Human ICOS deficiency abrogates the germinal center reaction and provides a monogenic model for common variable immunodeficiency

Activation of CXCR3+ Tfh cells and B cells in lymph nodes during acute HIV-1 infection correlates with HIV-specific antibody development

Lymph node T follicular helper (Tfh) cells and germinal center (GC) B cells are critical to generate potent antibodies but are rarely possible to study in humans. To understand how Tfh/GC B-cell interactions during acute HIV-1 infection (AHI) impact the generation of HIV-specific antibodies, we performed a unique cross-sectional analysis of inguinal lymph node biopsies taken prior to antiretroviral therapy (ART) initiation in AHI. Although total Tfh and GC B cell frequencies did not change during AHI, increased frequencies of proliferating Th1-like CXCR3+ Tfh, CXCR3+ non-GC B cells, and total CXCR3+ GC B cells correlated with gp120-specific IgG antibody levels in AHI. Frequencies of proliferating CXCR3+ Tfh in AHI also correlated with gp120-specific IgG antibody levels after 48 weeks of ART, antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and increased antibody binding to infected cells after ART. Importantly, while beneficial for antibody development, CXCR3+ Tfh cells were also infected by HIV-1 at higher frequencies than their CXCR3- counterparts and may contribute to the initial dissemination of HIV-1 in follicles. Together, these data suggest that activation of CXCR3+ Tfh cells is associated with induction of the germinal center response and subsequent antibody development, making these cells an important target for future therapeutic interventions.

IMPORTANCE

Early initiation of antiretroviral therapy (ART) is important to limit the seeding of the long-lasting HIV-1 reservoir; however, it also precludes the development of HIV-specific antibodies that can help control the virus if ART is stopped. Antibody development occurs within germinal centers in the lymph node and requires activation of both antigen-specific B cells and T follicular helper cells (Tfh), a specialized CD4+ cell that provides B cell help. To understand how early ART initiation may prohibit antibody development, we analyzed the frequencies and activation status of Tfh and B cells in lymph node biopsies collected in the different stages of acute HIV-1 infection. Our data suggest that decreased antibody development after early ART initiation may be due to limited germinal center development at the time of treatment and that new interventions that target activation of CXCR3+ Tfh may be beneficial to increase long-term HIV-specific antibody levels.

Using T-Cell Subsets to Better Characterize Immunoresiliency and Immunodeficiency in Patients with Recurrent Infections

BACKGROUND/OBJECTIVES

Common Variable Immunodeficiency Disease (CVID) and other immunodeficiencies can present in subtle and variable ways. Whether or not a genetic lesion can be identified, there are not well understood biomarkers that quantitatively describe how severe a deficiency is. Here we discuss two possible ranking systems, CD4/CD8 T cell ratios and Immune Health Grades, and how such data maybe applicable to some immunodeficiencies.

METHODS

This is not a systematic review, but we identify papers relating to immunodeficiencies with enough data to comment on the CD4/CD8 and Immune Health Grade. We also summarized relevant data publicly available from USIDNET, a website that compiles data on immunodeficiencies, and provide two new cases that illustrate ways that this information can alter clinical assessment.

RESULTS

We review the HIV literature on CD4/CD8 T cell data and how this correlates with both immunologic function and comorbidity better than CD4 count alone. The ratio aslso relates to a new system called Immune Health Grades (IHG) derived from young adult to elderly subjects from many NIH cohorts without HIV. CVID is often thought of as an antibody problem, but in fact most patients also have low CD4/CD8 ratio and other cellular abnormalities. We review IDNET to categorize nine molecular immunodeficiencies including two subcategories of CVID into low, normal, or high ratios. Finally, we present two new cases in the literature of patients with recurrent infection and discuss how viewing the cases through the "lens" of CD4/CD8 ratio and IHG can facilitate clinical decisions.

CONCLUSIONS

Emerging data suggests at least some immunodeficiencies can be grouped by how abnormal their CD4/CD8 ratio or IHG. This represents a clinically available biomarker that can be tracked to see if the condition is worsening or not.

Cancer Trends in Inborn Errors of Immunity: A Systematic Review and Meta-Analysis

BACKGROUND

Patients with inborn errors of immunity (IEI) are susceptible to developing cancer due to defects in the immune system. The prevalence of cancer is higher in IEI patients compared to the immunocompetent population and cancers are considered as an important and common cause of death in IEI patients.

OBJECTIVES

To systematically review demographic, genetic and cancer-related data of IEI patients with a history of malignancy. Moreover, we performed a meta-analysis aiming to determine the frequency of cancer in patients with different types of IEI.

METHODS

We conducted electronic searches on Embase, Web of Science, PubMed, and Scopus (until September 2023) introducing terms related to IEI and cancer. Studies with human subjects with confirmed IEI who had developed at least one malignancy during their lifetime were included.

RESULTS

A total number of 4607 IEI patients with a cancer history were included in the present study. Common variable immunodeficiency (CVID) had the highest number of reported cases (1284 cases), mainly due to a higher relative proportion of patients with predominantly antibody deficiencies (PAD) and their increased life expectancy contributing to the higher detection and reporting of cancers among these patients. The most common malignancy was hematologic/blood cancers (3026 cases, mainly diffuse large B cell lymphoma). A total number of 1173 cases (55.6%) succumbed to cancer, with the highest rate of bone marrow failure (64.9%). Among the patients with monogenic defects in IEI-associated genes, the majority of cases had ATM deficiency (926 cases), but the highest cancer frequency rate belonged to NBS1 deficiency (50.5%). 1928 cases out of total 4607 eligible cases had detailed data to allow further statistical analysis that revealed BRCA2 deficiency had the earliest cancer development (~ 38 months), lowest cure frequency, and highest fatality rate (85%), while ATM deficiency had the lowest cure frequency and highest fatality rate (72%) among total cases reviewed with exclusion of Fanconi anemia.

CONCLUSION

The overall reported cancer frequency in the cases reviewed with and without exclusion of Fanconi anemia was 11.1% (95% confidence interval: 9.8-12.5%) and 12.0% (95% confidence interval: 10.6-13.5%), respectively. Our study revealed that the incidence of cancer is significantly dependent on the molecular and pathway defects in IEI patients, and individualized early screening and appropriate treatment, might improve the prognosis of these patients.

The role of dendritic cells in the instruction of helper T cells in the allergic march

Allergy is a complex array of diseases influenced by innate and adaptive immunity, genetic polymorphisms, and environmental triggers. Atopic dermatitis is a chronic inflammatory skin disease characterized by barrier defects and immune dysregulation, sometimes leading to asthma and food allergies because of the atopic march. During atopic skin inflammation, Langerhans cells and dendritic cells (DCs) in the skin capture and deliver allergen information to local lymph nodes. DCs are essential immune sensors coordinating immune reactions by capturing and presenting antigens to T cells. In the context of allergic responses, DCs play a crucial role in instructing two types of helper T cells-type 2 helper T (Th2) cells and follicular helper T (TFH) cells-in allergic responses and IgE antibody responses. In skin sensitization, the differentiation and function of Th2 cells and TFH cells are influenced by skin-derived factors, including epithelial cytokines, chemokines, and signalling pathways to modify the function of migratory DCs and conventional DCs. In this review, we aim to understand the specific mechanisms involving DCs in allergic responses to provide insights into the pathogenesis of allergic diseases and potential therapeutic strategies.

Evolution of pathologic B-cell subsets and serum environment-specific sIgEs in patients with atopic dermatitis and controls, from infancy to adulthood

BACKGROUND

While B-cells have historically been implicated in allergy development, a growing body of evidence supports their role in atopic dermatitis (AD). B-cell differentiation across ages in AD, and its relation to disease severity scores, has not been well defined.

OBJECTIVE

To compare the frequency of B-cell subsets in blood of 0-5, 6-11, 12-17, and ≥18 years old patients with AD versus age-matched controls.

METHODS

Flow cytometry was used to measure B-cell subset frequencies in the blood of 27 infants, 17 children, 11 adolescents, and 31 adults with moderate-to-severe AD and age-matched controls. IgD/CD27 and CD24/CD38 core gating systems and an 11-color flow cytometry panel were used to determine frequencies of circulating B-cell subsets. Serum total and allergen-specific IgE (sIgEs) levels were measured using ImmunoCAP®.

