Differences in CD80 and CD86 transendocytosis reveal CD86 as a key target for CTLA-4 immune regulation.

CD28 and CTLA-4 (CD152) play essential roles in regulating T cell immunity, balancing the activation and inhibition of T cell responses, respectively. Although both receptors share the same ligands, CD80 and CD86, the specific requirement for two distinct ligands remains obscure. In the present study, we demonstrate that, although CTLA-4 targets both CD80 and CD86 for destruction via transendocytosis, this process results in separate fates for CTLA-4 itself. In the presence of CD80, CTLA-4 remained ligand bound, and was ubiquitylated and trafficked via late endosomes and lysosomes. In contrast, in the presence of CD86, CTLA-4 detached in a pH-dependent manner and recycled back to the cell surface to permit further transendocytosis. Furthermore, we identified clinically relevant mutations that cause autoimmune disease, which selectively disrupted CD86 transendocytosis, by affecting either CTLA-4 recycling or CD86 binding. These observations provide a rationale for two distinct ligands and show that defects in CTLA-4-mediated transendocytosis of CD86 are associated with autoimmunity.

Tet2 and Tet3 in B cells are required to repress CD86 and prevent autoimmunity.

A contribution of epigenetic modifications to B cell tolerance has been proposed but not directly tested. Here we report that deficiency of ten-eleven translocation (Tet) DNA demethylase family members Tet2 and Tet3 in B cells led to hyperactivation of B and T cells, autoantibody production and lupus-like disease in mice. Mechanistically, in the absence of Tet2 and Tet3, downregulation of CD86, which normally occurs following chronic exposure of self-reactive B cells to self-antigen, did not take place. The importance of dysregulated CD86 expression in Tet2- and Tet3-deficient B cells was further demonstrated by the restriction, albeit not complete, on aberrant T and B cell activation following anti-CD86 blockade. Tet2- and Tet3-deficient B cells had decreased accumulation of histone deacetylase 1 (HDAC1) and HDAC2 at the Cd86 locus. Thus, our findings suggest that Tet2- and Tet3-mediated chromatin modification participates in repression of CD86 on chronically stimulated self-reactive B cells, which contributes, at least in part, to preventing autoimmunity.

cis-B7:CD28 interactions at invaginated synaptic membranes provide CD28 co-stimulation and promote CD8+ T cell function and anti-tumor immunity.

B7 ligands (CD80 and CD86), expressed by professional antigen-presenting cells (APCs), activate the main co-stimulatory receptor CD28 on T cells in trans. However, in peripheral tissues, APCs expressing B7 ligands are relatively scarce. This raises the questions of whether and how CD28 co-stimulation occurs in peripheral tissues. Here, we report that CD8+ T cells displayed B7 ligands that interacted with CD28 in cis at membrane invaginations of the immunological synapse as a result of membrane remodeling driven by phosphoinositide-3-kinase (PI3K) and sorting-nexin-9 (SNX9). cis-B7:CD28 interactions triggered CD28 signaling through protein kinase C theta (PKCθ) and promoted CD8+ T cell survival, migration, and cytokine production. In mouse tumor models, loss of T cell-intrinsic cis-B7:CD28 interactions decreased intratumoral T cells and accelerated tumor growth. Thus, B7 ligands on CD8+ T cells can evoke cell-autonomous CD28 co-stimulation in cis in peripheral tissues, suggesting cis-signaling as a general mechanism for boosting T cell functionality.

Obesity induces PD-1 on macrophages to suppress anti-tumour immunity.

Obesity is a leading risk factor for progression and metastasis of many cancers1,2, yet can in some cases enhance survival3-5 and responses to immune checkpoint blockade therapies, including anti-PD-1, which targets PD-1 (encoded by PDCD1), an inhibitory receptor expressed on immune cells6-8. Although obesity promotes chronic inflammation, the role of the immune system in the obesity-cancer connection and immunotherapy remains unclear. It has been shown that in addition to T cells, macrophages can express PD-19-12. Here we found that obesity selectively induced PD-1 expression on tumour-associated macrophages (TAMs). Type I inflammatory cytokines and molecules linked to obesity, including interferon-γ, tumour necrosis factor, leptin, insulin and palmitate, induced macrophage PD-1 expression in an mTORC1- and glycolysis-dependent manner. PD-1 then provided negative feedback to TAMs that suppressed glycolysis, phagocytosis and T cell stimulatory potential. Conversely, PD-1 blockade increased the level of macrophage glycolysis, which was essential for PD-1 inhibition to augment TAM expression of CD86 and major histocompatibility complex I and II molecules and ability to activate T cells. Myeloid-specific PD-1 deficiency slowed tumour growth, enhanced TAM glycolysis and antigen-presentation capability, and led to increased CD8+ T cell activity with a reduced level of markers of exhaustion. These findings show that obesity-associated metabolic signalling and inflammatory cues cause TAMs to induce PD-1 expression, which then drives a TAM-specific feedback mechanism that impairs tumour immune surveillance. This may contribute to increased cancer risk yet improved response to PD-1 immunotherapy in obesity.

