Epithelial-derived interleukin-23 promotes oral mucosal immunopathology.

At mucosal surfaces, epithelial cells provide a structural barrier and an immune defense system. However, dysregulated epithelial responses can contribute to disease states. Here, we demonstrated that epithelial cell-intrinsic production of interleukin-23 (IL-23) triggers an inflammatory loop in the prevalent oral disease periodontitis. Epithelial IL-23 expression localized to areas proximal to the disease-associated microbiome and was evident in experimental models and patients with common and genetic forms of disease. Mechanistically, flagellated microbial species of the periodontitis microbiome triggered epithelial IL-23 induction in a TLR5 receptor-dependent manner. Therefore, unlike other Th17-driven diseases, non-hematopoietic-cell-derived IL-23 served as an initiator of pathogenic inflammation in periodontitis. Beyond periodontitis, analysis of publicly available datasets revealed the expression of epithelial IL-23 in settings of infection, malignancy, and autoimmunity, suggesting a broader role for epithelial-intrinsic IL-23 in human disease. Collectively, this work highlights an important role for the barrier epithelium in the induction of IL-23-mediated inflammation.

Diapedesis-Induced Integrin Signaling via LFA-1 Facilitates Tissue Immunity by Inducing Intrinsic Complement C3 Expression in Immune Cells.

Intrinsic complement C3 activity is integral to human T helper type 1 (Th1) and cytotoxic T cell responses. Increased or decreased intracellular C3 results in autoimmunity and infections, respectively. The mechanisms regulating intracellular C3 expression remain undefined. We identified complement, including C3, as among the most significantly enriched biological pathway in tissue-occupying cells. We generated C3-reporter mice and confirmed that C3 expression was a defining feature of tissue-immune cells, including T cells and monocytes, occurred during transendothelial diapedesis, and depended on integrin lymphocyte-function-associated antigen 1 (LFA-1) signals. Immune cells from patients with leukocyte adhesion deficiency type 1 (LAD-1) had reduced C3 transcripts and diminished effector activities, which could be rescued proportionally by intracellular C3 provision. Conversely, increased C3 expression by T cells from arthritis patients correlated with disease severity. Our study defines integrins as key controllers of intracellular complement, demonstrates that perturbations in the LFA-1-C3-axis contribute to primary immunodeficiency, and identifies intracellular C3 as biomarker of severity in autoimmunity.

Functional neutrophil disorders: Chronic granulomatous disease and beyond.

Since their description by Metchnikoff in 1905, phagocytes have been increasingly recognized to be the entities that traffic to sites of infection and inflammation, engulf and kill infecting organisms, and clear out apoptotic debris all the while making antigens available and accessible to the lymphoid organs for future use. Therefore, phagocytes provide the gateway and the first check in host protection and immune response. Disorders in killing and chemotaxis lead not only to infection susceptibility, but also to autoimmunity. We aim to describe chronic granulomatous disease and the leukocyte adhesion deficiencies as well as myeloperoxidase deficiency and G6PD deficiency as paradigms of critical pathways.

Anti-Interleukin-23 Autoantibodies in Adult-Onset Immunodeficiency.

BACKGROUND: Autoantibodies against interleukin-12 (anti-interleukin-12) are often identified in patients with thymoma, but opportunistic infections develop in only some of these patients. Interleukin-12 (with subunits p40 and p35) shares a common subunit with interleukin-23 (subunits p40 and p19). In a patient with disseminated Burkholderia gladioli infection, the identification of both anti-interleukin-23 and anti-interleukin-12 prompted further investigation. METHODS: Among the patients (most of whom had thymoma) who were known to have anti-interleukin-12, we screened for autoantibodies against interleukin-23 (anti-interleukin-23). To validate the potential role of anti-interleukin-23 with respect to opportunistic infection, we tested a second cohort of patients with thymoma as well as patients without either thymoma or known anti-interleukin-12 who had unusual infections. RESULTS: Among 30 patients with anti-interleukin-12 who had severe mycobacterial, bacterial, or fungal infections, 15 (50%) also had autoantibodies that neutralized interleukin-23. The potency of such neutralization was correlated with the severity of these infections. The neutralizing activity of anti-interleukin-12 alone was not associated with infection. In the validation cohort of 91 patients with thymoma, the presence of anti-interleukin-23 was associated with infection status in 74 patients (81%). Overall, neutralizing anti-interleukin-23 was detected in 30 of 116 patients (26%) with thymoma and in 30 of 36 patients (83%) with disseminated, cerebral, or pulmonary infections. Anti-interleukin-23 was present in 6 of 32 patients (19%) with severe intracellular infections and in 2 of 16 patients (12%) with unusual intracranial infections, including Cladophialophora bantiana and Mycobacterium avium complex. CONCLUSIONS: Among patients with a variety of mycobacterial, bacterial, or fungal infections, the presence of neutralizing anti-interleukin-23 was associated with severe, persistent opportunistic infections. (Funded by the National Institute of Allergy and Infectious Diseases and others.).

