Defective TCR expression in transgenic mice constructed using cDNA-based alpha- and beta-chain genes under the control of heterologous regulatory elements

TCR-Independent Metabolic Reprogramming Precedes Lymphoma-Driven Changes in T-cell Fate

Chronic T-cell receptor (TCR) signaling in the tumor microenvironment is known to promote T-cell dysfunction. However, we reasoned that poorly immunogenic tumors may also compromise T cells by impairing their metabolism. To address this, we assessed temporal changes in T-cell metabolism, fate, and function in models of B-cell lymphoma driven by Myc, a promoter of energetics and repressor of immunogenicity. Increases in lymphoma burden most significantly impaired CD4+ T-cell function and promoted regulatory T cell (Treg) and Th1-cell differentiation. Metabolomic analyses revealed early reprogramming of CD4+ T-cell metabolism, reduced glucose uptake, and impaired mitochondrial function, which preceded changes in T-cell fate. In contrast, B-cell lymphoma metabolism remained robust during tumor progression. Finally, mitochondrial functions were impaired in CD4+ and CD8+ T cells in lymphoma-transplanted OT-II and OT-I transgenic mice, respectively. These findings support a model, whereby early, TCR-independent, metabolic interactions with developing lymphomas limits T cell-mediated immune surveillance.

CD137L and CD4 T cells limit BCL6-expressing pre-germinal center B cell expansion and BCL6-driven B cell malignancy

Aberrant expression of the proto-oncogene BCL6 is a driver of tumorigenesis in diffuse large B cell lymphoma (DLBCL). Mice overexpressing BCL6 from the B cell-specific immunoglobulin heavy chain μ intron promoter (Iμ-Bcl6^Tg/+ ) develop B cell lymphomas with features typical of human DLBCL. While the development of B cell lymphoma in these mice is tightly controlled by T cells, the mechanisms of this immune surveillance are poorly understood. Here we show that CD4 T cells contribute to the control of lymphoproliferative disease in lymphoma-prone Iμ-Bcl6^Tg/+ mice. We reveal that this CD4 T cell immuno-surveillance requires signaling by the co-stimulatory molecule CD137 ligand (CD137L; also known as 4-1BBL), which may promote the transition of pre-malignant B cells with an activated phenotype into the germinal center stage via reverse signaling, preventing their hazardous accumulation. Thus, CD137L-mediated CD4 T cell immuno-surveillance adds another layer of protection against B cell malignancy to that provided by CD8 T cell cytotoxicity.

Mapping autophagosome contents identifies interleukin-7 receptor-α as a key cargo modulating CD4+ T cell proliferation

CD4+ T cells are pivotal cells playing roles in the orchestration of humoral and cytotoxic immune responses. It is known that CD4+ T cell proliferation relies on autophagy, but identification of the autophagosomal cargo involved is missing. Here we create a transgenic mouse model, to enable direct mapping of the proteinaceous content of autophagosomes in primary cells by LC3 proximity labelling. Interleukin-7 receptor-α, a cytokine receptor mostly found in naïve and memory T cells, is reproducibly detected in autophagosomes of activated CD4+ T cells. Consistently, CD4+ T cells lacking autophagy show increased interleukin-7 receptor-α surface expression, while no defect in internalisation is observed. Mechanistically, excessive surface interleukin-7 receptor-α sequestrates the common gamma chain, impairing the interleukin-2 receptor assembly and downstream signalling crucial for T cell proliferation. This study shows that key autophagy substrates can be reliably identified in this mouse model and help mechanistically unravel autophagy's contribution to healthy physiology and disease.

The SNARE protein Vti1b is recruited to the sites of BCR activation but is redundant for antigen internalisation, processing and presentation

In order to fulfil the special requirements of antigen-specific activation and communication with other immune cells, B lymphocytes require finely regulated endosomal vesicle trafficking. How the endosomal machinery is regulated in B cells remains largely unexplored. In our previous proximity proteomic screen, we identified the SNARE protein Vti1b as one of the strongest candidates getting accumulated to the sites of early BCR activation. In this report, we follow up on this finding and investigate the localisation and function of Vti1b in B cells. We found that GFP-fused Vti1b was concentrated at the Golgi complex, around the MTOC, as well as in the Rab7⁺ lysosomal vesicles in the cell periphery. Upon BCR activation with soluble antigen, Vti1b showed partial localization to the internalized antigen vesicles, especially in the periphery of the cell. Moreover, upon BCR activation using surface-bound antigen, Vti1b polarised to the immunological synapse, colocalising with the Golgi complex, and with lysosomes at actin foci. To test for a functional role of Vti1b in early B cell activation, we used primary B cells isolated from Vit1b-deficient mouse. However, we found no functional defects in BCR signalling, immunological synapse formation, or processing and presentation of the internalized antigen, suggesting that the loss of Vti1b in B cells could be compensated by its close homologue Vti1a or other SNAREs.

Jmjd1c demethylates STAT3 to restrain plasma cell differentiation and rheumatoid arthritis

Appropriate regulation of B cell differentiation into plasma cells is essential for humoral immunity while preventing antibody-mediated autoimmunity; however, the underlying mechanisms, especially those with pathological consequences, remain unclear. Here, we found that the expression of Jmjd1c, a member of JmjC domain histone demethylase, in B cells but not in other immune cells, protected mice from rheumatoid arthritis (RA). In humans with RA, JMJD1C expression levels in B cells were negatively associated with plasma cell frequency and disease severity. Mechanistically, Jmjd1c demethylated STAT3, rather than histone substrate, to restrain plasma cell differentiation. STAT3 Lys140 hypermethylation caused by Jmjd1c deletion inhibited the interaction with phosphatase Ptpn6 and resulted in abnormally sustained STAT3 phosphorylation and activity, which in turn promoted plasma cell generation. Germinal center B cells devoid of Jmjd1c also acquired strikingly increased propensity to differentiate into plasma cells. STAT3 Lys140Arg point mutation completely abrogated the effect caused by Jmjd1c loss. Mice with Jmjd1c overexpression in B cells exhibited opposite phenotypes to Jmjd1c-deficient mice. Overall, our study revealed Jmjd1c as a critical regulator of plasma cell differentiation and RA and also highlighted the importance of demethylation modification for STAT3 in B cells.

The function of Wtap in N6-adenosine methylation of mRNAs controls T cell receptor signaling and survival of T cells

T cell antigen-receptor (TCR) signaling controls the development, activation and survival of T cells by involving several layers and numerous mechanisms of gene regulation. N⁶-methyladenosine (m⁶A) is the most prevalent messenger RNA modification affecting splicing, translation and stability of transcripts. In the present study, we describe the Wtap protein as essential for m⁶A methyltransferase complex function and reveal its crucial role in TCR signaling in mouse T cells. Wtap and m⁶A methyltransferase functions were required for the differentiation of thymocytes, control of activation-induced death of peripheral T cells and prevention of colitis by enabling gut RORγt⁺ regulatory T cell function. Transcriptome and epitranscriptomic analyses reveal that m⁶A modification destabilizes Orai1 and Ripk1 mRNAs. Lack of post-transcriptional repression of the encoded proteins correlated with increased store-operated calcium entry activity and diminished survival of T cells with conditional genetic inactivation of Wtap. These findings uncover how m⁶A modification impacts on TCR signal transduction and determines activation and survival of T cells.