RESULTS

Adolescents with AD had lower frequencies of major B-cells subsets (p < .03). CD23 expression increased with age and was higher in AD compared to controls across all age groups (p < .04). In AD patients, multiple positive correlations were observed between IL-17-producing T-cells and B-cell subsets, most significantly non-switched memory (NSM) B-cells (r = .41, p = .0005). AD severity positively correlated with a list of B-cell subsets (p < .05). IL-9 levels gradually increased during childhood, reaching a peak in adolescence, paralleling allergen sensitization, particularly in severe AD. Principal component analysis of the aggregated environmental sIgE data showed that while controls across all ages tightly clustered together, adolescents with AD demonstrated distinct clustering patterns relative to controls.

CONCLUSIONS

Multiple correlations between B-cells and T-cells, as well as disease severity measures, suggest a complex interplay of immune pathways in AD. Unique B-cell signature during adolescence, with concurrent allergen sensitization and IL-9 surge, point to a potentially wider window of opportunity to implement interventions that may prevent the progression of the atopic march.

In vivo CAR T cell therapy against angioimmunoblastic T cell lymphoma

BACKGROUND

For angioimmunoblastic T cell lymphoma (AITL), a rare cancer, no specific treatments are available and survival outcome is poor. We previously developed a murine model for AITL that mimics closely human disease and allows to evaluate new treatments. As in human AITL, the murine CD4+ follicular helper T (Tfh) cells are drivers of the malignancy. Therefore, chimeric antigen receptor (CAR) T cell therapy might represent a new therapeutic option.

METHODS

To prevent fratricide among CAR T cells when delivering an CD4-specific CAR, we used a lentiviral vector (LV) encoding an anti-CD4 CAR, allowing exclusive entry into CD8 T cells.

RESULTS

These anti-CD4CAR CD8-targeted LVs achieved in murine AITL biopsies high CAR-expression levels in CD8 T cells. Malignant CD4 Tfh cells were eliminated from the mAITL lymphoma, while the CAR + CD8 T cells expanded upon encounter with the CD4 receptor and were shaped into functional cytotoxic cells. Finally, in vivo injection of the CAR + CD8-LVs into our preclinical AITL mouse model carrying lymphomas, significantly prolonged mice survival. Moreover, the in vivo generated functional CAR + CD8 T cells efficiently reduced neoplastic T cell numbers in the mAITL tumors.

CONCLUSION

This is the first description of in vivo generated CAR T cells for therapy of a T cell lymphoma. The strategy described offers a new therapeutic concept for patients suffering from CD4-driven T cell lymphomas.

Patients and mice with deficiency in the SNARE protein SYNTAXIN-11 have a secondary B cell defect

SYNTAXIN-11 (STX11) is a SNARE protein that mediates the fusion of cytotoxic granules with the plasma membrane at the immunological synapses of CD8 T or NK cells. Autosomal recessive inheritance of deleterious STX11 variants impairs cytotoxic granule exocytosis, causing familial hemophagocytic lymphohistiocytosis type 4 (FHL-4). In several FHL-4 patients, we also observed hypogammaglobulinemia, elevated frequencies of naive B cells, and increased double-negative DN2:DN1 B cell ratios, indicating a hitherto unrecognized role of STX11 in humoral immunity. Detailed analysis of Stx11-deficient mice revealed impaired CD4 T cell help for B cells, associated with disrupted germinal center formation, reduced isotype class switching, and low antibody avidity. Mechanistically, Stx11-/- CD4 T cells exhibit impaired membrane fusion leading to reduced CD107a and CD40L surface mobilization and diminished IL-2 and IL-10 secretion. Our findings highlight a critical role of STX11 in SNARE-mediated membrane trafficking and vesicle exocytosis in CD4 T cells, important for successful CD4 T cell-B cell interactions. Deficiency in STX11 impairs CD4 T cell-dependent B cell differentiation and humoral responses.

ICOS agonist vopratelimab modulates follicular helper T cells and improves B cell function in common variable immunodeficiency

Common variable immunodeficiency (CVID) is an immune defect characterized by hypogammaglobulinemia and impaired development of B cells into plasma cells. As follicular helper T cells (TFH) play a central role in humoral immunity, we examined TFH cells in CVID, and investigated whether an inducible T cell co-stimulator (ICOS) agonist, vopratelimab, could modulate TFH, B cell interactions and enhance immunoglobulin production. CVID subjects had decreased TFH17 and increased TFH1 subsets; this was associated with increased transitional B cells and decreased IgG+ B and IgD-IgM-CD27+ memory B cells. ICOS expression on CVID CD4+ T cells was also decreased. However, ICOS activation of CD4+ T cells by vopratelimab significantly increased total CVID TFH, TFH2, cell numbers, as well as IL-4, IL-10 and IL-21 secretion in vitro. Vopratelimab treatment also increased plasma cells, IgG+ B cells, reduced naïve & transitional B cells and significantly increased IgG1 secretion by CVID B cells. Interestingly, vopratelimab treatment also restored IgA secretion in PBMCs from several CVID patients who had a complete lack of endogenous serum IgA. Our data demonstrate the potential of TFH modulation in restoring TFH and enhancing B cell maturation in CVID. The effects of an ICOS agonist in antibody defects warrants further investigation. This biologic may also be of therapeutic interest in other clinical settings of antibody deficiency.

Transcriptional regulation of Tfh dynamics and the formation of immunological synapses

Inside germinal centers (GCs), antigen-specific B cells rely on precise interactions with immune cells and strategic localization between the dark and light zones to clonally expand, undergo affinity maturation, and differentiate into long-lived plasma cells or memory B cells. Follicular helper T (Tfh) cells, the key gatekeepers of GC-dependent humoral immunity, exhibit remarkable dynamic positioning within secondary lymphoid tissues and rely on intercellular interactions with antigen-presenting cells (APCs) during their differentiation and execution of B-cell-facilitating functions within GCs. In this review, we briefly cover the transcriptional regulation of Tfh cell differentiation and function and explore the molecular mechanisms governing Tfh cell motility, their interactions with B cells within GCs, and the impact of their dynamic behavior on humoral responses.

Agonist Antibodies for Cancer Immunotherapy: History, Hopes, and Challenges

Immunotherapy is among the most promising new treatment modalities to arise over the last two decades; antibody drugs are delivering immunotherapy to millions of patients with many different types of cancer. Initial success with antibody therapeutics came in the form of direct targeting or cytotoxic antibodies, such as rituximab and trastuzumab, which bind directly to tumor cells to elicit their destruction. These were followed by immunomodulatory antibodies that elicit antitumor responses by either stimulating immune cells or relieving tumor-mediated suppression. By far the most successful approach in the clinic to date has been relieving immune suppression, with immune checkpoint blockade now a standard approach in the treatment of many cancer types. Despite equivalent and sometimes even more impressive effects in preclinical models, agonist antibodies designed to stimulate the immune system have lagged behind in their clinical translation. In this review, we document the main receptors that have been targeted by agonist antibodies, consider the various approaches that have been evaluated to date, detail what we have learned, and consider how their anticancer potential can be unlocked.

Helios characterized circulating follicular helper T cells with enhanced functional phenotypes and was increased in patients with systemic lupus erythematosus

Helios was related to the immunosuppressive capacity and stability of regulatory T cells. However, the significance of Helios in follicular help T (TFH) and follicular regulatory T (TFR) cells is unclear. This research aimed to clarify the significance of Helios (IKZF2) in TFH and TFR cells and its clinical value in systemic lupus erythematosus (SLE). IKZF2 mRNA in different cell subsets was analyzed. Helios+ percentages in TFH and TFR cells were identified in the peripheral blood of 75 SLE patients and 62 HCs (healthy controls). PD-1 and ICOS expression were compared between Helios+ and Helios- cells. The capacity of TFH cells to secrete IL-21 and TFR cells to secrete IL-10 was measured. Correlation analysis and receiver operating characteristic (ROC) curve analysis were conducted to assess the clinical significance of Helios-related TFH and TFR cell subsets in SLE. There was Helios expression in TFH and TFR cells. PD-1 and ICOS were lower in Helios+ TFR than in Helios- TFR. ICOS was increased in Helios+ TFH cells compared with Helios- TFH cells, and ICOS in Helios+ TFH cells was downregulated in SLE. Helios+ TFH cells secreted more IL-21 than Helios- TFH cells, and Helios+ TFH cells from SLE patients had a stronger IL-21 secretion than HCs. Helios+ TFH percentages were negatively correlated with C3 and C4 and positively related to CRP and SLEDAI, and the AUC of Helios+ TFH to distinguish SLE from HC was 0.7959. Helios characterizes circulating TFH cells with enhanced function. Increased Helios+ TFH cells could reflect the autoimmune status of SLE.

