Follicular helper T cell differentiation requires continuous antigen presentation that is independent of unique B cell signaling

Microneedle-delivered adeno-associated virus vaccine amplified anti-viral immunity by improving antigen-presenting cells infection

Adeno-associated viruses (AAV) have significant potential as vaccine carriers due to their excellent biosafety and efficient antigen gene delivery. However, most AAV vaccines show limited capacity to transduce antigen-presenting cells (APCs) following intramuscular injection which may cause inadequate cellular immune responses and undesired side effects due to transducing other tissues or cells. Herein, we developed a soluble microneedle patch for targeting the AAV vaccines to the epidermal and dermal APCs. To preserve the biological activity of the AAV vaccine, the microneedles were fabricated via an optimized two-step low-temperature strategy and using 20 % trehalose as a protective agent. AAV serotype 8, which expresses the trimeric receptor-binding domain (RBD) of the SARS-CoV-2 spike protein (AAV8-RBD), remained 100 % biological activity after being loaded into the microneedles (MN-A8R). Upon a single-dose vaccination on the dorsal skin of mice, MN-A8R efficiently recruited APCs to the vaccination site and improved AAV8-RBD infection in APCs. Furthermore, MN-A8R prompted an increased formation of germinal centers in the draining lymph nodes. Compared to hypodermic needle-mediated intradermal injection, MN-A8R induced significantly stronger cellular immune responses and long-lasting, high-quality neutralizing antibodies. Importantly, MN-A8R demonstrated more comprehensive and robust cross-protection against three common SARS-CoV-2 pseudoviruses for at least six months. Our findings highlight the use of optimized polymeric microneedles for preserving AAV vaccine biological activity and enhancing the AAV vaccine efficacy by up-regulating APC infection.

Circulatory age-associated B cells: Their distinct transcriptomic characteristics and clinical significance in drug-naïve patients with rheumatoid arthritis

Age-associated B cells (ABCs) have been implicated in the pathogenesis of autoimmune diseases. However, the global gene expression and clinical significance of circulatory ABCs in rheumatoid arthritis (RA) remain poorly understood. Here, single-cell RNA sequencing identified nine B cell subsets in peripheral blood of RA patients, including ABCs. Increased phagocytosis and antigen presentation were functionally enriched by the genes expressed differentially in ABCs. Network analysis and in vitro experiments demonstrated SYK as a key regulator defining the myeloid-like phenotypes in ABCs. Flow cytometry showed that the proportion of ABCs correlated with RA activity and serum tumor necrosis factor-alpha level. Notably, ABCs above a cutoff threshold specifically distinguished RA from healthy controls and indicated higher disease activity. This study highlights the myeloid characteristics of circulatory ABCs regulated by SYK in RA. Increased ABCs may reflect disease activity and could serve as a potential biomarker in RA.

T follicular helper and memory B cells in IgE recall responses

IgE antibodies raised against innocuous environmental antigens cause allergic diseases like allergic rhinitis, food allergy, and allergic asthma. While some allergies are often outgrown, others (peanut, shellfish, tree nut) are lifelong in the majority of individuals. Lifelong allergies are the result of persistent production of allergen-specific IgE. However, IgE antibodies and the plasma cells that secrete them tend to be short-lived. Persistent allergen-specific IgE titres are thought to be derived from the continued renewal of IgE plasma cells from memory B cells in response to allergen encounters. The initial generation of allergen-specific IgE is driven by B cell activation by IL-4 producing Tfh cells, but the cellular and molecular mechanisms of the long-term production of IgE are poorly characterized. This review investigates the mechanisms governing IgE production and Tfh activation in the primary and recall responses, towards the objective of identifying molecular targets for therapeutic intervention that durably inactivate the IgE recall response.

The protozoan commensal Tritrichomonas musculis is a natural adjuvant for mucosal IgA

Immunoglobulin (Ig) A supports mucosal immune homeostasis and host-microbiota interactions. While commensal bacteria are known for their ability to promote IgA, the role of non-bacterial commensal microbes in the induction of IgA remains elusive. Here, we demonstrate that permanent colonization with the protozoan commensal Tritrichomonas musculis (T.mu) promotes T cell-dependent, IgA class-switch recombination, and intestinal accumulation of IgA-secreting plasma cells (PC). T.mu colonization specifically drives the expansion of T follicular helper cells and a unique ICOS+ non-Tfh cell population, accompanied by an increase in germinal center B cells. Blockade of ICOS:ICOSL co-stimulation or MHCII-expression on B cells is central for the induction of IgA following colonization by T.mu, implicating a previously underappreciated mode of IgA induction following protozoan commensal colonization. Finally, T.mu further improves the induction of IgA-secreting PC specific to orally ingested antigens and their peripheral dissemination, identifying T.mu as a "natural adjuvant" for IgA. Collectively, these findings propose a protozoa-driven mode of IgA induction to support intestinal immune homeostasis.

BAFF promotes follicular helper T cell development and germinal center formation through BR3 signal

T follicular helper (Tfh) cells represent an important subset of CD4+ T cells that is crucial to the maturation and differentiation of B cells and the production of high-affinity antibodies. Because B cell activating-factor (BAFF), a vital B cell survival factor, is also crucial to B cell maturation and differentiation, we assessed the effects of BAFF on Tfh cell development and function. We demonstrated that deficiency of BAFF, but not of APRIL, markedly inhibited Tfh cell development, germinal center (GC) formation, and antigen-specific antibody production. The promoting effect of BAFF on Tfh cell development was dependent on expression of BR3 on T cells, and its promoting effect on GC formation was dependent on expression of BR3 on both T cells and B cells. BAFF directly promoted expression of the Tfh cell-characteristic genes via NF-κB signaling. This effect did need BR3 expression. Thus, BAFF not only has direct effects on B cells, but it also has direct effects on Tfh cell differentiation via engagement of BR3, which collectively promoted GC formation and production of high-affinity antibodies. This dual effect of BAFF on B cells and Tfh cells may help explain the clinical utility of BAFF antagonists in the management of certain autoimmune diseases.

Two-dose priming immunization amplifies humoral immunity by synchronizing vaccine delivery with the germinal center response

Prolonging exposure to subunit vaccines during the primary immune response enhances humoral immunity. Escalating-dose immunization (EDI), administering vaccines every other day in an increasing pattern over 2 weeks, is particularly effective but challenging to implement clinically. Here, using an HIV Env trimer/saponin adjuvant vaccine, we explored simplified EDI regimens and found that a two-shot regimen administering 20% of the vaccine followed by the remaining 80% of the dose 7 days later increased TFH responses 6-fold, antigen-specific germinal center (GC) B cells 10-fold, and serum antibody titers 10-fold compared with bolus immunization. Computational modeling of TFH priming and the GC response suggested that enhanced activation/antigen loading on dendritic cells and increased capture of antigen delivered in the second dose by follicular dendritic cells contribute to these effects, predictions we verified experimentally. These results suggest that a two-shot priming approach can be used to substantially enhance responses to subunit vaccines.

Reciprocal regulation of T follicular helper cells and dendritic cells drives colitis development

The immunological mechanisms underlying chronic colitis are poorly understood. T follicular helper (TFH) cells are critical in helping B cells during germinal center reactions. In a T cell transfer colitis model, a lymphoid structure composed of mature dendritic cells (DCs) and TFH cells was found within T cell zones of colonic lymphoid follicles. TFH cells were required for mature DC accumulation, the formation of DC-T cell clusters and colitis development. Moreover, DCs promoted TFH cell differentiation, contributing to colitis development. A lineage-tracing analysis showed that, following migration to the lamina propria, TFH cells transdifferentiated into long-lived pathogenic TH1 cells, promoting colitis development. Our findings have therefore demonstrated the reciprocal regulation of TFH cells and DCs in colonic lymphoid follicles, which is critical in chronic colitis pathogenesis.

