The cytokine TGF-ß co-opts signaling via STAT3-STAT4 to promote the differentiation of human TFH cells.

Understanding the developmental mechanisms of follicular helper T cells (TFH cells) in humans is relevant to the clinic. However, the factors that drive the differentiation of human CD4+ helper T cells into TFH cells remain largely undefined. Here we found that transforming growth factor-ß (TGF-ß) provided critical additional signals for the transcription factors STAT3 and STAT4 to promote initial TFH differentiation in humans. This mechanism did not appear to be shared by mouse helper T cells. Developing human TFH cells that expressed the transcriptional repressor Bcl-6 also expressed RORγt, a transcription factor typically expressed by the TH17 subset of helper T cells. Our study documents a mechanism by which TFH cells and TH17 cells emerge together in inflammatory environments in humans, as is often observed in many human autoimmune diseases.

Etiology-independent activation of the LTß-LTßR-RELB axis drives aggressiveness and predicts poor prognosis in HCC.

BACKGROUND AND AIMS: HCC is the most common primary liver tumor, with an increasing incidence worldwide. HCC is a heterogeneous malignancy and usually develops in a chronically injured liver. The NF-κB signaling network consists of a canonical and a noncanonical branch. Activation of canonical NF-κB in HCC is documented. However, a functional and clinically relevant role of noncanonical NF-κB and its downstream effectors is not established. APPROACH AND RESULTS: Four human HCC cohorts (total n = 1462) and 4 mouse HCC models were assessed for expression and localization of NF-κB signaling components and activating ligands. In vitro , NF-κB signaling, proliferation, and cell death were measured, proving a pro-proliferative role of v-rel avian reticuloendotheliosis viral oncogene homolog B (RELB) activated by means of NF-κB-inducing kinase. In vivo , lymphotoxin beta was identified as the predominant inducer of RELB activation. Importantly, hepatocyte-specific RELB knockout in a murine HCC model led to a lower incidence compared to controls and lower maximal tumor diameters. In silico , RELB activity and RELB-directed transcriptomics were validated on the The Cancer Genome Atlas HCC cohort using inferred protein activity and Gene Set Enrichment Analysis. In RELB-active HCC, pathways mediating proliferation were significantly activated. In contrast to v-rel avian reticuloendotheliosis viral oncogene homolog A, nuclear enrichment of noncanonical RELB expression identified patients with a poor prognosis in an etiology-independent manner. Moreover, RELB activation was associated with malignant features metastasis and recurrence. CONCLUSIONS: This study demonstrates a prognostically relevant, etiology-independent, and cross-species consistent activation of a lymphotoxin beta/LTßR/RELB axis in hepatocarcinogenesis. These observations may harbor broad implications for HCC, including possible clinical exploitation.

OX40 Ligand Contributes to Human Lupus Pathogenesis by Promoting T Follicular Helper Response.

Increased activity of T follicular helper (Tfh) cells plays a major pathogenic role in systemic lupus erythematosus (SLE). However, the mechanisms that cause aberrant Tfh cell responses in SLE remain elusive. Here we showed the OX40 ligand (OX40L)-OX40 axis contributes to the aberrant Tfh response in SLE. OX40L was expressed by myeloid antigen-presenting cells (APCs), but not B cells, in blood and in inflamed tissues in adult and pediatric SLE patients. The frequency of circulating OX40L-expressing myeloid APCs positively correlated with disease activity and the frequency of ICOS(+) blood Tfh cells in SLE. OX40 signals promoted naive and memory CD4(+) T cells to express multiple Tfh cell molecules and were sufficient to induce them to become functional B cell helpers. Immune complexes containing RNA induced OX40L expression on myeloid APCs via TLR7 activation. Our study provides a rationale to target the OX40L-OX40 axis as a therapeutic modality for SLE.

Blood Tfh cells come with colors.

Blood CXCR5⁺ CD4⁺ T cells share phenotypic and functional similarities with T follicular helper cells. Studies by He et al. (2013) and Locci et al. (2013) in this issue of Immunity provide insight into their ontogeny and functionally distinct subsets.

Bcl-xL as prognostic marker and potential therapeutic target in cholangiocarcinoma.