Human IgM-expressing memory B cells

A hallmark of T cell dependent (TD) humoral immune responses is the generation of long-lived memory B cells. The generation of these cells occurs primarily in the germinal center (GC) reaction, where antigen-activated B cells undergo affinity maturation as a major consequence of the combined processes of proliferation, somatic hypermutation of their immunoglobulin V (IgV) region genes, and selection for improved affinity of their B-cell antigen receptors. As many B cells also undergo class-switching to IgG or IgA in these TD responses, there was traditionally a focus on class-switched memory B cells in both murine and human studies on memory B cells. However, it has become clear that there is also a large subset of IgM-expressing memory B cells, which have important phenotypic and functional similarities but also differences to class-switched memory B cells. There is an ongoing discussion about the origin of distinct subsets of human IgM+ B cells with somatically mutated IgV genes. We argue here that the vast majority of human IgM-expressing B cells with somatically mutated IgV genes in adults is indeed derived from GC reactions, even though a generation of some mostly lowly mutated IgM+ B cells from other differentiation pathways, mainly in early life, may exist.

Altered Phenotypes of Colonic and Peripheral Blood Follicular Helper and Follicular Cytotoxic T Cells in Mice with DSS-Induced Colitis

Background

Follicular helper T (Tfh), follicular regulatory T (Tfr), and follicular cytotoxic T (Tfc) cells play important roles in autoimmune diseases. Nevertheless, their changes of functional phenotypes in ulcerative colitis (UC), most importantly, their changes in colon tissue as the target-organ, have not been explored.

Methods

DSS-colitis was induced in Balb/c mice and lymphocytes were collected from spleen, mesenteric lymph nodes, peripheral blood and colon. Tfh, Tfr, and Tfc cells were analyzed using flow cytometry based on their CD4+CXCR5+FOXP3-Tfh, CD4+CXCR5+FOXP3+Tfr and CD8+CXCR5+Tfc expressions. Various functional characterization markers including CD44, CD62L, TIGIT, CD226, PD-1, ICOS, Helios, CTLA-4 and Bcl6 were analyzed in the T cell subsets of the organs.

Results

Tfh and Tfr cells in the colon were significantly increased in DSS-colitis mice. Additionally, the proportions of Tfr and Tfc cells in the peripheral blood were also increased, while Tfc cell proportions in the colon were decreased. The proportion of naïve cells in the Tfh, Tfr and Tfc cells in the colon and peripheral blood decreased, while the proportion of effector memory T cells increased. The TIGIT+CD226-Tfh and Tfc cells were upregulated in the colon of DSS-colitis mice. The PD-1+, ICOS+ and PD-1+ICOS+ Tfh cells were increased in both the colonic and peripheral blood Tfh and Tfc of DSS-colitis mice. The Bcl6+ proportions in the Tfh and Tfr were increased in the colon of DSS-colitis mice.

Conclusion

The colonic and peripheral blood Tfh and Tfc cells of DSS-colitis mice have a significantly activated T cell phenotype, which may play a significant role in the pathogenesis of UC.

Cytokine Response Following SARS-CoV-2 Antigen Stimulation in Patients with Predominantly Antibody Deficiencies

Predominantly antibody deficiencies (PADs) are inborn disorders characterized by immune dysregulation and increased susceptibility to infections. Response to vaccination, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), may be impaired in these patients, and studies on responsiveness correlates, including cytokine signatures to antigen stimulation, are sparse. In this study, we aimed to describe the spike-specific cytokine response following whole-blood stimulation with SARS-CoV-2 spike peptides in patients with PAD (n = 16 with common variable immunodeficiency and n = 15 with selective IgA deficiency) and its relationship with the occurrence of coronavirus disease 2019 (COVID-19) during up to 10-month follow-up period. Spike-induced antibody and cytokine production was measured using ELISA (anti-spike IgG, IFN-γ) and xMAP technology (interleukin-1β (IL-1β), IL-4, IL-6, IL-10, IL-15, IL-17A, IL-21, TNF-α, TGF-β1). No difference was found in the production of cytokines between patients with PAD and controls. Anti-spike IgG and cytokine levels did not predict contraction of COVID-19. The only cytokine that distinguished between vaccinated and naturally infected unvaccinated PAD patients was IFN-γ (median 0.64 (IQR = 1.08) in vaccinated vs. 0.10 (IQR = 0.28) in unvaccinated). This study describes the spike-specific cytokine response to SARS-CoV-2 antigens, which is not predictive of contracting COVID-19 during the follow-up.

ICOS costimulation is indispensable for the differentiation of T follicular regulatory cells

ICOS is a T-cell costimulatory receptor critical for Tfh cell generation and function. However, the role of ICOS in Tfr cell differentiation remains unclear. Using Foxp3-Cre-mediated ICOS knockout (ICOS FC) mice, we show that ICOS deficiency in Treg-lineage cells drastically reduces the number of Tfr cells during GC reactions but has a minimal impact on conventional Treg cells. Single-cell transcriptome analysis of Foxp3+ cells at an early stage of the GC reaction suggests that ICOS normally inhibits Klf2 expression to promote follicular features including Bcl6 up-regulation. Furthermore, ICOS costimulation promotes nuclear localization of NFAT2, a known driver of CXCR5 expression. Notably, ICOS FC mice had an unaltered overall GC B-cell output but showed signs of expanded autoreactive B cells along with elevated autoantibody titers. Thus, our study demonstrates that ICOS costimulation is critical for Tfr cell differentiation and highlights the importance of Tfr cells in maintaining humoral immune tolerance during GC reactions.

Chromosomal Numerical Aberrations and Rare Copy Number Variation in Patients with Inflammatory Bowel Disease

BACKGROUND AND AIMS

Inflammatory bowel diseases [IBD] have a complex polygenic aetiology. Rare genetic variants can cause monogenic intestinal inflammation. The impact of chromosomal aberrations and large structural abnormalities on IBD susceptibility is not clear. We aimed to comprehensively characterise the phenotype and prevalence of patients with IBD who possess rare numerical and structural chromosomal abnormalities.

METHODS

We performed a systematic literature search of databases PubMed and Embase; and analysed gnomAD, Clinvar, the 100 000 Genomes Project, and DECIPHER databases. Further, we analysed international paediatric IBD cohorts to investigate the role of IL2RA duplications in IBD susceptibility.

RESULTS

A meta-analysis suggests that monosomy X [Turner syndrome] is associated with increased expressivity of IBD that exceeds the population baseline (1.86%, 95% confidence interval [CI] 1.48 to 2.34%) and causes a younger age of IBD onset. There is little evidence that Klinefelter syndrome, Trisomy 21, Trisomy 18, mosaic Trisomy 9 and 16, or partial trisomies contribute to IBD susceptibility. Copy number analysis studies suggest inconsistent results. Monoallelic loss of X-linked or haploinsufficient genes is associated with IBD by hemizygous or heterozygous deletions, respectively. However, haploinsufficient gene deletions are detected in healthy reference populations, suggesting that the expressivity of IBD might be overestimated. One duplication that has previously been identified as potentially contributing to IBD risk involves the IL2RA/IL15R loci. Here we provide additional evidence that a microduplication of this locus may predispose to very-early-onset IBD by identifying a second case in a distinct kindred. However, the penetrance of intestinal inflammation in this genetic aberration is low [<2.6%].

CONCLUSIONS

Turner syndrome is associated with increased susceptibility to intestinal inflammation. Duplication of the IL2RA/IL15R loci may contribute to disease risk.

Common Variable Immunodeficiency: More Pathways than Roads to Rome

Fifty years have elapsed since the term common variable immunodeficiency (CVID) was introduced to accommodate the many and varied antibody deficiencies being identified in patients with suspected inborn errors of immunity (IEIs). Since then, how the term is understood and applied for diagnosis and management has undergone many revisions, though controversy persists on how exactly to define and classify CVID. Many monogenic disorders have been added under its aegis, while investigations into polygenic, epigenetic, and somatic contributions to CVID susceptibility have gained momentum. Expansion of the overall IEI landscape has increasingly revealed genotypic and phenotypic overlap between CVID and various other immunological conditions, while increasingly routine genotyping of CVID patients continues to identify an incredible diversity of pathophysiological mechanisms affecting even single genes. Though many questions remain to be answered, the lessons we have already learned from CVID biology have greatly informed our understanding of adaptive, but also innate, immunity.

