFH and TFR cells are still capable of localizing to GCs. Here we comprehensively assess chemokine receptor expression by follicular T cells during a model humoral immune response in the spleen. In addition to the known follicular T cell chemokine receptors Cxcr5 and Cxcr4, we show that follicular T cells express high levels of Ccr6, Ccr2 and Cxcr3 transcripts and we identify functional expression of CCR6 protein by both TFH and TFR cells. Notably, a greater proportion of TFR cells expressed CCR6 compared to TFH cells and gating on CCR6+CXCR5hiPD-1hi T cells strongly enriched for TFR cells. Examination of Ccr6-/- mice revealed that CCR6 is not essential for development of the GC response in the spleen, and mixed bone marrow chimera experiments found no evidence for an intrinsic requirement for CCR6 in TFR cell development or localisation during splenic humoral responses. These findings point towards multiple functionally redundant chemotactic signals regulating T cell localisation in the GC.

Restoration of Follicular T Regulatory/Helper Cell Balance by OX40L-JAG1 Cotreatment Suppresses Lupus Nephritis in NZBWF1/j Mice.

Class-switched antinuclear autoantibodies produced by T follicular helper (TFH) cell-dependent germinal center (GC) B cell response play an essential pathogenic role in lupus nephritis (LN). The role of T follicular regulatory (TFR) cells, an effector subset of CD4+Foxp3+ T regulatory cells (Tregs), which are specialized in suppressing TFH-GC response and Ab production, remains elusive in LN. Contrasting reports have shown increased/reduced circulating TFR cells in human lupus that might not accurately reflect their presence in the GCs of relevant lymphoid organs. In this study, we report a progressive reduction in TFR cells and decreased TFR/TFH ratio despite increased Tregs in the renal lymph nodes of NZBWF1/j mice, which correlated with increased GC-B cells and proteinuria onset. Cotreatment with soluble OX40L and Jagged-1 (JAG1) proteins increased Tregs, TFR cells, and TFR/TFH ratio, with a concomitant reduction in TFH cells, GC B cells, and anti-dsDNA IgG Ab levels, and suppressed LN onset. Mechanistic studies showed attenuated TFH functions and diminished GC events such as somatic hypermutation and isotype class-switching in OX40L-JAG1-treated mice. RNA sequencing studies revealed inhibition of hypoxia-inducible factor 1-α (HIF-1a) and STAT3 signaling in T conventional cells from OX40L-JAG1-treated mice, which are critical for the glycolytic flux and differentiation into TFH cell lineage. Therefore, the increased TFR/TFH ratio seen in OX40L-JAG1-treated mice could involve both impaired differentiation of TFH cells from T conventional cells and expansion of TFR cells. We show a key role for GC-TFR/TFH imbalance in LN pathogenesis and how restoring homeostatic balance can suppress LN.

Development of allergen-specific IgE in a food-allergy model requires precisely timed B cell stimulation and is inhibited by Fgl2.

SUMMARYImmunoglobulin E (IgE) responses are a central feature of allergic disease. Using a well-established food-allergy model in mice, we show that two sensitizations with cognate B cell antigen (Ag) and adjuvant 7 days apart promotes optimal development of IgE+ germinal center (GC) B cells and high-affinity IgE production. Intervals of 3 or 14 days between Ag sensitizations lead to loss of IgE+ GC B cells and an undetectable IgE response. The immunosuppressive factors Fgl2 and CD39 are down-regulated in T follicular helper (TFH) cells under optimal IgE-sensitization conditions. Deletion of Fgl2 in TFH and T follicular regulatory (TFR) cells, but not from TFR cells alone, increase Ag-specific IgE levels and IgE-mediated anaphylactic responses. Overall, we find that Ag-specific IgE responses require precisely timed stimulation of IgE+ GC B cells by Ag. Furthermore, we show that Fgl2 is expressed by TFH cells and represses IgE. This work has implications for the development and treatment of food allergies.

Targeting the Retinoid X Receptor Pathway Prevents and Ameliorates Murine Chronic Graft-Versus-Host Disease.