Intrahepatic, perihilar, and distal cholangiocarcinoma (iCCA, pCCA, dCCA) are highly malignant tumours with increasing mortality rates due to therapy resistances. Among the mechanisms mediating resistance, overexpression of anti-apoptotic Bcl-2 proteins (Bcl-2, Bcl-xL , Mcl-1) is particularly important. In this study, we investigated whether antiapoptotic protein patterns are prognostically relevant and potential therapeutic targets in CCA. Bcl-2 proteins were analysed in a pan-cancer cohort from the NCT/DKFZ/DKTK MASTER registry trial (n = 1140, CCA n = 72) via RNA-sequencing and transcriptome-based protein activity interference revealing high ranks of CCA for Bcl-xL and Mcl-1. Expression of Bcl-xL , Mcl-1, and Bcl-2 was assessed in human CCA tissue and cell lines compared with cholangiocytes by immunohistochemistry, immunoblotting, and quantitative-RT-PCR. Immunohistochemistry confirmed the upregulation of Bcl-xL and Mcl-1 in iCCA tissues. Cell death of CCA cell lines upon treatment with specific small molecule inhibitors of Bcl-xL (Wehi-539), of Mcl-1 (S63845), and Bcl-2 (ABT-199), either alone, in combination with each other or together with chemotherapeutics was assessed by flow cytometry. Targeting Bcl-xL induced cell death and augmented the effect of chemotherapy in CCA cells. Combined inhibition of Bcl-xL and Mcl-1 led to a synergistic increase in cell death in CCA cell lines. Correlation between Bcl-2 protein expression and survival was analysed within three independent patient cohorts from cancer centers in Germany comprising 656 CCA cases indicating a prognostic value of Bcl-xL in CCA depending on the CCA subtype. Collectively, these observations identify Bcl-xL as a key protein in cell death resistance of CCA and may pave the way for clinical application.

Specific Targeting of Antiapoptotic Bcl-2 Proteins as a Radiosensitizing Approach in Solid Tumors.

Avoidance of therapy-induced apoptosis is a hallmark of acquired resistance towards radiotherapy. Thus, breaking resistance still challenges modern cancer therapy. The Bcl-2 protein family is known for its regulatory role in apoptosis signaling, making Bcl-2, Mcl-1 and Bcl-xL promising targets. This study evaluates the effects of highly specific inhibitors for Bcl-xL (WEHI-539), Bcl-2 (ABT-199) and Mcl-1 (S63845) as radiosensitizers. Covering a broad spectrum of solid tumors, Non-Small-Cell Lung Cancer (NSCLC), Head and Neck Squamous Cell Carcinoma (HNSCC) and synovial sarcoma cell lines were exposed to fractionated radiation as standard therapy with or without Bcl-2 protein inhibition. Protein expression was detected by Western blot and cell death was assessed by flow cytometry measuring apoptosis. In contrast to NSCLC, a high level of Bcl-xL and its upregulation during radiotherapy indicated radioresistance in HNSCC and synovial sarcoma. Radioresistant cell lines across all entities benefited synergistically from combined therapy with Bcl-xL inhibition and fractionated radiation. In NSCLC cell lines, Mcl-1 inhibition significantly augmented radiotherapy independent of the expression level. Our data suggest that among antiapoptotic Bcl-2 proteins, targeting Bcl-xL may break resistance to radiation in HNSCC, synovial sarcoma and NSCLC in vitro. In NSCLC, Mcl-1 might be a promising target that needs further investigation.

Nuclear Translocation of RELB Is Increased in Diseased Human Liver and Promotes Ductular Reaction and Biliary Fibrosis in Mice.

