Helen F. Matthews

Combined Immunodeficiency Associated with DOCK8 Mutations

BACKGROUND Recurrent sinopulmonary and cutaneous viral infections with elevated serum levels of IgE are features of some variants of combined immunodeficiency. The genetic causes of these variants are unknown. METHODS We collected longitudinal clinical data on 11 patients from eight families who had recurrent sinopulmonary and cutaneous viral infections. We performed comparative genomic hybridization arrays and targeted gene sequencing. Variants with predicted loss-of-expression mutations were confirmed by means of a quantitative reverse-transcriptase-polymerase-chain-reaction assay and immunoblotting. We evaluated the number and function of lymphocytes with the use of in vitro assays and flow cytometry. RESULTS Patients had recurrent otitis media, sinusitis, and pneumonias; recurrent Staphylococcus aureus skin infections with otitis externa; recurrent, severe herpes simplex virus or herpes zoster infections; extensive and persistent infections with molluscum contagiosum; and human papillomavirus infections. Most patients had severe atopy with anaphylaxis; several had squamous-cell carcinomas, and one had T-cell lymphoma-leukemia. Elevated serum IgE levels, hypereosinophilia, low numbers of T cells and B cells, low serum IgM levels, and variable IgG antibody responses were common. Expansion in vitro of activated CD8 T cells was impaired. Novel homozygous or compound heterozygous deletions and point mutations in the gene encoding the dedicator of cytokinesis 8 protein (DOCK8) led to the absence of DOCK8 protein in lymphocytes. CONCLUSIONS Autosomal recessive DOCK8 deficiency is associated with a novel variant of combined immunodeficiency.

Second messenger role for Mg2+ revealed by human T-cell immunodeficiency

The magnesium ion, Mg2+, is essential for all life as a cofactor for ATP, polyphosphates such as DNA and RNA, and metabolic enzymes, but whether it plays a part in intracellular signalling (as Ca2+ does) is unknown. Here we identify mutations in the magnesium transporter gene, MAGT1, in a novel X-linked human immunodeficiency characterized by CD4 lymphopenia, severe chronic viral infections, and defective T-lymphocyte activation. We demonstrate that a rapid transient Mg2+ influx is induced by antigen receptor stimulation in normal T cells and by growth factor stimulation in non-lymphoid cells. MAGT1 deficiency abrogates the Mg2+ influx, leading to impaired responses to antigen receptor engagement, including defective activation of phospholipase Cγ1 and a markedly impaired Ca2+ influx in T cells but not B cells. These observations reveal a role for Mg2+ as an intracellular second messenger coupling cell-surface receptor activation to intracellular effectors and identify MAGT1 as a possible target for novel therapeutics.Summary The magnesium ion, Mg2+, is essential for all life as a cofactor for ATP, polyphosphates such as DNA and RNA, and metabolic enzymes, but whether it plays a role in intracellular signaling similar to Ca2+ is unknown. In this study, we identify mutations in the magnesium transporter gene, MAGT1, in a novel X-linked human immunodeficiency characterized by CD4 lymphopenia, severe chronic viral infections, and defective T lymphocyte activation. We demonstrate that a rapid transient Mg2+ influx is induced by antigen receptor stimulation in T cells or growth factor stimulation in non-lymphoid cells. MagT1 deficiency abrogates the Mg2+ influx leading to impaired responses to antigen receptor engagement including defective activation of phospholipase Cγ and a markedly impaired Ca2+ influx in T cells but not B cells. These observations reveal a role for Mg2+ as an intracellular second messenger and identify MagT1 as a possible target for novel therapeutics.

Early-onset lymphoproliferation and autoimmunity caused by germline STAT3 gain-of-function mutations.

Germline loss-of-function mutations in the transcription factor signal transducer and activator of transcription 3 (STAT3) cause immunodeficiency, whereas somatic gain-of-function mutations in STAT3 are associated with large granular lymphocytic leukemic, myelodysplastic syndrome, and aplastic anemia. Recently, germline mutations in STAT3 have also been associated with autoimmune disease. Here, we report on 13 individuals from 10 families with lymphoproliferation and early-onset solid-organ autoimmunity associated with 9 different germline heterozygous mutations in STAT3. Patients exhibited a variety of clinical features, with most having lymphadenopathy, autoimmune cytopenias, multiorgan autoimmunity (lung, gastrointestinal, hepatic, and/or endocrine dysfunction), infections, and short stature. Functional analyses demonstrate that these mutations confer a gain-of-function in STAT3 leading to secondary defects in STAT5 and STAT1 phosphorylation and the regulatory T-cell compartment. Treatment targeting a cytokine pathway that signals through STAT3 led to clinical improvement in 1 patient, suggesting a potential therapeutic option for such patients. These results suggest that there is a broad range of autoimmunity caused by germline STAT3 gain-of-function mutations, and that hematologic autoimmunity is a major component of this newly described disorder. Some patients for this study were enrolled in a trial registered at www.clinicaltrials.gov as #NCT00001350.

