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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.

Microbial invasion into the intestinal mucosa after allogeneic hematopoietic cell transplantation (allo-HCT) triggers neutrophil activation and requires antibiotic interventions to prevent sepsis. However, antibiotics lead to a loss of microbiota diversity, which is connected to a higher incidence of acute graft-versus-host disease (aGVHD). Antimicrobial therapies that eliminate invading bacteria and reduce neutrophil-mediated damage without reducing the diversity of the microbiota are therefore highly desirable. A potential solution would be the use of antimicrobial antibodies that target invading pathogens, ultimately leading to their elimination by innate immune cells. In a mouse model of aGVHD, we investigated the potency of active and passive immunization against the conserved microbial surface polysaccharide poly-N-acetylglucosamine (PNAG) that is expressed on numerous pathogens. Treatment with monoclonal or polyclonal antibodies to PNAG (anti-PNAG) or vaccination against PNAG reduced aGVHD-related mortality. Anti-PNAG treatment did not change the intestinal microbial diversity as determined by 16S ribosomal DNA sequencing. Anti-PNAG treatment reduced myeloperoxidase activation and proliferation of neutrophil granulocytes (neutrophils) in the ileum of mice developing GVHD. In vitro, anti-PNAG treatment showed high antimicrobial activity. The functional role of neutrophils was confirmed by using neutrophil-deficient LysM(cre) Mcl1(fl/fl) mice that had no survival advantage under anti-PNAG treatment. In summary, the control of invading bacteria by anti-PNAG treatment could be a novel approach to reduce the uncontrolled neutrophil activation that promotes early GVHD and opens a new avenue to interfere with aGVHD without affecting commensal intestinal microbial diversity.

Immune profiling of COVID-19 patients has identified numerous alterations in both innate and adaptive immunity. However, whether those changes are specific to SARS-CoV-2 or driven by a general inflammatory response shared across severely ill pneumonia patients remains unknown. Here, we compared the immune profile of severe COVID-19 with non-SARS-CoV-2 pneumonia ICU patients using longitudinal, high-dimensional single-cell spectral cytometry and algorithm-guided analysis. COVID-19 and non-SARS-CoV-2 pneumonia both showed increased emergency myelopoiesis and displayed features of adaptive immune paralysis. However, pathological immune signatures suggestive of T cell exhaustion were exclusive to COVID-19. The integration of single-cell profiling with a predicted binding capacity of SARS-CoV-2-petides to the patients’ HLA profile further linked the COVID-19 immunopathology to impaired virus recognition. Towards clinical translation, circulating NKT cell frequency was identified as a predictive biomarker for patient outcome. Our comparative immune map serves to delineate treatment strategies to interfere with the immunopathologic cascade exclusive to severe COVID-19., Graphical Abstract, The pathogen-specific immune alterations in severe COVID-19 remain unknown. Using longitudinal, high-dimensional single-cell spectral cytometry and algorithm-guided comparison of COVID-19 vs. non-SARS-CoV-2-pneumonia patient samples, Kreutmair et al. identify T and NK cell immune signatures specific to SARS-CoV-2. They furthermore reveal NKT cell frequency as a predictive biomarker for COVID-19 outcome prediction and link impaired virus recognition to HLA genetics.

Purpose Common variable immune deficiency (CVID) confers an increased risk of lymphoid neoplasms, but reports describing the precise WHO specification of the lymphoma subtypes and their immunological environment are lacking. We therefore classified lymphomas—occurring in a cohort of 21 adult CVID patients during a 17-year period at our center—according to the 2016 WHO classification and characterized the local and systemic immunological context Results The median time between the onset of CVID and lymphoma was 14 years. Patients showed a high prevalence of preceding immune dysregulation: lymphadenopathy (n = 13, 62%), splenomegaly (n = 18, 86%), autoimmune cytopenia (n = 14, 67%), and gastrointestinal involvement (n = 15, 71%). The entities comprised extranodal marginal zone lymphoma (n = 6), diffuse large B cell lymphoma (n = 7), plasmablastic lymphoma (n = 1), classic Hodgkin lymphoma (n = 4, including three cases with germline CTLA4 mutations), T cell large granular lymphocytic leukemia (n = 2), and peripheral T cell lymphoma, not otherwise specified (n = 1), but no follicular lymphoma. An Epstein-Barr virus association was documented in eight of 16 investigated lymphomas. High expression of PDL1 by tumor cells in five and of PDL1 and PD1 by tumor-infiltrating macrophages and T cells in 12 of 12 investigated lymphomas suggested a tolerogenic immunological tumor environment. Conclusion In summary, a diverse combination of specific factors like genetic background, chronic immune activation, viral trigger, and impaired immune surveillance contributes to the observed spectrum of lymphomas in CVID. In the future, targeted therapies, e.g., PD1/PDL1 inhibitors in CVID associated lymphomas with a tolerogenic environment may improve therapy outcome.