Dominant-activating germline mutations in the gene encoding the PI(3)K catalytic subunit p110δ result in T cell senescence and human immunodeficiency.

The p110δ subunit of phosphatidylinositol-3-OH kinase (PI(3)K) is selectively expressed in leukocytes and is critical for lymphocyte biology. Here we report fourteen patients from seven families who were heterozygous for three different germline, gain-of-function mutations in PIK3CD (which encodes p110δ). These patients presented with sinopulmonary infections, lymphadenopathy, nodular lymphoid hyperplasia and viremia due to cytomegalovirus (CMV) and/or Epstein-Barr virus (EBV). Strikingly, they had a substantial deficiency in naive T cells but an over-representation of senescent effector T cells. In vitro, T cells from patients exhibited increased phosphorylation of the kinase Akt and hyperactivation of the metabolic checkpoint kinase mTOR, enhanced glucose uptake and terminal effector differentiation. Notably, treatment with rapamycin to inhibit mTOR activity in vivo partially restored the abundance of naive T cells, largely 'rescued' the in vitro T cell defects and improved the clinical course.

Clinical and functional spectrum of RAC2-related immunodeficiency.

ABSTRACT: Mutations in the small Rho-family guanosine triphosphate hydrolase RAC2, critical for actin cytoskeleton remodeling and intracellular signal transduction, are associated with neonatal severe combined immunodeficiency (SCID), infantile neutrophilic disorder resembling leukocyte adhesion deficiency (LAD), and later-onset combined immune deficiency (CID). We investigated 54 patients (23 previously reported) from 37 families yielding 15 novel RAC2 missense mutations, including one present only in homozygosity. Data were collected from referring physicians and literature reports with updated clinical information. Patients were grouped by presentation: neonatal SCID (n = 5), infantile LAD-like disease (n = 5), or CID (n = 44). Disease correlated to RAC2 activity: constitutively active RAS-like mutations caused neonatal SCID, dominant-negative mutations caused LAD-like disease, whereas dominant-activating mutations caused CID. Significant T- and B-lymphopenia with low immunoglobulins were seen in most patients; myeloid abnormalities included neutropenia, altered oxidative burst, impaired neutrophil migration, and visible neutrophil macropinosomes. Among 42 patients with CID with clinical data, upper and lower respiratory infections and viral infections were common. Twenty-three distinct RAC2 mutations, including 15 novel variants, were identified. Using heterologous expression systems, we assessed downstream effector functions including superoxide production, p21-activated kinase 1 binding, AKT activation, and protein stability. Confocal microscopy showed altered actin assembly evidenced by membrane ruffling and macropinosomes. Altered protein localization and aggregation were observed. All tested RAC2 mutant proteins exhibited aberrant function; no single assay was sufficient to determine functional consequence. Most mutants produced elevated superoxide; mutations unable to support superoxide formation were associated with bacterial infections. RAC2 mutations cause a spectrum of immune dysfunction, ranging from early onset SCID to later-onset combined immunodeficiencies depending on RAC2 activity. This trial was registered at www.clinicaltrials.gov as #NCT00001355 and #NCT00001467.

A randomized, placebo-controlled phase 3 trial of the PI3Kδ inhibitor leniolisib for activated PI3Kδ syndrome.

