Mónica Martínez-Gallo

TACI mutations and impaired B-cell function in subjects with CVID and healthy heterozygotes

BACKGROUND Mutations in the gene coding for the transmembrane activator and calcium-modulating cyclophilin ligand interactor (TACI) are found in 8% to 10% of subjects with common variable immunodeficiency (CVID). Although heterozygous mutations may coincide with immunodeficiency in a few families, most mutation-bearing relatives are not hypogammaglobulinemic. Thus, the role of TACI mutations in producing the immune defect remains unclear. OBJECTIVE This study examined the expression and function of TACI mutations in healthy heterozygous relatives. METHODS We examined the surface and intracellular expression of TACI protein in EBV-transformed B cells of patients and relatives with mutations in 7 families, binding of a proliferation-inducing ligand, and secretion of IgG and IgA by ligand-activated B cells. We tested whether Toll-like receptor 9 agonists increased TACI expression and whether an agonistic anti-TACI antibody could induce activation-induced cytidine deaminase mRNA in those with mutations. RESULTS Intracellular and extracellular TACI expression was defective for B cells of all subjects with mutations, including subjects with CVID and relatives. Although Toll-like receptor 9 triggering normally up-regulates B-cell TACI expression, this was defective for all subjects with mutations. Triggering TACI by an agonistic antibody showed loss of activation-induced cytidine deaminase mRNA induction in all mutation-bearing B cells. However, ligand-induced IgG and IgA production was normal for healthy relatives but not for subjects with CVID. CONCLUSION Thus, B cells of relatives of subjects with CVID who have mutations in TACI but normal immune globulin levels still have detectable in vitro B-cell defects.

Role of the STAT1 pathway in apoptosis induced by fludarabine and JAK kinase inhibitors in B-cell chronic lymphocytic leukemia

Signal transducers and activators of transcription (STAT) proteins comprise a family of transcription factors that have been implicated in tumoral transformation, especially in hematological malignancies. Because of this, the JAK/STAT pathway is attractive as a therapeutic target in these tumors. In the present study, we analyzed the ability of fludarabine and two JAK kinase inhibitors, AG490 and WHI-P131, to block STAT1 activation and induce apoptosis on B-cell chronic lymphocytic leukemia (B-CLL) cells. All drugs were able to induce a high percentage of apoptosis on B-CLL cells from all patients studied. However, only AG490 and WHI-P131 were able to strongly suppress the STAT1 activation of B-CLL cells. In conclusion, our data show that JAK kinase inhibitors, such as AG490 and WHI-P131 are able to inhibit the STAT1 pathway on B-CLL cells and are strong inductors of apoptosis on these cells.

Gene expression signature of tolerance and lymphocyte subsets in stable renal transplants: Results of a cross-sectional study

BACKGROUND In kidney transplants operational tolerance has been associated with up-regulation of B cell differentiation genes and an increased number of total, naive and transitional peripheral B cells. The aim is to evaluate tolerance biomarkers in different cohorts of stable renal transplants under immunosuppression. METHODS This is a cross-sectional study conducted in renal transplants. We evaluate genetic tolerance signature and lymphocyte subsets in stable transplants treated with calcineurin inhibitors (CNI) at 1 (n=15), 5 (n=14) and 10 (n=16) years, and azathioprine-treated transplants followed 30 years (n=8). Healthy volunteers (n=10) and patients with chronic rejection (n=15) served as controls. RESULTS We confirm that peripheral expression of IGKV1D-13 and IGKV4-1 genes by RT-PCR distinguish tolerant (n=10) from stable transplants (n=10) provided by the International Tolerance Network. Tolerance signature was defined as the lowest expression for both genes in tolerant patients. In CNI-treated patients, genetic signature of tolerance and B cells showed a time-dependent increase not observed in azathioprine-treated patients (p<0.01). Genetic tolerance signature was observed in 0% at 1, 7% at 5 and 25% at 10-years while it was not observed in azathioprine-treated and chronic rejection patients. Fifteen out of 16 CNI-treated transplants at 10 years were revaluated 3 months apart. Nine did not show the tolerance signature in any determination, 4 in one and 2 in both determinations. Genetic signature of tolerance was associated with an increase of total, naive and transitional B cells (p<0.05). CONCLUSIONS IGKV1D-13 and IGKV4-1 gene expression and its linked B cell populations increase during follow up in CNI-treated patients. At 10 years, 2 out of 15 CNI treated patients consistently express biomarkers associated with true tolerance. In azathioprine-treated patients these biomarkers were down-regulated.