Lymphoid stromal cells - potential implications for the pathogenesis of CVID

Non-hematopoietic lymphoid stromal cells (LSC) maintain lymph node architecture and form niches allowing the migration, activation, and survival of immune cells. Depending on their localization in the lymph node, these cells display heterogeneous properties and secrete various factors supporting the different activities of the adaptive immune response. LSCs participate in the transport of antigen from the afferent lymph as well as in its delivery into the T and B cell zones and organize cell migration via niche-specific chemokines. While marginal reticular cells (MRC) are equipped for initial B-cell priming and T zone reticular cells (TRC) provide the matrix for T cell-dendritic cell interactions within the paracortex, germinal centers (GC) only form when both T- and B cells successfully interact at the T-B border and migrate within the B-cell follicle containing the follicular dendritic cell (FDC) network. Unlike most other LSCs, FDCs are capable of presenting antigen via complement receptors to B cells, which then differentiate within this niche and in proximity to T follicular helper (T_FH) cells into memory and plasma cells. LSCs are also implicated in maintenance of peripheral immune tolerance. In mice, TRCs induce the alternative induction of regulatory T cells instead of T_FH cells by presenting tissue-restricted self-antigens to naïve CD4 T cells via MHC-II expression. This review explores potential implications of our current knowledge of LSC populations regarding the pathogenesis of humoral immunodeficiency and autoimmunity in patients with autoimmune disorders or common variable immunodeficiency (CVID), the most common form of primary immunodeficiency in humans.

Deciphering imprints of impaired memory B-cell maturation in germinal centers of three patients with common variable immunodeficiency

Common variable immunodeficiency (CVID), characterized by recurrent infections, low serum class-switched immunoglobulin isotypes, and poor antigen-specific antibody responses, comprises a heterogeneous patient population in terms of clinical presentation and underlying etiology. The diagnosis is regularly associated with a severe decrease of germinal center (GC)-derived B-cell populations in peripheral blood. However, data from B-cell differentiation within GC is limited. We present a multiplex approach combining histology, flow cytometry, and B-cell receptor repertoire analysis of sorted GC B-cell populations allowing the modeling of distinct disturbances in GCs of three CVID patients. Our results reflect pathophysiological heterogeneity underlying the reduced circulating pool of post-GC memory B cells and plasmablasts in the three patients. In patient 1, quantitative and qualitative B-cell development in GCs is relatively normal. In patient 2, irregularly shaped GCs are associated with reduced somatic hypermutation (SHM), antigen selection, and class-switching, while in patient 3, high SHM, impaired antigen selection, and class-switching with large single clones imply increased re-cycling of cells within the irregularly shaped GCs. In the lymph nodes of patients 2 and 3, only limited numbers of memory B cells and plasma cells are formed. While reduced numbers of circulating post GC B cells are a general phenomenon in CVID, the integrated approach exemplified distinct defects during GC maturation ranging from near normal morphology and function to severe disturbances with different facets of impaired maturation of memory B cells and/or plasma cells. Integrated dissection of disturbed GC B-cell maturation by histology, flow cytometry, and BCR repertoire analysis contributes to unraveling defects in the essential steps during memory formation.

Inflammatory Cytokine-Neutralizing Antibody Treatment Prevented Increases in Follicular Helper T Cells and Follicular Regulatory T Cells in a Mouse Model of Arthritis

Background

Follicular T helper (TFH) and follicular regulatory T (TFR) cells play important roles in humoral immunity. Nevertheless, their significance in rheumatoid arthritis (RA) pathogenesis has not been fully elucidated. As an important treatment strategy, the effect of inflammatory factor-neutralizing antibodies on TFH and TFR in RA remains unclear.

Methods

We used the collagen-induced arthritis (CIA) mouse model to illustrate the quantity and functional changes in TFH and TFR cells. The changes of plasmablast, TFH and TFR cells in the spleen and peripheral blood of CIA mice were analyzed by flow cytometry. The levels of TFH and TFR and their functional subsets in the spleen after anti-inflammatory antibody treatment were analyzed and compared. The functional changes of TFH and TFR in CIA mice before and after treatment were detected by in vitro culture experiments.

Results

Plasmablast levels were increased in CIA spleen and peripheral blood and both TFH and TFR cell levels were upregulated. TFH and TFR cells were decreased significantly after the anti-inflammatory antibody treatment. TIGIT⁺ and TIGIT⁺CD226⁻ TFH cells in CIA mouse spleen were elevated and PD-1 and ICOS expression on spleen TFH and TFR cells was increased. Both the ability of TFH cells to secrete IL-21 and aid B cells and the ability of TFR cells to secrete IL-10 and inhibit TFH cells were enhanced in the CIA mice. After antibody treatment, the cell subsets and functions were recovered.

Conclusion

Germinal center TFH and TFR cells were increased and their functions were enhanced. With inflammatory factor-neutralizing antibody treatment, TFH and TFR subsets and their functions returned to normal. These findings provide important information on the dynamics of humoral immune-related cell subsets in RA and the effects of treatment on them.

Follicular helper T cell signature of replicative exhaustion, apoptosis, and senescence in common variable immunodeficiency

Common variable immunodeficiency (CVID) is the most frequent primary antibody deficiency whereby follicular helper T (Tfh) cells fail to establish productive responses with B cells in germinal centers. Here, we analyzed the frequency, phenotype, transcriptome, and function of circulating Tfh (cTfh) cells in CVID patients displaying autoimmunity as an additional phenotype. A group of patients showed a high frequency of cTfh1 cells and a prominent expression of PD-1 and ICOS as well as a cTfh mRNA signature consistent with highly activated, but exhausted, senescent, and apoptotic cells. Plasmatic CXCL13 levels were elevated in this group and positively correlated with cTfh1 cell frequency and PD-1 levels. Monoallelic variants in RTEL1, a telomere length- and DNA repair-related gene, were identified in four patients belonging to this group. Their blood lymphocytes showed shortened telomeres, while their cTfh were more prone to apoptosis. These data point toward a novel pathogenetic mechanism in CVID, whereby alterations in DNA repair and telomere elongation might predispose to antibody deficiency. A Th1, highly activated but exhausted and apoptotic cTfh phenotype was associated with this form of CVID.

Autoimmune Cytopenias in Common Variable Immunodeficiency Are a Diagnostic and Therapeutic Conundrum: An Update

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency (PID). CVID is a heterogenous condition and clinical manifestations may vary from increased susceptibility to infections to autoimmune manifestations, granulomatous disease, polyclonal lymphoproliferation, and increased risk of malignancy. Autoimmune manifestations may, at times, be the first and only clinical presentation of CVID, resulting in diagnostic dilemma for the treating physician.

Autoimmune cytopenias (autoimmune haemolytic anaemia and/or thrombocytopenia) are the most common autoimmune complications seen in patients with CVID. Laboratory investigations such as antinuclear antibodies, direct Coomb’s test and anti-platelet antibodies may not be useful in patients with CVID because of lack of specific antibody response. Moreover, presence of autoimmune cytopenias may pose a significant therapeutic challenge as use of immunosuppressive agents can be contentious in these circumstances. It has been suggested that serum immunoglobulins must be checked in all patients presenting with autoimmune cytopenia such as immune thrombocytopenia or autoimmune haemolytic anaemia.

It has been observed that patients with CVID and autoimmune cytopenias have a different clinical and immunological profile as compared to patients with CVID who do not have an autoimmune footprint. Monogenic defects have been identified in 10-50% of all patients with CVID depending upon the population studied. Monogenic defects are more likely to be identified in patients with CVID with autoimmune complications. Common genetic defects that may lead to CVID with an autoimmune phenotype include nuclear factor kappa B subunit 1 (NF-kB1), Lipopolysaccharide (LPS)-responsive beige-like anchor protein (LRBA), cytotoxic T lymphocyte antigen 4 (CTLA4), Phosphoinositide 3-kinase (PI3K), inducible T-cell costimulatory (ICOS), IKAROS and interferon regulatory factor-2 binding protein 2 (IRF2BP2).

In this review, we update on recent advances in pathophysiology and management of CVID with autoimmune cytopenias.

Novel T Follicular Helper-like T-Cell Lymphoma Therapies: From Preclinical Evaluation to Clinical Reality

Simple Summary

This work reviews the multiple efforts that have been and are being invested by researchers as well as clinicians to improve the treatment of a specific T-cell lymphoma called follicular helper peripheral T-cell lymphoma. Still, though treatments for B-cell lymphomas have improved, this particular T-cell lymphoma has little to no new therapeutic options that show marked improvements in the survival of the patients compared to treatment with chemotherapy. We report here the evaluation of targeted new therapies for this T-cell lymphoma in new preclinical models for this cancer or in clinical trials with the objective to offer better (combination) treatment options.