Activated phosphoinositide 3-kinase delta (PI3Kδ) syndrome (APDS) is an inborn error of immunity with clinical manifestations including infections, lymphoproliferation, autoimmunity, enteropathy, bronchiectasis, increased risk of lymphoma, and early mortality. Hyperactive PI3Kδ signaling causes APDS and is selectively targeted with leniolisib, an oral, small molecule inhibitor of PI3Kδ. Here, 31 patients with APDS aged ≥12 years were enrolled in a global, phase 3, triple-blinded trial and randomized 2:1 to receive 70 mg leniolisib or placebo twice daily for 12 weeks. Coprimary outcomes were differences from baseline in the index lymph node size and the percentage of naïve B cells in peripheral blood, assessed as proxies for immune dysregulation and deficiency. Both primary outcomes were met: the difference in the adjusted mean change (95% confidence interval [CI]) between leniolisib and placebo for lymph node size was -0.25 (-0.38, -0.12; P = .0006; N = 26) and for percentage of naïve B cells, was 37.30 (24.06, 50.54; P = .0002; N = 13). Leniolisib reduced spleen volume compared with placebo (adjusted mean difference in 3-dimensional volume [cm3], -186; 95% CI, -297 to -76.2; P = .0020) and improved key immune cell subsets. Fewer patients receiving leniolisib reported study treatment-related adverse events (AEs; mostly grades 1-2) than those receiving placebo (23.8% vs 30.0%). Overall, leniolisib was well tolerated and significant improvement over placebo was notable in the coprimary endpoints, reducing lymphadenopathy and increasing the percentage of naïve B cells, reflecting a favorable impact on the immune dysregulation and deficiency seen in patients with APDS. This trial was registered at www.clinicaltrials.gov as #NCT02435173.

Spectrum of LYST mutations in Chediak-Higashi syndrome: a report of novel variants and a comprehensive review of the literature.

INTRODUCTION: Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder characterised by partial oculocutaneous albinism, a bleeding diathesis, immunological dysfunction and neurological impairment. Bi-allelic loss-of-function variants in LYST cause CHS. LYST encodes the lysosomal trafficking regulator, a highly conserved 429 kDa cytoplasmic protein with an unknown function. METHODS: To further our understanding of the pathogenesis of CHS, we conducted clinical evaluations on individuals with CHS enrolled in our natural history study. Using genomic DNA Sanger sequencing, we identified novel pathogenic LYST variants. Additionally, we performed an extensive literature review to curate reported LYST variants and classified these novel and reported variants according to the American College of Medical Genetics/Association for Molecular Pathology variant interpretation guidelines. RESULTS: Our investigation unveiled 11 novel pathogenic LYST variants in eight patients with a clinical diagnosis of CHS, substantiated by the presence of pathognomonic giant intracellular granules. From these novel variants, together with a comprehensive review of the literature, we compiled a total of 147 variants in LYST, including 61 frameshift variants (41%), 44 nonsense variants (30%), 23 missense variants (16%), 13 splice site variants or small genomic deletions for which the coding effect is unknown (9%), 5 in-frame variants (3%) and 1 start-loss variant (1%). Notably, a genotype-phenotype correlation emerged, whereby individuals harbouring at least one missense or in-frame variant generally resulted in milder disease, while those with two nonsense or frameshift variants generally had more severe disease. CONCLUSION: The identification of novel pathogenic LYST variants and improvements in variant classification will provide earlier diagnoses and improved care to individuals with CHS.

Interim analysis: Open-label extension study of leniolisib for patients with APDS.

BACKGROUND: Activated phosphoinositide 3-kinase delta (PI3Kδ) syndrome (APDS; or p110δ-activating mutations causing senescent T cells, lymphadenopathy, and immunodeficiency) is an inborn error of immunity caused by PI3Kδ hyperactivity. Resultant immune deficiency and dysregulation lead to recurrent sinopulmonary infections, herpes viremia, autoimmunity, and lymphoproliferation. OBJECTIVE: Leniolisib, a selective PI3Kδ inhibitor, demonstrated favorable impact on immune cell subsets and lymphoproliferation over placebo in patients with APDS over 12 weeks. Here, we report results from an interim analysis of an ongoing open-label, single-arm extension study. METHODS: Patients with APDS aged 12 years or older who completed NCT02435173 or had previous exposure to PI3Kδ inhibitors were eligible. The primary end point was safety, assessed via investigator-reported adverse events (AEs) and clinical/laboratory evaluations. Secondary and exploratory end points included health-related quality of life, inflammatory markers, frequency of infections, and lymphoproliferation. RESULTS: Between September 2016 and August 2021, 37 patients (median age, 20 years; 42.3% female) were enrolled. Of these 37 patients, 26, 9, and 2 patients had previously received leniolisib, placebo, or other PI3Kδ inhibitors, respectively. At the data cutoff date (December 13, 2021), median leniolisib exposure was 102 weeks. Overall, 32 patients (87%) experienced an AE. Most AEs were grades 1 to 3; none were grade 4. One patient with severe baseline comorbidities experienced a grade 5 AE, determined as unrelated to leniolisib treatment. While on leniolisib, patients had reduced annualized infection rates (P = .004), and reductions in immunoglobulin replacement therapy occurred in 10 of 27 patients. Other observations include reduced lymphadenopathy and splenomegaly, improved cytopenias, and normalized lymphocyte subsets. CONCLUSIONS: Leniolisib was well tolerated and maintained durable outcomes with up to 5 years of exposure in 37 patients with APDS. CLINICALTRIALS: gov identifier: NCT02859727.