Most allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients receive peripheral blood stem cell grafts resulting in a 30%–70% incidence of chronic graft-versus-host disease (cGVHD), a major cause of mortality and morbidity in long-term survivors. While systemic steroids remain the standard of care for first-line therapy, patients may require long-term administration, and those with steroid-resistant or refractory cGVHD have a worse prognosis. Although durable and deep responses with second-line therapies can be achieved in some patients, there remains an urgent need for new therapies. In this study, we evaluated the efficacy of IRX4204, a novel agonist that activates RXRs and is in clinical trials for cancer treatment to prevent and treat cGVHD in two complementary murine models. In a major histocompatibility complex mismatched, non-sclerodermatous multiorgan system model with bronchiolitis obliterans, IRX4204 prevented and reversed cGVHD including associated pulmonary dysfunction with restoration of germinal center T-follicular helper: T-follicular regulatory cell balance. In a minor histocompatibility antigen disparate sclerodermatous model, IRX4204 treatment significantly prevented and ameliorated skin cGVHD by reducing Th1 and Th17 differentiation due to anti-inflammatory properties. Together, these results indicate that IRX4204 is a promising therapeutic option to treat cGVHD with bronchiolitis obliterans or sclerodermatous manifestations.

NFATc1/αA and Blimp-1 Support the Follicular and Effector Phenotype of Tregs.

CD4+CXCR5+Foxp3+ T-follicular regulatory (TFR) cells control the germinal center responses. Like T-follicular helper cells, they express high levels of Nuclear Factor of Activated T-cells c1 , predominantly its short isoform NFATc1/αA. Ablation of NFATc1 in Tregs prevents upregulation of CXCR5 and migration of TFR cells into B-cell follicles. By contrast, constitutive active NFATc1/αA defines the surface density of CXCR5, whose level determines how deep a TFR migrates into the GC and how effectively it controls antibody production. As one type of effector Treg, TFR cells express B lymphocyte-induced maturation protein-1 (Blimp-1). Blimp-1 can directly repress Cxcr5 and NFATc1/αA is necessary to overcome this Blimp-1-mediated repression. Interestingly, Blimp-1 even reinforces the recruitment of NFATc1 to Cxcr5 by protein-protein interaction and by those means cooperates with NFATc1 for Cxcr5 transactivation. On the contrary, Blimp-1 is necessary to counterbalance NFATc1/αA and preserve the Treg identity. This is because although NFATc1/αA strengthens the follicular development of Tregs, it bears the inherent risk of causing an ex-Treg phenotype.

Assessment of the Impact of Cytokines on TFH, TREG, and TFR Cell Populations After Influenza Infection.

Within the last several years, great strides have been made in understanding the molecular and cellular mechanisms that control the generation of T follicular helper (TFH), T regulatory (TREG), and T follicular regulatory (TFR) cells. As a result, it is now clear that cytokines play a critical role in regulating the development and function of these CD4+ T cell subsets. One of the critical limitations when studying the effect of individual cytokines in these populations is differentiating between the intrinsic and extrinsic effects of these cytokines in vivo. Here we describe how to utilize mixed bone marrow chimeras in combination with MHC class II tetramers to characterize the direct role played by cytokines on controlling the development, function, and maintenance of TFH, TREG, and TFR cells in vivo.

Using Mass Cytometry to Address Tfh and Tfr Heterogeneity.

Recent advances in single-cell technologies have made it possible to gather increased amounts of information about even rare cell subtypes. In particular, mass cytometry is able to assess the expression of 30-50 proteins on millions of cells. Within CD4 T-cells, T-follicular helper cells (Tfh) and their regulatory counterpart, T-follicular regulatory cells (Tfr), localize to the B-cell follicle and have specialized roles in the maintenance and regulation of B-cell antibody production. The frequency of Tfh and Tfr in circulation has also been associated with ongoing antibody responses.In this chapter, we detail methods to analyze the frequency and phenotype of the populations of Tfh and Tfr found in humans by mass cytometry.