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.

Engineering a Therapeutic Protein to Enhance the Study of Anti-Drug Immunity

The development of anti-drug antibodies represents a significant barrier to the utilization of protein-based therapies for a wide variety of diseases. While the rate of antibody formation can vary depending on the therapeutic employed and the target patient population receiving the drug, the antigen-specific immune response underlying the development of anti-drug antibodies often remains difficult to define. This is especially true for patients with hemophilia A who, following exposure, develop antibodies against the coagulation factor, factor VIII (FVIII). Models capable of studying this response in an antigen-specific manner have been lacking. To overcome this challenge, we engineered FVIII to contain a peptide (323-339) from the model antigen ovalbumin (OVA), a very common tool used to study antigen-specific immunity. FVIII with an OVA peptide (FVIII-OVA) retained clotting activity and possessed the ability to activate CD4 T cells specific to OVA323-339 in vitro. When compared to FVIII alone, FVIII-OVA also exhibited a similar level of immunogenicity, suggesting that the presence of OVA323-339 does not substantially alter the anti-FVIII immune response. Intriguingly, while little CD4 T cell response could be observed following exposure to FVIII-OVA alone, inclusion of anti-FVIII antibodies, recently shown to favorably modulate anti-FVIII immune responses, significantly enhanced CD4 T cell activation following FVIII-OVA exposure. These results demonstrate that model antigens can be incorporated into a therapeutic protein to study antigen-specific responses and more specifically that the CD4 T cell response to FVIII-OVA can be augmented by pre-existing anti-FVIII antibodies.

IL-21 has a critical role in establishing germinal centers by amplifying early B cell proliferation

The proliferation and differentiation of antigen‐specific B cells, including the generation of germinal centers (GC), are prerequisites for long‐lasting, antibody‐mediated immune protection. Affinity for antigen determines B cell recruitment, proliferation, differentiation, and competitiveness in the response, largely through determining access to T cell help. However, how T cell‐derived signals contribute to these outcomes is incompletely understood. Here, we report how the signature cytokine of follicular helper T cells, IL‐21, acts as a key regulator of the initial B cell response by accelerating cell cycle progression and the rate of cycle entry, increasing their contribution to the ensuing GC. This effect occurs over a wide range of initial B cell receptor affinities and correlates with elevated AKT and S6 phosphorylation. Moreover, the resultant increased proliferation can explain the IL‐21‐mediated promotion of plasma cell differentiation. Collectively, our data establish that IL‐21 acts from the outset of a T cell‐dependent immune response to increase cell cycle progression and fuel cyclic re‐entry of B cells, thereby regulating the initial GC size and early plasma cell output.

CD4+ T helper 2 cells suppress breast cancer by inducing terminal differentiation

Cancer immunology research is largely focused on the role of cytotoxic immune responses against advanced cancers. Herein, we demonstrate that CD4⁺ T helper (Th2) cells directly block spontaneous breast carcinogenesis by inducing the terminal differentiation of the cancer cells. Th2 cell immunity, stimulated by thymic stromal lymphopoietin, caused the epigenetic reprogramming of the tumor cells, activating mammary gland differentiation and suppressing epithelial–mesenchymal transition. Th2 polarization was required for this tumor antigen–specific immunity, which persisted in the absence of CD8⁺ T and B cells. Th2 cells directly blocked breast carcinogenesis by secreting IL-3, IL-5, and GM-CSF, which signaled to their common receptor expressed on breast tumor cells. Importantly, Th2 cell immunity permanently reverted high-grade breast tumors into low-grade, fibrocystic-like structures. Our findings reveal a critical role for CD4⁺ Th2 cells in immunity against breast cancer, which is mediated by terminal differentiation as a distinct effector mechanism for cancer immunoprevention and therapy.

High-Fat Diet-Induced Obesity Alters Dendritic Cell Homeostasis by Enhancing Mitochondrial Fatty Acid Oxidation

Obesity is associated with increased cancer risk and weak responses to vaccination and sepsis treatment. Although dendritic cells (DCs) are fundamental for the initiation and maintenance of competent immune responses against pathogens and tumors, how obesity alters the normal physiology of these myeloid cells remains largely unexplored. In this study, we report that obesity caused by prolonged high-fat diet feeding disrupts the metabolic and functional status of mouse splenic DCs (SpDCs). High-fat diet-induced obesity drastically altered the global transcriptional profile of SpDCs, causing severe changes in the expression of gene programs implicated in lipid metabolism and mitochondrial function. SpDCs isolated from obese mice demonstrated enhanced mitochondrial respiration provoked by increased fatty acid oxidation (FAO), which drove the intracellular accumulation of reactive oxygen species that impaired Ag presentation to T cells. Accordingly, treatment with the FAO inhibitor etomoxir, or antioxidants such as vitamin E or N-acetyl-l-cysteine, restored the Ag-presenting capacity of SpDCs isolated from obese mice. Our findings reveal a major detrimental effect of obesity in DC physiology and suggest that controlling mitochondrial FAO or reactive oxygen species overproduction may help improve DC function in obese individuals.

Type of PaperY192 within the SH2 Domain of Lck Regulates TCR Signaling Downstream of PLC-γ1 and Thymic Selection

Signaling via the TCR, which is initiated by the Src-family tyrosine kinase Lck, is crucial for the determination of cell fates in the thymus. Because of its pivotal role, ablation of Lck results in a profound block of T-cell development. Here, we show that, in addition to its well-known function in the initiation of TCR signaling, Lck also acts at a more downstream level. This novel function of Lck is determined by the tyrosine residue (Y192) located in its SH2 domain. Thymocytes from knock-in mice expressing a phosphomimetic Y192E mutant of Lck initiate TCR signaling upon CD3 cross-linking up to the level of PLC-γ1 phosphorylation. However, the activation of downstream pathways including Ca²⁺ influx and phosphorylation of Erk1/2 are impaired. Accordingly, positive and negative selections are blocked in Lck^Y192E knock-in mice. Collectively, our data indicate that Lck has a novel function downstream of PLCγ-1 in the regulation of thymocyte differentiation and selection.

T Cell-Intrinsic Vitamin A Metabolism and Its Signaling Are Targets for Memory T Cell-Based Cancer Immunotherapy

Memory T cells play an essential role in infectious and tumor immunity. Vitamin A metabolites such as retinoic acid are immune modulators, but the role of vitamin A metabolism in memory T-cell differentiation is unclear. In this study, we identified retinol dehydrogenase 10 (Rdh10), which metabolizes vitamin A to retinal (RAL), as a key molecule for regulating T cell differentiation. T cell-specific Rdh10 deficiency enhanced memory T-cell formation through blocking RAL production in infection model. Epigenetic profiling revealed that retinoic acid receptor (RAR) signaling activated by vitamin A metabolites induced comprehensive epigenetic repression of memory T cell-associated genes, including TCF7, thereby promoting effector T-cell differentiation. Importantly, memory T cells generated by Rdh deficiency and blocking RAR signaling elicited potent anti-tumor responses in adoptive T-cell transfer setting. Thus, T cell differentiation is regulated by vitamin A metabolism and its signaling, which should be novel targets for memory T cell-based cancer immunotherapy.