Oncogenic Ras mutations occur in various leukemias. It was unclear if, besides the direct transforming effect via constant RAS/MEK/ERK signaling, an inflammation-related effect of KRAS contributes to the disease. Here, we identify a functional link between oncogenic KrasG12D and NLRP3 inflammasome activation in murine and human cells. Mice expressing active KrasG12D in the hematopoietic system developed myeloproliferation and cytopenia, which is reversed in KrasG12D mice lacking NLRP3 in the hematopoietic system. Therapeutic IL-1-receptor blockade or NLRP3-inhibition reduces myeloproliferation and improves hematopoiesis. Mechanistically, KrasG12D-RAC1 activation induces reactive oxygen species (ROS) production causing NLRP3 inflammasome-activation. In agreement with our observations in mice, patient-derived myeloid leukemia cells exhibit KRAS/RAC1/ROS/NLRP3/IL-1β axis activity. Our findings indicate that oncogenic KRAS not only act via its canonical oncogenic driver function, but also enhances the activation of the pro-inflammatory RAC1/ROS/NLRP3/IL-1β axis. This paves the way for a therapeutic approach based on immune modulation via NLRP3 blockade in KRAS-mutant myeloid malignancies.

Extracorporeal Photopheresis for Autoimmune Colitis Extracorporeal photopheresis has been an effective treatment for graft-versus-host disease. In this case, it was used to treat a patient with sev...

All reported patients with hypomorphic X-linked severe combined immunodeficiency (X-SCID) due to c.664C>T (p.R222C) mutations in the gene (IL2RG) encoding the common γ chain (γc) have presented with opportunistic infections within the first year of life, despite the presence of nearly normal NK and T cell numbers. Reporting five children of one extended family with hemizygous mutations in IL2RG, we explore potential diagnostic clues and extend our comprehension of the functional impact of this mutation. Whole exome sequencing (WES); detailed immune phenotyping; cytokine-induced STAT phosphorylation; B, T, and NK cell activation; and quantification of sjTRECs in five Arab children with c.664C>T (p.R222C) IL2RG mutation. The mean age at clinical presentation with respiratory tract infection or diarrhea was 6.8 (range: 2–12) months. None of the children presented with opportunistic infections. Diagnostic clues were early onset in the first year of life, and a suggestive family history associated with reduced naive CD4 T cells and absent switched memory B cells. Number and phenotype of NK cells and innate-like lymphocytes were normal. The diagnosis was made by WES and corroborated by absent STAT phosphorylation and reduced functional response after IL-2 and IL-21 stimulation. Four patients underwent successful hematopoietic stem cell transplantation. As early diagnosis and treatment are important, a high index of suspicion in the diagnosis of c.664C>T (p.R222C) X-SCID is needed. This requires prompt genetic testing by next generation sequencing in order to avoid unnecessary delays in the definite diagnosis since immunological work up may not be discriminating. Assays directly testing cytokine signaling or cytokine-dependent functions are helpful in confirming the functional impact of the identified hypomorphic variants.

