A boy with primary immunodeficiency, caused by a tyrosine kinase 2 (TYK2) mutation, presented with immune defects and a lifelong history of severe infections. Our aim was to determine whether allogeneic hematopoietic stem cell transplantation (HSCT) could restore the patient's immune defenses and reduce susceptibility to infection. In the absence of a suitable HLA-matched blood relative to act as a donor, the patient received an allogeneic HSCT from unrelated donors. The patient's clinical data were analyzed in the Children's Hospital of Chongqing Medical University (Chongqing, China) before transplantation and during the 4-year follow-up period using a combination of western blotting (e.g., TYK2 and STAT levels), qRT-PCR (e.g., T cell receptor rearrangement excision circles, kappa deletion element recombination circles, and TYK2 transcript levels), and flow cytometry (e.g., lymphocyte subpopulations and CD107α secretion). We found that HSCT significantly reduced the incidence of severe infections, restored normal TKY2 levels, and reversed defects such as impaired JAK/STAT signaling in response to interferon-α or interleukin-10 treatment. Although the patient did not develop acute graft-versus-host disease (GVHD) after transplantation, he did experience chronic GVHD symptoms in a number of organs, which were effectively managed. Our findings suggest that HSCT is a feasible strategy for reconstituting the immune system in TYK2-deficient patients; however, the factors associated with GVHD and autoimmune thyroiditis development in TYK2-deficient patients undergoing HSCT warrant further investigation.

PURPOSES:STAT1 is a transduction and transcriptional regulator that functions within the classical JAK/STAT pathway. In addition to chronic mucocutaneous candidiasis, bacterial infections are a common occurrence in patients with STAT1 gain-of-function (GOF) mutations. These patients often exhibit skewing of B cell subsets; however, the impact of STAT1-GOF mutations on B cell-mediated humoral immunity remains largely unexplored. It is also unclear whether these patients with IgG within normal range require regular intravenous immunoglobulin (IVIG) therapy. METHODS:Eleven patients (harboring nine different STAT1-GOF mutations) were enrolled. Reporter assays and immunoblot analyses were performed to confirm STAT1 mutations. Flow cytometry, deep sequencing, ELISA, and ELISpot were conducted to assess the impact of STAT1-GOF on humoral immunity. RESULTS:All patients exhibited increased levels of phospho-STAT1 and total STAT1 protein, with two patients carrying novel mutations. In vitro assays showed that these two novel mutations were GOF mutations. Three patients with normal total IgG levels received regular IVIG infusions, resulting in effective control of bacterial infections. Four cases showed impaired affinity and specificity of pertussis toxin-specific antibodies, accompanied by reduced generation of class-switched memory B cells. Patients also had a disrupted immunoglobulin heavy chain (IGH) repertoire, coupled with a marked reduction in the somatic hypermutation frequency of switched Ig transcripts. CONCLUSION:STAT1-GOF mutations disrupt B cell compartments and skew IGH characteristics, resulting in impaired affinity and antigen-specificity of antibodies and recurrent bacterial infections. Regular IVIG therapy can control these infections in patients, even those with normal total IgG levels.

BACH2-related immunodeficiency and autoimmunity (BRIDA) is an inborn error of immunity, newly reported in 2017, presenting with symptoms of immunoglobulin deficiency and ongoing colitis. Studies using a mouse model have demonstrated that BACH2 deficiency predisposes individuals to systemic lupus erythematosus (SLE); however, no BACH2 deficiency has been reported in SLE patients. Here we describe a patient with BRIDA presenting with early-onset SLE, juvenile dermatomyositis, and IgA deficiency. Whole exome sequencing analysis of the patient and her parents revealed a novel heterozygous point mutation in BACH2, c.G1727T, resulting in substitution of a highly conserved arginine with leucine (R576L), which is predicted to be deleterious, in the patient and her father. Reduced BACH2 expression and deficient transcriptional repression of the BACH2 target, BLIMP1, were detected in PBMCs or lymphoblastoid cell lines of our patient. Notably, extreme reduction of memory B cells was detected in the patient's father, although he had no obvious symptoms. SLE symptoms and recurrent fever were relieved by treatment with prednisone combined with tofacitinib. Thus, we present the second report of BRIDA and demonstrate that BACH2 may be a monogenic cause of SLE.

Abstract WHIM syndrome is a rare, autosomal dominant inborn errors of immunity characterized by warts, hypogammaglobulinemia, infection, and myelokathexis. It is caused mainly by heterozygous mutations at the C-terminus of the C-X-C chemokine receptor type 4 (CXCR4) gene. Here, we report a Chinese family of four harboring a novel mutation in the C-terminal domain of CXCR4 (c.1016_1017dupCT), which caused a frameshift at codon V340, resulting in an extension of 14 amino acids (p.V340L fs*27). All four patients had recurrent respiratory infections and neutropenia, but no hypogammaglobulinemia. However, the number of naïve T cells and B cell subsets was significantly lower than normal. Compared with a patient harboring hotspot mutation CXCR4R334X, those with the CXCR4V340fs mutation had a milder clinical and immunological phenotype. Accordingly, and similar to the CXCR4R334X mutation, the novel frameshift mutation CXCR4V340fs resulted in impaired receptor downregulation in patients’ PBMCs, and in HEK293T cells transfected with mutant plasmids, thereby increasing the amplitude and duration of p-AKT and p-ERK1/2 signaling after CXCL12 stimulation. Thus, we describe a novel pathogenic CXCR4 mutation causing familial WHIM syndrome.