Quorum Regulation via Nested Antagonistic Feedback Circuits Mediated by the Receptors CD28 and CTLA-4 Confers Robustness to T Cell Population Dynamics.

T cell responses upon infection display a remarkably reproducible pattern of expansion, contraction, and memory formation. If the robustness of this pattern builds entirely on signals derived from other cell types or if activated T cells themselves contribute to the orchestration of these population dynamics-akin to bacterial quorum regulation-is unclear. Here, we examined this question using time-lapse microscopy, genetic perturbation, bioinformatic predictions, and mathematical modeling. We found that ICAM-1-mediated cell clustering enabled CD8+ T cells to collectively regulate the balance between proliferation and apoptosis. Mechanistically, T cell expressed CD80 and CD86 interacted with the receptors CD28 and CTLA-4 on neighboring T cells; these interactions fed two nested antagonistic feedback circuits that regulated interleukin 2 production in a manner dependent on T cell density as confirmed by in vivo modulation of this network. Thus, CD8+ T cell-population-intrinsic mechanisms regulate cellular behavior, thereby promoting robustness of population dynamics.

CCR6 Defines Memory B Cell Precursors in Mouse and Human Germinal Centers, Revealing Light-Zone Location and Predominant Low Antigen Affinity.

Memory B cells (MBCs) and plasma cells (PCs) constitute the two cellular outputs of germinal center (GC) responses that together facilitate long-term humoral immunity. Although expression of the transcription factor BLIMP-1 identifies cells undergoing PC differentiation, no such marker exists for cells committed to the MBC lineage. Here, we report that the chemokine receptor CCR6 uniquely marks MBC precursors in both mouse and human GCs. CCR6+ GC B cells were highly enriched within the GC light zone (LZ), were the most quiescent of all GC B cells, exhibited a cell-surface phenotype and gene expression signature indicative of an MBC transition, and possessed the augmented response characteristics of MBCs. MBC precursors within the GC LZ predominantly possessed a low affinity for antigen but also included cells from within the high-affinity pool. These data indicate a fundamental dichotomy between the processes that drive MBC and PC differentiation during GC responses.

Dendritic Cells Coordinate the Development and Homeostasis of Organ-Specific Regulatory T Cells.

Although antigen recognition mediated by the T cell receptor (TCR) influences many facets of Foxp3(+) regulatory T (Treg) cell biology, including development and function, the cell types that present antigen to Treg cells in vivo remain largely undefined. By tracking a clonal population of Aire-dependent, prostate-specific Treg cells in mice, we demonstrated an essential role for dendritic cells (DCs) in regulating organ-specific Treg cell biology. We have shown that the thymic development of prostate-specific Treg cells required antigen presentation by DCs. Moreover, Batf3-dependent CD8α(+) DCs were dispensable for the development of this clonotype and had negligible impact on the polyclonal Treg cell repertoire. In the periphery, CCR7-dependent migratory DCs coordinated the activation of organ-specific Treg cells in the prostate-draining lymph nodes. Our results demonstrate that the development and peripheral regulation of organ-specific Treg cells are dependent on antigen presentation by DCs, implicating DCs as key mediators of organ-specific immune tolerance.

GPR174 signals via Gαs to control a CD86-containing gene expression program in B cells.