Regulating germinal center contraction

Immunology Germinal centers (GCs) in secondary lymphoid organs are where mature B cells expand and differentiate. Although GC formation is well studied, the control of GC duration and contraction is less well understood. Using intravital imaging of mouse GCs and single-cell RNA sequencing, Jacobsen et al. report that T follicular helper (TFH) cells are a critical player in this process. They found that some late-GC TFH cells upregulate the transcription factor FOXP3 and acquire a regulatory T cell–like phenotype. These cells are distinct from T follicular regulatory (TFR) cells and, unlike TFR cells, are needed to shut down the GC reaction. Tweaking this process may be key to extending GC lifetimes and enhancing antibody responses in the context of vaccination. Science , abe5146, this issue p. [eabe5146][1] [1]: /lookup/doi/10.1126/science.abe5146

Reconstructing TFR cell development

T Cells Antibody responses, including those against self-antigens, are tightly controlled within germinal centers by balancing the activity of T follicular regulatory (TFR) and T follicular helper (TFH) cells. Kumar et al. reconstructed the developmental trajectory of TFR cells using flow cytometry–indexed single-cell transcriptomics of follicular T cells isolated from human peripheral blood, lymph nodes, and tonsils. They used transcriptomics to support a model in which mature germinal center TFR cells arise from regulatory T cells, with circulating TFR cells representing a separate developmental pathway. These results suggest that mature TFR cells primarily arise independently from their less mature counterparts in peripheral blood, providing further insight into how human TFR cells develop. Sci. Immunol. 6 , eabd8411 (2021).

Modulating T Follicular Cells In Vivo Enhances Antigen-Specific Humoral Immunity.

Generation of high-affinity IgG is essential for defense against infections and cancer, which is the intended consequence of many vaccines, but can cause autoimmune and inflammatory diseases when inappropriately directed against self. The interplay of T follicular helper (TFH) cells and T follicular regulatory (TFR) cells is critical for the production of high-affinity IgG of a specific subclass. In this study, we sought to improve Ag-specific IgG responses with two interventions intended to transiently diminish TFR cell influence. First, adult mice were administered an antibiotic mixture (ABX) for an extended period to deplete the immunoregulatory intestinal microbiota. This intriguingly increased TFH cell and reduced TFR cell numbers. 2,4,6-Trinitrophenyl hapten conjugated to keyhole limpet hemocyanin immunization resulted in higher affinity 2,4,6-trinitrophenyl hapten-specific IgG1 in ABX mice compared with controls. In a model of IgG-driven inflammatory nephritis, ABX mice had significantly worse nephritis accompanied by higher affinity Ag-specific IgG2b and enriched TFH cells compared with controls. Second, we sought to functionally manipulate TFH and TFR cells, which both express the checkpoint inhibitory molecule, PD-1, by administration of anti-PD-1 during immunization. This intervention enhanced the affinity of Ag-specific IgG of the appropriate subclass and increased in TFH cells following 2,4,6-trinitrophenyl hapten conjugated to keyhole limpet hemocyanin immunization and nephritis induction. These results suggest that altering TFH and TFR cell ratios during immunization is an appealing strategy to qualitatively improve Ag- and subclass-specific IgG responses.

The Tumor Microenvironment in Follicular Lymphoma: Its Pro-Malignancy Role with Therapeutic Potential.