Design and Functional Characterization of HIV-1 Envelope Protein-Coupled T Helper Liposomes

Functionalization of experimental HIV-1 virus-like particle vaccines with heterologous T helper epitopes (T helper VLPs) can modulate the humoral immune response via intrastructural help (ISH). Current advances in the conjugation of native-like HIV-1 envelope trimers (Env) onto liposomes and encapsulation of peptide epitopes into these nanoparticles renders this GMP-scalable liposomal platform a feasible alternative to VLP-based vaccines. In this study, we designed and analyzed customizable Env-conjugated T helper liposomes. First, we passively encapsulated T helper peptides into a well-characterized liposome formulation displaying a dense array of Env trimers on the surface. We confirmed the closed pre-fusion state of the coupled Env trimers by immunogold staining with conformation-specific antibodies. These peptide-loaded Env-liposome conjugates efficiently activated Env-specific B cells, which further induced proliferation of CD4+ T cells by presentation of liposome-derived peptides on MHC-II molecules. The peptide encapsulation process was then quantitatively improved by an electrostatically driven approach using an overall anionic lipid formulation. We demonstrated that peptides delivered by liposomes were presented by DCs in secondary lymphoid organs after intramuscular immunization of mice. UFO (uncleaved prefusion optimized) Env trimers were covalently coupled to peptide-loaded anionic liposomes by His-tag/NTA(Ni) interactions and EDC/Sulfo-NHS crosslinking. EM imaging revealed a moderately dense array of well-folded Env trimers on the liposomal surface. The conformation was verified by liposomal surface FACS. Furthermore, anionic Env-coupled T helper liposomes effectively induced Env-specific B cell activation and proliferation in a comparable range to T helper VLPs. Taken together, we demonstrated that T helper VLPs can be substituted with customizable and GMP-scalable liposomal nanoparticles as a perspective for future preclinical and clinical HIV vaccine applications. The functional nanoparticle characterization assays shown in this study can be applied to other systems of synthetic nanoparticles delivering antigens derived from various pathogens.

Epicutaneous allergen immunotherapy induces a profound and selective modulation in skin dendritic cell subsets

BACKGROUND

Epicutaneous immunotherapy (EPIT) protocols have recently been developed to restore tolerance in patients with food allergy (FA). The mechanisms by which EPIT protocols promote desensitization rely on a profound immune deviation of pathogenic T and B cell responses.

OBJECTIVE

To date, little is known about the contribution of skin dendritic cells (skDCs) to T cell remodeling and EPIT efficacy.

METHODS

We capitalized on a preclinical model of food allergy to ovalbumin (OVA) to characterize the phenotype and functions of OVA⁺ skDCs throughout the course of EPIT.

RESULTS

Our results showed that both Langerhans cells (LCs) and dermal conventional cDC1 and cDC2 subsets retained their ability to capture OVA in the skin and to migrate toward the skin-draining lymph nodes during EPIT. However, their activation/maturation status was significantly impaired, as evidenced by the gradual and selective reduction of CD86, CD40, and OVA protein expression in respective subsets. Phenotypic changes during EPIT were also characterized by a progressive diversification of single cell gene signatures within each DC subset. Interestingly, we observed that OVA⁺ LCs progressively lost their capacity to prime CD4⁺ T_EFF, but gained T_REG stimulatory properties. In contrast, cDC1 were inefficient in priming CD4⁺ T_EFF or in reactivating T_MEMin vitro, while cDC2 retained moderate stimulatory properties, and progressively biased type-2 immunity toward type-1 and type-17 responses.

CONCLUSIONS

Our results therefore emphasize that the acquisition of distinct phenotypic and functional specializations by skDCs during EPIT is at the cornerstone of the desensitization process.

Modulating albumin-mediated transport of peptide-drug conjugates for antigen-specific Treg induction

The therapeutic potential of antigen-specific regulatory T cells (Treg) has been extensively explored, leading to the development of several tolerogenic vaccines. Dexamethasone-antigen conjugates represent a prominent class of tolerogenic vaccines that enable coordinated delivery of antigen and dexamethasone to target immune cells. The importance of nonspecific albumin association towards the biodistribution of antigen-adjuvant conjugates has gained increasing attention, by which hydrophobic and electrostatic interactions govern the association capacity. Using an ensemble of computational and experimental techniques, we evaluate the impact of charged residues adjacent to the drug conjugation site in dexamethasone-antigen conjugates (Dex-K/E4-OVA323, K: lysine, E: glutamate) towards their albumin association capacity and induction of antigen-specific Treg. We find that Dex-K4-OVA323 possesses a higher albumin association capacity than Dex-E4-OVA323, leading to enhanced liver distribution and antigen-presenting cell uptake. Furthermore, using an OVA323-specific adoptive-transfer mouse model, we show that Dex-K4-OVA323 selectively upregulated OVA323-specific Treg cells, whereas Dex-E4-OVA323 exerted no significant effect on Treg cells. Our findings serve as a guide to optimize the functionality of dexamethasone-antigen conjugate amid switching vaccine epitope sequences. Moreover, our study demonstrates that moderating the residues adjacent to the conjugation sites can serve as an engineering approach for future peptide-drug conjugate development.

Extrathymic expression of Aire controls the induction of effective TH17 cell-mediated immune response to Candida albicans

Patients with loss of function in the gene encoding the master regulator of central tolerance AIRE suffer from a devastating disorder called autoimmune polyendocrine syndrome type 1 (APS-1), characterized by a spectrum of autoimmune diseases and severe mucocutaneous candidiasis. Although the key mechanisms underlying the development of autoimmunity in patients with APS-1 are well established, the underlying cause of the increased susceptibility to Candida albicans infection remains less understood. Here, we show that Aire⁺MHCII⁺ type 3 innate lymphoid cells (ILC3s) could sense, internalize and present C. albicans and had a critical role in the induction of Candida-specific T helper 17 (T_H17) cell clones. Extrathymic Rorc-Cre-mediated deletion of Aire resulted in impaired generation of Candida-specific T_H17 cells and subsequent overgrowth of C. albicans in the mucosal tissues. Collectively, our observations identify a previously unrecognized regulatory mechanism for effective defense responses against fungal infections.

