B-cell Deficiency: A De Novo IKZF1 Patient and Review of the Literature

Signaling pathways and regulation of gene expression in hematopoietic cells

Cellular functions are regulated by signal transduction pathway networks consisting of protein-modifying enzymes that control the activity of many downstream proteins. Protein kinases and phosphatases regulate gene expression by reversible phosphorylation of transcriptional factors, which are their direct substrates. Casein kinase II (CK2) is a serine/threonine kinase that phosphorylates a large number of proteins that have critical roles in cellular proliferation, metabolism and survival. Altered function of CK2 has been associated with malignant transformation, immunological disorders and other types of diseases. Protein phosphatase 1 (PP1) is a serine/threonine phosphatase, which regulates the phosphorylation status of many proteins that are essential for cellular functions. IKAROS is a DNA-binding protein, which functions as a regulator of gene transcription in hematopoietic cells. CK2 directly phosphorylates IKAROS at multiple phosphosites which determines IKAROS activity as a regulator of gene expression. PP1 binds to IKAROS via the PP1-consensus recognition site and dephosphorylates serine/threonine residues that are phosphorylated by CK2. Thus, the interplay between CK2 and PP1 signaling pathways have opposing effects on the phosphorylation status of their mutual substrate - IKAROS. This review summarizes the effects of CK2 and PP1 on IKAROS role in regulation of gene expression and its function as a tumor suppressor in leukemia.

Inborn errors of human IKAROS: LOF and GOF variants associated with primary immunodeficiency

IKAROS/IKZF1 plays a pivotal role in lymphocyte differentiation and development. Germline mutations in IKZF1, which have been shown to be associated with primary immunodeficiency, can be classified through four different mechanisms of action depending on the protein expression and its functional defects: haploinsufficiency, dimerization defective, dominant negative, and gain of function. These different mechanisms are associated with variable degrees of susceptibility to infectious diseases, autoimmune disorders, allergic diseases, and malignancies. To date, more than 30 heterozygous IKZF1 germline variants have been reported in patients with primary immunodeficiency. Here we review recent discoveries and clinical/immunological characterization of IKAROS-associated diseases that are linked to different mechanisms of action in IKAROS function.

Common Variable Immunodeficiency Associated with a De Novo IKZF1 Variant and a Low Humoral Immune Response to the SARS-CoV-2 Vaccine

BACKGROUND AND AIMS

Common variable immunodeficiency (CVID) comprises a group of diseases with heterogeneous clinical and immunological manifestations. Several mutations have been identified in genes encoding proteins essential for immune function. Our aim was to phenotypically and genotypically characterize a patient diagnosed with CVID and study his response to the SARS-CoV-2 vaccine.

METHODS

We performed a next-generation sequencing analysis, a CMIA, and an ELISA to analyze the humoral and cellular response to the SARS-CoV-2 vaccine, respectively. We also employed flow cytometry and immunoturbidimetry to assess the patient's global immune status.

RESULTS

We found a low humoral but positive cellular response to the SARS-CoV-2 vaccine. NGS screening revealed a transition from guanine to adenine at position c.485 of the IKZF1 gene in heterozygosity, giving rise to the R162Q variant, which was not present in his parents.

CONCLUSIONS

The R162Q variant of the IKZF1 gene has been associated with CVID type 13, but always with an autosomal dominant inheritance with high penetrance. Therefore, we present for the first time a case of CVID associated with a de novo heterozygous R162Q variant in the IKZF1 gene in a patient with a low humoral immune response to the complete COVID-19 vaccination program.

Genetic Biomarkers and Their Clinical Implications in B-Cell Acute Lymphoblastic Leukemia in Children

Acute lymphoblastic leukemia (ALL) is a heterogeneous group of hematologic malignancies characterized by abnormal proliferation of immature lymphoid cells. It is the most commonly diagnosed childhood cancer with an almost 80% cure rate. Despite favorable survival rates in the pediatric population, a significant number of patients develop resistance to therapy, resulting in poor prognosis. ALL is a heterogeneous disease at the genetic level, but the intensive development of sequencing in the last decade has made it possible to broaden the study of genomic changes. New technologies allow us to detect molecular changes such as point mutations or to characterize epigenetic or proteomic profiles. This process made it possible to identify new subtypes of this disease characterized by constellations of genetic alterations, including chromosome changes, sequence mutations, and DNA copy number alterations. These genetic abnormalities are used as diagnostic, prognostic and predictive biomarkers that play an important role in earlier disease detection, more accurate risk stratification, and treatment. Identification of new ALL biomarkers, and thus a greater understanding of their molecular basis, will lead to better monitoring of the course of the disease. In this article, we provide an overview of the latest information on genomic alterations found in childhood ALL and discuss their impact on patients' clinical outcomes.

