Wayne Bainter

A missense mutation in TFRC, encoding transferrin receptor 1, causes combined immunodeficiency

Patients with a combined immunodeficiency characterized by normal numbers but impaired function of T and B cells had a homozygous p.Tyr20His substitution in transferrin receptor 1 (TfR1), encoded by TFRC. The substitution disrupts the TfR1 internalization motif, resulting in defective receptor endocytosis and markedly increased TfR1 expression on the cell surface. Iron citrate rescued the lymphocyte defects, and expression of wild-type but not mutant TfR1 rescued impaired transferrin uptake in patient-derived fibroblasts. TfrcY20H/Y20H mice recapitulated the immunological defects of patients. Despite the critical role of TfR1 in erythrocyte development and function, patients had only mild anemia and only slightly increased TfR1 expression in erythroid precursors. We show that STEAP3, a metalloreductase expressed in erythroblasts, associates with TfR1 and partially rescues transferrin uptake in patient-derived fibroblasts, suggesting that STEAP3 may provide an accessory TfR1 endocytosis signal that spares patients from severe anemia. These findings demonstrate the importance of TfR1 in adaptive immunity.

A novel mutation in ORAI1 presenting with combined immunodeficiency and residual T-cell function.

Lymphocyte phenotype (normal range) Lymphocyte count (cells/mL)* 7,310 (3,400-9,000) CD3 (cells/mL) 4,553 (1,900-5,900) CD3CD4 3,972 (1,400-4,300) Naive CD3CD4CD45RA 30.1% (50%-85%) Memory CD3CD4CD45RO 69.9% (15%-50%) CD3CD8 516 (500-1,700) Naive CD3CD8CD45RA 65.8% (50%-85%) Memory CD3CD8CD45RO 34.2% (15%-50%) T-cell oligoclonality Not detectable CD19 (cells/mL) 2,159 (610-2,600) IgDCD27 89.6% (65.8%-91.4%) IgDCD27 2.1% (3.6%-18.8%) IgDCD27 4.2% (0.9%-14.1%) CD16/CD56 (cells/mL) 312 (160-950) Immunoglobulins (mg/dL) (normal range) IgG 731 (215-714) IgA 433 (8.1-68) IgM 101 (35-102) IgE 6 (0.44-16.3) Lymphocyte proliferation (cpm) (control§) PHA 128,077 (222,208) Pokeweed mitogen 102,413 (141,446) Concanavalin A 32,560 (64,276) Background 403 (775) Tetanus 8,252 (61,433) Diphtheria 6,543 (54,298) Background 2,310 (4,452) Cytotoxicity studies NK-cell lytic units Not detectable (>3.1) Cytotoxic T-lymphocyte lytic units 1.6 (6)

A digenic human immunodeficiency characterized by IFNAR1 and IFNGR2 mutations

Primary immunodeficiencies are often monogenic disorders characterized by vulnerability to specific infectious pathogens. Here, we performed whole-exome sequencing of a patient with disseminated Mycobacterium abscessus, Streptococcus viridians bacteremia, and cytomegalovirus (CMV) viremia and identified mutations in 2 genes that regulate distinct IFN pathways. The patient had a homozygous frameshift deletion in IFNGR2, which encodes the signal transducing chain of the IFN-&ggr; receptor, that resulted in minimal protein expression and abolished downstream signaling. The patient also harbored a homozygous deletion in IFNAR1 (IFNAR1*557Gluext*46), which encodes the IFN-&agr; receptor signaling subunit. The IFNAR1*557Gluext*46 resulted in replacement of the stop codon with 46 additional codons at the C-terminus. The level of IFNAR1*557Gluext*46 mutant protein expressed in patient fibroblasts was comparable to levels of WT IFNAR1 in control fibroblasts. IFN-&agr;–induced signaling was impaired in the patient fibroblasts, as evidenced by decreased STAT1/STAT2 phosphorylation, nuclear translocation of STAT1, and expression of IFN-&agr;–stimulated genes critical for CMV immunity. Pretreatment with IFN-&agr; failed to suppress CMV protein expression in patient fibroblasts, whereas expression of WT IFNAR1 restored IFN-&agr;–mediated suppression of CMV. This study identifies a human IFNAR1 mutation and describes a digenic immunodeficiency specific to type I and type II IFNs.

A novel mutation in FOXN1 resulting in SCID: a case report and literature review.

• FOXN1 mutations classically cause T cell lymphopenia, but may also permit non-maternal T cells.

Human RELA haploinsufficiency results in autosomal-dominant chronic mucocutaneous ulceration.

The treatment of chronic mucocutaneous ulceration is challenging, and only some patients respond selectively to inhibitors of tumor necrosis factor-&agr; (TNF). TNF activates opposing pathways leading to caspase-8–mediated apoptosis as well as nuclear factor &kgr;B (NF-&kgr;B)–dependent cell survival. We investigated the etiology of autosomal-dominant, mucocutaneous ulceration in a family whose proband was dependent on anti-TNF therapy for sustained remission. A heterozygous mutation in RELA, encoding the NF-&kgr;B subunit RelA, segregated with the disease phenotype and resulted in RelA haploinsufficiency. The patients’ fibroblasts exhibited increased apoptosis in response to TNF, impaired NF-&kgr;B activation, and defective expression of NF-&kgr;B–dependent antiapoptotic genes. Rela+/− mice have similarly impaired NF-&kgr;B activation, develop cutaneous ulceration from TNF exposure, and exhibit severe dextran sodium sulfate–induced colitis, ameliorated by TNF inhibition. These findings demonstrate an essential contribution of biallelic RELA expression in protecting stromal cells from TNF-mediated cell death, thus delineating the mechanisms driving the effectiveness of TNF inhibition in this disease.