Translational regulation of TFH cell differentiation and autoimmune pathogenesis

Little is known regarding T cell translational regulation. We demonstrate that T follicular helper (TFH) cells use a previously unknown mechanism of selective messenger RNA (mRNA) translation for their differentiation, role in B cell maturation, and in autoimmune pathogenesis. We show that TFH cells have much higher levels of translation factor eIF4E than non-TFH CD4+ T cells, which is essential for translation of TFH cell fate-specification mRNAs. Genome-wide translation studies indicate that modest down-regulation of eIF4E activity by a small-molecule inhibitor or short hairpin RN impairs TFH cell development and function. In mice, down-regulation of eIF4E activity specifically reduces TFH cells among T helper subtypes, germinal centers, B cell recruitment, and antibody production. In experimental autoimmune encephalomyelitis, eIF4E activity down-regulation blocks TFH cell participation in disease pathogenesis while promoting rapid remission and spinal cord remyelination. TFH cell development and its role in autoimmune pathogenesis involve selective mRNA translation that is highly druggable.

Mesothelial cell-derived antigen-presenting cancer-associated fibroblasts induce expansion of regulatory T cells in pancreatic cancer

Recent studies have identified a unique cancer-associated fibroblast (CAF) population termed antigen-presenting CAFs (apCAFs), characterized by the expression of major histocompatibility complex class II molecules, suggesting a function in regulating tumor immunity. Here, by integrating multiple single-cell RNA-sequencing studies and performing robust lineage-tracing assays, we find that apCAFs are derived from mesothelial cells. During pancreatic cancer progression, mesothelial cells form apCAFs by downregulating mesothelial features and gaining fibroblastic features, a process induced by interleukin-1 and transforming growth factor β. apCAFs directly ligate and induce naive CD4+ T cells into regulatory T cells (Tregs) in an antigen-specific manner. Moreover, treatment with an antibody targeting the mesothelial cell marker mesothelin can effectively inhibit mesothelial cell to apCAF transition and Treg formation induced by apCAFs. Taken together, our study elucidates how mesothelial cells may contribute to immune evasion in pancreatic cancer and provides insight on strategies to enhance cancer immune therapy.

Recirculating Foxp3+ regulatory T cells are restimulated in the thymus under Aire control

Thymically-derived Foxp3+ regulatory T cells (Treg) critically control immunological tolerance. These cells are generated in the medulla through high affinity interactions with medullary thymic epithelial cells (mTEC) expressing the Autoimmune regulator (Aire). Recent advances have revealed that thymic Treg contain not only developing but also recirculating cells from the periphery. Although Aire is implicated in the generation of Foxp3+ Treg, its role in the biology of recirculating Treg remains elusive. Here, we show that Aire regulates the suppressive signature of recirculating Treg independently of the remodeling of the medullary 3D organization throughout life where Treg reside. Accordingly, the adoptive transfer of peripheral Foxp3+ Treg in AireKO recipients led to an impaired suppressive signature upon their entry into the thymus. Furthermore, recirculating Treg from AireKO mice failed to attenuate the severity of multiorgan autoimmunity, demonstrating that their suppressive function is altered. Using bone marrow chimeras, we reveal that mTEC-specific expression of Aire controls the suppressive signature of recirculating Treg. Finally, mature mTEC lacking Aire were inefficient in stimulating peripheral Treg both in polyclonal and antigen-specific co-culture assays. Overall, this study demonstrates that Aire confers to mTEC the ability to restimulate recirculating Treg, unravelling a novel function for this master regulator in Treg biology.

Central tolerance is impaired in the middle-aged thymic environment

One of the earliest hallmarks of immune aging is thymus involution, which not only reduces the number of newly generated and exported T cells, but also alters the composition and organization of the thymus microenvironment. Thymic T‐cell export continues into adulthood, yet the impact of thymus involution on the quality of newly generated T‐cell clones is not well established. Notably, the number and proportion of medullary thymic epithelial cells (mTECs) and expression of tissue‐restricted antigens (TRAs) decline with age, suggesting the involuting thymus may not promote efficient central tolerance. Here, we demonstrate that the middle‐aged thymic environment does not support rapid motility of medullary thymocytes, potentially diminishing their ability to scan antigen presenting cells (APCs) that display the diverse self‐antigens that induce central tolerance. Consistent with this possibility, thymic slice assays reveal that the middle‐aged thymic environment does not support efficient negative selection or regulatory T‐cell (Treg) induction of thymocytes responsive to either TRAs or ubiquitous self‐antigens. This decline in central tolerance is not universal, but instead impacts lower‐avidity self‐antigens that are either less abundant or bind to TCRs with moderate affinities. Additionally, the decline in thymic tolerance by middle age is accompanied by both a reduction in mTECs and hematopoietic APC subsets that cooperate to drive central tolerance. Thus, age‐associated changes in the thymic environment result in impaired central tolerance against moderate‐avidity self‐antigens, potentially resulting in export of increasingly autoreactive naive T cells, with a deficit of Treg counterparts by middle age.

Inhibitors of the Actin-Bundling Protein Fascin-1 Developed for Tumor Therapy Attenuate the T-Cell Stimulatory Properties of Dendritic Cells

Simple Summary

Expression of the actin-bundling protein Fascin-1 (Fscn1) is largely restricted to neuronal cells and to activated dendritic cells (DCs). DCs are important inducers of (antitumor) immune responses. In tumor cells, de novo expression of Fscn-1 correlates with their invasive and metastatic activities. Pharmacological Fscn1 inhibitors, which are currently under clinical trials for tumor therapy, were demonstrated to counteract tumor metastasis. Within this study, we were interested in better understanding the effects of Fscn1 inhibitors on DCs and discovered that two distinct Fascin-1 inhibitors affect the immune-phenotype and T-cell stimulatory activity of DCs. Our results suggest that systemic application of Fscn1 inhibitors for tumor therapy may also modulate antitumor immune responses.

Abstract

Background: Stimulated dendritic cells (DCs), which constitute the most potent population of antigen-presenting cells (APCs), express the actin-bundling protein Fascin-1 (Fscn1). In tumor cells, de novo expression of Fscn1 correlates with their invasive and metastatic properties. Therefore, Fscn1 inhibitors have been developed to serve as antitumor agents. In this study, we were interested in better understanding the impact of Fscn1 inhibitors on DCs. Methods: In parallel settings, murine spleen cells and bone-marrow-derived DCs (BMDCs) were stimulated with lipopolysaccharide in the presence of Fscn1 inhibitors (NP-G2-044 and BDP-13176). An analysis of surface expression of costimulatory and coinhibitory receptors, as well as cytokine production, was performed by flow cytometry. Cytoskeletal alterations were assessed by confocal microscopy. The effects on the interactions of BMDCs with antigen-specific T cells were monitored by time lapse microscopy. The T-cell stimulatory and polarizing capacity of BMDCs were measured in proliferation assays and cytokine studies. Results: Administration of Fscn1 inhibitors diminished Fscn1 expression and the formation of dendritic processes by stimulated BMDCs and elevated CD273 (PD-L2) expression. Fscn1 inhibition attenuated the interaction of DCs with antigen-specific T cells and concomitant T-cell proliferation. Conclusions: Systemic administration of Fscn1 inhibitors for tumor therapy may also modulate DC-induced antitumor immune responses.