A prospective study on the natural history of patients with profound combined immunodeficiency: An interim analysis

Background: Absent T‐cell immunity resulting in life‐threatening infections provides a clear rationale for hematopoetic stem cell transplantation (HSCT) in patients with severe combined immunodeficiency (SCID). Combined immunodeficiencies (CIDs) and “atypical” SCID show reduced, not absent T‐cell immunity. If associated with infections or autoimmunity, they represent profound combined immunodeficiency (P‐CID), for which outcome data are insufficient for unambiguous early transplant decisions. Objectives: We sought to compare natural histories of severity‐matched patients with/without subsequent transplantation and to determine whether immunologic and/or clinical parameters may be predictive for outcome. Methods: In this prospective and retrospective observational study, we recruited nontransplanted patients with P‐CID aged 1 to 16 years to compare natural histories of severity‐matched patients with/without subsequent transplantation and to determine whether immunologic and/or clinical parameters may be predictive for outcome. Results: A total of 51 patients were recruited (median age, 9.6 years). Thirteen of 51 had a genetic diagnosis of “atypical” SCID and 14 of 51 of CID. About half of the patients had less than 10% naive T cells, reduced/absent T‐cell proliferation, and at least 1 significant clinical event/year, demonstrating their profound immunodeficiency. Nineteen patients (37%) underwent transplantation within 1 year of enrolment, and 5 of 51 patients died. Analysis of the HSCT decisions revealed the anticipated heterogeneity, favoring an ongoing prospective matched‐pair analysis of patients with similar disease severity with or without transplantation. Importantly, so far neither the genetic diagnosis nor basic measurements of T‐cell immunity were good predictors of disease evolution. Conclusions: The P‐CID study for the first time characterizes a group of patients with nontypical SCID T‐cell deficiencies from a therapeutic perspective. Because genetic and basic T‐cell parameters provide limited guidance, prospective data from this study will be a helpful resource for guiding the difficult HSCT decisions in patients with P‐CID.

Clinical and structural impact of mutations affecting the residue Phe367 of FOXP3 in patients with IPEX syndrome.

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a monogenic autoimmune disease characterized by early-onset life-threatening multisystemic autoimmunity. This rare hereditary disorder is caused by loss-of-function mutations in the gene encoding the forkhead box P3 (FOXP3) transcription factor, which plays a key role in the differentiation and function of CD4(+)CD25(+) natural regulatory T cells (Tregs), essential for the establishment and maintenance of natural tolerance. We identified a novel mutation in the FOXP3 gene affecting the Phe367 residue of the protein (F367V) in a family with three male siblings affected by IPEX. Two other mutations affecting the FOXP3 Phe367 residue (F367L and F367C) have been described previously. This unique situation of three mutations affecting the same residue in FOXP3 led us to study the molecular impact of these mutations on the structure of FOXP3 protein. Structure analysis showed that Phe367 is involved in a rich interaction network related to both monomer and dimer structure stabilization, and is crucial for FOXP3 regulatory activity. The relevance of this location is confirmed by the results of SIFT and PolyPhen-2 pathogenicity predictions for F367V mutation. In summary, as assessment of the pathogenicity of a novel mutation is crucial to achieve a proper molecular diagnosis, we analysed the impact of mutations affecting the Phe367 residue using a combined approach that provides a mechanistic view of their pathogenic effect.

Age-specific pediatric reference ranges for immunoglobulins and complement proteins on the Optilite™ automated turbidimetric analyzer

Measurement of immunoglobulins and complement proteins are frontline tests used in the assessment of immune system integrity, and reference values can vary with age. Their measurement provides an insight into the function of the innate and adaptive immune systems.

LRBA Deficiency in a Patient with a Novel Homozygous Mutation due to Chromosome 4 Segmental Uniparental Isodisomy

