Genotype and functional correlates of disease phenotype in deficiency of adenosine deaminase 2 (DADA2)

BACKGROUND

Deficiency of adenosine deaminase 2 (DADA2) is a syndrome with pleiotropic manifestations including vasculitis and hematologic compromise. A systematic definition of the relationship between adenosine deaminase 2 (ADA2) mutations and clinical phenotype remains unavailable.

OBJECTIVE

We sought to test whether the impact of ADA2 mutations on enzyme function correlates with clinical presentation.

METHODS

Patients with DADA2 with severe hematologic manifestations were compared with vasculitis-predominant patients. Enzymatic activity was assessed using expression constructs reflecting all 53 missense, nonsense, insertion, and deletion genotypes from 152 patients across the DADA2 spectrum.

RESULTS

We identified patients with DADA2 presenting with pure red cell aplasia (n = 5) or bone marrow failure (BMF, n = 10) syndrome. Most patients did not exhibit features of vasculitis. Recurrent infection, hepatosplenomegaly, and gingivitis were common in patients with BMF, of whom half died from infection. Unlike patients with DADA2 with vasculitis, patients with pure red cell aplasia and BMF proved largely refractory to TNF inhibitors. ADA2 variants associated with vasculitis predominantly reflected missense mutations with at least 3% residual enzymatic activity. In contrast, pure red cell aplasia and BMF were associated with missense mutations with minimal residual enzyme activity, nonsense variants, and insertions/deletions resulting in complete loss of function.

CONCLUSIONS

Functional interrogation of ADA2 mutations reveals an association of subtotal function loss with vasculitis, typically responsive to TNF blockade, whereas more extensive loss is observed in hematologic disease, which may be refractory to treatment. These findings establish a genotype-phenotype spectrum in DADA2.

Ion beam induced 18F-radiofluorination: straightforward synthesis of gaseous radiotracers for the assessment of regional lung ventilation using positron emission tomography

A simple, straightforward and efficient method for the synthesis of [¹⁸F]CF₄ and [¹⁸F]SF₆ based on an ion beam-induced isotopic exchange reaction is presented. Positron emission tomography ventilation studies in rodents using [¹⁸F]CF₄ showed a uniform distribution of the radiofluorinated gas within the lungs and rapid elimination after discontinuation of the administration.

DOCK8 Deficiency Presenting as an IPEX-Like Disorder

PURPOSE

The dedicator of cytokinesis 8 (DOCK8) deficiency is an autosomal recessive-combined immunodeficiency whose clinical spectra include recurrent infections, autoimmunity, malignancies, elevated serum IgE, eczema, and food allergies. Here, we report on patients with loss of function DOCK8 mutations with profound immune dysregulation suggestive of an immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX)-like disorder.

METHODS

Immunophenotyping of lymphocyte subpopulations and analysis of DOCK8 protein expression were evaluated by flow cytometry. T regulatory (T_reg) cells were isolated by cell sorting, and their suppressive activity was analyzed by flow cytometry. Gene mutational analysis was performed by whole-exome and Sanger sequencing.

RESULTS

Patient 1 (P1) presented at 10 months of age with chronic severe diarrhea and active colitis in the absence of an infectious trigger, severe eczema with elevated serum IgE, and autoimmune hemolytic anemia, suggestive of an IPEX-related disorder. Whole-exome sequencing revealed a homozygous nonsense mutation in DOCK8 at the DOCK-homology region (DHR)-1 (c.1498C>T; p. R500X). Patient P2, a cousin of P1 who carries the same DOCK8 nonsense mutation, presented with eczema and recurrent ear infections in early infancy, and she developed persistent diarrhea by 3 years of age. Patient P3 presented with lymphoproliferation, severe eczema with allergic dysregulation, and chronic diarrhea with colitis. She harbored a homozygous loss of function DOCK8 mutation (c.2402 -1G→A). T_reg cell function was severely compromised by both DOCK8 mutations.

CONCLUSION

DOCK8 deficiency may present severe immune dysregulation with features that may overlap with those of IPEX and other IPEX-like disorders.

Detection of Sp110 by Flow Cytometry and Application to Screening Patients for Veno-occlusive Disease with Immunodeficiency

Mutations in Sp110 are the underlying cause of veno-occlusive disease with immunodeficiency (VODI), a combined immunodeficiency that is difficult to treat and often fatal. Because early treatment is critically important for patients with VODI, broadly usable diagnostic tools are needed to detect Sp110 protein deficiency. Several factors make establishing the diagnosis of VODI challenging: (1) Current screening strategies to identify severe combined immunodeficiency are based on measuring T cell receptor excision circles (TREC). This approach will fail to identify VODI patients because the disease is not associated with severe T cell lymphopenia at birth; (2) the SP110 gene contains 17 exons, making it a challenge for Sanger sequencing. The recently developed next-generation sequencing (NGS) platforms that can rapidly determine the sequence of all 17 exons are available in only a few laboratories; (3) there is no standard functional assay to test for the effects of novel mutations in Sp110; and (4) it has been difficult to use flow cytometry to identify patients who lack Sp110 because of the low level of Sp110 protein in peripheral blood lymphocytes. We report here a novel flow cytometric assay that is easily performed in diagnostic laboratories and might thus become a standard assay for the evaluation of patients who may have VODI. In addition, the assay will facilitate investigations directed at understanding the function of Sp110.