Controlling the speed of antigens transport in dendritic cells improves humoral and cellular immunity for vaccine

Vaccines are an effective intervention for preventing infectious diseases. Currently many vaccine strategies are designed to improve vaccine efficacy by controlling antigen release, typically involving various approaches at the injection site. Yet, strategies for intracellular slow-release of antigens in vaccines are still unexplored. Our study showed that controlling the degradation of antigens in dendritic cells and slowing their transport from early endosomes to lysosomes markedly enhances both antigen-specific T-cell immune responses and germinal center B cell responses. This leads to the establishment of sustained humoral and cellular immunity in vivo imaging and flow cytometry indicated this method not only prolongs antigen retention at the injection site but also enhances antigen concentration in lymph nodes, surpassing traditional Aluminium (Alum) adjuvants. Additionally, we demonstrated that the slow antigen degradation induces stronger follicular helper T cell responses and increases proportions of long-lived plasma cells and memory B cells. Overall, these findings propose that controlling the speed of antigens transport in dendritic cells can significantly boost vaccine efficacy, offering an innovative avenue for developing highly immunogenic next-generation vaccines.

TGF-β specifies TFH versus TH17 cell fates in murine CD4+ T cells through c-Maf

T follicular helper (TFH) cells are essential for effective antibody responses, but deciphering the intrinsic wiring of mouse TFH cells has long been hampered by the lack of a reliable protocol for their generation in vitro. We report that transforming growth factor-β (TGF-β) induces robust expression of TFH hallmark molecules CXCR5 and Bcl6 in activated mouse CD4+ T cells in vitro. TGF-β-induced mouse CXCR5+ TFH cells are phenotypically, transcriptionally, and functionally similar to in vivo-generated TFH cells and provide critical help to B cells. The study further reveals that TGF-β-induced CXCR5 expression is independent of Bcl6 but requires the transcription factor c-Maf. Classical TGF-β-containing T helper 17 (TH17)-inducing conditions also yield separate CXCR5+ and IL-17A-producing cells, highlighting shared and distinct cell fate trajectories of TFH and TH17 cells. We demonstrate that excess IL-2 in high-density T cell cultures interferes with the TGF-β-induced TFH cell program, that TFH and TH17 cells share a common developmental stage, and that c-Maf acts as a switch factor for TFH versus TH17 cell fates in TGF-β-rich environments in vitro and in vivo.

Modularized viromimetic polymer nanoparticle vaccines (VPNVaxs) to elicit durable and effective humoral immune responses

Virus-like particle (VLP) vaccines had shown great potential during the COVID-19 pandemic, and was thought to be the next generation of antiviral vaccine technology due to viromimetic structures. However, the time-consuming and complicated processes in establishing a current recombinant-protein-based VLP vaccine has limited its quick launch to the out-bursting pandemic. To simplify and optimize VLP vaccine design, we herein report a kind of viromimetic polymer nanoparticle vaccine (VPNVax), with subunit receptor-binding domain (RBD) proteins conjugated to the surface of polyethylene glycol-b-polylactic acid (PEG-b-PLA) nanoparticles for vaccination against SARS-CoV-2. The preparation of VPNVax based on synthetic polymer particle and chemical post-conjugation makes it possible to rapidly replace the antigens and construct matched vaccines at the emergence of different viruses. Using this modular preparation system, we identified that VPNVax with surface protein coverage of 20%-25% had the best immunostimulatory activity, which could keep high levels of specific antibody titers over 5 months and induce virus neutralizing activity when combined with an aluminum adjuvant. Moreover, the polymer nano-vectors could be armed with more immune-adjuvant functions by loading immunostimulant agents or chemical chirality design. This VPNVax platform provides a novel kind of rapidly producing and efficient vaccine against different variants of SARS-CoV-2 as well as other viral pandemics.

T follicular helper cells expansion in transplant recipients correlates with graft infiltration and adverse outcomes

Introduction

The process of immunization following vaccination in humans bears similarities to that of immunization with allografts. Whereas vaccination aims to elicit a rapid response, in the transplant recipient, immunosuppressants slow the immunization to alloantigens. The induction of CD4+CXCR5+ T follicular helper (Tfh) cells has been shown to correlate with the success of vaccine immunization.

Method

We studied a cohort of 65 transplant recipients who underwent histological evaluation concurrent with PBMC isolation and follow-up sampling to investigate the phenotypic profiles in the blood and allotissue and analyze their association with clinical events.

Results

The proportion of circulating Tfh cells was heterogeneous over time. Patients in whom this compartment increased had lower CCR7-PD1+CD4+CXCR5+ T cells during follow-up. These patients exhibited more alloreactive CD4+ T cells using HLA-DR-specific tetramers and a greater proportion of detectable circulating plasmablasts than the controls. Examination of baseline biopsies revealed that expansion of the circulating Tfh compartment did not follow prior intragraft leukocyte infiltration. However, multicolor immunofluorescence microscopy of the grafts showed a greater proportion of CXCR5+ T cells than in the controls. CD4+CXCR5+ cells were predominantly PD1+ and were in close contact with B cells in situ. Despite clinical stability at baseline, circulating Tfh expansion was associated with a higher risk of a composite of anti-HLA donor-specific antibodies, rejection, lower graft function, or graft loss.

Conclusion

In otherwise stable patients post-transplant, circulating Tfh expansion can identify ongoing alloreactivity, detectable before allograft injury. Tfh expansion is relevant clinically because it predicts poor graft prognosis. These findings have implications for immune surveillance.

Inflammatory Demyelinating Diseases of the Central Nervous System

Over the past decades, a large number of immunomodulatory or immunosuppressive treatments have been approved to treat central nervous system (CNS) demyelinating disorders such as multiple sclerosis (MS). Owing to the heterogeneity of patients with CNS demyelinating diseases, there is no clinical treatment that can adequately control all disease subtypes. Although significant progress has been made for relapsing-remitting MS, effective management of the progressive phase of MS has not yet been achieved. This is at least in part caused by our incomplete understanding of the mechanisms driving disease progression, despite our increasing knowledge regarding the underlying cellular and molecular mechanisms. Here, we summarized our current knowledge regarding the mechanisms of CNS demyelinating disorders and their animal models to identify open questions and challenges for existing concepts. We also discussed potential strategies for the future design of immune therapies to treat CNS demyelinating disorders.