A randomized double-blinded trial to assess recurrence of systemic allergic reactions following COVID-19 mRNA vaccination.

BACKGROUND: Systemic allergic reactions (sARs) following coronavirus disease 2019 (COVID-19) mRNA vaccines were initially reported at a higher rate than after traditional vaccines. OBJECTIVE: We aimed to evaluate the safety of revaccination in these individuals and to interrogate mechanisms underlying these reactions. METHODS: In this randomized, double-blinded, phase 2 trial, participants aged 16 to 69 years who previously reported a convincing sAR to their first dose of COVID-19 mRNA vaccine were randomly assigned to receive a second dose of BNT162b2 (Comirnaty) vaccine and placebo on consecutive days in a blinded, 1:1 crossover fashion at the National Institutes of Health. An open-label BNT162b2 booster was offered 5 months later if the second dose did not result in severe sAR. None of the participants received the mRNA-1273 (Spikevax) vaccine during the study. The primary end point was recurrence of sAR following second dose and booster vaccination; exploratory end points included biomarker measurements. RESULTS: Of 111 screened participants, 18 were randomly assigned to receive study interventions. Eight received BNT162b2 second dose followed by placebo; 8 received placebo followed by BNT162b2 second dose; 2 withdrew before receiving any study intervention. All 16 participants received the booster dose. Following second dose and booster vaccination, sARs recurred in 2 participants (12.5%; 95% CI, 1.6 to 38.3). No sAR occurred after placebo. An anaphylaxis mimic, immunization stress-related response (ISRR), occurred more commonly than sARs following both vaccine and placebo and was associated with higher predose anxiety scores, paresthesias, and distinct vital sign and biomarker changes. CONCLUSIONS: Our findings support revaccination of individuals who report sARs to COVID-19 mRNA vaccines. Distinct clinical and laboratory features may distinguish sARs from ISRRs.

Perturbations of the T-cell receptor repertoire in response to SARS-CoV-2 in immunocompetent and immunocompromised individuals.

BACKGROUND: Functional T-cell responses are essential for virus clearance and long-term protection after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, whereas certain clinical factors, such as older age and immunocompromise, are associated with worse outcome. OBJECTIVE: We sought to study the breadth and magnitude of T-cell responses in patients with coronavirus disease 2019 (COVID-19) and in individuals with inborn errors of immunity (IEIs) who had received COVID-19 mRNA vaccine. METHODS: Using high-throughput sequencing and bioinformatics tools to characterize the T-cell receptor ß repertoire signatures in 540 individuals after SARS-CoV-2 infection, 31 IEI recipients of COVID-19 mRNA vaccine, and healthy controls, we quantified HLA class I- and class II-restricted SARS-CoV-2-specific responses and also identified several HLA allele-clonotype motif associations in patients with COVID-19, including a subcohort of anti-type 1 interferon (IFN-1)-positive patients. RESULTS: Our analysis revealed that elderly patients with COVID-19 with critical disease manifested lower SARS-CoV-2 T-cell clonotype diversity as well as T-cell responses with reduced magnitude, whereas the SARS-CoV-2-specific clonotypes targeted a broad range of HLA class I- and class II-restricted epitopes across the viral proteome. The presence of anti-IFN-I antibodies was associated with certain HLA alleles. Finally, COVID-19 mRNA immunization induced an increase in the breadth of SARS-CoV-2-specific clonotypes in patients with IEIs, including those who had failed to seroconvert. CONCLUSIONS: Elderly individuals have impaired capacity to develop broad and sustained T-cell responses after SARS-CoV-2 infection. Genetic factors may play a role in the production of anti-IFN-1 antibodies. COVID-19 mRNA vaccines are effective in inducing T-cell responses in patients with IEIs.