Visualisation of dual radiolabelled poly(lactide-co-glycolide) nanoparticle degradation in vivo using energy-discriminant SPECT

The determination of nanoparticle (NP) stability and degradation in vivo is essential for the accurate evaluation of NP biodistribution in medical applications and for understanding their toxicological effects. Such determination is particularly challenging because NPs are extremely difficult to detect and quantify once distributed in a biological system. Radiolabelling with positron or gamma emitters and subsequent imaging studies using positron emission tomography (PET) or single-photon emission computerised tomography (SPECT) are some of the few valid alternatives. However, NPs that degrade or radionuclides that detach or are released from the NPs can cause artefact. Here, submicron-sized poly(lactide-co-glycolide) nanoparticles (PLGA-NPs) stabilised with bovine serum albumin (BSA) were dual radiolabelled using gamma emitters with different energy spectra incorporated into the core and coating. To label the core, ¹¹¹In-doped iron oxide NPs were encapsulated inside PLGA-NPs during NP preparation, and the BSA coating was labelled by electrophilic substitution using ¹²⁵I. After intravenous administration into rats, energy-discriminant SPECT resolved each radioisotope independently. Imaging revealed different fates for the core and coating, with a fraction of the two radionuclides co-localising in the liver and lungs for long periods of time after administration, suggesting that NPs are stable in these organs. Organ harvesting followed by gamma counting corroborated the SPECT results. The general methodology reported here represents an excellent alternative for visualising the degradation process of multi-labelled NPs in vivo and can be extended to a wide range of engineered NPs.

Straightforward synthesis of radioiodinated Cc-substituted o-carboranes: towards a versatile platform to enable the in vivo assessment of BNCT drug candidates

Due to their high boron content and rich chemistry, dicarba-closo-dodecaboranes (carboranes) are promising building blocks for the development of drug candidates with application in Boron Neutron Capture Therapy. However, the non-invasive determination of their pharmacokinetic properties to predict therapeutic efficacy is still a challenge. Herein, we have reported the unprecedented preparation of mono-[(125)I] iodinated decaborane via a catalyst-assisted isotopic exchange. Subsequent reactions of the radiolabelled species with acetylenes in acetonitrile under microwave heating yield the corresponding (125)I-labelled, Cc-substituted o-carboranes with good overall radiochemical yields in short reaction times. The same synthetic strategy was successfully applied to the preparation of (131)I-labelled analogues, and further extension to other radioisotopes of iodine such as (124)I (positron emitter) or (123)I (gamma emitter) can be envisaged. Hence, the general strategy reported here is suitable for the preparation of a wide range of radiolabelled Cc-substituted o-carborane derivatives. The labelled compounds might be subsequently investigated in vivo by using nuclear imaging techniques such as Single Photon Emission Computerized Tomography or Positron Emission Tomography.

The extended clinical phenotype of 64 patients with dedicator of cytokinesis 8 deficiency

BACKGROUND

Mutations in dedicator of cytokinesis 8 (DOCK8) cause a combined immunodeficiency (CID) also classified as autosomal recessive (AR) hyper-IgE syndrome (HIES). Recognizing patients with CID/HIES is of clinical importance because of the difference in prognosis and management.

OBJECTIVES

We sought to define the clinical features that distinguish DOCK8 deficiency from other forms of HIES and CIDs, study the mutational spectrum of DOCK8 deficiency, and report on the frequency of specific clinical findings.

METHODS

Eighty-two patients from 60 families with CID and the phenotype of AR-HIES with (64 patients) and without (18 patients) DOCK8 mutations were studied. Support vector machines were used to compare clinical data from 35 patients with DOCK8 deficiency with those from 10 patients with AR-HIES without a DOCK8 mutation and 64 patients with signal transducer and activator of transcription 3 (STAT3) mutations.

RESULTS

DOCK8-deficient patients had median IgE levels of 5201 IU, high eosinophil levels of usually at least 800/μL (92% of patients), and low IgM levels (62%). About 20% of patients were lymphopenic, mainly because of low CD4(+) and CD8(+) T-cell counts. Fewer than half of the patients tested produced normal specific antibody responses to recall antigens. Bacterial (84%), viral (78%), and fungal (70%) infections were frequently observed. Skin abscesses (60%) and allergies (73%) were common clinical problems. In contrast to STAT3 deficiency, there were few pneumatoceles, bone fractures, and teething problems. Mortality was high (34%). A combination of 5 clinical features was helpful in distinguishing patients with DOCK8 mutations from those with STAT3 mutations.

CONCLUSIONS

DOCK8 deficiency is likely in patients with severe viral infections, allergies, and/or low IgM levels who have a diagnosis of HIES plus hypereosinophilia and upper respiratory tract infections in the absence of parenchymal lung abnormalities, retained primary teeth, and minimal trauma fractures.