Two-dose "extended priming" immunization amplifies humoral immune responses by synchronizing vaccine delivery with the germinal center response

"Extended priming" immunization regimens that prolong exposure of the immune system to vaccines during the primary immune response have shown promise in enhancing humoral immune responses to a variety of subunit vaccines in preclinical models. We previously showed that escalating-dosing immunization (EDI), where a vaccine is dosed every other day in an increasing pattern over 2 weeks dramatically amplifies humoral immune responses. But such a dosing regimen is impractical for prophylactic vaccines. We hypothesized that simpler dosing regimens might replicate key elements of the immune response triggered by EDI. Here we explored "reduced ED" immunization regimens, assessing the impact of varying the number of injections, dose levels, and dosing intervals during EDI. Using a stabilized HIV Env trimer as a model antigen combined with a potent saponin adjuvant, we found that a two-shot extended-prime regimen consisting of immunization with 20% of a given vaccine dose followed by a second shot with the remaining 80% of the dose 7 days later resulted in increased total GC B cells, 5-10-fold increased frequencies of antigen-specific GC B cells, and 10-fold increases in serum antibody titers compared to single bolus immunization. Computational modeling of the GC response suggested that this enhanced response is mediated by antigen delivered in the second dose being captured more efficiently as immune complexes in follicles, predictions we verified experimentally. Our computational and experimental results also highlight how properly designed reduced ED protocols enhance activation and antigen loading of dendritic cells and activation of T helper cells to amplify humoral responses. These results suggest that a two-shot priming approach can be used to substantially enhance responses to subunit vaccines.

'Persistent germinal center responses: slow-growing trees bear the best fruits'

Germinal centers (GCs) are key microanatomical sites in lymphoid organs where responding B cells mature and undergo affinity-based selection. The duration of the GC reaction has long been assumed to be relatively brief, but recent studies in humans, nonhuman primates, and mice indicate that GCs can last for weeks to months after initial antigen exposure. This review examines recent studies investigating the factors that influence GC duration, including antigen persistence, T-follicular helper cells, and mode of immunization. Potential mechanisms for how persistent GCs influence the B-cell repertoire are considered. Overall, these studies provide a blueprint for how to design better vaccines that elicit persistent GC responses.

Antigen-specific B cells direct T follicular-like helper cells into lymphoid follicles to mediate Mycobacterium tuberculosis control

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a global cause of death. Granuloma-associated lymphoid tissue (GrALT) correlates with protection during TB, but the mechanisms of protection are not understood. During TB, the transcription factor IRF4 in T cells but not B cells is required for the generation of the TH1 and TH17 subsets of helper T cells and follicular helper T (TFH)-like cellular responses. A population of IRF4+ T cells coexpress the transcription factor BCL6 during Mtb infection, and deletion of Bcl6 (Bcl6fl/fl) in CD4+ T cells (CD4cre) resulted in reduction of TFH-like cells, impaired localization within GrALT and increased Mtb burden. In contrast, the absence of germinal center B cells, MHC class II expression on B cells, antibody-producing plasma cells or interleukin-10-expressing B cells, did not increase Mtb susceptibility. Indeed, antigen-specific B cells enhance cytokine production and strategically localize TFH-like cells within GrALT via interactions between programmed cell death 1 (PD-1) and its ligand PD-L1 and mediate Mtb control in both mice and macaques.

AP-1-independent NFAT signaling maintains follicular T cell function in infection and autoimmunity

Coordinated gene expression programs enable development and function of T cell subsets. Follicular helper T (Tfh) cells coordinate humoral immune responses by providing selective and instructive cues to germinal center B cells. Here, we show that AP-1-independent NFAT gene expression, a program associated with hyporesponsive T cell states like anergy or exhaustion, is also a distinguishing feature of Tfh cells. NFAT signaling in Tfh cells, maintained by NFAT2 autoamplification, is required for their survival. ICOS signaling upregulates Bcl6 and induces an AP-1-independent NFAT program in primary T cells. Using lupus-prone mice, we demonstrate that genetic disruption or pharmacologic inhibition of NFAT signaling specifically impacts Tfh cell maintenance and leads to amelioration of autoantibody production and renal injury. Our data provide important conceptual and therapeutic insights into the signaling mechanisms that regulate Tfh cell development and function.

Multidimensional Analysis of Lung Lymph Nodes in a Mouse Model of Allergic Lung Inflammation following PM2.5 and Indeno[1,2,3-cd]pyrene Exposure

BACKGROUND

Ambient particulate matter with an aerodynamic diameter of ≤2.5 μm (PM2.5) is suggested to act as an adjuvant for allergen-mediated sensitization and recent evidence suggests the importance of T follicular helper (Tfh) cells in allergic diseases. However, the impact of PM2.5 exposure and its absorbed polycyclic aromatic hydrocarbon (PAHs) on Tfh cells and humoral immunity remains unknown.

OBJECTIVES

We aimed to explore the impact of environmental PM2.5 and indeno[1,2,3-cd]pyrene (IP), a prominent PAH, as a model, on Tfh cells and the subsequent pulmonary allergic responses.

METHODS

PM2.5- or IP-mediated remodeling of cellular composition in lung lymph nodes (LNs) was determined by mass cytometry in a house dust mite (HDM)-induced mouse allergic lung inflammation model. The differentiation and function of Tfh cells in vitro were analyzed by flow cytometry, quantitative reverse transcription polymerase chain reaction, enzyme-linked immunosorbent assay, chromatin immunoprecipitation, immunoprecipitation, and western blot analyses.

RESULTS

Mice exposed to PM2.5 during the HDM sensitization period demonstrated immune cell population shifts in lung LNs as compared with those sensitized with HDM alone, with a greater number of differentiated Tfh2 cells, enhanced allergen-induced immunoglobulin E (IgE) response and pulmonary inflammation. Similarly enhanced phenotypes were also found in mice exposed to IP and sensitized with HDM. Further, IP administration was found to induce interleukin-21 (Il21) and Il4 expression and enhance Tfh2 cell differentiation in vitro, a finding which was abrogated in aryl hydrocarbon receptor (AhR)-deficient CD4+ T cells. Moreover, we showed that IP exposure increased the interaction of AhR and cellular musculoaponeurotic fibrosarcoma (c-Maf) and its occupancy on the Il21 and Il4 promoters in differentiated Tfh2 cells.

DISCUSSION

These findings suggest that the PM2.5 (IP)-AhR-c-Maf axis in Tfh2 cells was important in allergen sensitization and lung inflammation, thus adding a new dimension in the understanding of Tfh2 cell differentiation and function and providing a basis for establishing the environment-disease causal relationship. https://doi.org/10.1289/EHP11580.

CXCR5+PD-1++ CD4+ T cells colonize infant intestines early in life and promote B cell maturation

Gastrointestinal infections are a major cause for serious clinical complications in infants. The induction of antibody responses by B cells is critical for protective immunity against infections and requires CXCR5+PD-1++ CD4+ T cells (TFH cells). We investigated the ontogeny of CXCR5+PD-1++ CD4+ T cells in human intestines. While CXCR5+PD-1++ CD4+ T cells were absent in fetal intestines, CXCR5+PD-1++ CD4+ T cells increased after birth and were abundant in infant intestines, resulting in significant higher numbers compared to adults. These findings were supported by scRNAseq analyses, showing increased frequencies of CD4+ T cells with a TFH gene signature in infant intestines compared to blood. Co-cultures of autologous infant intestinal CXCR5+PD-1+/-CD4+ T cells with B cells further demonstrated that infant intestinal TFH cells were able to effectively promote class switching and antibody production by B cells. Taken together, we demonstrate that functional TFH cells are numerous in infant intestines, making them a promising target for oral pediatric vaccine strategies.

The Immunobiology and Pathogenesis of Celiac Disease

Among human leukocyte antigen (HLA)-associated disorders, celiac disease has an immunopathogenesis that is particularly well understood. The condition is characterized by hypersensitivity to cereal gluten proteins, and the disease lesion is localized in the gut. Still, the diagnosis can be made by detection of highly disease-specific autoantibodies to transglutaminase 2 in the blood. We now have mechanistic insights into how the disease-predisposing HLA-DQ molecules, via presentation of posttranslationally modified gluten peptides, are connected to the generation of these autoantibodies. This review presents our current understanding of the immunobiology of this common disorder that is positioned in the border zone between food hypersensitivity and autoimmunity.