A MLR-Based Approach to Analyze Regulators of T Lymphocyte Activation In Vivo

Depending on the context, robust and durable T lymphocyte activation is either desirable, as in the case of anti-tumor responses, or unwanted, in cases of autoimmunity when chronic stimulation leads to self-tissue damage. Therefore, reliable in vivo models are of great importance to identify and validate regulatory pathways of T lymphocyte activation. Here, we describe an in vivo mixed-lymphocyte-reaction (MLR) approach, which is based on the so-called parent-into-F1 (P → F1) mouse model in combination with the congenic marker CD45.1/2 and cell proliferation dye-labeling. This setup allows us to track adoptively transferred allogenic CD4+ and CD8+ T lymphocytes and analyze their phenotype as well as the proliferation by flow cytometry in the blood and spleen. We could show hypo-reactive responses of T lymphocytes isolated from knockout mice with a known defect in T lymphocyte activation. Thus, this MLR-based in vivo model provides the opportunity to analyze positive regulators of T cell responses under physiological conditions of polyclonal T lymphocyte activation in vivo.

Antigen presentation safeguards the integrity of the hematopoietic stem cell pool

Hematopoietic stem and progenitor cells (HSPCs) are responsible for the production of blood and immune cells. Throughout life, HSPCs acquire oncogenic aberrations that can cause hematological cancers. Although molecular programs maintaining stem cell integrity have been identified, safety mechanisms eliminating malignant HSPCs from the stem cell pool remain poorly characterized. Here, we show that HSPCs constitutively present antigens via major histocompatibility complex class II. The presentation of immunogenic antigens, as occurring during malignant transformation, triggers bidirectional interactions between HSPCs and antigen-specific CD4+ T cells, causing stem cell proliferation, differentiation, and specific exhaustion of aberrant HSPCs. This immunosurveillance mechanism effectively eliminates transformed HSPCs from the hematopoietic system, thereby preventing leukemia onset. Together, our data reveal a bidirectional interaction between HSPCs and CD4+ T cells, demonstrating that HSPCs are not only passive receivers of immunological signals but also actively engage in adaptive immune responses to safeguard the integrity of the stem cell pool.

ADAMTS7 Attenuates House Dust Mite-Induced Airway Inflammation and Th2 Immune Responses

PURPOSE

ADAMTS7 is a secreted metalloproteinase enzyme and proteoglycan associated with the early progression of coronary artery disease. However, there is limited information regarding the role of ADAMTS7 in lung adaptive immunity and inflammation. Thus, we sought to assess whether ADAMTS7 expression in the lung modulates house dust mite (HDM)-induced airway inflammation and Th2 immune response.

METHODS

The role of ADAMTS7 in HDM-induced airway disease was assessed in ADAMTS7-deficient (ADAMTS7^-/-) mice and compared with the wild-type control mice by flow cytometry, ELISA, and histopathology. Furthermore, the antigen priming capability of dendritic cells (DC) was determined ex vivo by employing coculture with CD4⁺ OT-II cells.

RESULTS

ADAMTS7^-/- mice develop an augmented eosinophilic airway inflammation, mucous cell metaplasia, and increased Th2 immune response to inhaled HDM. In addition, allergen uptake by lung DC and migration to draining mediastinal lymph node were significantly increased in ADAMTS7^-/- mice, which shows an enhanced capacity to mount allergen-specific T-cell proliferation and effector Th2 cytokine productions. We propose that the mechanism by which ADAMTS7 negatively regulates DC function involves attenuated antigen uptake and presentation capabilities, which reduces allergic sensitization and Th2 immune responses in the lung.

CONCLUSION

In aggregate, we provide compelling evidence that ADAMTS7 plays a pivotal role in allergic airway disease and Th2 immunity and would be an attractive target for asthma.

Reversal of the T cell immune system reveals the molecular basis for T cell lineage fate determination in the thymus

T cell specificity and function are linked during development, as MHC-II-specific TCR signals generate CD4 helper T cells and MHC-I-specific TCR signals generate CD8 cytotoxic T cells, but the basis remains uncertain. We now report that switching coreceptor proteins encoded by Cd4 and Cd8 gene loci functionally reverses the T cell immune system, generating CD4 cytotoxic and CD8 helper T cells. Such functional reversal reveals that coreceptor proteins promote the helper-lineage fate when encoded by Cd4, but promote the cytotoxic-lineage fate when encoded in Cd8—regardless of the coreceptor proteins each locus encodes. Thus, T cell lineage fate is determined by cis-regulatory elements in coreceptor gene loci and is not determined by the coreceptor proteins they encode, invalidating coreceptor signal strength as the basis of lineage fate determination. Moreover, we consider that evolution selected the particular coreceptor proteins that Cd4 and Cd8 gene loci encode to avoid generating functionally reversed T cells because they fail to promote protective immunity against environmental pathogens.

To determine how T cell lineage fates are determined in the thymus, Singer and colleagues generated ‘FlipFlop’ mice with a functionally reversed T cell immune system that distinguishes TCR signal strength versus TCR signal duration.

Acute T-Cell-Driven Inflammation Requires the Endoglycosidase Heparanase-1 from Multiple Cell Types

It has been accepted for decades that T lymphocytes and metastasising tumour cells traverse basement membranes (BM) by deploying a battery of degradative enzymes, particularly proteases. However, since many redundant proteases can solubilise BM it has been difficult to prove that proteases aid cell migration, particularly in vivo. Recent studies also suggest that other mechanisms allow BM passage of cells. To resolve this issue we exploited heparanase-1 (HPSE-1), the only endoglycosidase in mammals that digests heparan sulfate (HS), a major constituent of BM. Initially we examined the effect of HPSE-1 deficiency on a well-characterised adoptive transfer model of T-cell-mediated inflammation. We found that total elimination of HPSE-1 from this system resulted in a drastic reduction in tissue injury and loss of target HS. Subsequent studies showed that the source of HPSE-1 in the transferred T cells was predominantly activated CD4⁺ T cells. Based on bone marrow chimeras, two cellular sources of HPSE-1 were identified in T cell recipients, one being haematopoiesis dependent and the other radiation resistant. Collectively our findings unequivocally demonstrate that an acute T-cell-initiated inflammatory response is HPSE-1 dependent and is reliant on HPSE-1 from at least three different cell types.

TNF-α sculpts a maturation process in vivo by pruning tolerogenic dendritic cells

It remains unclear how the pro-immunogenic maturation of conventional dendritic cells (cDCs) abrogates their tolerogenic functions. Here, we report that the loss of tolerogenic functions depends on the rapid death of BTLAhi cDC1s, which, in the steady state, are present in systemic peripheral lymphoid organs and promote tolerance that limits subsequent immune responses. A canonical inducer of maturation, lipopolysaccharide (LPS), initiates a burst of tumor necrosis factor alpha (TNF-α) production and the resultant acute death of BTLAhi cDC1s mediated by tumor necrosis factor receptor 1. The ablation of these individual tolerogenic cDCs is amplified by TNF-α produced by neighboring cells. This loss of tolerogenic cDCs is transient, accentuating the restoration of homeostatic conditions through biological turnover of cDCs in vivo. Therefore, our results reveal that the abrogation of tolerogenic functions during an acute immunogenic maturation depends on an ablation of the tolerogenic cDC population, resulting in a dynamic remodeling of the cDC functional landscape.