GPR174 is abundantly expressed in B and T lymphocytes and has a role in restraining T cell responses, but the function of GPR174 in B cells is less clear. Here we report that upon in vitro culture B cells undergo a spontaneous GPR174-dependent activation process that is associated with marked changes in gene expression, including up-regulation of Cd86, Nr4a1, Ccr7, and phosphodiesterases. B cells lacking Gαs show a block in induction of the GPR174-dependent program. Spontaneous up-regulation of CD86 in cultured B cells is dependent on protein kinase A. Both GPR174- and Gαs-deficient B cells show enhanced survival in culture. In vivo, GPR174 contributes to NUR77 expression in follicular B cells and is needed for establishing a marginal zone compartment of normal size. Treatment of mice with lysophosphatidylserine (lysoPS), a GPR174 ligand, is sufficient to promote CD86 up-regulation by follicular B cells. These findings demonstrate that GPR174 can signal via Gαs to modulate B cell gene expression and show this can occur in vivo in response to lysoPS. Additionally, the findings illuminate a pathway that might be targeted to improve systems for the in vitro study of B cell responses.

K33 only mutant ubiquitin augments bone marrow-derived dendritic cell-mediated CTL priming via PI3K-Akt pathway.

To explore the effect of K33 only mutant ubiquitin (K33O) on bone marrow-derived dendritic cells' (BMDCs') maturity, antigen uptake capability, surface molecule expressions and BMDC-mediated CTL priming, and further investigate the role of PI3K-Akt engaged in K33O-increased BMDC maturation, antigen uptake and presentation, surface molecule expressions and BMDC-based CTL priming. BMDCs were conferred K33O and other ubiquitin mutants (K33R, K48R, K63R-mutant ubiquitin) incubation or LY294002 and wortmannin pretreatment. PI3K-Akt phosphorylation, antigen uptake, antigenic presentation and CD86/MHC class I expression in BMDC were determined by western blot or flow cytometry. BMDC-based CTL proliferation and priming were determined by in vitro mixed lymphocyte reaction (MLR), ex vivo enzyme-linked immunospot assay (Elispot) and flow cytometry with intracellular staining, respectively. The treatment with K33O effectively augmented PI3K-Akt phosphorylation, BMDCs' antigen uptake, antigenic presentation, CD86/MHC class I and CD11c expressions. MLR, Elispot and flow cytometry revealed that K33O treatment obviously enhanced CTL proliferation, CTL priming and perforin/granzyme B expression. The pretreatment with PI3K-Akt inhibitors efficiently abrogated K33O's effects on BMDC. The replenishment of K33 only mutant ubiquitin augments BMDC-mediated CTL priming in bone marrow-derived dendritic cells via PI3K-Akt signalling.

Control of Memory Phenotype T Lymphocyte Homeostasis: Role of Costimulation.

Foxp3+ T regulatory cells (Tregs), CD4+Foxp3- T cells, and CD8+ T cells are composed of naive phenotype (NP) and memory phenotype (MP) subsets. Ten to 20% of each MP T cell population are cycling (Ki-67+) in vivo. We investigated the contribution of costimulatory (CD28) and coinhibitory (CTLA-4, PD-1) receptors on MP T cell homeostatic proliferation in vivo in the mouse. Blockade of CD28-CD80/CD86 signaling completely abolished MP Tregs and profoundly inhibited MP CD4+Foxp3- T cell proliferation, but it did not affect MP CD8+ T cell proliferation. Marked enhancement of homeostatic proliferation of MP Tregs and MP CD4+Foxp3- T cells was seen after blocking CTLA4-CD80/CD86 interactions and PD-1-PD-L1/2 interactions, and greater enhancement was seen with blockade of both pathways. The CD28 pathway also played an important role in the expansion of Tregs and MP T cells after treatment of mice with agonistic Abs to members of the TNF receptor superfamily, which can act directly (anti-GITR, anti-OX40, anti-4-1BB) or indirectly (anti-CD40) on T cells. Induction of a cytokine storm by blocking the interaction of NK inhibitory receptors with MHC class I had no effect on Treg homeostasis, enhanced MP CD4+ proliferation, and expansion in a CD28-dependent manner, but it enhanced MP CD8+ T cell proliferation in a CD28-independent manner. Because MP T cells exert potent biologic effects primarily before the induction of adaptive immune responses, these findings have important implications for the use of biologic agents designed to suppress autoimmune disease or enhance T effector function in cancer that may have negative effects on MP T cells.

A better understanding of the role of the CTLA-CD80/86 axis in the treatment of autoimmune diseases.