The Diagnostic Value of Neutrophil to Lymphocyte Ratio as an Effective Biomarker for Neuromyelitis Optica Spectrum Disorder

Background

Neuromyelitis Optica (NMO) is a serious condition associated with inflammation. Early diagnosis and detection are critical for early intervention. In this systematic review, we investigate the role of the neutrophil to lymphocyte ratio (NLR) as an important biomarker for NMO.

Methods

Ten studies were selected that were sufficiently high quality and then checked for quality. The studies were organized by English language and selective inclusion criteria.

Results

NLR was significantly increased in NMO patients compared to controls. The ratio was specifically proportional to severity of disease. More severe disease had a higher ratio.

Conclusion

NLR offers a reliable and affordable method for early detection of disease severity. This can help guide appropriate treatment selection and monitor treatment response.

Secreted heat shock protein gp96-Ig and OX40L-Fc combination vaccine enhances SARS-CoV-2 Spike (S) protein-specific B and T cell immune responses

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gp96-Ig-S-OX40L-Fc vaccine enhances S-specific IgG responses.

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gp96-Ig-S-OX40L-Fc vaccine enhances TFH cell responses.

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gp96-Ig-S-OX40L-Fc vaccine enhances lungs S-specific CD8 + T cell responses.

Encouraging protection results from current mRNA-based SARS-CoV-2 vaccine platforms are primarily due to the induction of SARS- CoV-2- specific B cell antibody and CD4 + T cell. Even though, current mRNA vaccine platforms are adept in inducing SARS-CoV2-specific CD8 + T cell, much less is known about CD8 T cells contribution to the overall vaccine protection. Our allogeneic cellular vaccine, based on a secreted form of the heat-shock protein gp96-Ig, achieves high frequencies of polyclonal CD8 + T cell responses to tumor and infectious antigens through antigen cross-priming in vivo. We and others have shown that gp96-Ig, in addition to antigen-specific CD8 + T cell anti-tumor and anti-pathogen immunity, primes antibody responses as well. Here, we generated a cell-based vaccine that expresses SARS-Cov-2 Spike (S) protein and simultaneously secretes gp96-Ig and OX40L-Fc fusion proteins. We show that co-secretion of gp96-Ig-S peptide complexes and the OX40L-Fc costimulatory fusion protein in allogeneic cell lines results in enhanced activation of S protein-specific IgG antibody responses. These findings were further strengthened by the observation that this vaccine platform induces T follicular helper cells (TFH) and protein-S -specific CD8 + T cells. Thus, a cell-based gp96-Ig vaccine/OX40-L fusion protein regimen provides encouraging translational data that this vaccine platform induces pathogen-specific CD8+, CD4 + T and B cell responses, and may cohesively work as a booster for FDA-approved vaccines. Our vaccine platform can be rapidly engineered and customized based on other current and future pathogen sequences.

The immunopathology of B lymphocytes during stroke-induced injury and repair

B cells, also known as B lymphocytes or lymphoid lineage cells, are a historically understudied cell population with regard to brain-related injuries and diseases. However, an increasing number of publications have begun to elucidate the different phenotypes and roles B cells can undertake during central nervous system (CNS) pathology, including following ischemic and hemorrhagic stroke. B cell phenotype is intrinsically linked to function following stroke, as they may be beneficial or detrimental depending on the subset, timing, and microenvironment. Factors such as age, sex, and presence of co-morbidity also influence the behavior of post-stroke B cells. The following review will briefly describe B cells from origination to senescence, explore B cell function by integrating decades of stroke research, differentiate between the known B cell subtypes and their respective activity, discuss some of the physiological influences on B cells as well as the influence of B cells on certain physiological functions, and highlight the differences between B cells in healthy and disease states with particular emphasis in the context of ischemic stroke.

The application of exosomes in the treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a heterogeneous and invasive breast cancer (BC) subtype that is estrogen receptor-negative, progesterone receptor-negative, and human epidermal growth factor receptor 2 (Her2)-negative. So far, the treatment of TNBC is still ineffective due to the lack of well-defined molecular targets. Exosomes are nanosized extracellular vesicles composed of lipid bilayers. They originate from various types of donor cells and release a complex mixture of contents including diverse nucleic acid types (miRNA, LnRNA, siRNA, and DNA) and proteins; after binding to recipient cells the exosomes release their contents that execute their biological functions. Exosomes have been reported to play an important role in the tumorigenesis of TNBC, including tumor initiation, metastasis, angiogenesis, cell proliferation, immune escape, and drug resistance. On the other hand, exosomes can be valuable biomarkers for diagnosis, monitoring, and treatment of TNBC. More interestingly, exosomes can be harnessed as a nanosized drug-delivery system specifically targeting TNBC. In this review, we present the most recent mechanistic findings and clinical applications of exosomes in TNBC therapy, focusing on their use as diagnostic and prognostic biomarkers, nanoscale drug delivery platforms, and immunotherapeutic agents. In addition, the associated challenges and future directions of using exosomes for TNBC treatment will be discussed.

Evolution of antigen-specific follicular helper T cell transcription from effector function to memory

Understanding how follicular helper T cells (TFH) regulate the specialization, maturation, and differentiation of adaptive B cell immunity is crucial for developing durable high-affinity immune protection. Using indexed single-cell molecular strategies, we reveal a skewed intraclonal assortment of higher-affinity T cell receptors and the distinct molecular programming of the localized TFH compartment compared with emigrant conventional effector T_H cells. We find a temporal shift in B cell receptor class switch, which permits identification of inflammatory and anti-inflammatory modules of transcriptional programming that subspecialize TFH function before and during the germinal center (GC) reaction. Late collapse of this local primary GC reaction reveals a persistent post-GC TFH population that discloses a putative memory TFH program. These studies define subspecialized antigen-specific TFH transcriptional programs that progressively change with antibody class-specific evolution of high-affinity B cell immunity and a memory TFH transcriptional program that emerges upon local GC resolution.

Interleukin-21, acting beyond the immunological synapse, independently controls T follicular helper and germinal center B cells

Germinal centers (GCs), transient structures within B cell follicles and central to affinity maturation, require the coordinated behavior of T and B cells. IL-21, a pleiotropic T cell-derived cytokine, is key to GC biology through incompletely understood mechanisms. By genetically restricting production and receipt of IL-21 in vivo, we reveal how its independent actions on T and B cells combine to regulate the GC. IL-21 established the magnitude of the GC B cell response by promoting CD4⁺ T cell expansion and differentiation in a dose-dependent manner and with paracrine activity. Within GC, IL-21 specifically promoted B cell centroblast identity and, when bioavailability was high, plasma cell differentiation. Critically, these actions may occur irrespective of cognate T-B interactions, making IL-21 a general promoter of growth as distinct to a mediator of affinity-driven selection via synaptic delivery. This promiscuous activity of IL-21 explains the consequences of IL-21 deficiency on antibody-based immunity.