In the follicular lymphoma (FL) microenvironment, CXCR5+ICOS+PD1+BCL6+ follicular helper T (Tfh) cells, which closely correlate with FL B cells in neoplastic follicles, play a major role in supporting FL. Interleukin-4 secreted by Tfh cells triggers the upregulation of the lymphocyte chemoattractant CXCL12 in stromal cell precursors, in particular by fibroblastic reticular cells (FRCs). In turn, mesenchymal stem cells (MSCs) can be committed to FRC differentiation in the bone marrow and lymph nodes involved by FL. Noteworthy, MSCs can promote the differentiation of Tfh cells into highly immunosuppressive T-follicular regulatory cells. The tumor suppressor HVEM is highly mutated in FL cells, and its deficiency increases Tfh cell frequency. In contrast, PI3Kδ inhibition impedes the recruitment of Tfh/regulatory T cells and impairs the proliferation of follicular dendritic cells (FDCs) and FDC-induced angiogenesis. Since TIGIT ligands are expressed by FDCs, the immune checkpoint receptor TIGIT plays an important role in tumor-infiltrating T cells. Thus, TIGIT blockade might invigorate cytotoxic T cells in the FL microenvironment. Given their potential to simultaneously reduce the neoplastic B cells, Tfh, and TFR cells could also reinforce the effects of the cytotoxic T cells. This combinatory strategy should be explored as a treatment option to tackle FL.

Potential Application of T-Follicular Regulatory Cell Therapy in Transplantation

Regulatory T cells (Tregs) constitute a small proportion of circulating CD4+ T cells that function to maintain homeostasis and prevent autoimmunity. In light of their powerful immunosuppressive and tolerance-promoting properties, Tregs have become an interesting potential candidate for therapeutic use in conditions such as solid organ transplant or to treat autoimmune and inflammatory conditions. Clinical studies have demonstrated the safety of polyclonally expanded Tregs in graft-versus-host disease, type 1 diabetes, and more recently in renal and liver transplantation. However, Tregs are heterogenous. Recent insights indicate that only a small proportion of Tregs, called T follicular regulatory cells (Tfr) regulate interactions between B cells and T follicular helper (Tfh) cells within the germinal center. Tfr have been mainly described in mouse models due to the challenges of sampling secondary lymphoid organs in humans. However, emerging human studies, characterize Tfr as being CD4+CD25+FOXP3+CXCR5+ cells with different levels of PD-1 and ICOS expression depending on their localization, in the blood or the germinal center. The exact role they play in transplantation remains to be elucidated. However, given the potential ability of these cells to modulate antibody responses to allo-antigens, there is great interest in exploring translational applications in situations where B cell responses need to be regulated. Here, we review the current knowledge of Tfr and the role they play focusing on human diseases and transplantation. We also discuss the potential future applications of Tfr therapy in transplantation and examine the evidence for a role of Tfr in antibody production, acute and chronic rejection and tertiary lymphoid organs. Furthermore, the potential impact of immunosuppression on Tfr will be explored. Based on preclinical research, we will analyse the rationale of Tfr therapy in solid organ transplantation and summarize the different challenges to be overcome before Tfr therapy can be implemented into clinical practice.

Altered chromatin landscape in circulating T follicular helper and regulatory cells following grass pollen subcutaneous and sublingual immunotherapy

Allergen-specific immunotherapy is a disease-modifying treatment that induces long-term T-cell tolerance. We sought to evaluate the role of circulating CXCR5+PD-1+ T follicular helper (cTFH) and T follicular regulatory (TFR) cells following grass pollen subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) and the accompanying changes in their chromatin landscape. Phenotype and function of cTFH cells were initially evaluated in the grass pollen-allergic (GPA) group (n= 28) and nonatopic healthy controls (NAC, n= 13) by mathematical algorithms developed to manage high-dimensional data and cell culture, respectively. cTFH and TFR cells were further enumerated in NAC (n= 12), GPA (n= 14), SCIT- (n= 10), and SLIT- (n= 8) treated groups. Chromatin accessibility in cTFH and TFR cells was assessed by assay for transposase-accessible chromatin sequencing (ATAC-seq) to investigate epigenetic mechanisms underlying the differences between NAC, GPA, SCIT, and SLIT groups. cTFH cells were shown to be distinct from TH2- and TH2A-cell subsets, capable of secreting IL-4 and IL-21. Both cytokines synergistically promoted B-cell class switching to IgE and plasma cell differentiation. Grass pollen allergen induced cTFH-cell proliferation in the GPA group but not in the NAC group (P< .05). cTFH cells were higher in the GPA group compared with the NAC group and were lower in the SCIT and SLIT groups (P< .01). Time-dependent induction of IL-4, IL-21, and IL-6 was observed in nasal mucosa following intranasal allergen challenge in the GPA group but not in SCIT and SLIT groups. TFR and IL-10+ cTFH cells were induced in SCIT and SLIT groups (all, P< .01). ATAC-seq analyses revealed differentially accessible chromatin regions in all groups. For the first time, we showed dysregulation of cTFH cells in the GPA group compared to NAC, SCIT, and SLIT groups and induction of TFR and IL-10+ cTFH cells following SCIT and SLIT. Changes in the chromatin landscape were observed following allergen-specific immunotherapy in cTFH and TFR cells.