Anti-IL12p40 autoantibodies in a teenage girl with multiple recurrent abscesses.

More frequent among adults, phenocopies may be caused by somatic mutations or anti-cytokine autoantibodies, mimicking the phenotypes of primary immunodeficiencies. A fourteen-year-old girl was referred for a two-year history of weight loss and multiple recurrent abscesses, complicated recurrent pneumonia, pyelonephritis, osteomyelitis, and septic shock, without fever. She had started with nausea, hyporexia, and weight loss, then with abscesses in her hands, knee, ankle, and spleen. She also developed a rib fracture and left thoracic herpes zoster. The patient was cachectic, with normal vital signs, bilateral crackles on chest auscultation, tumefaction of the knee joint, and poorly healed wounds in hands and chest, oozing a yellowish fluid. Chest computed tomography revealed multiple bilateral bronchiectases. Laboratory workup reported chronic anemia, leukocytosis, neutrophilia, mild lymphopenia, thrombocytosis, pan-hypergammaglobulinemia, and elevated acute serum reactants. Lymphocyte subsets were low but present. Mycobacterium tuberculosis was detected via polymerase chain reaction in a bone biopsy specimen from ankle osteomyelitis. Whole-exome sequencing failed to identify a monogenic defect. Interleukin-12 was found markedly elevated in the serum of the patient. Phosphorylation of STAT4, induced by increasing doses of IL-12, was neutralized by patient serum, confirming the presence of anti-IL12 autoantibodies. IL-12 and IL-23 are crucial cytokines in the defense against intracellular microorganisms, the induction of interferon-gamma production by lymphocytes, and other inflammatory functions. Patients who develop neutralizing serum autoantibodies against IL12 manifest late in life with weight loss, multiple recurrent abscesses, poor wound healing, and fistulae. Treatment with anti-CD20 monoclonal antibodies was effective.

Dual ß-lactam for treatment of pulmonary Mycobacterium abscessus in a child.

Treatment of Mycobacterium abscessus infection presents significant challenges, exacerbated by the emergence of macrolide-resistant strains that necessitate the use of multiple antimicrobials in combination and carry the potential for significant toxic effects. Select dual beta-lactam combinations, with or without beta-lactamase inhibitors, have been shown to be highly active in vitro. Herein, we describe a 6-year-old child with underlying mild bilateral lower lobe cylindrical bronchiectatic lung disease who developed pulmonary Mycobacterium abscessus infection and was treated with a multi-drug regimen including two ß-lactam antibiotics, achieving both early clinical and microbiological cure. This case highlights the potential benefit of dual ß-lactam therapy for the treatment of drug-resistant Mycobacterium abscessus infection.

Evolution toward extremely high imipenem resistance in Mycobacterium abscessus outbreak strains.

Treatment of Mycobacterium abscessus pulmonary disease requires multiple antibiotics including intravenous ß-lactams (e.g., imipenem). M. abscessus produces a ß-lactamase (BlaMab) that inactivates ß-lactam drugs but less efficiently carbapenems. Due to intrinsic and acquired resistance in M. abscessus and poor clinical outcomes, it is critical to understand the development of antibiotic resistance both within the host and in the setting of outbreaks. We compared serial longitudinally collected M. abscessus subsp. massiliense isolates from the index case of a cystic fibrosis center outbreak and four outbreak-related strains. We found strikingly high imipenem resistance in the later patient isolates, including the outbreak strain (MIC > 512 µg/mL). The phenomenon was recapitulated upon exposure of intracellular bacteria to imipenem. Addition of the ß-lactamase inhibitor avibactam abrogated the resistant phenotype. Imipenem resistance was caused by an increase in ß-lactamase activity and increased blaMab mRNA level. Concurrent increase in transcription of the preceding ppiA gene indicated upregulation of the entire operon in the resistant strains. Deletion of the porin mspA coincided with the first increase in MIC (from 8 to 32 µg/mL). A frameshift mutation in msp2 responsible for the rough colony morphology and a SNP in ATP-dependent helicase hrpA cooccurred with the second increase in MIC (from 32 to 256 µg/mL). Increased BlaMab expression and enzymatic activity may have been due to altered regulation of the ppiA-blaMab operon by the mutated HrpA alone or in combination with other genes described above. This work supports using carbapenem/ß-lactamase inhibitor combinations for treating M. abscessus, particularly imipenem-resistant strains.