Abstract

The classification of peripheral T-cell lymphomas (PTCL) is constantly changing and contains multiple subtypes. Here, we focus on Tfh-like PTCL, to which angioimmunoblastic T-cell lymphoma (AITL) belongs, according to the last WHO classification. The first-line treatment of these malignancies still relies on chemotherapy but gives very unsatisfying results for these patients. Enormous progress in the last decade in terms of understanding the implicated genetic mutations leading to signaling and epigenetic pathway deregulation in Tfh PTCL allowed the research community to propose new therapeutic approaches. These findings point towards new biomarkers and new therapies, including hypomethylating agents, such as azacytidine, and inhibitors of the TCR-hyperactivating molecules in Tfh PTCL. Additionally, metabolic interference, inhibitors of the NF-κB and PI3K-mTOR pathways and possibly novel immunotherapies, such as antibodies and chimeric antigen receptors (CAR) directed against Tfh malignant T-cell surface markers, are discussed in this review among other new treatment options.

Immunomodulatory Properties of Immune Checkpoint Inhibitors-More than Boosting T-Cell Responses?

The approval of immune checkpoint inhibitors (ICI) that serve to enhance effector T-cell anti-tumor responses has strongly improved success rates in the treatment of metastatic melanoma and other tumor types. The currently approved ICI constitute monoclonal antibodies blocking cytotoxic T-lymphocyte-associated protein (CTLA)-4 and anti-programmed cell death (PD)-1. By this, the T-cell-inhibitory CTLA-4/CD80/86 and PD-1/PD-1L/2L signaling axes are inhibited. This leads to sustained effector T-cell activity and circumvents the immune evasion of tumor cells, which frequently upregulate PD-L1 expression and modulate immune checkpoint molecule expression on leukocytes. As a result, profound clinical responses are observed in 40-60% of metastatic melanoma patients. Despite the pivotal role of T effector cells for triggering anti-tumor immunity, mounting evidence indicates that ICI efficacy may also be attributable to other cell types than T effector cells. In particular, emerging research has shown that ICI also impacts innate immune cells, such as myeloid cells, natural killer cells and innate lymphoid cells, which may amplify tumoricidal functions beyond triggering T effector cells, and thus improves clinical efficacy. Effects of ICI on non-T cells may additionally explain, in part, the character and extent of adverse effects associated with treatment. Deeper knowledge of these effects is required to further develop ICI treatment in terms of responsiveness of patients to treatment, to overcome resistance to ICI and to alleviate adverse effects. In this review we give an overview into the currently known immunomodulatory effects of ICI treatment in immune cell types other than the T cell compartment.

Inducible T-Cell Costimulator Ligand Plays a Dual Role in Melanoma Metastasis upon Binding to Osteopontin or Inducible T-Cell Costimulator

Recently, we demonstrated that inducible T-cell costimulator (ICOS) shares its unique ligand (ICOSL) with osteopontin (OPN), and OPN/ICOSL binding promotes tumor metastasis and angiogenesis in the 4T1 breast cancer model. Literature showed that OPN promotes melanoma metastasis by suppressing T-cell activation and recruiting myeloid suppressor cells (MDSC). On the opposite, ICOS/ICOSL interaction usually sustains an antitumor response. Here, we engineered murine B16F10 melanoma cells, by transfecting or silencing ICOSL. In vitro data showed that loss of ICOSL favors anchorage-independent growth and induces more metastases in vivo, compared to ICOSL expressing cells. To dissect individual roles of the three molecules, we compared data from C57BL/6 with those from OPN-KO, ICOS-KO, and ICOSL-KO mice, missing one partner at a time. We found that OPN produced by the tumor microenvironment (TME) favors the metastasis by interacting with stromal ICOSL. This activity is dominantly inhibited by ICOS expressed on TME by promoting Treg expansion. Importantly, we also show that OPN and ICOSL highly interact in human melanoma metastases compared to primary tumors. Interfering with this binding may be explored in immunotherapy either for nonresponding or patients resistant to conventional therapies.

Inducible T-cell co-stimulator (ICOS) and ICOS ligand are novel players in the multiple-myeloma microenvironment

The inducible T-cell co-stimulator (ICOS) is a T-cell receptor that, once bound to ICOS ligand (ICOSL) expressed on several cell types including the B-cell lineage, plays a decisive role in adaptive immunity by regulating the interplay between B and T cells. In addition to its immunomodulatory functions, we have shown that ICOS/ICOSL signalling can inhibit the activity of osteoclasts, unveiling a novel mechanism of lymphocyte-bone cells interactions. ICOS and ICOSL can also be found as soluble forms, namely sICOS and sICOSL. Here we show that: (i) levels of sICOS and sICOSL are increased in multiple myeloma (MM) compared to monoclonal gammopathy of undetermined significance and smouldering MM; (ii) levels of sICOS and sICOSL variably correlate with several markers of tumour burden; and (iii) sICOS levels tend to be higher in Durie-Salmon stage II/III versus stage I MM and correlate with overall survival as an independent variable. Moreover, surface ICOS and ICOSL are expressed in both myeloma cells and normal plasma cells, where they probably regulate different functional stages. Finally, ICOSL triggering inhibits the migration of myeloma cell lines in vitro and the growth of ICOSL⁺ MOPC-21 myeloma cells in vivo. These results suggest that ICOS and ICOSL represent novel markers and therapeutic targets for MM.

The role of ICOS in allergic disease: Positive or Negative?

With the rapid increase in the incidence of allergic diseases, the mechanisms underlying the development of these diseases have received a great deal of attention, and this is particularly true in regard to the role of ICOS in allergic diseases. Current studies have revealed that ICOS affects the functional activity of multiple immune cells that modulate the adaptive immune system. Additionally, ICOS also plays a crucial role in mediating cellular immunity and coordinating the response of the entire immune system, and thus, it plays a role in allergic reactions. However, the ICOS/ICOS-ligand (ICOS-L) axis functions in a dual role during the development of multiple allergic diseases. In this review, we explore the role of ICOS/ICOSL in the context of different immune cells that function in allergic diseases, and we summarize recent advances in their contribution to these diseases.

Common variable immunodeficiency: different faces of the same disease

Introduction

Common variable immunodeficiency (CVID) is one of the primary humoral immunodeficiencies. Despite the inborn nature, the first symptoms may appear in both children and adults. It is characterized by hypogammaglobulinaemia, severe infections, autoimmunity, allergies, and a predisposition to cancer. A delay in diagnosis is a significant problem: the time from the first symptoms of the disease to diagnosis and the implementation of proper treatment is usually very long. The consequence can be irreversible complications, which is why it is so important to promote knowledge on this immunodeficiency.

Aim

To present the clinical and laboratory manifestation of primary immunodeficiencies such as common variable immunodeficiency.

Material and methods

The study presents the clinical and laboratory phenotype of 14 patients diagnosed with CVID, aged 5 to 58 years. A detailed medical history was taken, and clinical symptoms, immunological test results and complications were analysed in each patient. According to the ESID guidelines, in the differential diagnosis process of CVID the secondary hypogammaglobulinaemia was excluded.

Results

The follow-up period ranged from 39 to 133 months (median: 79 months). The median delay for the entire group was 5 years, which was shorter in children than in adults. In the presented group, the infectious phenotype (pneumonia, sinusitis) was dominant. Autoimmune and allergic diseases, malignant tumours and enteropathies have also been observed.

Conclusions

The diagnostic delay is still too long, especially in adults, which can lead to serious and irreversible complications. Early diagnosis and appropriate treatment with intravenous and subcutaneous immunoglobulins reduces the frequency of infections and their potential complications.