Leucine-rich repeat containing 8A (LRRC8A)–dependent volume-regulated anion channel activity is dispensable for T-cell development and function

Background: Leucine‐rich repeat containing 8A (LRRC8A) is an ubiquitously expressed transmembrane protein with 17 leucine‐rich repeats (LRRs) at its C‐terminal end and is an essential component of the volume‐regulated anion channel (VRAC), which controls cellular volume. A heterozygous mutation in LRRC8A that truncates the 2 terminal LRRs was reported in a patient with agammaglobulinemia and absent B cells and was demonstrated to exert a dominant negative effect on T‐ and B‐cell development in mice. Lrrc8a−/− mice have severely defective T‐cell development and function. It is not known whether the T‐ and B‐cell defects caused by LRRC8A deficiency are caused by loss of VRAC activity. Objective: We sought to determine whether VRAC activity is required for normal T‐cell development and function. Methods: VRAC activity was examined by using patch‐clamp analysis. Flow cytometry was used to examine T‐cell development. T‐cell proliferation, cytokine secretion, and antibody titers were measured by using standard techniques. Results: We demonstrate that the spontaneous mouse mutant ébouriffé (ebo/ebo) harbors a homozygous 2‐bp frameshift mutation in Lrrc8a that truncates the 15 terminal LRRs of LRRC8A. The Lrrc8aebo mutation does not affect protein expression but drastically diminishes VRAC activity in T cells. ebo/ebo mice share features with Lrrc8a−/− mice that include curly hair, infertility, reduced longevity, and kidney abnormalities. However, in contrast to Lrrc8a−/− mice, ebo/ebo mice have normal T‐cell development and function and intact antibody response to T‐dependent antigen. Conclusion: LRRC8A‐dependent VRAC activity is dispensable for T‐cell development and function.

Clinical, immunologic, and genetic spectrum of 696 patients with combined immunodeficiency

Background: Combined immunodeficiencies (CIDs) are diseases of defective adaptive immunity with diverse clinical phenotypes. Although CIDs are more prevalent in the Middle East than Western countries, the resources for genetic diagnosis are limited. Objectives: This study aims to characterize the categories of patients with CIDs in Iran clinically and genetically. Methods: Clinical and laboratory data were obtained from 696 patients with CIDs. Patients were subdivided into those with syndromic (344 patients) and nonsyndromic (352 patients) CIDs. Targeted DNA sequencing was performed on 243 (34.9%) patients. Results: The overall diagnostic yield of the 243 sequenced patients was 77.8% (189 patients). The clinical diagnosis of hyper‐IgE syndrome (P < .001), onset of disease at greater than 5 years (P = .02), and absence of multiple affected family members (P = .04) were significantly more frequent in the patients without a genetic diagnosis. An autosomal recessive disease was found in 62.9% of patients, reflecting the high rate of consanguinity in this cohort. Mutations impairing VDJ recombination and DNA repair were the most common underlying causes of CIDs. However, in patients with syndromic CIDs, autosomal recessive mutations in ataxia‐telangiectasia mutated (ATM), autosomal dominant mutations in signal transducer and activator of transcription 3 (STAT3), and microdeletions in 22q11.21 were the most commonly affected genomic loci. Patients with syndromic CIDs had a significantly lower 5‐year survival rate rather than those with nonsyndromic CIDs. Conclusions: This study provides proof of principle for the application of targeted next‐generation sequencing panels in countries with limited diagnostic resources. The effect of genetic diagnosis on clinical care requires continued improvements in therapeutic resources for these patients.

A novel mutation in NCF2 associated with autoimmune disease and a solitary late-onset infection.

Chronic granulomatous disease (CGD) is typically characterized by recurrent infections, granulomatous disease, and an increased susceptibility to autoimmune disease. We report a novel homozygous mutation in NCF2 that permits residual expression of an alternatively spliced variant in a patient with duodenitis and systemic lupus erythematosus (SLE), followed by a late-onset, single pulmonary infection in the setting of immunosuppressive medications. This report highlights the importance of considering CGD in patients who present initially exclusively with autoimmune disease.

A young girl with severe cerebral fungal infection due to card 9 deficiency

Pattern recognition receptors (PRRs), receptors of the innate immune system, are important in interaction with pathogens. Caspase Recruitment Domain-containing protein 9 (CARD9), a member of PRRs, is an intracellular adaptor protein important in fungal defense. CARD9 deficiency causes a rare primary immunodeficiency (PID) characterized by superficial and deep fungal infections. We report a 17year-old female with a homozygous nonsense mutation in CARD9, who presented with severe cerebral fungal infection of the central nervous system. She was also found to have an heterozygous NLRP12 mutation, which may have had add-on effect on the severity of the infection.

Combined immunodeficiency due to a homozygous mutation in ORAI1 that deletes the C-terminus that interacts with STIM 1.

ORAI1 is the pore-forming subunit of the calcium release-activated calcium channel responsible for calcium influx into cells triggered by endoplasmic reticulum store depletion. We report here a patient with severe combined immunodeficiency and absent store-operated calcium entry due to a novel mutation in ORAI1 that results in the expression of a C-terminally truncated protein that abolishes ORAI1 binding to STIM1.