Control of foreign Ag-specific Ab responses by Treg and Tfr.

Regulatory T cells (Tregs) expressing the transcription factor Foxp3 play a critical role in the control of immune homeostasis including the regulation of humoral immunity. Recently, it has become clear that a specialized subset of Tregs, T-follicular regulatory cells (Tfr), have a particular role in the control of T-follicular helper (Tfh) cell-driven germinal center (GC) responses. Following similar differentiation signals as received by Tfh, Tfr gain expression of characteristic chemokine receptors and transcription factors such as CXCR5 and BCL6 allowing them to travel to the B-cell follicle and deliver in situ suppression. It seems clear that Tfr are critical for the prevention of autoimmune antibody induction. However, their role in the control of foreign antigen-specific antibody responses appears more complex with various reports demonstrating either increased or decreased antigen-specific antibody responses following inhibition of Tfr function. Due to their recent discovery, our understanding of Tfr formation and function still has many gaps. In this review, we discuss our current knowledge of both Tregs and Tfr in the context of humoral immunity and how these cells might be manipulated in order to better control vaccine responses.

Harnessing Activin A Adjuvanticity to Promote Antibody Responses to BG505 HIV Envelope Trimers.

T follicular helper (TFH) cells are powerful regulators of affinity matured long-lived plasma cells. Eliciting protective, long-lasting antibody responses to achieve persistent immunity is the goal of most successful vaccines. Thus, there is potential in manipulating TFH cell responses. Herein, we describe an HIV vaccine development approach exploiting the cytokine activin A to improve antibody responses against recombinant HIV Envelope (Env) trimers in non-human primates. Administration of activin A improved the magnitude of Env-specific antibodies over time and promoted a significant increase in Env-specific plasma cells in the bone marrow. The boost in antibody responses was associated with reduced frequencies of T follicular regulatory (TFR) cells and increased germinal center T follicular helper (GC-TFH) to TFR cell ratios. Overall, these findings suggest that adjuvants inducing activin A production could potentially be incorporated in future rational design vaccine strategies aimed at improving germinal centers, long-lived plasma cells, and sustained antibody responses.

T &lt;sub&gt;FR&lt;/sub&gt; Cells Inhibit Anti-Tumor Immunity and are Responsive to Immune Checkpoint Blockade

Immune checkpoint blockade (ICB) has shown remarkable clinical success in boosting anti-tumor immunity. However, the breadth of its cellular targets and specific mode of action remain elusive. We find that T follicular regulatory (TFR) cells are present in high numbers in multiple tumors, inhibit anti-tumor immunity and are responsive to ICB. TCR-seq data, trajectory analyses and adoptive transfer studies indicate intratumoral TREG to TFR cell conversion. When compared to TREG cells, TFR cells exhibited enhanced suppressive capacity. In syngeneic tumor models, anti-PD-1 treatment increased the number of tumor-infiltrating TFR cells. Conditional knockout of TFR cells or depletion of TFR cells with anti-CTLA-4 antibody prior to anti-PD-1 treatment, improved tumor control in mice. Notably, in a cohort of melanoma patients, treatment with anti-CTLA-4 followed by anti-PD-1 at progression was associated with better long-term survival outcomes than anti-PD-1 or anti-CTLA-4 monotherapy, anti-PD-1 followed by anti CTLA-4 at progression or concomitant combination therapy.