BACKGROUND & AIMS: Cholangiocyte proliferation and ductular reaction contribute to the onset and progression of liver diseases. Little is known about the role of the transcription factor nuclear factor-κB (NF-κB) in this process. We investigated the activities of the RELB proto-oncogene NF-κB subunit in human cholangiocytes and in mouse models of liver disease characterized by a ductular reaction. METHODS: We obtained liver tissue samples from patients with primary sclerosing cholangitis, primary biliary cholangitis, hepatitis B or C virus infection, autoimmune hepatitis, alcoholic liver disease, or without these diseases (controls) from a tissue bank in Germany. Tissues were analyzed by immunohistochemistry for levels of RELB and lymphotoxin ß (LTB). We studied mice with liver parenchymal cell (LPC)-specific disruption of the cylindromatosis (CYLD) lysine 63 deubiquitinase gene (Cyld), with or without disruption of Relb (CyldΔLPC mice and Cyld/RelbΔLPC mice) and compared them with C57BL/6 mice (controls). Mice were fed 5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or standard chow diets to induce biliary injury or were given injections of CCl4 to induce non-cholestatic liver fibrosis. Liver tissues were analyzed by histology, immunohistochemistry, immunoblots, in situ hybridization, and quantitative real-time polymerase chain reaction. Cholangiocytes were isolated from normal human liver, incubated with LTB receptor agonist, and transfected with small interfering RNAs to knock down RELB. RESULTS: In liver tissues from patients with primary sclerosing cholangitis, primary biliary cholangitis, chronic infection with hepatitis B or C virus, autoimmune hepatitis, or alcoholic liver disease, we detected increased nuclear translocation of RELB and increased levels of LTB in cholangiocytes that formed reactive bile ducts compared with control liver tissues. Human cholangiocytes, but not those with RELB knockdown, proliferated with exposure to LTB. The phenotype of CyldΔLPC mice, which included ductular reaction, oval cell activation, and biliary fibrosis, was completely lost from Cyld/RelbΔLPC mice. Compared with livers from control mice, livers from CyldΔLPC mice (but not Cyld/RelbΔLPC mice) had increased levels of mRNAs encoding cytokines (LTB; CD40; and tumor necrosis factor superfamily [TNFSF] members TNFSF11 [RANKL], TNFSF13B [BAFF], and TNFSF14 [LIGHT]) produced by reactive cholangiocytes. However, these strains of mice developed similar levels of liver fibrosis in response to CCl4 exposure. CyldΔLPC mice and Cyld/RelbΔLPC mice had improved liver function on the DDC diet compared with control mice fed the DDC diet. CONCLUSION: Reactive bile ducts in patients with chronic liver diseases have increased levels of LTB and nuclear translocation of RELB. RELB is required for the ductular reaction and development of biliary fibrosis in CyldΔLPC mice. Deletion of RELB and CYLD from LPCs protects mice from DDC-induced cholestatic liver fibrosis.

Human blood CXCR5(+)CD4(+) T cells are counterparts of T follicular cells and contain specific subsets that differentially support antibody secretion.

Although a fraction of human blood memory CD4(+) T cells expresses chemokine (C-X-C motif) receptor 5 (CXCR5), their relationship to T follicular helper (Tfh) cells is not well established. Here we show that human blood CXCR5(+)CD4(+) T cells share functional properties with Tfh cells and appear to represent their circulating memory compartment. Blood CXCR5(+)CD4(+) T cells comprised three subsets: T helper 1 (Th1), Th2, and Th17 cells. Th2 and Th17 cells within CXCR5(+), but not within CXCR5(-), compartment efficiently induced naive B cells to produce immunoglobulins via interleukin-21 (IL-21). In contrast, Th1 cells from both CXCR5(+) and CXCR5(-) compartments lacked the capacity to help B cells. Patients with juvenile dermatomyositis, a systemic autoimmune disease, displayed a profound skewing of blood CXCR5(+) Th cell subsets toward Th2 and Th17 cells. Importantly, the skewing of subsets correlated with disease activity and frequency of blood plasmablasts. Collectively, our study suggests that an altered balance of Tfh cell subsets contributes to human autoimmunity.

Knockdown of Atg7 Induces Nuclear-LC3 Dependent Apoptosis and Augments Chemotherapy in Colorectal Cancer Cells.

Autophagy is a catabolic process that enables cells to degrade obsolete content and refuel energy depots. In colorectal cancer (CRC) autophagy has been shown to promote tumorigenesis through energy delivery in the condition of uncontrolled proliferation. With this study, we aimed at evaluating whether autophagy sustains CRC cell viability and if it impacts therapy resistance. Initially, a colorectal cancer tissue micro array, containing mucosa (n = 10), adenoma (n = 18) and adenocarcinoma (n = 49) spots, was stained for expression of essential autophagy proteins LC3b, Atg7, p62 and Beclin-1. Subsequently, central autophagy proteins were downregulated in CRC cells using siRNA technology. Viability assays, flow cytometry and immunoblotting were performed and three-dimensional cell culture was utilized to study autophagy in a tissue mimicking environment. In our study we found an upregulation of Atg7 in CRC. Furthermore, we identified Atg7 as crucial factor within the autophagy network for CRC cell viability. Its disruption induced cell death via triggering apoptosis and in combination with conventional chemotherapy it exerted synergistic effects in inducing CRC cell death. Cell death was strictly dependent on nuclear LC3b, since simultaneous knockdown of Atg7 and LC3b completely restored viability. This study unravels a novel cell death preventing function of Atg7 in interaction with LC3b, thereby unmasking a promising therapeutic target in CRC.

Foxp1 expression is essential for sex-specific murine neonatal ultrasonic vocalization.