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.

Calcium Signaling Is Impaired in PTEN-Deficient T Cell Acute Lymphoblastic Leukemia

PTEN (Phosphatase and TENsin homolog) is a well-known tumor suppressor involved in numerous types of cancer, including T-cell acute lymphoblastic leukemia (T-ALL). In human, loss-of-function mutations of PTEN are correlated to mature T-ALL expressing a T-cell receptor (TCR) at their cell surface. In accordance with human T-ALL, inactivation of Pten gene in mouse thymocytes induces TCRαβ⁺ T-ALL development. Herein, we explored the functional interaction between TCRαβ signaling and PTEN. First, we performed single-cell RNA sequencing (scRNAseq) of PTEN-deficient and PTEN-proficient thymocytes. Bioinformatic analysis of our scRNAseq data showed that pathological Pten^del thymocytes express, as expected, Myc transcript, whereas inference of pathway activity revealed that these Pten^del thymocytes display a lower calcium pathway activity score compared to their physiological counterparts. We confirmed this result using ex vivo calcium flux assay and showed that upon TCR activation tumor Pten^del blasts were unable to release calcium ions (Ca²⁺) from the endoplasmic reticulum to the cytosol. In order to understand such phenomena, we constructed a mathematical model centered on the mechanisms controlling the calcium flux, integrating TCR signal strength and PTEN interactions. This qualitative model displays a dynamical behavior coherent with the dynamics reported in the literature, it also predicts that PTEN affects positively IP3 (inositol 1,4,5-trisphosphate) receptors (ITPR). Hence, we analyzed Itpr expression and unraveled that ITPR proteins levels are reduced in PTEN-deficient tumor cells compared to physiological and leukemic PTEN-proficient cells. However, calcium flux and ITPR proteins expression are not defective in non-leukemic PTEN-deficient T cells indicating that beyond PTEN loss an additional alteration is required. Altogether, our study shows that ITPR/Calcium flux is a part of the oncogenic landscape shaped by PTEN loss and pinpoints a putative role of PTEN in the regulation of ITPR proteins in thymocytes, which remains to be characterized.

Pyruvate enhances oral tolerance via GPR31

CX3CR1 high myeloid cells in the small intestine mediate the induction of oral tolerance by driving regulatory T (Treg) cells. Bacterial metabolites, e.g., pyruvate and lactate, induce a dendrite extension of CX3CR1 high myeloid cells into the intestinal lumen via GPR31. However, it remains unclear whether the pyruvate-GPR31 axis is involved in the induction of oral tolerance. Here, we show that pyruvate enhances oral tolerance in a GPR31-dependent manner. In ovalbumin (OVA)-fed Gpr31-deficient mice, an OVA-induced delayed-type hypersensitivity response was substantially induced, demonstrating the defective induction of oral tolerance in Gpr31-deficient mice. The percentage of RORγt+ Treg cells in the small intestine was reduced in Gpr31-deficient mice. In pyruvate-treated wild-type mice, a low dose of OVA efficiently induced oral tolerance. IL-10 production from intestinal CX3CR1 high myeloid cells was increased by OVA ingestion in wild-type mice, but not in Gpr31-deficient mice. CX3CR1 high myeloid cell-specific IL-10-deficient mice showed a defective induction of oral tolerance to OVA and a decreased accumulation of OVA-specific Treg cells in the small intestine. These findings demonstrate that pyruvate enhances oral tolerance through a GPR31-dependent effect on intestinal CX3CR1 high myeloid cells.

A Pathogenic Th17/CD38+ Macrophage Feedback Loop Drives Inflammatory Arthritis through TNF-α

The pathobiology of rheumatoid inflammatory diseases, including rheumatoid arthritis (RA) and psoriatic arthritis, involves the interplay between innate and adaptive immune components and resident synoviocytes. Single-cell analyses of patient samples and relevant mouse models have characterized many cellular subsets in RA. However, the impact of interactions between cell types is not fully understood. In this study, we temporally profiled murine arthritic synovial isolates at the single-cell level to identify perturbations similar to those found in human RA. Notably, murine macrophage subtypes like those found in RA patients were expanded in arthritis and linked to promoting the function of Th17 cells in the joint. In vitro experiments identified a capacity for murine macrophages to maintain the functionality and expansion of Th17 cells. Reciprocally, murine Th17 cell-derived TNF-α induced CD38⁺ macrophages that enhanced Th17 functionality. Murine synovial CD38⁺ macrophages were expanded during arthritis, and their depletion or blockade via TNF-α neutralization alleviated disease while reducing IL-17A-producing cells. These findings identify a cellular feedback loop that promotes Th17 cell pathogenicity through TNF-α to drive inflammatory arthritis.

Competition for refueling rather than cyclic reentry initiation evident in germinal centers

Antibody affinity maturation occurs in germinal centers (GCs) through iterative rounds of somatic hypermutation and proliferation in dark zones (DZs) and selection in light zones (LZs). GC B cells exit cell cycle a number of hours before entering LZs; therefore, continued participation in responses requires that they subsequently reenter cell cycle and move back to DZs, a process known as cyclic reentry. Affinity enhancements are thought to arise by B cells having to compete to initiate cyclic reentry each time they enter LZs, with T cell help being a major determinant; however, direct proof is lacking. Using Fucci2 mice, we confirmed an association between B cell receptor affinity and the first step of cyclic reentry, S phase initiation from a resting LZ state. However, neither T cell ablation nor MHCII deletion prevented resting LZ cells from reentering cell cycle, and this late G₁-S transition was also not detectably restricted by competition. In contrast, using BATF induction as exemplar, we found that T cells "refueled" LZ cells in an affinity-dependent manner that was limited by both competition and cells' intrinsic antigen-acquiring abilities. Therefore, cyclic reentry initiation and B cell refueling are independently regulated in GCs, which may contribute to permitting cells of different competencies to be sustained alongside each other and allow T cell support to be provided across a dynamic range commensurate with affinity. We speculate that this less binary selection mechanism could help GCs nurture complex antibody maturation pathways and support the clonal diversity required for countering fast-evolving pathogens.

Nematode ascarosides attenuate mammalian type 2 inflammatory responses

Animal proof-of-concept studies have shown that roundworms have a protective effect against immune-dysregulated disorders, but it has been difficult to study in human trials without individual nematode-derived molecules to develop and test. We discovered that ascarosides, molecules that are secreted by diverse nematodes, suppress asthma in a rodent model via modulation of expression of Il33, a key epithelial cytokine for induction of type 2 immunity, in addition to decreasing memory-type pathogenic Th2 cells and ILC2s and increasing the Il10-expressing subpopulation of interstitial macrophages in the lung. Thus, ascarosides suppress type 2 immune response by affecting both innate and adaptive immunity and could define a potent class of small molecule drugs to treat allergic airway diseases.