Background A subgroup of patients with common variable immunodeficiency (CVID) experience immune dysregulation manifesting as autoimmunity, lymphoproliferation, and organ inflammation and thereby increasing morbidity and mortality. Therefore treatment of these complications demands a deeper comprehension of their cause and pathophysiology. Objectives On the basis of the identification of an interferon signature in patients with CVID with secondary complications and a skewed follicular helper T-cell differentiation in defined monogenic immunodeficiencies, we sought to determine the profile of CD4 memory T cells in blood and secondary lymphatic tissues of these patients. Methods We quantified T H 1/T H 2/T H 17 CD4 memory T cells in blood and lymph nodes of patients with CVID using flow cytometry, analyzed their function, and correlated all findings to the burden of immune dysregulation. Results Patients with CVID with immune dysregulation had a skewed memory CD4 T-cell differentiation toward a CXCR3 + CCR6 − T H 1 phenotype both in blood and lymph nodes. Consistent with our phenotypic findings, we observed a higher IFN-γ production in peripheral CD4 memory T cells and lymph node–derived follicular helper T cells of patients with CVID compared with those of healthy control subjects. Increased IFN-γ production was accompanied by a poor germinal center output, an accumulation of T-box transcription factor (T-bet) + B cells in lymph nodes, and an accumulation of T-bet + CD21 low B cells in peripheral blood of affected patients. Conclusion Identification of excessive IFN-γ production by blood and lymph node–derived T cells of patients with CVID with immune dysregulation will offer new therapeutic avenues for this subgroup. CD21 low B cells might serve as a marker of this IFN-γ–associated dysregulation.

This study investigated whether circulating α4β7+ expressing T cells could serve as a potential marker for gastrointestinal (GI) disease activity in patients with CVID. The analysis of α4β7+ T cells in the peripheral blood of 36 patients and 22 healthy donors (HD) revealed increased percentages of α4β7+ conventional memory CD4 T cells and Tregs, but not among CD8 T-cell populations in patients with CVID compared to HD. No differences between patients with and without chronic or acute GI symptoms were observed. EUROClass smB- and 21lo patients, had higher percentages of α4β7+ memory CD4 T cells compared to HD and smB+ or 21norm patients, respectively. In summary, the detection of α4β7+ T cells in the peripheral blood did not correlate with active or chronic gastrointestinal disease. The increase of these cells in smB- and 21lo patients adds another piece to the immune dysregulation observed in these patients.

Background In a substantial number of patients with non-cystic fibrosis (CF) bronchiectasis an etiology cannot be found. Various complex immunodeficiency syndromes account for a significant portion of these patients but the mechanism elucidating the predisposition for suppurative lung disease often remains unknown. Objective To investigate the cause and mechanism predisposing a patient to severe bronchiectasis. Methods A patient presenting with severe non-CF bronchiectasis was investigated. Whole exome analysis (WES) was performed and complemented by extensive immunophenotyping. Results The genetic analysis revealed an autosomal dominant gain-of-function mutation (AD- GOF) in the signal transducer and activator of transcription 1 (STAT1) in the patient. STAT1 phosphorylation studies showed increased phosphorylation of STAT1 after stimulation with interferon γ (IFN-γ). Immunophenotyping showed normal counts of CD4 and CD8 T cells, B and NK cells, but a reduction of all memory B cells especially class switched memory B cells. Minor changes in the CD8 T cell subpopulations were seen. Conclusions Early use of WES in the investigation of non-CF bronchiectasis was highly advantageous. The degree of impairment in class-switched memory B cells may predispose patients with AD- GOF mutations in STAT1 to suppurative sinopulmonary disease.

Brain malignancies can either originate from within the CNS (gliomas) or invade from other locations in the body (metastases). A highly immunosuppressive tumor microenvironment (TME) influences brain tumor outgrowth. Whether the TME is predominantly shaped by the CNS micromilieu or by the malignancy itself is unknown, as is the diversity, origin, and function of CNS tumor-associated macrophages (TAMs). Here, we have mapped the leukocyte landscape of brain tumors using high-dimensional single-cell profiling (CyTOF). The heterogeneous composition of tissue-resident and invading immune cells within the TME alone permitted a clear distinction between gliomas and brain metastases (BrM). The glioma TME presented predominantly with tissue-resident, reactive microglia, whereas tissue-invading leukocytes accumulated in BrM. Tissue-invading TAMs showed a distinctive signature trajectory, revealing tumor-driven instruction along with contrasting lymphocyte activation and exhaustion. Defining the specific immunological signature of brain tumors can facilitate the rational design of targeted immunotherapy strategies.