The role of B cells and their interactions with stromal cells in the context of inflammatory autoimmune diseases

Interactions between B cells and stromal cells have essential functions in immune cell development and responses. During chronic inflammation, the pro-inflammatory microenvironment leads to changes in stromal cells, which acquire a pathogenic phenotype specific to each organ and disease. B cells are recruited to the site of inflammation and interact with these pathogenic stromal cells contributing to the disease's severity. In addition to producing autoantibodies, B cells contribute to the pathogenesis of autoimmune inflammatory diseases by serving as professional antigen-presenting cells, producing cytokines, and through additional mechanisms. This review describes the role of B cells and their interactions with stromal cells in chronic inflammation, with a focus on human disease, using three selected autoimmune inflammatory diseases: rheumatoid arthritis, systemic lupus erythematosus and multiple sclerosis. Understanding B cells roles and their interaction with stromal cells will help develop new therapeutic options for the treatment of autoimmune diseases.

Antigen-Presenting B Cells Program the Efferent Lymph T Helper Cell Response

B cells interact with T follicular helper (Tfh) cells in germinal centers (GCs) to generate high-affinity antibodies. Much less is known about how cognate T–B-cell interactions influence Th cells that enter circulation and peripheral tissues. Therefore, we generated mice lacking MHC-II expressing B cells and, by thoracic duct cannulation, analyzed Th cells in the efferent lymph at defined intervals post-immunization. Focusing on gut-draining mesenteric lymph nodes (MLNs), we show that antigen-specific α₄β₇⁺ gut-homing effector Th cells enter the circulation prior to CXCR5⁺PD-1⁺ Tfh-like cells. B cells appear to have no or limited impact on the early generation and egress of gut-homing Th cells but are critical for the subsequent appearance of Tfh-like cells that peak in the lymph before GCs have developed. At this stage, antigen-presenting B cells also reduce the proportion of α₄β₇⁺ Th cells in the MLN and efferent lymph. Furthermore, cognate B-cell interaction drives a broad transcriptional program in Th cells, including IL-4 that is confined to the Tfh cell lineage. The IL-4-producing Tfh-like cells originate from Bcl6⁺ precursors in the LNs and have gut-homing capacity. Hence, B cells program the efferent lymph Th cell response within a limited window of time after antigenic challenge.

ICOS Expression Is Required for Maintenance but Not the Formation of Germinal Centers in the Spleen in Response to Plasmodium yoelii Infection

Inducible T cell costimulator (ICOS) plays a key role in the differentiation and maintenance of follicular helper T (Tfh) cells and, thus, germinal center (GC) formation. Previously, our laboratory showed in a Plasmodium chabaudi infection model that Icos-/- mice were significantly impaired in their ability to form GCs despite persistent infection and, thus, a continued antigen (Ag) load. Here, we show that the resolution of primary infection with Plasmodium yoelii was delayed in Icos-/- mice. This phenotype was associated with a reduction in the accumulation of Tfh-like and GC Tfh cells and an early deficiency in Ag-specific antibody (Ab) production. However, Icos-/- mice could form GCs, although they were less frequent in number than in wild-type (WT) mice. Nonetheless, the Ag-specific Abs from Icos-/- mice lacked signs of affinity maturation, suggesting functional defects associated with these GCs. Eventually, these GC structures dissipated more rapidly in Icos-/- mice than in WT mice. Moreover, the ability of Icos-/- mice to form these GC structures is not reliant on the high Ag loads associated with P. yoelii infections, as GC formation was preserved in Icos-/- mice treated with atovaquone. Finally, mice were unable to form secondary GCs in the absence of ICOS after rechallenge. Overall, these data demonstrate the necessity of ICOS in the maintenance of Tfh cells, the formation and maintenance of sufficient numbers of functioning GCs, and the ability to generate new GC structures after reinfection with P. yoelii.

Tfh-cell-derived interleukin 21 sustains effector CD8+ T cell responses during chronic viral infection

CD4+ T cell-derived interleukin 21 (IL-21) sustains CD8+ T cell responses during chronic viral infection, but the helper subset that confers this protection remains unclear. Here, we applied scRNA and ATAC-seq approaches to determine the heterogeneity of IL-21+CD4+ T cells during LCMV clone 13 infection. CD4+ T cells were comprised of three transcriptionally and epigenetically distinct populations: Cxcr6+ Th1 cells, Cxcr5+ Tfh cells, and a previously unrecognized Slamf6+ memory-like (Tml) subset. T cell differentiation was specifically redirected toward the Tml subset during chronic, but not acute, LCMV infection. Although this subset displayed an enhanced capacity to accumulate and some developmental plasticity, it remained largely quiescent, which may hinder its helper potential. Conversely, mixed bone marrow chimera experiments revealed that Tfh cell-derived IL-21 was critical to sustain CD8+ T cell responses and viral control. Thus, strategies that bolster IL-21+Tfh cell responses may prove effective in enhancing CD8+ T cell-mediated immunity.

Strong influenza-induced TFH generation requires CD4 effectors to recognize antigen locally and receive signals from continuing infection

Influenza infection elicits strong, long-lived protective antibodies, but most current influenza vaccines give weaker, short-lived protection. We noted that live virus is still replicating, making antigen and causing inflammation at 7 d postinfection (dpi), while an inactivated vaccine provides antigen for at most 4 dpi. We show that the generation of key T follicular helper cells (T_FH) requires they recognize antigen locally at 6 dpi in the presence of ongoing viral infection. This creates a checkpoint that restricts T_FH responses to dangerous infections that persist through the checkpoint. Using a live attenuated vaccine, akin to Flumist, we found that adding a second dose at 6 d generated a strong T_FH response, suggesting an approach to improve vaccine strategies.

While influenza infection induces robust, long-lasting, antibody responses and protection, including the T follicular helper cells (T_FH) required to drive B cell germinal center (GC) responses, most influenza vaccines do not. We investigated the mechanisms that drive strong T_FH responses during infection. Infection induces viral replication and antigen (Ag) presentation lasting through the CD4 effector phase, but Ag and pathogen recognition receptor signals are short-lived after vaccination. We analyzed the need for both infection and Ag presentation at the effector phase, using an in vivo sequential transfer model to time their availability. Differentiation of CD4 effectors into T_FH and GC-T_FH required that they recognize Ag locally in the site of T_FH development, at the effector phase, but did not depend on specific Ag-presenting cells (APCs). In addition, concurrent signals from infection were necessary even when sufficient Ag was presented. Providing these signals with a second dose of live attenuated influenza vaccine at the effector phase drove T_FH and GC-T_FH development equivalent to live infection. The results suggest that vaccine approaches can induce strong T_FH development that supports GC responses akin to infection, if they supply these effector phase signals at the right time and site. We suggest that these requirements create a checkpoint that ensures T_FH only develop fully when infection is still ongoing, thereby avoiding unnecessary, potentially autoimmune, responses.

In vivo CRISPR screens reveal a HIF-1α-mTOR-network regulates T follicular helper versus Th1 cells

T follicular helper (Tfh) cells provide signals to initiate and maintain the germinal center (GC) reaction and are crucial for the generation of robust, long-lived antibody responses, but how the GC microenvironment affects Tfh cells is not well understood. Here we develop an in vivo T cell-intrinsic CRISPR-knockout screen to evaluate Tfh and Th1 cells in an acute viral infection model to identify regulators of Tfh cells in their physiological setting. Using a screen of druggable-targets, alongside genetic, transcriptomic and cellular analyses, we identify a function of HIF-1α in suppressing mTORC1-mediated and Myc-related pathways, and provide evidence that VHL-mediated degradation of HIF-1α is required for Tfh development; an expanded in vivo CRISPR screen reveals multiple components of these pathways that regulate Tfh versus Th1 cells, including signaling molecules, cell-cycle regulators, nutrient transporters, metabolic enzymes and autophagy mediators. Collectively, our data serve as a resource for studying Tfh versus Th1 decisions, and implicate the VHL-HIF-1α axis in fine-tuning Tfh generation.