Large deletions and point mutations involving the dedicator of cytokinesis 8 (DOCK8) in the autosomal-recessive form of hyper-IgE syndrome

BACKGROUND

The genetic etiologies of the hyper-IgE syndromes are diverse. Approximately 60% to 70% of patients with hyper-IgE syndrome have dominant mutations in STAT3, and a single patient was reported to have a homozygous TYK2 mutation. In the remaining patients with hyper-IgE syndrome, the genetic etiology has not yet been identified.

OBJECTIVES

We aimed to identify a gene that is mutated or deleted in autosomal recessive hyper-IgE syndrome.

METHODS

We performed genome-wide single nucleotide polymorphism analysis for 9 patients with autosomal-recessive hyper-IgE syndrome to locate copy number variations and homozygous haplotypes. Homozygosity mapping was performed with 12 patients from 7 additional families. The candidate gene was analyzed by genomic and cDNA sequencing to identify causative alleles in a total of 27 patients with autosomal-recessive hyper-IgE syndrome.

RESULTS

Subtelomeric biallelic microdeletions were identified in 5 patients at the terminus of chromosome 9p. In all 5 patients, the deleted interval involved dedicator of cytokinesis 8 (DOCK8), encoding a protein implicated in the regulation of the actin cytoskeleton. Sequencing of patients without large deletions revealed 16 patients from 9 unrelated families with distinct homozygous mutations in DOCK8 causing premature termination, frameshift, splice site disruption, and single exon deletions and microdeletions. DOCK8 deficiency was associated with impaired activation of CD4+ and CD8+T cells.

CONCLUSION

Autosomal-recessive mutations in DOCK8 are responsible for many, although not all, cases of autosomal-recessive hyper-IgE syndrome. DOCK8 disruption is associated with a phenotype of severe cellular immunodeficiency characterized by susceptibility to viral infections, atopic eczema, defective T-cell activation and T(h)17 cell differentiation, and impaired eosinophil homeostasis and dysregulation of IgE.

WASP regulates suppressor activity of human and murine CD4(+)CD25(+)FOXP3(+) natural regulatory T cells

A large proportion of Wiskott-Aldrich syndrome (WAS) patients develop autoimmunity and allergy. CD4⁺CD25⁺FOXP3⁺ natural regulatory T (nTreg) cells play a key role in peripheral tolerance to prevent immune responses to self-antigens and allergens. Therefore, we investigated the effect of WAS protein (WASP) deficiency on the distribution and suppressor function of nTreg cells. In WAS^−/− mice, the steady-state distribution and phenotype of nTreg cells in the thymus and spleen were normal. However, WAS^−/− nTreg cells engrafted poorly in immunized mice, indicating perturbed homeostasis. Moreover, WAS^−/− nTreg cells failed to proliferate and to produce transforming growth factor β upon T cell receptor (TCR)/CD28 triggering. WASP-dependent F-actin polarization to the site of TCR triggering might not be involved in WAS^−/− nTreg cell defects because this process was also inefficient in wild-type (WT) nTreg cells. Compared with WT nTreg cells, WAS^−/− nTreg cells showed reduced in vitro suppressor activity on both WT and WAS^−/− effector T cells. Similarly, peripheral nTreg cells were present at normal levels in WAS patients but failed to suppress proliferation of autologous and allogeneic CD4⁺ effector T cells in vitro. Thus, WASP appears to play an important role in the activation and suppressor function of nTreg cells, and a dysfunction or incorrect localization of nTreg cells may contribute to the development of autoimmunity in WAS patients.

Long-term therapy with recombinant interferon-gamma (rIFN-gamma) for atopic dermatitis

BACKGROUND

Interferon-gamma (IFN-gamma) is a potent cytokine that modulates IL-4-induced immune responses. Atopic dermatitis is associated with increased IgE levels and decreased IFN-gamma production. Recent phase I and phase II studies have suggested that short-term rIFN-gamma therapy is effective in the treatment of severe atopic dermatitis.

OBJECTIVE

We evaluated the safety and efficacy of long-term use of rIFN-gamma for severe atopic dermatitis.

METHODS

Fifteen patients were treated for a minimum of 22 months with 50 micrograms/m2 rIFN-gamma qd or qod. Patients were monitored every 3 months for safety, efficacy, and linear growth in pediatric patients.

RESULTS

Data represented a total of 47 patient years, which included 29 pediatric patient years. There was a statistically significant decrease in mean total body surface area involvement over time (P < .001, ANOVA). Mean total body surface area involvement was 61.6% at baseline and decreased to 18.5% at 24 months (P < .001). Likewise, there was a statistically significant decrease in the clinical severity parameters. The mean total clinical severity score was 11.4 at baseline and decreased to 6.3 at 24 months (P < .001). Statistically significant decreases in WBC, neutrophil counts, and eosinophil counts were observed compared with baseline counts. No other significant laboratory abnormalities or growth problems were seen.

CONCLUSIONS

We conclude that rIFN-gamma appears to be a safe long-term therapy for patients with severe atopic dermatitis.