The protein cytotoxic T lymphocyte antigen-4 (CTLA-4) is an essential negative regulator of immune responses and its loss causes fatal autoimmunity in mice. We investigated a large autosomal-dominant family with five individuals presenting with a complex immune dysregulation syndrome characterized by hypogammaglobulinemia, recurrent infections and multiple autoimmune features. We identified a heterozygous nonsense mutation in exon 1 of CTLA4. Screening of 71 unrelated patients with comparable clinical phenotypes identified five additional families (nine individuals) with novel splice site and missense mutations in CTLA4. While clinical penetrance was incomplete (eight adults of a total of 19 CTLA4 mutation carriers were considered unaffected), CTLA-4 protein expression was decreased in regulatory T cells (Treg cells) in patients and carriers with CTLA4 mutations. Whilst Treg cells were generally present at elevated numbers, their suppressive function, CTLA-4 ligand binding and transendocytosis of CD80 were impaired. Mutations in CTLA4 were also associated with decreased circulating B cell numbers and antibody levels. Taken together, mutations in CTLA-4 resulting in CTLA-4 haploinsufficiency or impaired ligand binding results in a complex syndrome with features of both autoimmunity and immunodeficiency.

Highlights d Leukocyte invasion is higher in brain metastasis than in CNSendogenous cancers d The tumor type shapes the differentiation of monocytederived macrophages d Brain metastases harbor a high frequency of regulatory T cells d Both activation and exhaustion are prevalent in lymphocytes of the metastatic TME

Non-canonical NF-κB-pathway signaling is integral in immunoregulation. Heterozygous mutations in NFKB2 have recently been established as a molecular cause of common variable immunodeficiency (CVID) and DAVID-syndrome, a rare condition combining deficiency of anterior pituitary hormone with CVID. Here, we investigate 15 previously unreported patients with primary immunodeficiency (PID) from eleven unrelated families with heterozygous NFKB2-mutations including eight patients with the common p.Arg853* nonsense mutation and five patients harboring unique novel C-terminal truncating mutations. In addition, we describe the clinical phenotype of two patients with proximal truncating mutations. Cohort analysis extended to all 35 previously published NFKB2-cases revealed occurrence of early-onset PID in 46/50 patients (mean age of onset 5.9 years, median 4.0 years). ACTH-deficiency occurred in 44%. Three mutation carriers have deceased, four developed malignancies. Only two mutation carriers were clinically asymptomatic. In contrast to typical CVID, most patients suffered from early-onset and severe disease manifestations, including clinical signs of T cell dysfunction e.g., chronic-viral or opportunistic infections. In addition, 80% of patients suffered from (predominately T cell mediated) autoimmune (AI) phenomena (alopecia > various lymphocytic organ-infiltration > diarrhea > arthritis > AI-cytopenia). Unlike in other forms of CVID, auto-antibodies or lymphoproliferation were not common hallmarks of disease. Immunophenotyping showed largely normal or even increased quantities of naïve and memory CD4+ or CD8+ T-cells and normal T-cell proliferation. NK-cell number and function were also normal. In contrast, impaired B-cell differentiation and hypogammaglobinemia were consistent features of NFKB2-associated disease. In addition, an array of lymphocyte subpopulations, such as regulatory T cell, Th17-, cTFH-, NKT-, and MAIT-cell numbers were decreased. We conclude that heterozygous damaging mutations in NFKB2 represent a distinct PID entity exceeding the usual clinical spectrum of CVID. Impairment of the non-canonical NF-κB pathways affects function and differentiation of numerous lymphocyte-subpopulations and thus causes a heterogeneous, more severe form of PID phenotype with early-onset. Further characteristic features are multifaceted, primarily T cell-mediated autoimmunity, such as alopecia, lymphocytic organ infiltration, and in addition frequently ACTH-deficiency.

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 B cells might serve as a marker of this IFN-γ-associated dysregulation.

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 Kras G12D and NLRP3 inflammasome activation in murine and human cells. Mice expressing active Kras G12D in the hematopoietic system developed myeloproliferation and cytopenia, which is reversed in Kras G12D mice lacking NLRP3 in the hematopoietic system. Therapeutic IL-1-receptor blockade or NLRP3-inhibition reduces myeloproliferation and improves hematopoiesis. Mechanistically, Kras G12D-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.

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.

Keller et al. describe for the first time human LAT deficiency, which causes severe immune dysregulation with autoimmunity, lymphoproliferation, and progressive immunodeficiency.

No abstract