T follicular helper (Tfh) and T help type 1 (Th1) cells both arise from naïve CD4 T cells, but detailed knowledge of their differentiation remains incomplete. Here the authors pursue an in vivo CRISPR screen to identify genes, focusing on druggable targets, regulating Tfh versus Th1 to provide a resource for related studies, while also implicating HIF-1α and VHL in this regulation.

The concerted change in the distribution of cell cycle phases and zone composition in germinal centers is regulated by IL-21

Humoral immune responses require germinal centres (GC) for antibody affinity maturation. Within GC, B cell proliferation and mutation are segregated from affinity-based positive selection in the dark zone (DZ) and light zone (LZ) substructures, respectively. While IL-21 is known to be important in affinity maturation and GC maintenance, here we show it is required for both establishing normal zone representation and preventing the accumulation of cells in the G1 cell cycle stage in the GC LZ. Cell cycle progression of DZ B cells is unaffected by IL-21 availability, as is the zone phenotype of the most highly proliferative GC B cells. Collectively, this study characterises the development of GC zones as a function of time and B cell proliferation and identifies IL-21 as an important regulator of these processes. These data help explain the requirement for IL-21 in normal antibody affinity maturation.

T cell activation niches-Optimizing T cell effector function in inflamed and infected tissues

Successful immunity to infection, malignancy, and tissue damage requires the coordinated recruitment of numerous immune cell subsets to target tissues. Once within the target tissue, effector T cells rely on local chemotactic cues and structural cues from the tissue matrix to navigate the tissue, interact with antigen-presenting cells, and release effector cytokines. This highly dynamic process has been "caught on camera" in situ by intravital multiphoton imaging. Initial studies revealed a surprising randomness to the pattern of T cell migration through inflamed tissues, behavior thought to facilitate chance encounters with rare antigen-bearing cells. Subsequent tissue-wide visualization has uncovered a high degree of spatial preference when it comes to T cell activation. Here, we discuss the basic tenants of a successful effector T cell activation niche, taking cues from the dynamics of Tfh positioning in the lymph node germinal center. In peripheral tissues, steady-state microanatomical organization may direct the location of "pop-up" de novo activation niches, often observed as perivascular clusters, that support early effector T cell activation. These perivascular activation niches appear to be regulated by site-specific chemokines that coordinate the recruitment of dendritic cells and other innate cells for local T cell activation, survival, and optimized effector function.

Follicular T-Helper Cells in Marginal Zone Lymphoma: Evidence of an Organoid Immune Response

INTRODUCTION

Primary cutaneous marginal zone B-cell lymphoma (MZL) follows an indolent clinical course. Histopathologically, there is a polymorphous infiltrate that includes small lymphocyte-like and centrocyte-like B cells and plasma cells usually with a substantial T-cell fraction. Primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder, in which the signature cells have a follicular T-helper (TFH) phenotype and are admixed with numerous B cells. Thus, both present histologies of combined B-cell and T-cell infiltrates and represent differential diagnoses. The presence of TFH in MZL has yet to be elucidated.

METHODS

Forty-one biopsies from 40 cases of MZL and 7 cases of lymphoid hyperplasia cutis (LCH) were stained with antibodies to follicular T-helper cells, including Bcl-6, PD-1, ICOS, and CD10, as part of their diagnostic workup, were reviewed, and the stained slides were evaluated semiquantitively. Five reactive lymph nodes were also evaluated as controls.

RESULTS

All cases of MZL and LCH contained TFH, albeit usually in low proportions. There were repeated differences in levels of expression between TFH markers, with PD1 and Bcl-6 being the most prevalent. The pattern of involvement in MZL and LCH closely mirrored that observed in the reactive lymph nodes.

CONCLUSION

MZL includes TFH cells, similar to reactive lymph nodes, and a complexity of cell types. This provides evidence of an organoid immune response challenging its simple categorization as a malignancy.

Durable CD4 T-Cell Memory Generation Depends on Persistence of High Levels of Infection at an Effector Checkpoint that Determines Multiple Fates

We have discovered that the determination of CD4 effector and memory fates after infection is regulated not only by initial signals from antigen and pathogen recognition, but also by a second round of such signals at a checkpoint during the effector response. Signals to effectors determine their subsequent fate, inducing further progression to tissue-restricted follicular helpers, cytotoxic CD4 effectors, and long-lived memory cells. The follicular helpers help the germinal center B-cell responses that give rise to high-affinity long-lived antibody responses and memory B cells that synergize with T-cell memory to provide robust long-lived protection. We postulate that inactivated vaccines do not provide extended signals from antigen and pathogen beyond a few days, and thus elicit ineffective CD4 T- and B-cell effector responses and memory. Defining the mechanisms that underlie effective responses should provide insights necessary to develop vaccine strategies that induce more effective and durable immunity.

BCL6 controls contact-dependent help delivery during follicular T-B cell interactions

BCL6 is required for development of follicular T helper (Tfh) cells to support germinal center (GC) formation. However, it is not clear what unique functions programmed by BCL6 can explain its absolute essentiality in T cells for GC formation. We found that ablation of one Bcl6 allele did not appreciably alter early T cell activation and follicular localization but inhibited GC formation and Tfh cell maintenance. BCL6 impinged on Tfh calcium signaling and also controlled Tfh entanglement with and CD40L delivery to B cells. Amounts of BCL6 protein and nominal frequencies of Tfh cells markedly changed within hours after strengths of T-B cell interactions were altered in vivo, while CD40L overexpression rectified both defective GC formation and Tfh cell maintenance because of the BCL6 haploinsufficiency. Our results reveal BCL6 functions in Tfh cells that are essential for GC formation and suggest that BCL6 helps maintain Tfh cell phenotypes in a T cell non-autonomous manner.

System-Level Scenarios for the Elucidation of T Cell-Mediated Germinal Center B Cell Differentiation

Germinal center (GC) reactions are vital to the correct functioning of the adaptive immune system, through formation of high affinity, class switched antibodies. GCs are transient anatomical structures in secondary lymphoid organs where specific B cells, after recognition of antigen and with T cell help, undergo class switching. Subsequently, B cells cycle between zones of proliferation and somatic hypermutation and zones where renewed antigen acquisition and T cell help allows for selection of high affinity B cells (affinity maturation). Eventually GC B cells first differentiate into long-lived memory B cells (MBC) and finally into plasma cells (PC) that partially migrate to the bone marrow to encapsulate into long-lived survival niches. The regulation of GC reactions is a highly dynamically coordinated process that occurs between various cells and molecules that change in their signals. Here, we present a system-level perspective of T cell-mediated GC B cell differentiation, presenting and discussing the experimental and computational efforts on the regulation of the GCs. We aim to integrate Systems Biology with B cell biology, to advance elucidation of the regulation of high-affinity, class switched antibody formation, thus to shed light on the delicate functioning of the adaptive immune system. Specifically, we: i) review experimental findings of internal and external factors driving various GC dynamics, such as GC initiation, maturation and GCBC fate determination; ii) draw comparisons between experimental observations and mathematical modeling investigations; and iii) discuss and reflect on current strategies of modeling efforts, to elucidate B cell behavior during the GC tract. Finally, perspectives are specifically given on to the areas where a Systems Biology approach may be useful to predict novel GCBC-T cell interaction dynamics.