The adapter protein linker for activation of T cells (LAT) is a critical signaling hub connecting T cell antigen receptor triggering to downstream T cell responses. In this study, we describe the first kindred with defective LAT signaling caused by a homozygous mutation in exon 5, leading to a premature stop codon deleting most of the cytoplasmic tail of LAT, including the critical tyrosine residues for signal propagation. The three patients presented from early childhood with combined immunodeficiency and severe autoimmune disease. Unlike in the mouse counterpart, reduced numbers of T cells were present in the patients. Despite the reported nonredundant role of LAT in Ca2+ mobilization, residual T cells were able to induce Ca2+ influx and nuclear factor (NF) kappa B signaling, whereas extracellular signal-regulated kinase (ERK) signaling was completely abolished. This is the first report of a LAT-related disease in humans, manifesting by a progressive combined immune deficiency with severe autoimmune disease. Funding Agencies|German Federal Ministry of Education and Research [BMBF 01EO1303]; Deutsche Forschungsgemeinschaft [DFG WA 1597/4-1]; Hebrew University; Hadassah Medical Center; Excellence Initiative of the German Research Foundation (Spemann Graduate School) [GSC-4]

The aim of this study was to identify characteristics of hypogammaglobulinemia secondary to glucocorticoid therapy and their value in the differential diagnosis to primary forms of antibody deficiency. We investigated prevalence and character of hypogammaglobulinemia in a cohort of 36 patients with giant cell arteritis (GCA) and polymyalgia rheumatica (PMR) on glucocorticoid therapy in comparison to a gender- and age-matched cohort of hospital controls. We therefore determined serum immunoglobulin levels as well as B- and T cell-subsets in the peripheral blood of all participants. In addition, prior serum immunoglobulin levels and clinical data of the GCA and PMR patients were extracted from the electronic patient data-base. 21/36 GCA/PMR patients on glucocorticoid treatment developed antibody deficiency. In 19 patients this included IgG and in 13 patients IgG was the only affected isotype. The reduction of IgG was persistent in nearly 50 % of these patients during the observed period. GCA/PMR patients had reduced circulating naive and transitional B cells (p = 0.0043 and p = 0.0002 respectively) while IgM, IgG and IgA memory B cells were preserved. Amongst T-cell subsets, we found a reduction of CD4 memory T cells (p

Background:ALPS patients show impaired generation of humoral memory for T independent antigens whereas they generate memory for self-antigens due to impaired FAS-dependent removal of autoreactive germinal center B cells. It is known that FAS signaling via caspase activation results in cell apoptosis. However, FAS ligation may also initiate or modulate non-apoptotic signaling as shown for example by its ability to activate NF-κB. Recent data implicate a regulatory role of FAS in the modulation of mTOR signaling in ALPS double-negative T cells. Moreover, a recently described C194V FAS mutation disturbs its post-translational modification leading to impaired apoptosis induction while non-apoptotic signalling is still intact. Consequently, C194V FAS protects from the autoimmune phenotype in the murine ALPS system. This supports the view that FAS may prevent autoimmunity with other mechanisms than inducing apoptosis.Objectives:We hypothesize that FAS mutations impair this modulatory signaling, leading to hyper-activation of B cells. Therefore we aim to investigate non apoptotic FAS signaling in B cells derived from healthy individuals and ALPS patients.Methods:We studied resting and activated B cells in ALPS patients in presence or absence of FAS ligand by flow cytometry analysing relevant molecules to the CD40 signaling pathway. We used mass cytometry to perform functional phenotyping of B cells isolated from secondary lymphoid organs. Proteomic studies were performed to identify potential signaling circuits and RNA sequencing to study the consequences of FAS signaling on B cell fate.Results:In CD40L activated B cells, FAS signaling results in specific modulation of the mTOR signaling pathway. This modulation is absent in ALPS derived B cells. In line with these data germinal center B cells and plasmablast from secondary lymphoid organs of ALPS patients show hyperactive mTOR signaling pathway. Proteomic studies identify a circuit that links FAS to the phosphatase PTEN via DAXX and the deubiquitinase USP7.Conclusion:We describe a new role of FAS in the regulation of B cell activation. Defects in FAS signaling in ALPS contribute to dysregulation of the mTOR signaling pathway and disturbed B cell development.Disclosure of Interests:None declared