Lymphocyte-Directed Immunomodulation Remits Thymoma-Associated Autoimmune Pneumonitis.

BACKGROUND: Thymoma presents with several autoimmune manifestations and is associated with secondary autoimmune regulator (AIRE) deficiency. Pneumonitis has recently been described as an autoimmune manifestation associated with thymoma presenting with similar clinical, radiographic, histological, and autoantibody features as seen in patients with inherited AIRE deficiency who suffer from Autoimmune PolyEndocrinopathy-Candidiasis-Ectodermal Dystrophy (APECED) syndrome. OBJECTIVES: To treat two patients with biopsy-proven thymoma-associated pneumonitis with lymphocyte-directed immunomodulation. METHODS: Two patients with thymoma were enrolled on IRB-approved protocols at the NIH Clinical Center. We performed history and physical examination; laboratory, radiographic, histologic and pulmonary function evaluations; and measurement of the lung-directed autoantibodies KCNRG and BPIFB1 prior to and at 1- and 6-months following initiation of lymphocyte-directed immunomodulation with azathioprine with or without rituximab. RESULTS: Combination T- and B-lymphocyte-directed immunomodulation resulted in improvement of clinical, functional, and radiographic parameters at 6-month follow-up evaluations in both patients with sustained remission up to 12-36 months following treatment initiation. CONCLUSION: Lymphocyte-directed immunomodulation remitted autoimmune pneumonitis in two patients with thymoma.

Inflammasomes Coordinate Pyroptosis and Natural Killer Cell Cytotoxicity to Clear Infection by a Ubiquitous Environmental Bacterium.

Defective neutrophils in patients with chronic granulomatous disease (CGD) cause susceptibility to extracellular and intracellular infections. Microbes must first be ejected from intracellular niches to expose them to neutrophil attack, so we hypothesized that inflammasomes detect certain CGD pathogens upstream of neutrophil killing. Here, we identified one such ubiquitous environmental bacterium, Chromobacterium violaceum, whose extreme virulence was fully counteracted by the NLRC4 inflammasome. Caspase-1 protected via two parallel pathways that eliminated intracellular replication niches. Pyroptosis was the primary bacterial clearance mechanism in the spleen, but both pyroptosis and interleukin-18 (IL-18)-driven natural killer (NK) cell responses were required for liver defense. NK cells cleared hepatocyte replication niches via perforin-dependent cytotoxicity, whereas interferon-γ was not required. These insights suggested a therapeutic approach: exogenous IL-18 restored perforin-dependent cytotoxicity during infection by the inflammasome-evasive bacterium Listeria monocytogenes. Therefore, inflammasomes can trigger complementary programmed cell death mechanisms, directing sterilizing immunity against intracellular bacterial pathogens.

Asymmetric Action of STAT Transcription Factors Drives Transcriptional Outputs and Cytokine Specificity.

Interleukin-6 (IL-6) and IL-27 signal through a shared receptor subunit and employ the same downstream STAT transcription proteins, but yet are ascribed unique and overlapping functions. To evaluate the specificity and redundancy for these cytokines, we quantified their global transcriptomic changes and determined the relative contributions of STAT1 and STAT3 using genetic models and chromatin immunoprecipitation-sequencing (ChIP-seq) approaches. We found an extensive overlap of the transcriptomes induced by IL-6 and IL-27 and few examples in which the cytokines acted in opposition. Using STAT-deficient cells and T cells from patients with gain-of-function STAT1 mutations, we demonstrated that STAT3 is responsible for the overall transcriptional output driven by both cytokines, whereas STAT1 is the principal driver of specificity. STAT1 cannot compensate in the absence of STAT3 and, in fact, much of STAT1 binding to chromatin is STAT3 dependent. Thus, STAT1 shapes the specific cytokine signature superimposed upon STAT3's action.

TCF3 haploinsufficiency defined by immune, clinical, gene-dosage, and murine studies.

