Inherited human ezrin deficiency impairs adaptive immunity.

BACKGROUND: Inborn errors of immunity (IEI) are a group of monogenic diseases that confer susceptibility to infection, autoimmunity, and cancer. Despite the life-threatening consequences of some IEI, their genetic cause remains unknown in many patients. OBJECTIVE: We investigated a patient with an IEI of unknown genetic etiology. METHODS: Whole-exome sequencing identified a homozygous missense mutation of the gene encoding ezrin (EZR), substituting a threonine for an alanine at position 129. RESULTS: Ezrin is one of the subunits of the ezrin, radixin, and moesin (ERM) complex. The ERM complex links the plasma membrane to the cytoskeleton and is crucial for the assembly of an efficient immune response. The A129T mutation abolishes basal phosphorylation and decreases calcium signaling, leading to complete loss of function. Consistent with the pleiotropic function of ezrin in myriad immune cells, multidimensional immunophenotyping by mass and flow cytometry revealed that in addition to hypogammaglobulinemia, the patient had low frequencies of switched memory B cells, CD4+ and CD8+ T cells, MAIT, γδ T cells, and centralnaive CD4+ cells. CONCLUSIONS: Autosomal-recessive human ezrin deficiency is a newly recognized genetic cause of B-cell deficiency affecting cellular and humoral immunity.

Chronic hypogammaglobulinemia after allogeneic stem cell transplantation and their treatment with subcutaneous immunoglobulin in pediatric patients.

INTRODUCTION: Hypogammaglobulinemia in the first months after allogeneic hematopoietic stem cell transplantation (HSCT) is common in paediatric patients. During this phase, replacement therapy with human immunoglobulin must be administered parenterally to prevent infections. In some cases, this hypogammaglobulinemia persists over time, which forces further treatment when the patient is usually no longer a carrier of a central line, making them ideal candidates for subcutaneous replacement therapy. There is little published literature describing the use of this method in paediatric patients undergoing HSCT, widely described in replacement treatment in children with primary immunodeficiencies with very good results. PATIENTS AND METHODS: An observational, descriptive, longitudinal and retrospective study is carried out. During the years 2008-2019, we evaluated all paediatric patients undergoing HSCT in our center with persistent chronic hypogammaglobulinemia (for over a year). The treatment phase with intravenous immunoglobulin (Privigen®) and the first four years of treatment with subcutaneous immunoglobulin (Hizentra®) are evaluated using a questionnaire. RESULTS: During the years 2008-2019, 175 patients underwent HSCT, 143 (82%) of whom exceeded three months after transplantation. Three (2%) of them had persistent hypogammaglobulinemia. All three share factors described in the literature involved in immune reconstitution. After analysing the questionnaire, it is observed that switching from intravenous to subcutaneous gammaglobulin has involved a great improvement in their quality of life. CONCLUSIONS: The origin of chronic hypogammaglobulinemia in our patients shows different factors and cannot be attributed to a single cause. Due to the limited number of patients no conclusions can be drawn at the population level. We have been able to observe that replacement treatment with Hizentra 20% has been as effective as the intravenous administration without evidence of an increase in bacterial infections. Furthermore, it has also led to an improvement in quality of life and increased comfort, as the patients themselves have stated.

From Severe Combined Immunodeficiency to Omenn syndrome after hematopoietic stem cell transplantation in a RAG1 deficient family.

BACKGROUND: Mutations in RAG genes cause a spectrum of severe immunodeficiencies ranging from Severe Combined Immunodeficiency (SCID) T-B-NK+ to Omenn syndrome (OS) through intermediate phenotypes, even for the same alteration. Nowadays, hematopoietic stem cell transplantation (HSCT) is the unique curative treatment available. METHODS: We describe three related patients from a Moroccan consanguineous family. Patient 1 developed at 1 month of age moderate eczematous dermatitis with eosinophilia, followed by infections and enteritis. He was transplanted and received reduced intensity conditioning regimen previous to HSCT. His brother, patient 2, was born preterm with a severe neonatal erythroderma, hepatosplenomegaly and lymphadenopathy. Patient 3, cousin of the two siblings, was also born preterm and fulfilled all criteria for classical OS. Immunological evaluation was performed and RAG genes were sequenced. RESULTS: Immunological data from all three patients were very diversed, from T lymphopenia to marked lymphocytosis, and different degrees of eosinophilia and IgE levels. Non-responder T cells and absent B cells were constant. All patients presented the same homozygous mutation in RAG1 gene (c.631delT). Patient 1 fully recovered both clinically and immunologically after HSCT. Two years later, he lost the accomplished lymphoid chimera and the disease relapsed as a classical OS, leading to patient's death. CONCLUSIONS: This is the first report of a RAG1 deficient patient with a changed clinical and immunological phenotype from SCID to OS after HSCT. The use of a myeloablative conditioning regimen that eliminates reminiscent T cells might have improved patient's outcome and it should be considered in similar cases.

The polymorphism p.G219R of CD40L does not cause immunological alterations in vivo: conclusions from a X-linked hyper IgM syndrome kindred.

Hyper-IgM syndromes (HIGM) are characterized by low levels of IgG, IgA and IgE and normal to high levels of IgM. Patients with these syndromes present recurrent infections due to an impaired immunoglobulin maturation. The most prevalent form of HIGM, X-linked hyper IgM syndrome (XHIM), is caused by mutations in the gene encoding the CD40 ligand (CD40LG). We present two siblings with XHIM caused by a large CD40LG deletion affecting more than half of the gene, and extended from the end of intron 3 to far upstream of the promoter regions. Genetic analysis in the maternal family discovered the CD40L(G219R) polymorphism in several members. Segregation of this polymorphism in the kindred indicated that the deletion of CD40LG was a de novo mutation in the mother. Although half of her CD4+ T cells did not express CD40L and the other half expressed the CD40L(G219R) variant, the mother was healthy. This suggests that this polymorphism is not pathogenic by itself although it has been recently related to X-linked lymphoproliferative syndrome.

Non-myeloablative hematopoietic stem cell transplantation in the treatment of severe idiopathic CD4+ lymphocytopenia.

A 40-year-old man with severe chronic idiopathic CD4+ lymphocytopenia complicated with opportunistic infections was successfully treated with non-myeloablative allogeneic hematopoietic stem cell transplantation. After conditioning with fludarabine plus low dose of total-body irradiation, CD34+ peripheral blood stem cells obtained by leukapheresis from his HLA-identical sister were infused. T cell and myeloid complete chimerism was achieved at day +28 and remained stable during the follow-up period. The patient did not develop infectious complications during the procedure. At 35 months of follow-up, his CD4+ T cell count was 1019 cells per microliter. Non-myeloablative allogeneic hematopoietic stem cell transplantation should be considered a treatment option for patients with severe forms of idiopathic CD4+ lymphocytopenia.