Mounting evidence suggests that nematode infection can protect against disorders of immune dysregulation. Administration of live parasites or their excretory/secretory (ES) products has shown therapeutic effects across a wide range of animal models for immune disorders, including asthma. Human clinical trials of live parasite ingestion for the treatment of immune disorders have produced promising results, yet concerns persist regarding the ingestion of pathogenic organisms and the immunogenicity of protein components. Despite extensive efforts to define the active components of ES products, no small molecules with immune regulatory activity have been identified from nematodes. Here we show that an evolutionarily conserved family of nematode pheromones called ascarosides strongly modulates the pulmonary immune response and reduces asthma severity in mice. Screening the inhibitory effects of ascarosides produced by animal-parasitic nematodes on the development of asthma in an ovalbumin (OVA) murine model, we found that administration of nanogram quantities of ascr#7 prevented the development of lung eosinophilia, goblet cell metaplasia, and airway hyperreactivity. Ascr#7 suppressed the production of IL-33 from lung epithelial cells and reduced the number of memory-type pathogenic Th2 cells and ILC2s in the lung, both key drivers of the pathology of asthma. Our findings suggest that the mammalian immune system recognizes ascarosides as an evolutionarily conserved molecular signature of parasitic nematodes. The identification of a nematode-produced small molecule underlying the well-documented immunomodulatory effects of ES products may enable the development of treatment strategies for allergic diseases.

Establishment of fetomaternal tolerance through glycan-mediated B cell suppression

Discrimination of self from non-self is fundamental to a wide range of immunological processes1. During pregnancy, the mother does not recognize the placenta as immunologically foreign because antigens expressed by trophoblasts, the placental cells that interface with the maternal immune system, do not activate maternal T cells2. Currently, these activation defects are thought to reflect suppression by regulatory T cells3. By contrast, mechanisms of B cell tolerance to trophoblast antigens have not been identified. Here we provide evidence that glycan-mediated B cell suppression has a key role in establishing fetomaternal tolerance in mice. B cells specific for a model trophoblast antigen are strongly suppressed through CD22-LYN inhibitory signalling, which in turn implicates the sialylated glycans of the antigen as key suppressive determinants. Moreover, B cells mediate the MHC-class-II-restricted presentation of antigens to CD4+ T cells, which leads to T cell suppression, and trophoblast-derived sialoglycoproteins are released into the maternal circulation during pregnancy in mice and humans. How protein glycosylation promotes non-immunogenic placental self-recognition may have relevance to immune-mediated pregnancy complications and to tumour immune evasion. We also anticipate that our findings will bolster efforts to harness glycan biology to control antigen-specific immune responses in autoimmune disease.

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.

Thymocytes trigger self-antigen-controlling pathways in immature medullary thymic epithelial stages

Interactions of developing T cells with Aire⁺ medullary thymic epithelial cells expressing high levels of MHCII molecules (mTEC^hi) are critical for the induction of central tolerance in the thymus. In turn, thymocytes regulate the cellularity of Aire⁺ mTEC^hi. However, it remains unknown whether thymocytes control the precursors of Aire⁺ mTEC^hi that are contained in mTEC^lo cells or other mTEC^lo subsets that have recently been delineated by single-cell transcriptomic analyses. Here, using three distinct transgenic mouse models, in which antigen presentation between mTECs and CD4⁺ thymocytes is perturbed, we show by high-throughput RNA-seq that self-reactive CD4⁺ thymocytes induce key transcriptional regulators in mTEC^lo and control the composition of mTEC^lo subsets, including Aire⁺ mTEC^hi precursors, post-Aire and tuft-like mTECs. Furthermore, these interactions upregulate the expression of tissue-restricted self-antigens, cytokines, chemokines, and adhesion molecules important for T-cell development. This gene activation program induced in mTEC^lo is combined with a global increase of the active H3K4me3 histone mark. Finally, we demonstrate that these self-reactive interactions between CD4⁺ thymocytes and mTECs critically prevent multiorgan autoimmunity. Our genome-wide study thus reveals that self-reactive CD4⁺ thymocytes control multiple unsuspected facets from immature stages of mTECs, which determines their heterogeneity.

Primary germinal center-resident T follicular helper cells are a physiologically distinct subset of CXCR5hiPD-1hi T follicular helper cells

T follicular helper (Tfh) cells are defined by a Bcl6+CXCR5hiPD-1hi phenotype, but only a minor fraction of these reside in germinal centers (GCs). Here, we examined whether GC-resident and -nonresident Tfh cells share a common physiology and function. Fluorescently labeled, GC-resident Tfh cells in different mouse models were distinguished by low expression of CD90. CD90neg/lo GCTfh cells required antigen-specific, MHCII+ B cells to develop and stopped proliferating soon after differentiation. In contrast, nonresident, CD90hi Tfh (GCTfh-like) cells developed normally in the absence of MHCII+ B cells and proliferated continuously during primary responses. The TCR repertoires of both Tfh subsets overlapped initially but later diverged in association with dendritic cell-dependent proliferation of CD90hi GCTfh-like cells, suggestive of TCR-dependency seen also in TCR-transgenic adoptive transfer experiments. Furthermore, the transcriptomes of CD90neg/lo and CD90hi GCTfh-like cells were enriched in different functional pathways. Thus, GC-resident and nonresident Tfh cells have distinct developmental requirements and activities, implying distinct functions.

Cancer-derived cholesterol sulfate is a key mediator to prevent tumor infiltration by effector T cells

Effective tumor immunotherapy requires physical contact of T cells with cancer cells. However, tumors often constitute a specialized microenvironment that excludes T cells from the vicinity of cancer cells, and its underlying mechanisms are still poorly understood. DOCK2 is a Rac activator critical for migration and activation of lymphocytes. We herein show that cancer-derived cholesterol sulfate (CS), a lipid product of the sulfotransferase SULT2B1b, acts as a DOCK2 inhibitor and prevents tumor infiltration by effector T cells. Using clinical samples, we found that CS was abundantly produced in certain types of human cancers such as colon cancers. Functionally, CS-producing cancer cells exhibited resistance to cancer-specific T-cell transfer and immune checkpoint blockade. Although SULT2B1b is known to sulfate oxysterols and inactivate their tumor-promoting activity, the expression levels of cholesterol hydroxylases, which mediate oxysterol production, are low in SULT2B1b-expressing cancers. Therefore, SULT2B1b inhibition could be a therapeutic strategy to disrupt tumor immune evasion in oxysterol-non-producing cancers. Thus, our findings define a previously unknown mechanism for tumor immune evasion and provide a novel insight into the development of effective immunotherapies.