BACKGROUND: TCF3 is a transcription factor contributing to early lymphocyte differentiation. Germline monoallelic dominant negative and biallelic loss-of-function (LOF) null TCF3 mutations cause a fully penetrant severe immunodeficiency. We identified 8 individuals from 7 unrelated families with monoallelic LOF TCF3 variants presenting with immunodeficiency with incomplete clinical penetrance. OBJECTIVE: We sought to define TCF3 haploinsufficiency (HI) biology and its association with immunodeficiency. METHODS: Patient clinical data and blood samples were analyzed. Flow cytometry, Western blot analysis, plasmablast differentiation, immunoglobulin secretion, and transcriptional activity studies were conducted on individuals carrying TCF3 variants. Mice with a heterozygous Tcf3 deletion were analyzed for lymphocyte development and phenotyping. RESULTS: Individuals carrying monoallelic LOF TCF3 variants showed B-cell defects (eg, reduced total, class-switched memory, and/or plasmablasts) and reduced serum immunoglobulin levels; most but not all presented with recurrent but nonsevere infections. These TCF3 LOF variants were either not transcribed or translated, resulting in reduced wild-type TCF3 protein expression, strongly suggesting HI pathophysiology for the disease. Targeted RNA sequencing analysis of T-cell blasts from TCF3-null, dominant negative, or HI individuals clustered away from healthy donors, implying that 2 WT copies of TCF3 are needed to sustain a tightly regulated TCF3 gene-dosage effect. Murine TCF3 HI resulted in a reduction of circulating B cells but overall normal humoral immune responses. CONCLUSION: Monoallelic LOF TCF3 mutations cause a gene-dosage-dependent reduction in wild-type protein expression, B-cell defects, and a dysregulated transcriptome, resulting in immunodeficiency. Tcf3+/- mice partially recapitulate the human phenotype, underscoring the differences between TCF3 in humans and mice.

Hematologically important mutations: Leukocyte adhesion deficiency (second update).

Leukocyte adhesion deficiency (LAD) is an immunodeficiency caused by defects in the adhesion of leukocytes (especially neutrophils) to the blood vessel wall. As a result, patients with LAD suffer from severe bacterial infections and impaired wound healing, accompanied by neutrophilia. In LAD-I, characterized directly after birth by delayed separation of the umbilical cord, mutations are found in ITGB2, the gene that encodes the ß subunit (CD18) of the ß2 integrins. In the rare LAD-II disease, the fucosylation of selectin ligands is disturbed, caused by mutations in SLC35C1, the gene that encodes a GDP-fucose transporter of the Golgi system. LAD-II patients lack the H and Lewis Lea and Leb blood group antigens. Finally, in LAD-III, the conformational activation of the hematopoietically expressed ß integrins is disturbed, leading to leukocyte and platelet dysfunction. This last syndrome is caused by mutations in FERMT3, encoding the kindlin-3 protein in all blood cells, involved in the regulation of ß integrin conformation. This article contains an update of the mutations that we consider to be relevant for the various forms of LAD.

SASH3 variants cause a novel form of X-linked combined immunodeficiency with immune dysregulation.

Sterile alpha motif (SAM) and Src homology-3 (SH3) domain-containing 3 (SASH3), also called SH3-containing lymphocyte protein (SLY1), is a putative adaptor protein that is postulated to play an important role in the organization of signaling complexes and propagation of signal transduction cascades in lymphocytes. The SASH3 gene is located on the X-chromosome. Here, we identified 3 novel SASH3 deleterious variants in 4 unrelated male patients with a history of combined immunodeficiency and immune dysregulation that manifested as recurrent sinopulmonary, cutaneous, and mucosal infections and refractory autoimmune cytopenias. Patients exhibited CD4+ T-cell lymphopenia, decreased T-cell proliferation, cell cycle progression, and increased T-cell apoptosis in response to mitogens. In vitro T-cell differentiation of CD34+ cells and molecular signatures of rearrangements at the T-cell receptor α (TRA) locus were indicative of impaired thymocyte survival. These patients also manifested neutropenia and B-cell and natural killer (NK)-cell lymphopenia. Lentivirus-mediated transfer of the SASH3 complementary DNA-corrected protein expression, in vitro proliferation, and signaling in SASH3-deficient Jurkat and patient-derived T cells. These findings define a new type of X-linked combined immunodeficiency in humans that recapitulates many of the abnormalities reported in mice with Sly1-/- and Sly1Δ/Δ mutations, highlighting an important role of SASH3 in human lymphocyte function and survival.