The expansion of human T-bethighCD21low B cells is T cell dependent

Accumulation of human CD21low B cells in peripheral blood is a hallmark of chronic activation of the adaptive immune system in certain infections and autoimmune disorders. The molecular pathways underpinning the development, function, and fate of these CD21low B cells remain incompletely characterized. Here, combined transcriptomic and chromatin accessibility analyses supported a prominent role for the transcription factor T-bet in the transcriptional regulation of these T-bethighCD21low B cells. Investigating essential signals for generating these cells in vitro established that B cell receptor (BCR)/interferon-γ receptor (IFNγR) costimulation induced the highest levels of T-bet expression and enabled their differentiation during cell cultures with Toll-like receptor (TLR) ligand or CD40L/interleukin-21 (IL-21) stimulation. Low proportions of CD21low B cells in peripheral blood from patients with defined inborn errors of immunity (IEI), because of mutations affecting canonical NF-κB, CD40, and IL-21 receptor or IL-12/IFNγ/IFNγ receptor/signal transducer and activator of transcription 1 (STAT1) signaling, substantiated the essential roles of BCR- and certain T cell–derived signals in the in vivo expansion of T-bethighCD21low B cells. Disturbed TLR signaling due to MyD88 or IRAK4 deficiency was not associated with reduced CD21low B cell proportions. The expansion of human T-bethighCD21low B cells correlated with an expansion of circulating T follicular helper 1 (cTfh1) and T peripheral helper (Tph) cells, identifying potential sources of CD40L, IL-21, and IFNγ signals. Thus, we identified important pathways to target autoreactive T-bethighCD21low B cells in human autoimmune conditions, where these cells are linked to pathogenesis and disease progression.

ICOS ligand and IL-10 synergize to promote host-microbiota mutualism

Genome-wide association studies have identified ICOSLG, which encodes the inducible costimulator ligand (ICOSLG or ICOSL) as a susceptibility locus for inflammatory bowel disease. ICOSL has been implicated in the enhancement of pattern recognition receptor signaling in dendritic cells, induction of IL-10 production by CD4 T cells, and the generation of high-affinity antibodies to specific antigens-all of which can potentially explain its involvement in gastrointestinal inflammation. Here, we show that murine ICOSL deficiency results in significant enrichment of IL-10-producing CD4 T cells particularly in the proximal large intestine. Transient depletion of IL-10-producing cells from adult ICOSL-deficient mice induced severe colonic inflammation that was prevented when mice were first treated with metronidazole. ICOSL-deficient mice displayed reduced IgA and IgG antibodies in the colon mucus and impaired serum antibody recognition of microbial antigens, including flagellins derived from mucus-associated bacteria of the Lachnospiraceae family. Confirming the synergy between ICOSL and IL-10, ICOSL deficiency coupled with CD4-specific deletion of the Il10 gene resulted in juvenile onset colitis that was impeded when pups were fostered by ICOSL-sufficient dams. In this setting, we found that both maternally acquired and host-derived antibodies contribute to the life anti-commensal antibody repertoire that mediates this protection in early life. Collectively, our findings reveal a partnership between ICOSL-dependent anti-commensal antibodies and IL-10 in adaptive immune regulation of the microbiota in the large intestine. Furthermore, we identify ICOSL deficiency as an effective platform for exploring the functions of anti-commensal antibodies in host-microbiota mutualism.

Beyond monogenetic rare variants: tackling the low rate of genetic diagnoses in predominantly antibody deficiency

Predominantly antibody deficiency (PAD) is the most prevalent form of primary immunodeficiency, and is characterized by broad clinical, immunological and genetic heterogeneity. Utilizing the current gold standard of whole exome sequencing for diagnosis, pathogenic gene variants are only identified in less than 20% of patients. While elucidation of the causal genes underlying PAD has provided many insights into the cellular and molecular mechanisms underpinning disease pathogenesis, many other genes may remain as yet undefined to enable definitive diagnosis, prognostic monitoring and targeted therapy of patients. Considering that many patients display a relatively late onset of disease presentation in their 2nd or 3rd decade of life, it is questionable whether a single genetic lesion underlies disease in all patients. Potentially, combined effects of other gene variants and/or non-genetic factors, including specific infections can drive disease presentation. In this review, we define (1) the clinical and immunological variability of PAD, (2) consider how genetic defects identified in PAD have given insight into B-cell immunobiology, (3) address recent technological advances in genomics and the challenges associated with identifying causal variants, and (4) discuss how functional validation of variants of unknown significance could potentially be translated into increased diagnostic rates, improved prognostic monitoring and personalized medicine for PAD patients. A multidisciplinary approach will be the key to curtailing the early mortality and high morbidity rates in this immune disorder.

Clinical Genomics for the Diagnosis of Monogenic Forms of Inflammatory Bowel Disease: A Position Paper From the Paediatric IBD Porto Group of European Society of Paediatric Gastroenterology, Hepatology and Nutrition

BACKGROUND

It is important to identify patients with monogenic IBD as management may differ from classical IBD. In this position statement we formulate recommendations for the use of genomics in evaluating potential monogenic causes of IBD across age groups.

METHODS

The consensus included paediatric IBD specialists from the Paediatric IBD Porto group of the European Society of Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) and specialists from several monogenic IBD research consortia. We defined key topics and performed a systematic literature review to cover indications, technologies (targeted panel, exome and genome sequencing), gene panel setup, cost-effectiveness of genetic screening, and requirements for the clinical care setting. We developed recommendations that were voted upon by all authors and Porto group members (32 voting specialists).

RESULTS

We recommend next-generation DNA-sequencing technologies to diagnose monogenic causes of IBD in routine clinical practice embedded in a setting of multidisciplinary patient care. Routine genetic screening is not recommended for all IBD patients. Genetic testing should be considered depending on age of IBD-onset (infantile IBD, very early-onset IBD, paediatric or young adult IBD), and further criteria, such as family history, relevant comorbidities, and extraintestinal manifestations. Genetic testing is also recommended in advance of hematopoietic stem cell transplantation. We developed a diagnostic algorithm that includes a gene panel of 75 monogenic IBD genes. Considerations are provided also for low resource countries.

CONCLUSIONS

Genomic technologies should be considered an integral part of patient care to investigate patients at risk for monogenic forms of IBD.

ICOSLG-mediated regulatory T-cell expansion and IL-10 production promote progression of glioblastoma

BACKGROUND

Targeting immune checkpoint proteins has recently gained substantial attention due to the dramatic success of this strategy in clinical trials for some cancers. Inducible T-cell co-stimulator ligand (ICOSLG) is a member of the B7 family of immune regulatory ligands, expression of which in cancer is implicated in disease progression due to regulation of antitumor adaptive immunity. Although aberrant ICOSLG expression has been reported in glioma cells, the underlying mechanisms that promote glioblastoma (GBM) progression remain elusive.

METHODS

Here, we investigated a causal role for ICOSLG in GBM progression by analyzing ICOSLG expression in both human glioma tissues and patient-derived GBM sphere cells (GSCs). We further examined its immune modulatory effects and the underlying molecular mechanisms.

RESULTS

Bioinformatics analysis and GBM tissue microarray showed that upregulation of ICOSLG expression was associated with poor prognosis in patients with GBM. ICOSLG expression was upregulated preferentially in mesenchymal GSCs but not in proneural GSCs in a tumor necrosis factor-α/nuclear factor-kappaB-dependent manner. Furthermore, ICOSLG expression by mesenchymal GSCs promoted expansion of T cells that produced interleukin-10. Knockdown of the gene encoding ICOSLG markedly reduced GBM tumor growth in immune competent mice, with a concomitant downregulation of interleukin-10 levels in the tumor microenvironment.

CONCLUSIONS

Inhibition of the ICOSLG-inducible co-stimulator axis in GBM may provide a promising immunotherapeutic approach for suppressing a subset of GBM with an elevated mesenchymal signature.

Osteopontin binds ICOSL promoting tumor metastasis

ICOSL/ICOS are costimulatory molecules pertaining to immune checkpoints; their binding transduces signals having anti-tumor activity. Osteopontin (OPN) is here identified as a ligand for ICOSL. OPN binds a different domain from that used by ICOS, and the binding induces a conformational change in OPN, exposing domains that are relevant for its functions. Here we show that in vitro, ICOSL triggering by OPN induces cell migration, while inhibiting anchorage-independent cell growth. The mouse 4T1 breast cancer model confirms these data. In vivo, OPN-triggering of ICOSL increases angiogenesis and tumor metastatization. The findings shed new light on ICOSL function and indicate that another partner beside ICOS may be involved; they also provide a rationale for developing alternative therapeutic approaches targeting this molecular trio.

Davide Raineri, Chiara Dianzani et al. show that osteopontin binds ICOSL at a different domain than the one used by ICOS. Activation of ICOSL by osteopontin induces cell migration in vitro and tumor metastatization in a 4T1 breast cancer mouse model; highlighting the functional role of this interaction in cancer progression.