Autism and speech and language deficits are predominantly found in boys, however the causative mechanisms for this sex bias are unknown. Human FOXP1 is associated with autism, intellectual disability and speech and language deficits. Its closely related family member FOXP2 is involved in speech and language disorder and Foxp2 deficient mice have demonstrated an absence of ultrasonic vocalizations (USVs). Since Foxp1 and Foxp2 form heterodimers for transcriptional regulation, we investigated USV in neonatal brain-specific Foxp1 KO mice. Foxp1 KO pups had strongly reduced USV and lacked the sex-specific call rate from WT pups, indicating that Foxp1 is essential for normal USV. As expression differences of Foxp1 or Foxp2 could explain the sex-dimorphic vocalization in WT animals, we quantified both proteins in the striatum and cortex at P7.5 and detected a sex-specific expression of Foxp2 in the striatum. We further analyzed Foxp1 and Foxp2 expression in the striatum and cortex of CD1 mice at different embryonic and postnatal stages and observed sex differences in both genes at E17.5 and P7.5. Sex hormones, especially androgens are known to play a crucial role in the sexual differentiation of vocalizations in many vertebrates. We show that Foxp1 and the androgen receptor are co-expressed in striatal medium spiny neurons and that brain-specific androgen receptor KO (ArNesCre) mice exhibit reduced Foxp1 expression in the striatum at E17.5 and P7.5 and an increased Foxp2 level in the cortex at P7.5. Thus, androgens may contribute to sex-specific differences in Foxp1 and Foxp2 expression and USV.

Human dendritic cells induce the differentiation of interleukin-21-producing T follicular helper-like cells through interleukin-12.

T follicular helper (Tfh) cells help development of antibody responses via interleukin-21 (IL-21). Here we show that activated human dendritic cells (DCs) induced naive CD4(+) T cells to become IL-21-producing Tfh-like cells through IL-12. CD4(+) T cells primed with IL-12 induced B cells to produce immunoglobulins in a fashion dependent on IL-21 and inducible costimulator (ICOS), thus sharing fundamental characteristics with Tfh cells. The induction of Tfh-like cells by activated DCs was inhibited by neutralizing IL-12. IL-12 induced two different IL-21-producers: IL-21(+)IFN-gamma(+)T-bet(+) Th1 cells and IL-21(+)IFN-gamma(-)T-bet(-) non-Th1 cells, in a manner dependent on signal transducer and activator of transcription 4 (STAT4). IL-12 also regulated IL-21 secretion by memory CD4(+) T cells. Thus, IL-12 produced by activated DCs regulates antibody responses via developing IL-21-producing Tfh-like cells and inducing IL-21 secretion from memory CD4(+) T cells. These data suggest that the developmental pathway of Tfh cells differs between mice and humans, which have considerable implications for vaccine development.

T follicular helper (Tfh) cells in lupus: Activation and involvement in SLE pathogenesis.

Systemic lupus erythematosus (SLE) is a chronic systemic inflammatory autoimmune disease characterized by a breakdown of tolerance to self. The autoantibodies generated in SLE are directed against nuclear components, with which they form immune complexes (ICs). ICs play key roles in organ and tissue damage, as well as in the activation of the innate and adaptive immune system during the disease course. Therefore, it is of prime importance to understand the mechanisms responsible for the development of B cells producing these pathogenic autoantibodies. There is compelling evidence that T follicular helper (Tfh) cells play a fundamental role in this process. In this review, we will summarize the current knowledge regarding the involvement of Tfh cells in SLE pathogenesis, and discuss potential strategies to target Tfh cells and/or molecules as a therapeutic modality of SLE.

T follicular helper cells, interleukin-21 and systemic lupus erythematosus.

SLE is a chronic systemic autoimmune disease characterized by a breakdown of tolerance to nuclear antigens and generation of high-affinity pathogenic autoantibodies. These autoantibodies form, with autoantigens, immune complexes that are involved in organ and tissue damages. Understanding how the production of these pathogenic autoantibodies arises is of prime importance. T follicular helper cells (Tfh) and IL-21 have emerged as central players in this process. This article reviews the pathogenic role of Tfh cells and IL-21 in SLE.

Phenotype and functions of memory Tfh cells in human blood.

Our understanding of the origin and functions of human blood CXCR5(+) CD4(+) T cells found in human blood has changed dramatically in the past years. These cells are currently considered to represent a circulating memory compartment of T follicular helper (Tfh) lineage cells. Recent studies have shown that blood memory Tfh cells are composed of phenotypically and functionally distinct subsets. Here, we review the current understanding of human blood memory Tfh cells and the subsets within this compartment. We present a strategy to define these subsets based on cell surface profiles. Finally, we discuss how increased understanding of the biology of blood memory Tfh cells may contribute insight into the pathogenesis of autoimmune diseases and the mode of action of vaccines.

IL-12 receptor ß1 deficiency alters in vivo T follicular helper cell response in humans.