LRBA deficiency was first described in 2012 as an autosomal recessive disorder caused by biallelic mutations in the LRBA gene (OMIM #614700). It was initially characterized as producing early-onset hypogammaglobulinemia, autoimmune manifestations, susceptibility to inflammatory bowel disease, and recurrent infection. However, further reports expanded this phenotype (including patients without hypogammaglobulinemia) and described LRBA deficiency as a clinically variable syndrome with a wide spectrum of clinical manifestations. We present the case of a female patient who presented with type 1 diabetes, psoriasis, oral thrush, and enlarged liver and spleen at the age of 8 months. She later experienced recurrent bacterial and viral infections, including pneumococcal meningitis and Epstein Barr viremia. She underwent two consecutive stem cell transplants at the age of 8 and 9 years, and ultimately died. Samples from the patient and her parents were subjected to whole exome sequencing, which revealed a homozygous 1-bp insertion in exon 23 of the patients LRBA gene, resulting in frameshift and premature stop codon. The patients healthy mother was heterozygous for the mutation and her father tested wild-type. This finding suggested that either one copy of the paternal chromosome 4 bore a deletion including the LRBA locus, or the patient inherited two copies of the mutant maternal LRBA allele. The patients sequencing data showed a 1-Mb loss of heterozygosity region in chromosome 4, including the LRBA gene. Comparative genomic hybridization array of the patients and fathers genomic DNA yielded normal findings, ruling out genomic copy number abnormalities. Here, we present the first case of LRBA deficiency due to a uniparental disomy (UPD). In contrast to classical Mendelian inheritance, UPD involves inheritance of 2 copies of a chromosomal region from only 1 parent. Specifically, our patient carried a small segmental isodisomy of maternal origin affecting 1 Mb of chromosome 4.

Evaluating the Genetics of Common Variable Immunodeficiency: Monogenetic Model and Beyond

Common variable immunodeficiency (CVID) is the most frequent symptomatic primary immunodeficiency characterized by recurrent infections, hypogammaglobulinemia and poor response to vaccines. Its diagnosis is made based on clinical and immunological criteria, after exclusion of other diseases that can cause similar phenotypes. Currently, less than 20% of cases of CVID have a known underlying genetic cause. We have analyzed whole-exome sequencing and copy number variants data of 36 children and adolescents diagnosed with CVID and healthy relatives to estimate the proportion of monogenic cases. We have replicated an association of CVID to p.C104R in TNFRSF13B and reported the second case of homozygous patient to date. Our results also identify five causative genetic variants in LRBA, CTLA4, NFKB1, and PIK3R1, as well as other very likely causative variants in PRKCD, MAPK8, or DOCK8 among others. We experimentally validate the effect of the LRBA stop-gain mutation which abolishes protein production and downregulates the expression of CTLA4, and of the frameshift indel in CTLA4 producing expression downregulation of the protein. Our results indicate a monogenic origin of at least 15–24% of the CVID cases included in the study. The proportion of monogenic patients seems to be lower in CVID than in other PID that have also been analyzed by whole exome or targeted gene panels sequencing. Regardless of the exact proportion of CVID monogenic cases, other genetic models have to be considered for CVID. We propose that because of its prevalence and other features as intermediate penetrancies and phenotypic variation within families, CVID could fit with other more complex genetic scenarios. In particular, in this work, we explore the possibility of CVID being originated by an oligogenic model with the presence of heterozygous mutations in interacting proteins or by the accumulation of detrimental variants in particular immunological pathways, as well as perform association tests to detect association with rare genetic functional variation in the CVID cohort compared to healthy controls.

Extended immunophenotyping reference values in a healthy pediatric population: INTERPRETATION OF EXTENDED IMMUNOPHENOTYPING PROFILES

For the accurate diagnosis of immunodeficiencies is crucial to compare patients’ immunology laboratory values with age‐sex matched controls, yet there is a paucity of normal values for most populations.

Th1-skewed profile and excessive production of proinflammatory cytokines in a NFKB1-deficient patient with CVID and severe gastrointestinal manifestations

Monoallelic loss-of-function mutations in NFKB1 were recently recognized as the most common monogenic cause of common variable immunodeficiency (CVID). The prototypic clinical phenotype of NFKB1-deficient patients includes common CVID features, such as hypogammaglobulinaemia and sinopulmonary infections, plus other highly variable individual manifestations. Here, we describe a patient with a profound CVID phenotype and severe gastrointestinal manifestations, including chronic and recurrent diarrhoea. Using an NGS customized panel of 323 genes related to primary immunodeficiencies, we identified a novel monoallelic loss-of-function mutation in NFKB1 leading to a truncated protein (c.1149delT/p.Gly384Glu ∗ 48). Interestingly, we also found a rare variant in NOD2 previously associated with Crohns disease (p.His352Arg). Our patient had hypogammaglobulinaemia with a small number of B cells, most of which were naïve. The most noteworthy findings included marked skewing towards a Th1 phenotype in peripheral blood T cells and excessive production of proinflammatory cytokines (IL-1β, TNFα). The patients 6-year-old daughter, a carrier of the NFKB1 mutation, is clinically asymptomatic, but has started to show cellular and molecular changes. This case of NFKB1 deficiency appears to be a combination of immunodeficiency and a hyperinflammatory state. The current situation of the patients daughter provides a glimpse of the preclinical phase of the condition.