2509 Background: Brain tumors can be both of intracranial origin (e.g. gliomas) or spread from another location in the body (metastases). Tumor growth in the CNS is commonly favored by a highly immunosuppressive tumor microenvironment (TME). Whether the TME is predominantly shaped by the CNS microenvironment or by the nature of the malignancy is unknown, as is the origin and function of CNS tumor-associated macrophages (TAM). Methods: We have mapped the leukocyte landscape of brain tumors using high-dimensional profiling with mass cytometry (CyTOF). We designed two CyTOF panels (one lymphoid and one myeloid focused) measuring 74 parameters at the single-cell level and analyzed samples from 47 individuals with the most common tumor entities being glioblastoma and metastases from melanoma and lung cancer as well as control tissue from epilepsy surgery. Results: The heterogeneous composition of tissue-resident and invading immune cells within the TME alone permitted a clear distinction between glioblastoma and metastases. Tissue-invading leukocytes accumulate in metastases, whereas gliomas predominantly contain tissue-resident reactive microglia. In gliomas, isocitrate dehydrogenase 1 (IDH1) mutations are associated with minimal host responses whereas IDH1-wildtype gliomas comprise monocyte-derived macrophages (MDM) similar to metastases. These MDM show a distinctive signature trajectory indicative of tumor-driven education. Conclusions: The immune cell composition of the brain tumor TME is tumor entity-specific, rather than dictated by the CNS tissue. Defining the distinct immunological signature of brain tumors can facilitate the rational design of targeted immunotherapy strategies.

The maintenance of B cell homeostasis requires a tight control of B cell generation, survival, activation, and maturation. In lymphocytes upon activation, increased sensitivity to apoptotic signals helps controlling differentiation and proliferation. The death receptor Fas is important in this context because genetic Fas mutations in humans lead to an autoimmune lymphoproliferative syndrome that is similar to lymphoproliferation observed in Fas-deficient mice. In contrast, the physiological role of TNF-related apoptosis-inducing ligand receptors (TRAIL-Rs) in humans has been poorly studied so far. Indeed, most studies have focused on tumor cell lines and on mouse models whose results are difficult to transpose to primary human B cells. In the present work, the expression of apoptosis-inducing TRAIL-R1 and TRAIL-R2 and of the decoy receptors TRAIL-R3 and TRAIL-R4 was systematically studied in all developmental stages of peripheral B cells isolated from the blood and secondary lymphoid organs. Expression of TRAIL-Rs is modulated along development, with highest levels observed in germinal center B cells. In addition, T-dependent and T-independent signals elicited induction of TRAIL-Rs with distinct kinetics, which differed among B cell subpopulations: switched memory cells rapidly upregulated TRAIL-R1 and -2 upon activation while naïve B cells only reached similar expression levels at later time points in culture. Increased expression of TRAIL-R1 and -2 coincided with a caspase-3-dependent sensitivity to TRAIL-induced apoptosis in activated B cells but not in freshly isolated resting B cells. Finally, both TRAIL-R1 and TRAIL-R2 could signal actively and both contributed to TRAIL-induced apoptosis. In conclusion, this study provides a systematic analysis of the expression of TRAIL-Rs in human primary B cells and of their capacity to signal and induce apoptosis. This dataset forms a basis to further study and understand the dysregulation of TRAIL-Rs and TRAIL expression observed in autoimmune diseases. Additionally, it will be important to foresee potential bystander immunomodulation when TRAIL-R agonists are used in cancer treatment.

Background Most patients with MHC class I (MHC-I) deficiency carry genetic defects in transporter associated with antigen processing 1 (TAP1) or TAP2 . The clinical presentation can vary, and about half of the patients have severe skin disease. Previously, one report described β 2 -microglobulin (β 2 m) deficiency as another monogenetic cause of MHC-I deficiency, but no further immunologic evaluation was performed. Objective We sought to describe the molecular and immunologic features of β 2 m deficiency in 2 Turkish siblings with new diagnoses. Methods Based on clinical and serologic findings, the genetic defect was detected by means of candidate gene analysis. The immunologic characterization comprises flow cytometry, ELISA, functional assays, and immunohistochemistry. Results Here we provide the first extensive clinical and immunologic description of β 2 m deficiency in 2 siblings. The sister had recurrent respiratory tract infections and severe skin disease, whereas the brother was fairly asymptomatic but had bronchiectasis. Not only polymorphic MHC-I but also the related CD1a, CD1b, CD1c, and neonatal Fc receptor molecules were absent from the surfaces of β 2 m-deficient cells. Absent neonatal Fc receptor surface expression led to low serum IgG and albumin levels in both siblings, whereas the heterozygous parents had normal results for all tested parameters except β 2 m mRNA (B2M) expression. Similar to TAP deficiency in the absence of a regular CD8 T-cell compartment, CD8 + γδ T cells were strongly expanded. Natural killer cells were normal in number but not "licensed to kill." Conclusion The clinical presentation of patients with β 2 m deficiency resembles that of patients with other forms of MHC-I deficiency, but because of the missing stabilizing effect of β 2 m on other members of the MHC-I family, the immunologic defect is more extensive than in patients with TAP deficiency.

