BACKGROUND-The molecular cause of inflammatory bowel disease is largely unknown.

Autosomal recessive severe congenital neutropenia (SCN) constitutes a primary immunodeficiency syndrome associated with increased apoptosis in myeloid cells, yet the underlying genetic defect remains unknown. Using a positional cloning approach and candidate gene evaluation, we identified a recurrent homozygous germline mutation in HAX1 in three pedigrees. After further molecular screening of individuals with SCN, we identified 19 additional affected individuals with homozygous HAX1 mutations, including three belonging to the original pedigree described by Kostmann. HAX1 encodes the mitochondrial protein HAX1, which has been assigned functions in signal transduction and cytoskeletal control. Here, we show that HAX1 is critical for maintaining the inner mitochondrial membrane potential and protecting against apoptosis in myeloid cells. Our findings suggest that HAX1 is a major regulator of myeloid homeostasis and underline the significance of genetic control of apoptosis in neutrophil development.

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Wiskott-Aldrich syndrome (WAS) is characterized by microthrombocytopenia, immunodeficiency, autoimmunity, and susceptibility to malignancies. In our hematopoietic stem cell gene therapy (GT) trial using a γ-retroviral vector, 9 of 10 patients showed sustained engraftment and correction of WAS protein (WASP) expression in lymphoid and myeloid cells and platelets. GT resulted in partial or complete resolution of immunodeficiency, autoimmunity, and bleeding diathesis. Analysis of retroviral insertion sites revealed >140,000 unambiguous integration sites and a polyclonal pattern of hematopoiesis in all patients early after GT. Seven patients developed acute leukemia [one acute myeloid leukemia (AML), four T cell acute lymphoblastic leukemia (T-ALL), and two primary T-ALL with secondary AML associated with a dominant clone with vector integration at the LMO2 (six T-ALL), MDS1 (two AML), or MN1 (one AML) locus]. Cytogenetic analysis revealed additional genetic alterations such as chromosomal translocations. This study shows that hematopoietic stem cell GT for WAS is feasible and effective, but the use of γ-retroviral vectors is associated with a substantial risk of leukemogenesis.

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Background T follicular helper (Tfh) cells underpin T-cell dependent humoral immunity and the success of most vaccines. Tfh cells also contribute to human immune disorders such as autoimmunity, immunodeficiency and malignancy. Understanding the molecular requirements for the generation and function of Tfh cells will provide strategies for targeting these cells to modulate their behavior in the setting of these immunological abnormalities. Objective To determine the signaling pathways and cellular interactions required for the development and function of Tfh cells in humans. Methods Human primary immunodeficiencies (PIDs) resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Circulating Tfh (cTfh) cell subsets, memory B cells and serum Ig levels were quantified and functionally assessed in healthy controls as well as patients with PIDs resulting from mutations in STAT3, STAT1, TYK2, IL21, IL21R, IL10R, IFNGR1/2, IL12RB1, CD40LG, NEMO, ICOS or BTK. Results Loss-of function (LOF) mutations in STAT3, IL10R, CD40LG, NEMO, ICOS or BTK reduced cTfh frequencies. STAT3, IL21/R LOF and STAT1 gain-of function mutations skewed cTfh differentiation towards a phenotype characterized by over-expression of IFNγ and programmed death -1 (PD-1). IFNγ inhibited cTfh function in vitro and in vivo, corroborated by hypergammaglobulinemia in patients with IFNGR1/2, STAT1 and IL12RB1 LOF mutations. Conclusion Specific mutations impact the quantity and quality of cTfh cells, highlighting the need to assess Tfh cells in patients by multiple criteria, including phenotype and function. Furthermore, IFNγ functions in vivo to restrain Tfh-induced B cell differentiation. These findings shed new light on Tfh biology and the integrated signaling pathways required for their generation, maintenance and effector function, and explain compromised humoral immunity in some PIDs.

Background Combined immunodeficiencies (CIDs) denote inborn errors of T-cell immunity with T cells present but quantitatively or functionally deficient. Impaired humoral immunity, either due to a primary B cell defect or secondary to the T-cell defect, is also frequent. Consequently, patients with CID display severe infections and/or autoimmunity. The specific molecular, cellular, and clinical features of many types of CID remain unknown. Methods We performed genetic and cellular immunological studies in five unrelated children who shared a history of early-onset invasive bacterial and viral infections, with lymphopenia and defective T-, B-, and NK-cell responses. Two patients died early in childhood, whereas the other three underwent allogeneic hematopoietic stem cell transplantation with normalization of T cell function and clinical improvement. Results We identified bi-allelic mutations in the Dedicator Of Cytokinesis 2 (DOCK2) gene in these five patients. RAC1 activation was impaired in T cells. Chemokine-induced migration and actin polymerization were defective in T, B, and NK cells. NK-cell degranulation was also affected. The production of interferon (IFN)-α and -λ by peripheral blood mononuclear cells (PBMCs) was diminished following virus infection. Moreover, in DOCK2-deficient fibroblasts, virus replication was increased and there was enhanced virus-induced cell death, which could be normalized by treatment with IFN-α2β or upon expression of wild-type DOCK2. Conclusions Autosomal recessive DOCK2 deficiency is a Mendelian disorder with pleiotropic defects of hematopoietic and non-hematopoietic immunity. Children with clinical features of CID, especially in the presence of early-onset, invasive infections may have this condition.