Compartmentalized multicellular crosstalk in lymph nodes coordinates the generation of potent cellular and humoral immune responses

Distributed throughout the body, lymph nodes (LNs) constitute an important crossroad where resident and migratory immune cells interact to initiate antigen‐specific immune responses supported by a dynamic 3‐dimensional network of stromal cells, that is, endothelial cells and fibroblastic reticular cells (FRCs). LNs are organized into four major subanatomically separated compartments: the subcapsular sinus (SSC), the paracortex, the cortex, and the medulla. Each compartment is underpinned by particular FRC subsets that physically support LN architecture and delineate functional immune niches by appropriately providing environmental cues, nutrients, and survival factors to the immune cell subsets they interact with. In this review, we discuss how FRCs drive the structural and functional organization of each compartment to give rise to prosperous interactions and coordinate immune cell activities. We also discuss how reciprocal communication makes FRCs and immune cells perfect compatible partners for the generation of potent cellular and humoral immune responses.

T Cell/B Cell Interactions in the Establishment of Protective Immunity

Follicular helper T cells (Tfh) are the T cell subset providing help to B cells for the generation of high-affinity antibodies and are therefore of key interest for the development of vaccination strategies against infectious diseases. In this review, we will discuss how the generation of Tfh cells and their interaction with B cells in secondary lymphoid organs can be optimized for therapeutic purposes. We will summarize different T cell subsets including Tfh-like peripheral helper T cells (Tph) capable of providing B cell help. In particular, we will highlight the novel concept of T cell/B cell interaction in non-lymphoid tissues as an important element for the generation of protective antibodies directly at the site of pathogen invasion.

Neuromyelitis optica spectrum disorders: from pathophysiology to therapeutic strategies

Neuromyelitis optica (NMO) is a chronic inflammatory autoimmune disease of the central nervous system (CNS) characterized by acute optic neuritis (ON) and transverse myelitis (TM). NMO is caused by a pathogenic serum IgG antibody against the water channel aquoporin 4 (AQP4) in the majority of patients. AQP4-antibody (AQP4-ab) presence is highly specific, and differentiates NMO from multiple sclerosis. It binds to AQP4 channels on astrocytes, triggering activation of the classical complement cascade, causing granulocyte, eosinophil, and lymphocyte infiltration, culminating in injury first to astrocyte, then oligodendrocytes followed by demyelination and neuronal loss. NMO spectrum disorder (NMOSD) has recently been defined and stratified based on AQP4-ab serology status. Most NMOSD patients experience severe relapses leading to permanent neurologic disability, making suppression of relapse frequency and severity, the primary objective in disease management. The most common treatments used for relapses are steroids and plasma exchange.Currently, long-term NMOSD relapse prevention includes off-label use of immunosuppressants, particularly rituximab. In the last 2 years however, three pivotal clinical trials have expanded the spectrum of drugs available for NMOSD patients. Phase III studies have shown significant relapse reduction compared to placebo in AQP4-ab-positive patients treated with satralizumab, an interleukin-6 receptor (IL-6R) inhibitor, inebilizumab, an antibody against CD19⁺ B cells; and eculizumab, an antibody blocking the C5 component of complement. In light of the new evidence on NMOSD pathophysiology and of preliminary results from ongoing trials with new drugs, we present this descriptive review, highlighting promising treatment modalities as well as auspicious preclinical and clinical studies.

Emerging Complexity in CD4+T Lineage Programming and Its Implications in Colorectal Cancer

The intestinal immune system has the difficult task of protecting a large environmentally exposed single layer of epithelium from pathogens without allowing inappropriate inflammatory responses. Unmitigated inflammation drives multiple pathologies, including the development of colorectal cancer. CD4⁺T cells mediate both the suppression and promotion of intestinal inflammation. They comprise an array of phenotypically and functionally distinct subsets tailored to a specific inflammatory context. This diversity of form and function is relevant to a broad array of pathologic and physiologic processes. The heterogeneity underlying both effector and regulatory T helper cell responses to colorectal cancer, and its impact on disease progression, is reviewed herein. Importantly, T cell responses are dynamic; they exhibit both quantitative and qualitative changes as the inflammatory context shifts. Recent evidence outlines the role of CD4⁺T cells in colorectal cancer responses and suggests possible mechanisms driving qualitative alterations in anti-cancer immune responses. The heterogeneity of T cells in colorectal cancer, as well as the manner and mechanism by which they change, offer an abundance of opportunities for more specific, and likely effective, interventional strategies.

In Vivo CD4+ T Cell Differentiation and Function: Revisiting the Th1/Th2 Paradigm

The discovery of CD4⁺ T cell subset-defining master transcription factors and framing of the Th1/Th2 paradigm ignited the CD4⁺ T cell field. Advances in in vivo experimental systems, however, have revealed that more complex lineage-defining transcriptional networks direct CD4⁺ T cell differentiation in the lymphoid organs and tissues. This review focuses on the layers of fate decisions that inform CD4⁺ T cell differentiation in vivo. Cytokine production by antigen-presenting cells and other innate cells influences the CD4⁺ T cell effector program [e.g., T helper type 1 (Th1), Th2, Th17]. Signals downstream of the T cell receptor influence whether individual clones bearing hallmarks of this effector program become T follicular helper cells, supporting development of B cells expressing specific antibody isotypes, or T effector cells, which activate microbicidal innate cells in tissues. These bifurcated, parallel axes allow CD4⁺ T cells to augment their particular effector program and prevent disease.

Default polyfunctional T helper 1 response to ample signal 1 alone

CD4+ T cells integrate well-defined signals from the T-cell receptor (TCR) (signal 1) and a host of costimulatory molecules (signal 2) to initiate clonal expansion and differentiation into diverse functional T helper (Th) subsets. However, our ability to guide the expansion of context-appropriate Th subsets by deploying these signals in vaccination remains limited. Using cell-based vaccines, we selectively amplified signal 1 by exclusive presentation of an optimized peptide:MHC II (pMHC II) complex in the absence of classic costimulation. Contrary to expectations, amplified signal 1 alone was strongly immunogenic and selectively expanded high-affinity TCR clonotypes, despite delivering intense TCR signals. In contrast to natural infection or standard vaccines, amplified signal 1, presented by a variety of professional and nonprofessional antigen-presenting cells (APCs), induced exclusively polyfunctional Th1 effector and memory cells, which protected against retroviral infection and tumor challenge, and expanded tumor-reactive CD4+ T cells otherwise rendered unresponsive in tumor-bearing hosts. Together, our findings uncover a default Th1 response to ample signal 1 and offer a means to selectively prime such protective responses by vaccination.

The OX40/OX40L Axis Regulates T Follicular Helper Cell Differentiation: Implications for Autoimmune Diseases

T Follicular helper (Tfh) cells, a unique subset of CD4+ T cells, play an essential role in B cell development and the formation of germinal centers (GCs). Tfh differentiation depends on various factors including cytokines, transcription factors and multiple costimulatory molecules. Given that OX40 signaling is critical for costimulating T cell activation and function, its roles in regulating Tfh cells have attracted widespread attention. Recent data have shown that OX40/OX40L signaling can not only promote Tfh cell differentiation and maintain cell survival, but also enhance the helper function of Tfh for B cells. Moreover, upregulated OX40 signaling is related to abnormal Tfh activity that causes autoimmune diseases. This review describes the roles of OX40/OX40L in Tfh biology, including the mechanisms by which OX40 signaling regulates Tfh cell differentiation and functions, and their close relationship with autoimmune diseases.