Patients with LRBA deficiency show CTLA4 loss and immune dysregulation responsive to abatacept therapy

Trafficking from bedside to bench Typically in translational research, a discovery in cell or molecular biology is later exploited to improve patient care. Occasionally, information flows in the opposite direction. Lo et al. found that patients with an autoimmune disorder caused by deficiency of a protein called LRBA responded dramatically to the drug abatacept (see the Perspective by Sansom). Abatacept contains a segment of a potent inhibitory immune receptor, CTLA4. Experiments prompted by this observation revealed the relationship between the two proteins: LRBA controls the intracellular trafficking and degradation of CTLA4. This information may further improve patient care, because other clinically approved drugs have the desired mechanism of action with potentially fewer side effects. Science, this issue p. 436; see also p. 377 A rare autoimmune disorder is caused by aberrant degradation of a potent inhibitory immune receptor. [Also see Perspective by Sansom] Mutations in the LRBA gene (encoding the lipopolysaccharide-responsive and beige-like anchor protein) cause a syndrome of autoimmunity, lymphoproliferation, and humoral immune deficiency. The biological role of LRBA in immunologic disease is unknown. We found that patients with LRBA deficiency manifested a dramatic and sustained improvement in response to abatacept, a CTLA4 (cytotoxic T lymphocyte antigen-4)–immunoglobulin fusion drug. Clinical responses and homology of LRBA to proteins controlling intracellular trafficking led us to hypothesize that it regulates CTLA4, a potent inhibitory immune receptor. We found that LRBA colocalized with CTLA4 in endosomal vesicles and that LRBA deficiency or knockdown increased CTLA4 turnover, which resulted in reduced levels of CTLA4 protein in FoxP3+ regulatory and activated conventional T cells. In LRBA-deficient cells, inhibition of lysosome degradation with chloroquine prevented CTLA4 loss. These findings elucidate a mechanism for CTLA4 trafficking and control of immune responses and suggest therapies for diseases involving the CTLA4 pathway.

Mg2+ regulates cytotoxic functions of NK and CD8 T cells in chronic EBV infection through NKG2D.

Magnesium to the Rescue Individuals with X-linked immunodeficiency with Mg2+ defect, Epstein-Barr virus (EBV) infection, and neoplasia (XMEN) disease are genetically deficient for expression of MAGT1, a magnesium transporter. Chaigne-Delalande et al. (p. 186) sought to better understand why these individuals are chronically infected with EBV at high viral loads and are susceptible to the development of lymphomas. CD8+ T cells and natural killer cells, which help to keep EBV infection in check, exhibited reduced cytotoxicity owing to their lower expression of the cell surface receptor NKG2D, which triggers cytolysis upon ligation. Magnesium supplementation in vitro and also in two XMEN patients restored levels of free Mg2+, increased NKG2D expression, and resulted in reduced amounts of EBV+ cells, suggesting that this may be an effective therapeutic approach for XMEN patients. Magnesium supplementation in patients with a primary immunodeficiency restores immune responses to Epstein-Barr virus. The magnesium transporter 1 (MAGT1) is a critical regulator of basal intracellular free magnesium (Mg2+) concentrations. Individuals with genetic deficiencies in MAGT1 have high levels of Epstein-Barr virus (EBV) and a predisposition to lymphoma. We show that decreased intracellular free Mg2+ causes defective expression of the natural killer activating receptor NKG2D in natural killer (NK) and CD8+ T cells and impairs cytolytic responses against EBV. Notably, magnesium supplementation in MAGT1-deficient patients restores intracellular free Mg2+ and NKG2D while concurrently reducing EBV-infected cells in vivo, demonstrating a link between NKG2D cytolytic activity and EBV antiviral immunity in humans. Moreover, these findings reveal a specific molecular function of free basal intracellular Mg2+ in eukaryotic cells.

Heterozygous splice mutation in PIK3R1 causes human immunodeficiency with lymphoproliferation due to dominant activation of PI3K

Lucas et al. identify humans with a gain-of-function mutation in PIK3R1, encoding the p85α subunit of PI3K. The splice site mutation causes in-frame skipping of exon 11, resulting in altered p85α association with p110δ that stabilizes the catalytic subunit but fails to properly inhibit catalytic activity. The patients have immunodeficiency and lymphoproliferation with skewing of CD8+ T cells toward terminally differentiated and senescent effector cells that have shortened telomeres.