Autoimmune diseases are diseases in which the regulatory mechanisms of the immune response are disturbed. As a result, the body loses self-tolerance. Since one of the main regulatory mechanisms of the immune response is the CTLA4-CD80/86 axis, this hypothesis suggests that autoimmune diseases potentially share a similar molecular basis of pathogenesis. Hence, investigating the CTLA4-CD80/86 axis may be helpful in finding an appropriate treatment strategy. Therefore, this study aims to investigate the molecular basis of the CTLA4-CD80/86 axis in the regulation of the immune response, and then its role in developing some autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, type 1 diabetes, and multiple sclerosis. As well, the main therapeutic strategies affecting the CTLA4-CD80/86 axis have been summarized to highlight the importance of this axis in management of autoimmune diseases.

Treg-expressed CTLA-4 depletes CD80/CD86 by trogocytosis, releasing free PD-L1 on antigen-presenting cells.

Foxp3-expressing CD4+CD25+ regulatory T cells (Tregs) constitutively and highly express the immune checkpoint receptor cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), whose Treg-specific deficiency causes severe systemic autoimmunity. As a key mechanism of Treg-mediated suppression, Treg-expressed CTLA-4 down-regulates the expression of CD80/CD86 costimulatory molecules on antigen-presenting cells (APCs). Here, we show that Treg-expressed CTLA-4 facilitated Treg-APC conjugation and immune synapse formation. The immune synapses thus formed provided a stable platform whereby Tregs were able to deplete CD80/CD86 molecules on APCs by extracting them via CTLA-4-dependent trogocytosis. The depletion occurred even with Tregs solely expressing a mutant CTLA-4 form lacking the cytoplasmic portion required for its endocytosis. The CTLA-4-dependent trogocytosis of CD80/CD86 also accelerated in vitro and in vivo passive transfer of other membrane proteins and lipid molecules from APCs to Tregs without their significant reduction on the APC surface. Furthermore, CD80 down-regulation or blockade by Treg-expressed membrane CTLA-4 or soluble CTLA-4-immunoglobulin (CTLA-4-Ig), respectively, disrupted cis-CD80/programmed death ligand-1 (PD-L1) heterodimers and increased free PD-L1 on dendritic cells (DCs), expanding a phenotypically distinct population of CD80lo free PD-L1hi DCs. Thus, Tregs are able to inhibit the T cell stimulatory activity of APCs by reducing their CD80/CD86 expression via CTLA-4-dependent trogocytosis. This CD80/CD86 reduction on APCs is able to exert dual suppressive effects on T cell immune responses by limiting CD80/CD86 costimulation to naïve T cells and by increasing free PD-L1 available for the inhibition of programmed death-1 (PD-1)-expressing effector T cells. Blockade of CTLA-4 and PD-1/PD-L1 in combination may therefore synergistically hinder Treg-mediated immune suppression, thereby effectively enhancing immune responses, including tumor immunity.

Dendritic Cells Promote the Differentiation of ILCs into NCR-ILC3s in the Lungs of Mice Exposed to Cigarette Smoke.

The involvement of Group 3 innate lymphoid cells (ILC3s) and dendritic cells (DCs) in chronic lung inflammation has been increasingly regarded as the key to understand the inflammatory mechanisms of smoke-related chronic obstructive pulmonary disease (COPD). However, the mechanism underlying the engagement of both remains unclear. Our study aimed to explore NCR-ILC3 differentiation in the lungs of mice exposed to cigarette smoke (CS) and to further investigate whether DCs activated by CS exposure contribute to the differentiation of ILCs into NCR-ILC3s. The study involved both in vivo and in vitro experiments. In the former, the frequencies of lung NCR-ILC3s and NKp46-IL-17A+ ILCs and the expression of DCs, CD40, CD86, IL-23, and IL-1ß quantified by flow cytometry were compared between CS-exposed mice and air-exposed mice. In the latter, NKp46-IL-17A+ ILC frequencies quantified by flow cytometry were compared after two cocultures, one involving lung CD45+Lin-CD127+ ILCs sorted from air-exposed mice and DCs sifted by CD11c magnetic beads from CS-exposed mice and another including identical CD45+Lin-CD127+ ILCs and DCs from air-exposed mice. The results indicated significant increases in the frequencies of NCR-ILC3s and NKp46-IL-17A+ ILCs; in the expression of DCs, CD40, CD86, IL-23, and IL-1ß in CS-exposed mice; and in the frequency of NKp46-IL-17A+ ILCs after the coculture with DCs from CS-exposed mice. In conclusion, CS exposure increases the frequency of lung ILCs and NCR-ILC3s. CS-induced DC activation enhances the differentiation of ILCs into NCR-ILC3s, which likely acts as a mediating step in the involvement of NCR-ILC3s in chronic lung inflammation.