Antibody responses represent a key immune protection mechanism. T follicular helper (Tfh) cells are the major CD4(+) T-cell subset that provides help to B cells to generate an antibody response. Tfh cells together with B cells form germinal centers (GCs), the site where high-affinity B cells are selected and differentiate into either memory B cells or long-lived plasma cells. We show here that interleukin-12 receptor ß1 (IL-12Rß1)-mediated signaling is important for in vivo Tfh response in humans. Although not prone to B cell-deficient-associated infections, subjects lacking functional IL-12Rß1, a receptor for IL-12 and IL-23, displayed substantially less circulating memory Tfh and memory B cells than control subjects. GC formation in lymph nodes was also impaired in IL-12Rß1-deficient subjects. Consistently, the avidity of tetanus toxoid-specific serum antibodies was substantially lower in these subjects than in age-matched controls. Tfh cells in tonsils from control individuals displayed the active form of signal transducer and activator of transcription 4 (STAT4), demonstrating that IL-12 is also acting on Tfh cells in GCs. Thus, our study shows that the IL-12-STAT4 axis is associated with the development and the functions of Tfh cells in vivo in humans.

Targeting human dendritic cell subsets for improved vaccines.

Dendritic cells (DCs) were discovered in 1973 by Ralph Steinman as a previously undefined cell type in the mouse spleen and are now recognized as a group of related cell populations that induce and regulate adaptive immune responses. Studies of the past decade show that, both in mice and humans, DCs are composed of subsets that differ in their localization, phenotype, and functions. These progresses in our understanding of DC biology provide a new framework for improving human health. In this review, we discuss human DC subsets in the context of their medical applications, with a particular focus on DC targeting.

Human tonsil B-cell lymphoma 6 (BCL6)-expressing CD4+ T-cell subset specialized for B-cell help outside germinal centers.

T follicular helper (Tfh) cells represent a Th subset engaged in the help of B-cell responses in germinal centers (GCs). Tfh cells abundantly express the transcription repressor B-cell lymphoma 6 (Bcl6), a factor that is necessary and sufficient for their development in vivo. Whether Tfh or Tfh-committed cells are involved in the help of B cells outside GCs remains unclear, particularly in humans. In this study, we identified a previously undefined BCL6-expressing CD4(+) T-cell subset in human tonsils. This subset expressed IL-7 receptor and chemokine receptor 5 (CXCR5) and inducible costimulator (ICOS) at low levels (CXCR5(lo)ICOS(lo)), and it was found exclusively outside GCs. CXCR5(lo)ICOS(lo) CD4(+) T cells secreted larger amounts of IL-21 and IL-10 than CXCR5(hi)ICOS(hi) GC-Tfh cells upon activation, and they induced proliferation and differentiation of naïve B cells into Ig-producing cells more efficiently than GC-Tfh cells. However, this subset lacked the capacity to help GC-B cells because of the induction of apoptosis of GC-B cells through the FAS/FAS-ligand interaction. CXCR5(lo)ICOS(lo) CD4(+) T cells expressed equivalent amounts of BCL6 transcript with CXCR5(hi)ICOS(hi) GC-Tfh cells, but they expressed less Bcl6 protein. Collectively, our study indicates that CXCR5(lo)ICOS(lo) CD4(+) T cells in human tonsils represent Tfh lineage-committed cells that provide help to naïve and memory B cells outside GCs.

Harnessing human dendritic cell subsets for medicine.

Immunity results from a complex interplay between the antigen-non-specific innate immune system and the antigen-specific adaptive immune system. The cells and molecules of the innate system employ non-clonal recognition receptors including lectins, Toll-like receptors, NOD-like receptors, and helicases. B and T lymphocytes of the adaptive immune system employ clonal receptors recognizing antigens or their derived peptides in a highly specific manner. An essential link between innate and adaptive immunity is provided by dendritic cells (DCs). DCs can induce such contrasting states as immunity and tolerance. The recent years have brought a wealth of information on the biology of DCs revealing the complexity of this cell system. Indeed, DC plasticity and subsets are prominent determinants of the type and quality of elicited immune responses. In this article, we summarize our recent studies aimed at a better understanding of the DC system to unravel the pathophysiology of human diseases and design novel human vaccines.

Human T follicular helper cells: development and subsets.

Antibody response constitutes one of the key immune protection mechanisms. T follicular helper (Tfh) cells represent the major CD4⁺ T cell subset that provides help to B cells to induce antibody response. How Tfh cells develop and how Tfh cells or their associated subsets regulate antibody response in humans remains largely unknown. In this review, we will summarize the recent discoveries on the biology of Tfh cells, with a particular focus on human Tfh cells.