Congenital B cell lymphocytosis explained by novel germline CARD11 mutations

Germline mutations in CARD11 that result in constitutive NF-κB activation and selective B cell expansion underlie congenital B cell lymphocytosis.

Additional Diverse Findings Expand the Clinical Presentation of DOCK8 Deficiency

We describe seven Turkish children with DOCK8 deficiency who have not been previously reported. Three patients presented with typical features of recurrent or severe cutaneous viral infections, atopic dermatitis, and recurrent respiratory or gastrointestinal tract infections. However, four patients presented with other features. Patient 1–1 featured sclerosing cholangitis and colitis; patient 2–1, granulomatous soft tissue lesion and central nervous system involvement, with primary central nervous system lymphoma found on follow-up; patient 3–1, a fatal metastatic leiomyosarcoma; and patient 4–2 showed no other symptoms initially besides atopic dermatitis. Similar to other previously reported Turkish patients, but in contrast to patients of non-Turkish ethnicity, the patients’ lymphopenia was primarily restricted to CD4+ T cells. Patients had homozygous mutations in DOCK8 that altered splicing, introduced premature terminations, destabilized protein, or involved large deletions within the gene. Genotyping of remaining family members showed that DOCK8 deficiency is a fully penetrant, autosomal recessive disease. In our patients, bone marrow transplantation resulted in rapid improvement followed by disappearance of viral skin lesions, including lesions resembling epidermodysplasia verruciformis, atopic dermatitis, and recurrent infections. Particularly for patients who feature unusual clinical manifestations, immunological testing, in conjunction with genetic testing, can prove invaluable in diagnosing DOCK8 deficiency and providing potentially curative treatment.

EBV-Related Lymphoproliferative Disease Complicating Therapy with the Anti-CD2 Monoclonal Antibody, Siplizumab, in Patients with T-Cell Malignancies

Purpose: We report an increased incidence of EBV-induced B-cell lymphoproliferative disease (LPD) in patients treated with siplizumab, an anti-CD2 antibody. The development of EBV-LPD has been associated with the use of immunosuppressive agents used in solid organ, bone marrow, and stem cell transplantation and in certain congenital immunodeficiencies. Experimental Design: We conducted a single-institution phase I dose-escalation trial of siplizumab, a humanized monoclonal antibody to CD2, in 29 patients with T-cell malignancies. Results: Although initial responses were encouraging, 4 (13.7%) patients developed EBV-LPD and the trial was stopped. Reductions in CD4+ and CD8+ cell count numbers in response to therapy were seen in all patients, but in those patients developing EBV-LPD a significantly greater reduction in natural killer (NK) cell number and CD2 expression on T cells was seen. These findings highlight the importance of NK-cell depletion and CD2 expression in addition to T-cell depletion in the etiology of EBV-LPD. Conclusions: The emergence of EBV-LPD may be associated with the ability of siplizumab to deplete both T and NK cells without affecting B cells. Agents that deplete T- and NK-cell populations without affecting B cell number should be screened for this potentially serious adverse event.

Somatic reversion in dedicator of cytokinesis 8 immunodeficiency modulates disease phenotype

BACKGROUND Autosomal recessive loss-of-function mutations in dedicator of cytokinesis 8 (DOCK8) cause a combined immunodeficiency characterized by atopy, recurrent infections, and cancer susceptibility. A genotype-phenotype explanation for the variable disease expression is lacking. OBJECTIVE We investigated whether reversions contributed to the variable disease expression. METHODS Patients followed at the National Institutes of Healths Clinical Center were studied. We performed detailed genetic analyses and intracellular flow cytometry to detect DOCK8 protein expression within lymphocyte subsets. RESULTS We identified 17 of 34 DOCK8-deficient patients who had germline mutations with variable degrees of reversion caused by somatic repair. Somatic repair of the DOCK8 mutations resulted from second-site mutation, original-site mutation, gene conversion, and intragenic crossover. Higher degrees of reversion were associated with recombination-mediated repair. DOCK8 expression was restored primarily within antigen-experienced T cells or natural killer cells but less so in naive T or B cells. Several patients exhibited multiple different repair events. Patients who had reversions were older and had less severe allergic disease, although infection susceptibility persisted. No patients were cured without hematopoietic cell transplantation. CONCLUSIONS In patients with DOCK8 deficiency, only certain combinations of germline mutations supported secondary somatic repair. Those patients had an ameliorated disease course with longer survival but still had fatal complications or required hematopoietic cell transplantation. These observations support the concept that some DOCK8-immunodeficient patients have mutable mosaic genomes that can modulate disease phenotype over time.