Development of a Protocol for Obtaining a Homologous Cell Product of Animal Origin Intended for Preclinical Studies of Antitumor Vaccine CaTeVac.

When developing a program of preclinical studies of human cell-based drugs intended for adoptive immunotherapy of cancer patients, the biological effect should be substantiated by data describing their immunological action. Administration and study of human autologous dendritic cell vaccine to immunocompetent animals are not adequate in terms of immunological compatibility. It is possible to use immunocompromised, knockout, or transgenic animals or to obtain a homologous cellular product, namely, a preparation based on animal cells using a technology similar to obtaining the original preparation for clinical practice in humans. Within the framework of this study, we have developed a protocol for obtaining a homologous cell product based on animal dendritic cells (mice, rats) according to a similar technology for obtaining human vaccine dendritic cells, and demonstrated the comparability of morphological characteristics and expression of differentiation antigens of dendritic cells (CD11c, CD80, CD86, and CD83) of animals (mice) and humans.

Endothelial mechanical stretch regulates the immunological synapse interface of renal endothelial cells in a sex-dependent manner.

Increased mechanical endothelial cell stretch contributes to the development of numerous cardiovascular and renal pathologies. Recent studies have shone a light on the importance of sex-dependent inflammation in the pathogenesis of renal disease states. The endothelium plays an intimate and critical role in the orchestration of immune cell activation through upregulation of adhesion molecules and secretion of cytokines and chemokines. While endothelial cells are not recognized as professional antigen-presenting cells, in response to cytokine stimulation, endothelial cells can express both major histocompatibility complex (MHC) I and MHC II. MHCs are essential to forming a part of the immunological synapse interface during antigen presentation to adaptive immune cells. Whether MHC I and II are increased under increased mechanical stretch is unknown. Due to hypertension being multifactorial, we hypothesized that increased mechanical endothelial stretch promotes the regulation of MHCs and key costimulatory proteins on mouse renal endothelial cells (MRECs) in a stretch-dependent manner. MRECs derived from both sexes underwent 5%, 10%, or 15% uniaxial cyclical stretch, and immunological synapse interface proteins were determined by immunofluorescence microscopy, immunoblot analysis, and RNA sequencing. We found that increased endothelial mechanical stretch conditions promoted downregulation of MHC I in male MRECs but upregulation in female MRECs. Moreover, MHC II was upregulated by mechanical stretch in both male and female MRECs, whereas CD86 and CD70 were regulated in a sex-dependent manner. By bulk RNA sequencing, we found that increased mechanical endothelial cell stretch promoted differential gene expression of key antigen processing and presentation genes in female MRECs, demonstrating that females have upregulation of key antigen presentation pathways. Taken together, our data demonstrate that mechanical endothelial stretch regulates endothelial activation and immunological synapse interface formation in renal endothelial cells in a sex-dependent manner.NEW & NOTEWORTHY Endothelial cells contribute to the development of renal inflammation and have the unique ability to express antigen presentation proteins. Whether increased endothelial mechanical stretch regulates immunological synapse interface proteins remains unknown. We found that antigen presentation proteins and costimulatory proteins on renal endothelial cells are modulated by mechanical stretch in a sex-dependent manner. Our data provide novel insights into the sex-dependent ability of renal endothelial cells to present antigens in response to endothelial mechanical stimuli.

Differential regulation of CD8+ CD86+ Vγ1.1+ γδT cell responses in skin barrier tissue protection and homeostatic maintenance.

Compared to αßT cells, γδT cells are more innate-like and preferentially function as the first line of defense in barrier tissues. Certain populations of γδT cells possess adaptive immune cell properties but their regulation is not well understood. We herein report that while innate-like γδT17 cells dominated in the skin of WT mice, Vγ1.1+ γδT cells with adaptive T cell-like properties predominantly expanded in the skin of TCRß-/- and B2m-/- mice. Commensal bacteria drove expansion of Vγ1.1+ skin γδT cells, functional properties of which correlated with local immune requirements. That is, Vγ1.1+ skin γδT cells in TCRß-/- mice were a heterogeneous population; while Vγ1.1+ skin γδT cells in B2m-/- mice were mostly CD8+ CD86+ cells that had a similar function of CD8+ CD86+ skin αßT cells in supporting local Treg cells. We also found that intrinsic TGF-ß receptor 2-derived signals in skin CD8+ αßT and γδT cells are required for their expression of CD86, a molecule important in supporting skin Treg cells. Our findings reveal broad functional potentials of γδT cells that are coordinately regulated with αßT cells to help maintain local tissue homeostasis.