Inborn errors of IKAROS and AIOLOS

IKAROS is a pioneer protein of the IKZF family of transcription factors that plays an essential role in lymphocyte development. Recently, inborn errors of IKAROS have been identified in patients with B cell deficiency and hypogammaglobulinemia, and these patients often present with recurrent sinopulmonary infection. Autoimmunity and hematologic malignancies are other characteristic complications seen in the patients with IKAROS deficiency. Missense mutation involving asparagine at the 159th position results in combined immunodeficiency, often presenting with Pneumocystis jirovecii pneumonia. Inborn errors of AIOLOS, HELIOS, and PEGASUS have also been reported in patients with B cell deficiency, Evans syndrome, and hereditary thrombocytopenia, respectively. Here, we briefly review the phenotype and genotype of IKZF mutations, especially IKAROS.

IKAROS Family Zinc Finger 1-Associated Diseases in Primary Immunodeficiency Patients

Ikaros zinc finger 1 (IKZF1 or Ikaros) is a hematopoietic zinc finger DNA-binding transcription factor that acts as a critical regulator of lymphocyte and myeloid differentiation. Loss-of-function germline heterozygous mutations in IKZF1 affecting DNA-binding were described as causative of 2 distinct primary immunodeficiency (PID)/inborn error of immunity diseases. Mutations acting by haploinsufficiency present with a common variable immune deficiency-like phenotype mainly characterized by increased susceptibility to infections. Mutations acting in a dominant negative fashion present with a combined immunodeficiency phenotype with high prevalence of Pneumocystis jirovecii pneumonia. Pathophysiology and manifestations of IKAROS-associated diseases in patients with PID are reviewed here.

Common Variable Immunodeficiency, Autoimmune Hemolytic Anemia, and Pancytopenia Associated With a Defect in IKAROS

OBJECTIVE

Mutations in IKZF1, which encodes Ikaros family zinc finger 1 (IKAROS) transcription factor, are associated with recurrent infections, cytopenia, autoimmune diseases, and hematologic malignancies. Diverse clinical phenotypes resulting from IKZF1 mutations include pulmonary fungal infections, cytopenia, autoimmune hemolytic anemia (AIHA), and malignancies. In this study, we aimed to assess the DNA-binding ability and pericentromeric (PC) localization of a variant of IKZF discovered in a patient.

MATERIALS AND METHODS

DNA-binding ability of a pathogenic IKZF variant was tested using electrophoretic mobility shift assay and PC localization of the variant was assessed by immunofluorescent microscopy in NIH3T3 cells.

RESULTS

Clinical features of a 3-month-old male infant who underwent hematopoietic stem cell transplantation because of an IKZF1 mutation-associated common variable immunodeficiency, AIHA, and pancytopenia are described. DNA studies revealed a heterozygous missense variant (IKZF1 NM_006060 c.427C>T; p.R143W). Cotransfection studies revealed that mutant R143W has a partial dominant-negative effect over PC targeting and DNA binding.

CONCLUSIONS

IKZF1 mutation must be kept in mind if neonatal AIHA, common variable immunodeficiency, and pancytopenia are observed.

Germline IKZF1 mutations and their impact on immunity: IKAROS-associated diseases and pathophysiology

Introduction: The transcription factor IKAROS and IKAROS family members are critical for the development of lymphocyte and other blood cell lineages. Germline heterozygous IKZF1 mutations have been described in primary immunodeficiency as well as in human hematologic malignancies, affecting both B and T cells. Depending on the allelic variants of IKZF1 mutations (haploinsufficiency and dominant negative) clinical phenotypes vary from bacterial, viral, or fungal infection to autoimmune disease and malignancy.Areas covered: In this review, the authors provide an overview of genotype-phenotype correlation and clinical manifestations in patients with IKZF1 mutations. The importance of accurate diagnosis and monitoring immunological changes is also discussed for the management of these complex and rare diseases. IKZF1/IKAROS, immunodeficiency, and CVID were used as the search terms in PubMed and Google Scholar.Expert opinion: Over the past 5 years both genetic and molecular studies have unveiled surprisingly diverse roles of IKZF1 mutations in primary immunodeficiency. While an increasing number of novel IKZF1 variants are being reported, limited, and complex laboratory testing is necessary to verify the mutation's pathogenicity. Therefore, the combination of understanding mechanistic concepts and clinical and immunological follow-up is necessary to increase our knowledge of IKAROS-associated diseases.

Update on Infections in Primary Antibody Deficiencies

Bacterial respiratory tract infections are the hallmark of primary antibody deficiencies (PADs). Because they are also among the most common infections in healthy individuals, PADs are usually overlooked in these patients. Careful evaluation of the history, including frequency, chronicity, and presence of other infections, would help suspect PADs. This review will focus on infections in relatively common PADs, discussing diagnostic challenges, and some management strategies to prevent infections.