The Antigen Presenting Potential of CD21low B Cells

Human CD21^low B cells are expanded in autoimmune (AI) diseases and display a unique phenotype with high expression of co-stimulatory molecules, compatible with a potential role as antigen-presenting cells (APCs). Thus, we addressed the co-stimulatory capacity of naïve-like, IgM-memory, switched memory and CD27^negIgD^neg memory CD21^low B cells in allogenic co-cultures with CD4 T cells. CD21^low B cells of patients with AI disorders expressed high levels of not only CD86, CD80, and HLA-DR (memory B cells) but also PD-L1 ex vivo and efficiently co-stimulated CD4 T cells of healthy donors (HD), as measured by upregulation of CD25, CD69, inducible co-stimulator (ICOS), and programmed cell death protein 1 (PD-1) and induction of cytokines. While the co-stimulatory capacity of the different CD21^low B-cell populations was over all comparable to CD21^pos counterparts of patients and HD, especially switched memory CD21^low B cells lacked the increased capacity of CD21^pos switched memory B-cells to induce high expression of ICOS, IL-2, IL-10, and IFN-γ. Acknowledging the limitation of the in vitro setting, CD21^low B cells do not seem to preferentially support a specific T_h effector response. In summary, our data implies that CD21^low B cells of patients with AI diseases can become competent APCs and may, when enriched for autoreactive B-cell receptors (BCR), potentially contribute to AI reactions as cognate interaction partners of autoreactive T cells at sites of inflammation.

Activated inducible co-stimulator-positive programmed cell death 1-positive follicular helper T cells indicate disease activity and severity in ulcerative colitis patients

Inducible co-stimulator-positive (ICOS) and programmed cell death 1-positive (PD-1) are important markers for follicular helper T cells (Tfh); however, their roles and clinical values in ulcerative colitis (UC) remain unknown. In this study, we recruited 68 UC patients and 34 healthy controls. Circulating ICOS⁺ , PD-1⁺ and ICOS⁺ PD-1⁺ Tfh subsets were analyzed by flow cytometry. Twelve active UC patients achieving remission after treatment with 5-aminosalicylic acid were followed-up and Tfh subset changes were analyzed. Serum immunoglobulin (Ig)G, C-reactive protein (CRP), interleukin (IL)-4 and IL-21 levels and B cell subsets were analyzed and Mayo scores were calculated. Correlation analyses were performed between Tfh subsets and the clinical indicators. Receiver operating characteristic (ROC) curves were generated to evaluate the efficiency of Tfh subsets for disease monitoring. We found that levels of ICOS⁺ , PD-1⁺ and ICOS⁺ PD-1⁺ Tfh cells were significantly increased in active UC and significantly decreased when achieving clinical remission. Activated ICOS⁺ PD-1⁺ Tfh cells were positively correlated with serum CRP and Mayo scores. Furthermore, ICOS⁺ PD-1⁺ Tfh cells were significantly correlated with circulating new memory B cells and plasmablasts, as well as serum IgG, IL-4 and IL-21. ROC analyses showed that when ICOS⁺ PD-1⁺ Tfh cells were used in combination with PD-1⁺ Tfh cells, the diagnostic efficacy in distinguishing active UC from stable remission patients was higher than that of any one used alone, with area under curve (AUC) value 0·931. Our findings suggest that increased ICOS⁺ PD-1⁺ Tfh cells are associated with the activation of B cells in the pathogenesis of UC, and may be a potential biomarker for UC disease monitoring.

In vivo Screen Identifies Zdhhc2 as a Critical Regulator of Germinal Center B Cell Differentiation

Germinal center (GC) B cell differentiation is critical for the production of affinity-matured pathogen-specific antibodies, the dysregulation of which may lead to humoral immunodeficiency or autoimmunity. The development of an in vivo screening system for factors regulating GC B cell differentiation has been a challenge. Here we describe a small-scale in vivo screening system with NP-specific B1-8^hi cells and a retroviral shRNA library targeting 78 candidate genes to search for B cell-intrinsic factors that specifically regulate GC B cell differentiation. Zdhhc2, a gene encoding palmitoyltransferase ZDHHC2 and highly expressed in GC B cells, is identified as a strong positive regulator of GC B cell differentiation. B1-8^hi cells transduced with Zdhhc2-shRNA are severely compromised in differentiating into GC B cells. A further analysis of in vitro differentiated B cells transduced with Zdhhc2-shRNA shows that Zdhhc2 is critical for the proliferation and the survival of B cells stimulated by CD40L, BAFF, and IL-21 and consequently impacts on their differentiation into GC B cells and post-GC B cells. These studies not only identify Zdhhc2 as a novel regulator of GC B cell differentiation but also represent a proof of concept of in vivo screen for regulators of GC B cell differentiation.

Rationale for CD40 pathway blockade in autoimmune rheumatic disorders

CD40 and its ligand CD40L (CD154) belong to the tumor necrosis factor receptor superfamily and are expressed by a variety of immune and non-immune cells. CD40L plays a central role in co-stimulation and regulation of the immune response via activation of cells expressing CD40. Imbalance of the CD40-CD40L co-stimulatory pathway has been reported in many autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome, thus supporting its role in the breach of immune tolerance that is typical of these diseases. Targeting CD40-CD40L signalling might represent a novel therapeutic option for several autoimmune disorders.

Preserved Cellular Immunity Upon Influenza Vaccination in Most Patients with Common Variable Immunodeficiency

BACKGROUND

Vaccination against influenza is recommended for patients with common variable immunodeficiency (CVID), although humoral immune responses in these patients are impaired and the evidence of effective T-cell responses in CVID is not well established.

OBJECTIVE

To determine plasmablast and T-cellular vaccination responses against influenza in patients with CVID.

METHODS

Patients with CVID and healthy controls were vaccinated with the quadrivalent vaccine Influsplit Tetra 2018/2019. Before and 1 week after vaccination plasmablasts and circulating inducible costimulator-expressing T follicular helper cells were measured to determine positive vaccine responses in these patients. In addition, antigen-specific T cells were determined by their upregulation of CD25 and OX40 after in vitro restimulation with the vaccine.

RESULTS

Most healthy controls but only 1 patient with CVID mounted a positive humoral immune response, measured by an increase in plasmablasts 1 week after vaccination. In contrast, most patients with CVID showed an increase in inducible costimulator⁺ T follicular helper cells and/or an increase in antigen-specific CD25⁺OX40⁺ T cells 1 week after vaccination, demonstrating a positive T-cellular immune response.

CONCLUSIONS

Despite the remaining challenge of accurately assessing the complexity of T-cell responses, the recommendation of vaccinating patients with CVID against influenza is reasonable.

Functions of Tfh Cells in Common Variable Immunodeficiency

Common variable immunodeficiency is the most common clinical primary immunodeficiency in adults. Its hallmarks are hypogammaglobulinemia and compromised B-cell differentiation into memory or antibody-secreting cells leading to recurrent infections. This disease is heterogeneous, with some patients harboring multiple complications such as lymphoproliferative disorders, autoimmune manifestations, or granulomatous inflammation. The mechanisms leading to these complications remain elusive despite numerous associations found in the literature. For instance, although described as a B cell intrinsic disease, numerous abnormalities have been reported in other immune cell compartments. Here, we tuned our attention to follicular helper T cells, a CD4⁺ T cell population specialized in B cell help, considering the recent publications showing an involvement of these cells in CVID pathogenesis.

ICOS-deficient and ICOS YF mutant mice fail to control Toxoplasma gondii infection of the brain

Resistance to chronic Toxoplasma gondii infection requires ongoing recruitment of T cells to the brain. Thus, the factors that promote, sustain, and regulate the T cell response to the parasite in the brain are of great interest. The costimulatory molecule ICOS (inducible T cell costimulator) has been reported to act largely through the PI3K pathway in T cells, and can play pro-inflammatory or pro-regulatory roles depending on the inflammatory context and T cell type being studied. During infection with T. gondii, ICOS promotes early T cell responses, while in the chronic stage of infection ICOS plays a regulatory role by limiting T cell responses in the brain. We sought to characterize the role of ICOS signaling through PI3K during chronic infection using two models of ICOS deficiency: total ICOS knockout (KO) mice and ICOS YF mice that are unable to activate PI3K signaling. Overall, ICOS KO and ICOS YF mice had similar severe defects in parasite-specific IgG production and parasite control compared to WT mice. Additionally, we observed expanded effector T cell populations and a loss of Treg frequency in the brains of both ICOS KO and ICOS YF mice. When comparing the remaining Treg populations in infected mice, ICOS KO Tregs expressed WT levels of Foxp3 and CD25, while ICOS YF Tregs expressed significantly less Foxp3 and CD25 compared to both WT and ICOS KO mice. Together, these results suggest that PI3K-independent signaling downstream of ICOS plays an important role in Treg stability in the context of chronic inflammation.