PURPOSE:CD81 deficiency is an extremely rare primary immunodeficiency disease characterized by severe and recurrent infections, IgA-related nephropathy, and profound hypogammaglobulinemia. Only one patient has been reported so far, and the pathogenesis remains unclear. Here, we identified a new case of CD81 deficiency and described its pathogenesis.METHODS:We analyzed the clinical, genetic, and immunological features of the patient with CD81 deficiency, and explored the pathogenesis of her antibody deficiencies.RESULTS:The major manifestation of this patient was unexpectedly not recurrent infections but IgA nephropathy with aberrant serum galactose-deficient IgA1. Whole-exome sequencing revealed novel biallelic mutations in CD81 gene that abolished the surface expression of CD81. B cells from the patient lack membrane CD19 and showed reduced switched memory B cells and transitional B cells. Decreased expression of key molecules pY and pBTK in BCR signaling were demonstrated by confocal microscopy. RNA sequencing revealed that genes associated with BCR signaling and immunoglobulins were downregulated in CD81-deficient B cells. In addition, the patient showed increased frequency of T follicular helper cells that biased to Th1-like subsets.CONCLUSION:We reported the second patient with CD81 deficiency in the world and illustrated aberrant BCR signaling in the patient, therefore helping to unravel the mechanism of antibody deficiency in CD81-deficient patients.

As a nonreceptor tyrosine kinase, Abelson tyrosine kinase (c-Abl) was first studied in chronic myelogenous leukaemia, and its role in lymphocytes has been well characterised. c-Abl is involved in B-cell development and CD19-associated B-cell antigen receptor (BCR) signalling. Although c-Abl regulates different metabolic pathways, the role of c-Abl is still unknown in B-cell metabolism. In this study, B-cell-specific c-Abl knockout (KO) mice (Mb1(Cre+/-)c-Abl(fl/fl)) were used to investigate how c-Abl regulates B-cell metabolism and BCR signalling. We found that the levels of activation positive BCR signalling proximal molecules, phosphorylated spleen tyrosine kinase (pSYK) and phosphorylated Bruton tyrosine kinase (pBTK), were decreased, while the level of key negative regulator, phosphorylated SH2-containing inositol phosphatase 1 (pSHIP1), was increased in Mb1(Cre+/-)c-Abl(fl/fl) mice. Furthermore, we found c-Abl deficiency weakened the B-cell spreading, formation of BCR signalosomes, and the polymerisation of actin during BCR activation, and also impaired the differentiation of germinal center (GC) B-cells both in quiescent condition and after immunisation. Moreover, B-cell mitochondrial respiration and the expression of B-cell metabolism-regulating molecules were downregulated in c-Abl deficiency mice. Overall, c-Abl, which involved in actin remodelling and B-cell metabolism, positively regulates BCR signalling and promotes GC differentiation.

Mutations in signal transducer and activator of transcription 1 (STAT1) cause a broad spectrum of disease phenotypes. Heterozygous STAT1 loss-of-function (LOF) mutations cause Mendelian susceptibility to mycobacterial diseases (MSMD) infection, which is attributable to impaired IFN-γ signaling. The identification of novel mutations may extend the phenotypes associated with autosomal dominant (AD) STAT1 deficiency. Five patients with heterozygous STAT1 variations were recruited and their clinical and immunologic phenotypes were analyzed, with particular reference to JAK-STAT1 signaling pathways. Four, heterozygous STAT1 deficiency mutations were identified, three of which were novel mutations. Two of the mutations were previously unreported mRNA splicing mutations in AD STAT1-deficient patients. Patients with heterozygous STAT1 deficiency suffered not only mycobacterial infection, but also intracellular non-mycobacterial bacterial infection and congenital multiple malformations. AD-LOF mutation impaired IFN-γ-mediated STAT1 phosphorylation, gamma-activated sequence (GAS), and IFN-stimulated response element (ISRE) transcription activity and IFN-induced gene expression to different extents, which might account for the diverse clinical manifestations observed in these patients. The infectious disease susceptibility and phenotypic spectrum of patients with AD STAT1-LOF are broader than simply MSMD. The susceptibility to infections and immunological deficiency phenotypes, observed in AD-LOF patients, confirms the importance of STAT1 in host–pathogen interaction and immunity. However, variability in the nature and extent of these phenotypes suggests that functional analysis is required to identify accurately novel, heterozygous STAT1 mutations, associated with pathogenicity. Aberrant splice of STAT1 RNA could result in AD-LOF for STAT1 signaling which need more cases for confirmation.