IKAROS-Associated Diseases in 2020: Genotypes, Phenotypes, and Outcomes in Primary Immune Deficiency/Inborn Errors of Immunity

IKAROS, encoded by IKZF1, is a zinc finger transcription factor and a critical regulator of hematopoiesis. Mutations in IKZF1 have been implicated in immune deficiency, autoimmunity, and malignancy in humans. Somatic IKZF1 loss-of-function mutations and deletions have been shown to increase predisposition to the development of B cell acute lymphoblastic leukemia (B-ALL) and associated with poor prognosis. In the last 4 years, germline heterozygous IKZF1 mutations have been reported in primary immune deficiency/inborn errors of immunity. These allelic variants, acting by either haploinsufficiency or dominant negative mechanisms affecting particular functions of IKAROS, are associated with common variable immunodeficiency, combined immunodeficiency, or primarily hematologic phenotypes in affected patients. In this review, we provide an overview of genetic, clinical, and immunological manifestations in patients with IKZF1 mutations, and the molecular and cellular mechanisms that contribute to their disease as a consequence of IKAROS dysfunction.

B-lymphocyte deficiency and recurrent respiratory infections in a 6-month-old female infant with mosaic monosomy 7

Monosomy 7 is generally considered as an acquired cytogenetic abnormality within hematopoietic cells, and indicates an especially high risk of progression to bone marrow failure, myelodysplastic syndrome (MDS) or juvenile myelomonocytic leukemia (JMML). We report a case of a 6-month-old female infant with mosaic monosomy 7 who presented with clinical and laboratory evidences of immunodeficiency. The patient had suffered from recurrent respiratory infections since she was born. Peripheral blood lymphocyte subsets revealed an extremely low level of CD19⁺ B lymphocytes (0.3∼0.8%, normal range: 6.4∼22.6%) and a decreased CD4/CD8 ratio (0.67∼1.12, normal range: 1.4∼2.0). Decreased serum levels of IgG (1.53 g/L, normal range: 4.09∼7.03 g/L), IgA (0.10 g/L, normal range: 0.21∼0.47 g/L) and IgM (0.26 g/L, normal range: 0.33∼0.73 g/L) were detected, while complements were normal. Excepting transient neutropenia, routine blood tests were within normal limits. Clinical exome sequencing identified a de novo mosaic monosomy 7, while no pathogenic mutation associated with immunodeficiency was detected. However, peripheral blood cytogenetic analysis was failure to detect monosomy 7 due to the very few cell mitosis. Subsequent fluorescence in situ hybridization (FISH) identified a mosaic monosomy 7 in 58 cells within a total number of 100 cells, which was consistent with clinical exome sequencing. Therefore, the patient was diagnosed with primary immunodeficiency disease (PID) due to mosaic monosomy 7. Intravenous treatment with multiple antibiotic agents and infusion of gamma globulin could control the patient's respiratory infections effectively. A better understanding of PIDs will enable effective treatments and prevention of infections in these patients.

Cellular signaling and epigenetic regulation of gene expression in leukemia

Alterations in normal regulation of gene expression is one of the key features of hematopoietic malignancies. In order to gain insight into the mechanisms that regulate gene expression in these diseases, we dissected the role of the Ikaros protein in leukemia. Ikaros is a DNA-binding, zinc finger protein that functions as a transcriptional regulator and a tumor suppressor in leukemia. The use of ChIP-seq, RNA-seq, and ATAC-seq—coupled with functional experiments—revealed that Ikaros regulates both the global epigenomic landscape and epigenetic signature at promoter regions of its target genes. Casein kinase II (CK2), an oncogenic kinase that is overexpressed in leukemia, directly phosphorylates Ikaros at multiple, evolutionarily-conserved residues. Phosphorylation of Ikaros impairs the protein's ability to regulate both the transcription of its target genes and global epigenetic landscape in leukemia. Treatment of leukemia cells with a specific inhibitor of CK2 restores Ikaros function, resulting in cytotoxicity of leukemia cells. Here, we review the mechanisms through which the CK2-Ikaros signaling axis regulates the global epigenomic landscape and expression of genes that control cellular proliferation in leukemia.

Familial Immune Thrombocytopenia Associated With a Novel Variant in IKZF1

We report a novel variant in IKZF1 associated with IKAROS haploinsufficiency in a patient with familial immune thrombocytopenia (ITP). IKAROS, encoded by the IKZF1 gene, is a hematopoietic zinc-finger transcription factor that can directly bind to DNA. We show that the identified IKZF1 variant (p.His195Arg) alters a completely conserved histidine residue required for the folding of the third zinc-finger of IKAROS protein, leading to a loss of characteristic immunofluorescence nuclear staining pattern. In our case, genetic testing was essential for the diagnosis of IKAROS haploinsufficiency, of which known presentations include infections, aberrant hematopoiesis, leukemia, and age-related decrease in humoral immunity. Our family study underscores that, after infections, ITP is the second most common clinical manifestation of IKAROS haploinsufficiency.