Pomalidomide restores immune recognition of primary effusion lymphoma through upregulation of ICAM-1 and B7-2.

Pomalidomide (Pom) is an immunomodulatory drug that has efficacy against Kaposi's sarcoma, a tumor caused by Kaposi's sarcoma-associated herpesvirus (KSHV). Pom also induces direct cytotoxicity in primary effusion lymphoma (PEL), a B-cell malignancy caused by KSHV, in part through downregulation of IRF4, cMyc, and CK1α as a result of its interaction with cereblon, a cellular E3 ubiquitin ligase. Additionally, Pom can reverse KSHV-induced downregulation of MHCI and co-stimulatory immune surface molecules ICAM-1 and B7-2 on PELs. Here, we show for the first time that Pom-induced increases in ICAM-1 and B7-2 on PEL cells lead to an increase in both T-cell activation and NK-mediated cytotoxicity against PEL. The increase in T-cell activation can be prevented by blocking ICAM-1 and/or B7-2 on the PEL cell surface, suggesting that both ICAM-1 and B7-2 are important for T-cell co-stimulation by PELs. To gain mechanistic insights into Pom's effects on surface markers, we generated Pom-resistant (PomR) PEL cells, which showed about 90% reduction in cereblon protein level and only minimal changes in IRF4 and cMyc upon Pom treatment. Pom no longer upregulated ICAM-1 and B7-2 on the surface of PomR cells, nor did it increase T-cell and NK-cell activation. Cereblon-knockout cells behaved similarly to the pomR cells upon Pom-treatment, suggesting that Pom's interaction with cereblon is necessary for these effects. Further mechanistic studies revealed PI3K signaling pathway as being important for Pom-induced increases in these molecules. These observations provide a rationale for the study of Pom as therapy in treating PEL and other KSHV-associated tumors.

The coinhibitory receptor CTLA-4 controls B cell responses by modulating T follicular helper, T follicular regulatory, and T regulatory cells.

The receptor CTLA-4 has been implicated in controlling B cell responses, but the mechanisms by which CTLA-4 regulates antibody production are not known. Here we showed deletion of CTLA-4 in adult mice increased Tfh and Tfr cell numbers and augmented B cell responses. In the effector phase, loss of CTLA-4 on Tfh cells resulted in heightened B cell responses, whereas loss of CTLA-4 on Tfr cells resulted in defective suppression of antigen-specific antibody responses. We also found that non-Tfr Treg cells could suppress B cell responses through CTLA-4 and that Treg and/or Tfr cells might downregulate B7-2 on B cells outside germinal centers as a means of suppression. Within the germinal center, however, Tfr cells potently suppress B cells through CTLA-4, but with a mechanism independent of altering B7-1 or B7-2. Thus, we identify multifaceted regulatory roles for CTLA-4 in Tfh, Tfr, and Treg cells, which together control humoral immunity.

Regulatory T cells control antigen-specific expansion of Tfh cell number and humoral immune responses via the coreceptor CTLA-4.

CD4(+)Foxp3-expressing Treg cells, which constitutively express the inhibitory coreceptor CTLA-4, are indispensable for immune homeostasis. We determined the roles of Treg cells and T follicular regulatory (Tfr) cells in the control of humoral immune responses. Depletion of Treg cells, blocking of CTLA-4 or a Treg cell specific reduction in CTLA-4 expression, resulted in an increase in the formation of antigen-specific Tfh cells, germinal center (GC), and plasma and memory B cells after vaccination. In the absence of Treg cell-expressed CTLA-4, large numbers of Tfr cells were present but were unable to restrain Tfh cell and GC formation. Temporary Treg cell depletion during primary immunization was sufficient to enhance secondary immune responses. Treg cells directly inhibited, via CTLA-4, B cell expression of CD80 and CD86, which was essential for Tfh cell formation. Thus, Treg and Tfr cells control Tfh cell and germinal center development, via CTLA-4-dependent regulation of CD80 and CD86 expression.