Single cell analysis of host response to helminth infection reveals the clonal breadth, heterogeneity, and tissue-specific programming of the responding CD4+ T cell repertoire

The CD4⁺ T cell response is critical to host protection against helminth infection. How this response varies across different hosts and tissues remains an important gap in our understanding. Using IL-4-reporter mice to identify responding CD4⁺ T cells to Nippostrongylus brasiliensis infection, T cell receptor sequencing paired with novel clustering algorithms revealed a broadly reactive and clonally diverse CD4⁺ T cell response. While the most prevalent clones and clonotypes exhibited some tissue selectivity, most were observed to reside in both the lung and lung-draining lymph nodes. Antigen-reactivity of the broader repertoires was predicted to be shared across both tissues and individual mice. Transcriptome, trajectory, and chromatin accessibility analysis of lung and lymph-node repertoires revealed three unique but related populations of responding IL-4⁺ CD4⁺ T cells consistent with T follicular helper, T helper 2, and a transitional population sharing similarity with both populations. The shared antigen reactivity of lymph node and lung repertoires combined with the adoption of tissue-specific gene programs allows for the pairing of cellular and humoral responses critical to the orchestration of anti-helminth immunity.

Using various “omic” approaches, the CD4⁺ T cell receptor (TCR) repertoire was explored after primary helminth infection. Infection generated a broadly reactive and clonally diverse CD4⁺ T cell response with the most prevalent clonotypes and predicted antigen specificities residing in both the lung and lung-draining lymph nodes. Tissue-specific programming of responding CD4⁺ T cells directed the establishment of committed Tfh and Th2 cells, both critical for driving distinct hallmarks of type-2 inflammation. These datasets help to explore the diverse yet tissue-specific nature of anti-helminth immunity.

A review of signaling and transcriptional control in T follicular helper cell differentiation

T follicular helper (Tfh) cells are a critical component of adaptive immunity and assist in optimal Ab-mediated defense. Multiple effector functions of Tfh support germinal center B cell survival, Ab class switching, and plasma cell maturation. In the past 2 decades, the phenotype and functional characteristics of GC Tfh have been clarified allowing for robust studies of the Th subset including activation signals and environmental cues controlling Tfh differentiation and migration during an immune response. A unique, 2-step differentiation process of Tfh has been proposed but the mechanisms underlying transition between unstable Tfh precursors and functional mature Tfh remain elusive. Likewise, newly identified transcriptional regulators of Tfh development have not yet been incorporated into our understanding of how these cells might function in disease. Here, we review the signals and downstream transcription factors that shape Tfh differentiation including what is known about the epigenetic processes that maintain Tfh identity. It is proposed that further evaluation of the stepwise differentiation pattern of Tfh will yield greater insights into how these cells become dysregulated in autoimmunity.

Regulation of Intrinsic and Bystander T Follicular Helper Cell Differentiation and Autoimmunity by Tsc1

T Follicular helper (Tfh) cells promote germinal center (GC) B cell responses to develop effective humoral immunity against pathogens. However, dysregulated Tfh cells can also trigger autoantibody production and the development of autoimmune diseases. We report here that Tsc1, a regulator for mTOR signaling, plays differential roles in Tfh cell/GC B cell responses in the steady state and in immune responses to antigen immunization. In the steady state, Tsc1 in T cells intrinsically suppresses spontaneous GC-Tfh cell differentiation and subsequent GC-B cell formation and autoantibody production. In immune responses to antigen immunization, Tsc1 in T cells is required for efficient GC-Tfh cell expansion, GC-B cell induction, and antigen-specific antibody responses, at least in part via promoting GC-Tfh cell mitochondrial integrity and survival. Interestingly, in mixed bone marrow chimeric mice reconstituted with both wild-type and T cell-specific Tsc1-deficient bone marrow cells, Tsc1 deficiency leads to enhanced GC-Tfh cell differentiation of wild-type CD4 T cells and increased accumulation of wild-type T regulatory cells and T follicular regulatory cells. Such bystander GC-Tfh cell differentiation suggests a potential mechanism that could trigger self-reactive GC-Tfh cell/GC responses and autoimmunity via neighboring GC-Tfh cells.

Antigen-dependent multistep differentiation of T follicular helper cells and its role in SARS-CoV-2 infection and vaccination

T follicular helper (Tfh) cells play an essential role in regulating the GC reaction and, consequently, the generation of high‐affinity antibodies and memory B cells. Therefore, Tfh cells are critical for potent humoral immune responses against various pathogens and their dysregulation has been linked to autoimmunity and cancer. Tfh cell differentiation is a multistep process, in which cognate interactions with different APC types, costimulatory and coinhibitory pathways, as well as cytokines are involved. However, it is still not fully understood how a subset of activated CD4⁺ T cells begins to express the Tfh cell‐defining chemokine receptor CXCR5 during the early stage of the immune response, how some CXCR5⁺ pre‐Tfh cells enter the B‐cell follicles and mature further into GC Tfh cells, and how Tfh cells are maintained in the memory compartment. In this review, we discuss recent advances on how antigen and cognate interactions are important for Tfh cell differentiation and long‐term persistence of Tfh cell memory, and how this is relevant to the current understanding of COVID‐19 pathogenesis and the development of potent SARS‐CoV‐2 vaccines.

Circulating Tfh cell and subsets distribution are associated with low-responsiveness to hepatitis B vaccination

Background

An estimated 5–10 % of healthy vaccinees lack adequate antibody response following receipt of a standard three-dose hepatitis B vaccination regimen. The cellular mechanisms responsible for poor immunological responses to hepatitis B vaccine have not been fully elucidated to date.

Methods

There were 61 low responders and 56 hyper responders involved in our study. Peripheral blood samples were mainly collected at D7, D14 and D28 after revaccinated with a further dose of 20 µg of recombinant hepatitis B vaccine.

Results

We found low responders to the hepatitis B vaccine presented lower frequencies of circulating follicular helper T (cTfh) cells, plasmablasts and a profound skewing away from cTfh2 and cTfh17 cells both toward cTfh1 cells. Importantly, the skewing of Tfh cell subsets correlated with IL-21 and protective antibody titers. Based on the key role of microRNAs involved in Tfh cell differentiation, we revealed miR-19b-1 and miR-92a-1 correlated with the cTfh cell subsets distribution and antibody production.

Conclusions

Our findings highlighted a decrease in cTfh cells and specific subset skewing contribute to reduced antibody responses in low responders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00290-7.

Dendritic Cell Regulation of T Helper Cells

As the professional antigen-presenting cells of the immune system, dendritic cells (DCs) sense the microenvironment and shape the ensuing adaptive immune response. DCs can induce both immune activation and immune tolerance according to the peripheral cues. Recent work has established that DCs comprise several phenotypically and functionally heterogeneous subsets that differentially regulate T lymphocyte differentiation. This review summarizes both mouse and human DC subset phenotypes, development, diversification, and function. We focus on advances in our understanding of how different DC subsets regulate distinct CD4⁺ T helper (Th) cell differentiation outcomes, including Th1, Th2, Th17, T follicular helper, and T regulatory cells. We review DC subset intrinsic properties, local tissue microenvironments, and other immune cells that together determine Th cell differentiation during homeostasis and inflammation.