Over a third of patients with common variable immunodeficiency (CVID) suffer from secondary complications like inflammatory organ disease, autoimmune manifestations, or lymphoproliferation contributing to increased morbidity and mortality in affected patients. Innate lymphoid cells (ILCs) have emerging roles in setting the milieu for physiological, but also pathological, immune responses and inflammation. We therefore sought to correlate the recently identified disturbed homeostasis of ILCs with alterations of the adaptive immune system in complex CVID patients (CVIDc). We quantified peripheral blood ILC and T helper cell subsets of 58 CVID patients by flow cytometry and compared the results to the clinical and immunological phenotype. Total ILCs were significantly reduced in peripheral blood of CVIDc patients compared to healthy individuals, but not to CVID patients who suffered only from infections (CVIDio). This reduction was mainly due to a decrease in ILC2s, while ILC3s were relatively increased in CVIDc compared to CVIDio patients. This alteration in ILC phenotype was more prominent in patients with an expansion of CD21low B cells, but we could not detect an association of the altered ILC phenotype with a TH1-shift among circulating CD4 T cells, which was also prominent in CVIDc patients. We confirm a relative shift in ILCs of CVIDc patients towards ILC3s which was associated with the expansion of CD21low B cells, but not overtly with the relative expansion of TH1-like T cells. Given the relative abundance of TH1-like T cells compared to ILCs, these probably represent a more prominent source of the observed IFNγ-signature in CVIDc patients.

Common variable immunodeficiency (CVID) is characterized by low levels of circulating immunoglobulins and compromised specific antibody response leading to frequent infections. Cytokines play an important role in the orchestration of the antibody response. Several previous studies have attempted to identify distinct cytokines responsible for the inflammatory changes and different manifestations of CVID, but there are conflicting results regarding the cytokine profiles in CVID patients. In light of this, an extensive review regarding the level of various cytokines and their potential therapeutic role in CVID patients was performed. This review delineates the contribution of interleukin (IL)-1, IL-2, IL-4, IL-5, IL-6, IL-7, IL-10, IL-12, IL-21, interferons, tumor necrosis factor (TNF)-α, IL-17, APRIL (a proliferation inducing ligand) and BAFF (B cell activating factor) in CVID disease and outline their potential therapeutic implications in these patients.

Given the severely reduced numbers of circulating class-switched memory B cells and plasmablasts in patients with common variable immunodeficiency (CVID) the germinal center (GC) reaction as the source of both populations is expected to be disturbed in many CVID patients. Therefore immunohistochemical studies were performed on lymph node (LN) biopsies from ten CVID patients with benign lymphoproliferation. According to the Sander classification the majority of patients presented with reactive lymphoid hyperplasia (7/10), 6/10 showed granulomatous inflammation. All cases showed some normal GCs but in 9/10 these concurred to a varying degree with hyperplastic, ill-defined GCs in the same LN. The percentage of ill-defined GCs correlated significantly with the percentage of circulating CD21(low) B cells suggesting a common origin of both immune reactions. In 9/10 CVID LNs significantly higher numbers of infiltrating CD8+ T cells were found in GCs of CVID patients compared to controls, but no HHV-8 and only in 2/10 LNs EBV infection was detected. Class switched plasma cells (PCs) were severely reduced in 8/10 LNs and if present, rarely found in the medulla of the LN. Based on the presence of large GCs in all examined patients, the reduction of circulating memory B cells and PCs points towards a failure of GC output rather than GC formation in CVID patients with lymphadenopathy.

Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative therapy for different malignant and non-malignant hematologic diseases. Major life-threatening complications after allo-HCT are acute graft-versus-host disease (aGVHD) and severe infections. The incidence of GVHD after allo-HCT remains high, despite prophylactic immunosuppressive medication. According to the CIBMTR database, 60% of patients undergoing allo-HCT develop at least grade II-IV aGVHD. Microbial invasion into the intestinal mucosa after allo-HCT triggers the activation of neutrophil granulocytes (neutrophils) and requires antibiotic treatment to prevent sepsis. However, antibiotics lead to a loss of microbial diversity, which is connected to a higher incidence of aGVHD. Anti-microbial therapies which eliminate invading bacteria and diminish neutrophil-mediated damage without reducing the diversity of the microbiota are therefore highly desirable. A potential solution for this could be the use of anti-microbial antibodies that target and mark invading pathogens resulting in their elimination by innate immune cells. Therefore we investigated the potency of both active and passive immunization against the conserved microbial surface polysaccharide Poly-N-acetylglucosamine (PNAG) which is expressed on various pathogens in a murine aGVHD model. We could detect reduced aGVHD related mortality in mice which underwent treatment with an antibody against PNAG (anti-PNAG) or were actively immunized against PNAG. Sequencing analysis of the microbiota before and after allo-HCT showed that anti-PNAG treatment did not have any effect luminal microbial diversity. Mechanistically, we could show that anti-PNAG antibody treatment caused more abundant neutrophil recruitment to the intestinal submucosa. This supports the concept that neutrophils are able to effectively eliminate any opsonized bacteria in this tissue, leading to reduced local inflammation. In agreement with this we observed lower intestinal inflammation and reduced myeloperoxidase activity as well as proliferation of neutrophils in the small intestine of mice treated with anti-PNAG antibody. We demonstrate the potency of targeting PNAG as a novel antimicrobial treatment option in aGVHD by reducing uncontrolled neutrophil activation and thereby interfering with aGVHD without affecting commensal intestinal microbial diversity. Anti-PNAG-antibodies enhance anti-microbial immunity, while reducing the activation of neutrophil-mediated downstream immunopathology which is a novel approach to reduce the severity of GVHD. This could be translated into a clinical application given the modest toxicity profile of vaccination and the availability of fully human anti-PNAG antibodies, both of which have been tested in phase 1 trials in humans (ClinicalTrials.gov Identifier: NCT02853617). Disclosures Cywes-Bentley: OneBiopharma, Inc.: Honoraria. Koenecke:Novartis: Other: none. Pier:OneBiopharma, Inc.: Equity Ownership, Honoraria; Alopexx Vaccine, LLC: Equity Ownership, Honoraria.

Common variable immunodeficiency (CVID) represents a large heterogeneous group of antibody deficiency syndromes associated with a plethora of clinical features and as yet largely undefined molecular causes. We are now seeing this heterogeneous group being increasingly defined into single-gene and polygenic disorders after stratification into homogeneous patient subgroups based on improved clinical and immunological criteria, including molecular, functional, immunohistological, and longitudinal and outcome information. In this perspective, we highlight recent developments in CVID, addressing mainly its genetic and immunological dimensions.

B-cell linker (BLNK) protein is a non-redundant adaptor molecule in the signaling pathway activated by (pre) B-cell antigen receptor signals. We present two siblings with a homozygous deleterious frameshift mutation in BLNK, resulting in a block of B cell development in the bone marrow at the preB1 to preB2 stage, absence of circulating B cells and agammaglobulinemia. This is the first description of an enteroviral infection associated arthritis and dermatitis in a patient with BLNK deficiency.

Combined immune deficiencies (CID) are defined by severely impaired adaptive immunity leading to increased susceptibility to opportunistic infections, immune dysregulation and malignancies. CID of moderate severity may not lead to death in infancy but still carry a high burden of morbidity and

International audience; Currently very little is known about the differential expression and function of the transcription factor SOX5 during B cell maturation. We identified two new splice variants of SOX5 in human B cells, encoding the known L-SOX5B isoform and a new shorter isoform L-SOX5F. The SOX5 transcripts are highly expressed during late stages of B-cell differentiation, including atypical memory B cells, activated CD21low B cells and germinal center B cells of tonsils. In tonsillar sections SOX5 expression was predominantly polarized to centrocytes within the light zone. After in vitro stimulation, SOX5 expression was down-regulated during proliferation while high expression levels were permissible for plasmablast differentiation. Overexpression of L-SOX5F in human primary B lymphocytes resulted in reduced proliferation, less survival of CD138neg B cells, but comparable numbers of CD138+CD38hi plasmablasts compared to control cells. Thus, our findings describe for the first time a functional role of SOX5 during late B cell development reducing the proliferative capacity and thus potentially affecting the differentiation of B cells during the germinal center response.