A purine metabolic checkpoint that prevents autoimmunity and autoinflammation

Still's disease, the paradigm of autoinflammation-cum-autoimmunity, predisposes for a cytokine storm with excessive T lymphocyte activation upon viral infection. Loss of function of the purine nucleoside enzyme FAMIN is the sole known cause for monogenic Still's disease. Here we discovered that a FAMIN-enabled purine metabolon in dendritic cells (DCs) restrains CD4⁺ and CD8⁺ T cell priming. DCs with absent FAMIN activity prime for enhanced antigen-specific cytotoxicity, IFNγ secretion, and T cell expansion, resulting in excessive influenza A virus-specific responses. Enhanced priming is already manifest with hypomorphic FAMIN-I254V, for which ∼6% of mankind is homozygous. FAMIN controls membrane trafficking and restrains antigen presentation in an NADH/NAD⁺-dependent manner by balancing flux through adenine-guanine nucleotide interconversion cycles. FAMIN additionally converts hypoxanthine into inosine, which DCs release to dampen T cell activation. Compromised FAMIN consequently enhances immunosurveillance of syngeneic tumors. FAMIN is a biochemical checkpoint that protects against excessive antiviral T cell responses, autoimmunity, and autoinflammation.

Bronchus-associated macrophages efficiently capture and present soluble inhaled antigens and are capable of local Th2 cell activation

In allergic asthma, allergen inhalation leads to local Th2 cell activation and peribronchial inflammation. However, the mechanisms for local antigen capture and presentation remain unclear. By two-photon microscopy of the mouse lung, we established that soluble antigens in the bronchial airway lumen were efficiently captured and presented by a population of CD11c⁺ interstitial macrophages with high CX3CR1-GFP and MHC class II expression. We refer to these cells as Bronchus-Associated Macrophages (BAMs) based on their localization underneath the bronchial epithelium. BAMs were enriched in collagen-rich regions near some airway branchpoints, where inhaled antigens are likely to deposit. BAMs engaged in extended interactions with effector Th2 cells and promoted Th2 cytokine production. BAMs were also often in contact with dendritic cells (DCs). After exposure to inflammatory stimuli, DCs migrated to draining lymph nodes, whereas BAMs remained lung resident. We propose that BAMs act as local antigen presenting cells in the lung and also transfer antigen to DCs.

Surface phenotypes of naive and memory B cells in mouse and human tissues

Memory B cells (MBCs) protect the body from recurring infections. MBCs differ from their naive counterparts (NBCs) in many ways, but functional and surface marker differences are poorly characterized. In addition, although mice are the prevalent model for human immunology, information is limited concerning the nature of homology in B cell compartments. To address this, we undertook an unbiased, large-scale screening of both human and mouse MBCs for their differential expression of surface markers. By correlating the expression of such markers with extensive panels of known markers in high-dimensional flow cytometry, we comprehensively identified numerous surface proteins that are differentially expressed between MBCs and NBCs. The combination of these markers allows for the identification of MBCs in humans and mice and provides insight into their functional differences. These results will greatly enhance understanding of humoral immunity and can be used to improve immune monitoring.

Short palate, lung, and nasal epithelial clone 1 (SPLUNC1) level determines steroid-resistant airway inflammation in aging

Asthma and its heterogeneity change with age. Increased airspace neutrophil numbers contribute to severe steroid-resistant asthma exacerbation in the elderly, which correlates with the changes seen in adults with asthma. However, whether that resembles the same disease mechanism and pathophysiology in aged and adults is poorly understood. Here, we sought to address the underlying molecular mechanism of steroid-resistant airway inflammation development and response to corticosteroid (Dex) therapy in aged mice. To study the changes in inflammatory mechanism, we used a clinically relevant treatment model of house-dust mite (HDM)-induced allergic asthma and investigated lung adaptive immune response in adult (20-22 wk old) and aged (80-82 wk old) mice. Our result indicates an age-dependent increase in airway hyperresponsiveness (AHR), mixed granulomatous airway inflammation comprising eosinophils and neutrophils, and Th1/Th17 immune response with progressive decrease in frequencies and numbers of HDM-bearing dendritic cells (DC) accumulation in the draining lymph node (DLn) of aged mice as compared with adult mice. RNA-Seq experiments of the aged lung revealed short palate, lung, and nasal epithelial clone 1 (SPLUNC1) as one of the steroid-responsive genes, which progressively declined with age and further by HDM-induced inflammation. Moreover, we found increased glycolytic reprogramming, maturation/activation of DCs, the proliferation of OT-II cells, and Th2 cytokine secretion with recombinant SPLUNC1 (rSPLUNC1) treatment. Our results indicate a novel immunomodulatory role of SPLUNC1 regulating metabolic adaptation/maturation of DC. An age-dependent decline in the SPLUNC1 level may be involved in developing steroid-resistant airway inflammation and asthma heterogeneity.

Irg1/itaconate metabolic pathway is a crucial determinant of dendritic cells immune-priming function and contributes to resolute allergen-induced airway inflammation

Itaconate is produced from the mitochondrial TCA cycle enzyme aconitase decarboxylase (encoded by immune responsive gene1; Irg1) that exerts immunomodulatory function in myeloid cells. However, the role of the Irg1/itaconate pathway in dendritic cells (DC)-mediated airway inflammation and adaptive immunity to inhaled allergens, which are the primary antigen-presenting cells in allergic asthma, remains largely unknown. House dust mite (HDM)-challenged Irg1^-/- mice displayed increases in eosinophilic airway inflammation, mucous cell metaplasia, and Th2 cytokine production with a mechanism involving impaired mite antigen presentations by DC. Adoptive transfer of HDM-pulsed DC from Irg1-deficient mice into naïve WT mice induced a similar phenotype of elevated type 2 airway inflammation and allergic sensitization. Untargeted metabolite analysis of HDM-pulsed DC revealed itaconate as one of the most abundant polar metabolites that potentially suppress mitochondrial oxidative damage. Furthermore, the immunomodulatory effect of itaconate was translated in vivo, where intranasal administration of 4-octyl itaconate 4-OI following antigen priming attenuated the manifestations of HDM-induced airway disease and Th2 immune response. Taken together, these data demonstrated for the first time a direct regulatory role of the Irg1/itaconate pathway in DC for the development of type 2 airway inflammation and suggest a possible therapeutic target in modulating allergic asthma.

Characterization of Mouse CD4 TCR and Its Targeting Antigen

The initial step of activation and differentiation of naïve CD4⁺ T cells is the TCR-antigenic stimulation. The specific antigen peptides (>11 residues) are presented by the class II MHC (MHC II) protein which expresses professional antigen-presenting cells (APCs). To recognize various peptides and highly polymorphic MHC molecules, a diverse TCR repertoire is achieved through random V(D)J rearrangement. Following TCR initiation, naive CD4⁺ T cells proliferate and differentiate into one of the lineages of T helper (Th) cells, including Th1, Th2, Th17, iTreg, and some new subsets, as defined by the signatures of functional cytokines. In this chapter, we provide a series of methods to identify antigens for a specific TCR in vitro and also track the dynamics of the specific TCR-expressing T cell in vivo.

In Vivo Imaging of Tfh Cells

Germinal centers (GCs) are microanatomical structures in secondary lymphoid organs where B cells undergo affinity maturation for antigen during the course of an immune response. This process is driven by a subset of T cells termed T follicular helper cells (Tfh) that through a multistep process gain access to the GC niche within the B cell follicle. This protocol details how to study Tfh behavior in vivo, on a single cell level, using two-photon intravital microscopy of the murine popliteal lymph node.