Role of Co-stimulatory Molecules in T Helper Cell Differentiation

CD4⁺ T cells play a central role in orchestrating the immune response to a variety of pathogens but also regulate autoimmune responses, asthma, allergic responses, as well as tumor immunity. To cover this broad spectrum of responses, naïve CD4⁺ T cells differentiate into one of several lineages of T helper cells, including Th1, Th2, Th17, and T_FH, as defined by their cytokine pattern and function. The fate decision of T helper cell differentiation integrates signals delivered through the T cell receptor, cytokine receptors, and the pattern of co-stimulatory signals received. In this review, we summarize the contribution of co-stimulatory and co-inhibitory receptors to the differentiation and maintenance of T helper cell responses.

Predominantly Antibody-Deficient Patients With Non-infectious Complications Have Reduced Naive B, Treg, Th17, and Tfh17 Cells

Background: Patients with predominantly antibody deficiency (PAD) suffer from severe and recurrent infections that require lifelong immunoglobulin replacement and prophylactic antibiotic treatment. Disease incidence is estimated to be 1:25,000 worldwide, and up to 68% of patients develop non-infectious complications (NIC) including autoimmunity, which are difficult to treat, causing high morbidity, and early mortality. Currently, the etiology of NIC is unknown, and there are no diagnostic and prognostic markers to identify patients at risk.

Objectives: To identify immune cell markers that associate with NIC in PAD patients.

Methods: We developed a standardized 11-color flow cytometry panel that was utilized for in-depth analysis of B and T cells in 62 adult PAD patients and 59 age-matched controls.

Results: Nine males had mutations in Bruton's tyrosine kinase (BTK) and were defined as having X-linked agammaglobulinemia. The remaining 53 patients were not genetically defined and were clinically diagnosed with agammaglobulinemia (n = 1), common variable immunodeficiency (CVID) (n = 32), hypogammaglobulinemia (n = 13), IgG subclass deficiency (n = 1), and specific polysaccharide antibody deficiency (n = 6). Of the 53, 30 (57%) had one or more NICs, 24 patients had reduced B-cell numbers, and 17 had reduced T-cell numbers. Both PAD–NIC and PAD+NIC groups had significantly reduced Ig class-switched memory B cells and naive CD4 and CD8 T-cell numbers. Naive and IgM memory B cells, Treg, Th17, and Tfh17 cells were specifically reduced in the PAD+NIC group. CD21^lo B cells and Tfh cells were increased in frequencies, but not in absolute numbers in PAD+NIC.

Conclusion: The previously reported increased frequencies of CD21^lo B cells and Tfh cells are the indirect result of reduced naive B-cell and T-cell numbers. Hence, correct interpretation of immunophenotyping of immunodeficiencies is critically dependent on absolute cell counts. Finally, the defects in naive B- and T-cell numbers suggest a mild combined immunodeficiency in PAD patients with NIC. Together with the reductions in Th17, Treg, and Tfh17 numbers, these key differences could be utilized as biomarkers to support definitive diagnosis and to predict for disease progression.

Dysregulations of follicular helper T cells through IL-21 pathway in age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of vision loss in the aged population. Aging and inflammation are thought to promote AMD pathogenesis in people with genetic predisposition. Follicular helper T (Tfh) cells play critical roles in inflammatory responses. Here, we investigated circulating Tfh cells in AMD patients. Circulating Tfh cells were defined as CXCR5⁺ CD4 T cells. Data showed that patients with the wet-type AMD presented significantly higher levels of Tfh cells than non-AMD controls. Interestingly, the Tfh cells from dry and wet AMD patients also presented significantly higher ICOS and PD-1 expression, together with higher IL-17 and IL-21 expression directly ex vivo and following PMA/ionomycin stimulation. The expression of IFNg and IL-10, on the other hand, was not different between Tfh cells from AMD patients and their counterparts in non-AMD controls. Functional analysis revealed that Tfh cells from AMD patients were better at inducing the production of IgG and IgA, and this effect was in an IL-21-dependent manner. Together, we demonstrated that the circulating Tfh cell responses were dysregulated in AMD patients.

Loss of human ICOSL results in combined immunodeficiency

Primary immunodeficiencies represent naturally occurring experimental models to decipher human immunobiology. We report a patient with combined immunodeficiency, marked by recurrent respiratory tract and DNA-based viral infections, hypogammaglobulinemia, and panlymphopenia. He also developed moderate neutropenia but without prototypical pyogenic infections. Using whole-exome sequencing, we identified a homozygous mutation in the inducible T cell costimulator ligand gene (ICOSLG; c.657C>G; p.N219K). Whereas WT ICOSL is expressed at the cell surface, the ICOSL^N219K mutation abrogates surface localization: mutant protein is retained in the endoplasmic reticulum/Golgi apparatus, which is predicted to result from deleterious conformational and biochemical changes. ICOSL^N219K diminished B cell costimulation of T cells, providing a compelling basis for the observed defect in antibody and memory B cell generation. Interestingly, ICOSL^N219K also impaired migration of lymphocytes and neutrophils across endothelial cells, which normally express ICOSL. These defects likely contributed to the altered adaptive immunity and neutropenia observed in the patient, respectively. Our study identifies human ICOSLG deficiency as a novel cause of a combined immunodeficiency.

Flow Cytometric-Based Analysis of Defects in Lymphocyte Differentiation and Function Due to Inborn Errors of Immunity

The advent of flow cytometry has revolutionized the way we approach our research and answer specific scientific questions. The flow cytometer has also become a mainstream diagnostic tool in most hospital and pathology laboratories around the world. In particular the application of flow cytometry has been instrumental to the diagnosis of primary immunodeficiencies (PIDs) that result from monogenic mutations in key genes of the hematopoietic, and occasionally non-hematopoietic, systems. The far-reaching applicability of flow cytometry is in part due to the remarkable sensitivity, down to the single-cell level, of flow-based assays and the extremely user-friendly platforms that enable comprehensive analysis, data interpretation, and importantly, robust and rapid methods for diagnosing PIDs. A prime example is the absence of peripheral blood B cells in patients with agammaglobulinemia due to mutations in BTK or related genes in the BCR signaling pathway. Similarly, the development of intracellular staining protocols to detect expression of SAP, XIAP, or DOCK8 expedites the rapid diagnosis of the X-linked lymphoproliferative diseases or an autosomal recessive form of hyper-IgE syndrome (HIES), respectively. It has also become evident that distinct cohorts of PID patients exhibit unique “lymphocyte phenotypic signatures” that are often diagnostic even prior to identifying the genetic lesion. Flow cytometry-based sorting provides a technique for separating specific subsets of immune cells such that they can be studied in isolation. Thus, flow-based assays can be utilized to measure immune cell function in patients with PIDs, such as degranulation by cytotoxic cells, cytokine expression by many immune cells (i.e., CD4⁺ and CD8⁺ T cells, macrophages etc.), B-cell differentiation, and phagocyte respiratory burst in vitro. These assays can also be performed using unfractionated PBMCs, provided the caveat that the composition of lymphocytes between healthy donors and the PID patients under investigation is recognized. These functional deficits can assist not only in the clinical diagnosis of PIDs, but also reveal mechanisms of disease pathogenesis. As we move into the next generation of multiparameter flow cytometers, here we review some of our experiences in the use of flow cytometry in the study, diagnosis, and unraveling the pathophysiology of PIDs.

Pathogenic and protective roles of B cells and antibodies in patients with chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a chronic inflammatory disease of the nose and sinuses that affects up to 12% of the population in Europe and the United States. This complex disease is likely driven by multiple environmental, genetic, and inflammatory mechanisms, and recent studies suggest that B cells might play a critical role in disease pathogenesis. B cells and their antibodies have undisputed roles in health and disease within the airway mucosae. Deficient or inadequate B-cell responses can lead to susceptibility to infectious disease in the nose, whereas excess antibody production, including autoantibodies, can promote damaging inflammation. Thus, patients with B-cell defects often have either chronic or recurrent acute infections, and this can be associated with nonpolypoid CRS. In contrast, many patients with CRS with nasal polyps, which is less likely to be driven by pathogens, have excess production of local immunoglobulins, including autoreactive antibodies. These B-cell responses activate complement in many patients and likely contribute to immunopathogenic responses. A better understanding of the B cell-associated mechanisms that drive disease in patients with CRS should be a high priority in the quest to understand the pathogenesis of this disease.