T-cell defects in patients with ARPC1B germline mutations account for combined immunodeficiency

Abstract

<jats:title>Abstract</jats:title> <jats:p>ARPC1B is a key factor for the assembly and maintenance of the ARP2/3 complex that is involved in actin branching from an existing filament. Germline biallelic mutations in ARPC1B have been recently described in 6 patients with clinical features of combined immunodeficiency (CID), whose neutrophils and platelets but not T lymphocytes were studied. We hypothesized that ARPC1B deficiency may also lead to cytoskeleton and functional defects in T cells. We have identified biallelic mutations in ARPC1B in 6 unrelated patients with early onset disease characterized by severe infections, autoimmune manifestations, and thrombocytopenia. Immunological features included T-cell lymphopenia, low numbers of naïve T cells, and hyper–immunoglobulin E. Alteration in ARPC1B protein structure led to absent/low expression by flow cytometry and confocal microscopy. This molecular defect was associated with the inability of patient-derived T cells to extend an actin-rich lamellipodia upon T-cell receptor (TCR) stimulation and to assemble an immunological synapse. ARPC1B-deficient T cells additionally displayed impaired TCR-mediated proliferation and SDF1-α−directed migration. Gene transfer of ARPC1B in patients’ T cells using a lentiviral vector restored both ARPC1B expression and T-cell proliferation in vitro. In 2 of the patients, in vivo somatic reversion restored ARPC1B expression in a fraction of lymphocytes and was associated with a skewed TCR repertoire. In 1 revertant patient, memory CD8+ T cells expressing normal levels of ARPC1B displayed improved T-cell migration. Inherited ARPC1B deficiency therefore alters T-cell cytoskeletal dynamics and functions, contributing to the clinical features of CID.</jats:p>

Partial loss of actin nucleator actin‐related protein 2/3 activity triggers blebbing in primary T lymphocytes

“…Nevertheless, our result is consistent with the recent study by Brigida et al ., which concluded that ARPC1B is also crucial for the Arp2/3 assembly and maintenance. They showed that alteration in the protein structure of ARPC1B hinders IS assembly . Together with our observations in bulk cytotoxicity assays, we propose that certain CTL functions as well as their adhesion to the target cells are facilitated by Arp2/3‐dependent cell morphology.…”

“…The formation of the IS could also be impaired, for example, as a result of the regulation of intracellular trafficking of organelles toward the immunological synapse. Approaches such as confocal imaging or rescue assays, which particularly enhance the TCR‐driven signaling machinery, can be used to further investigate this aspect …”

Targeted NGS Platforms for Genetic Screening and Gene Discovery in Primary Immunodeficiencies

“…The first 6 diagnoses were obtained in a cohort of 32 patients. Three SCID/CID patients with mutations in RAG1, IL7R and ARPC1B genes [ (40,(45)(46)(47) and Volpi et al, under revision] were diagnosed in 8 T cell defects (37,5%). Moreover, JAGN1 (48), CECR1 (43) and NRAS genes, associated to complex phenotypes, were identified in 12 of the Other PIDs group (25%) (Figure 3C).…”

Cryo-EM of human Arp2/3 complexes provides structural insights into actin nucleation modulation by ARPC5 isoforms

“…Loss-of-function mutations of ARPC1B give rise to multisystem inflammatory and immunodeficiency diseases (Brigida et al, 2018;Kahr et al, 2017;Kuijpers et al, 2017;Randzavola et al, 2019;Somech et al, 2017;Volpi et al, 2019), similar to Wiskott-Aldrich syndrome that is caused by mutations in the Arp2/3 activator WASP (Bosticardo et al, 2009). While some patients carry mutations causing premature protein termination and total loss of ARPC1B protein, four point mutations -W104S, A105V, V208F and A238T -have also been observed in patients (Brigida et al, 2018;Kahr et al, 2017;Volpi et al, 2019) (Figure 2A, right, purple spheres). W104, A105 and V208 are located in the core of the ARPC1B subunit β-propeller fold and this mutation likely destabilizes its tertiary fold, causing severely reduced protein levels in patients (Kahr et al, 2017).…”

“…Recent work has shown that the ARPC1 and ARPC5 isoforms differentially affect the actin nucleating properties of the Arp2/3 complex and the stability of the branched filament networks it generates (Abella et al, 2016). Furthermore, tissue-specific expression patterns of subunit isoforms, together with isoformspecific susceptibility to disease-causing point mutations, point to distinct physiological roles for particular Arp2/3 isoforms including cytotoxic T lymphocyte maintenance and activity (Brigida et al, 2018;Kahr et al, 2017;Kuijpers et al, 2017;Randzavola et al, 2019;Roman et al, 2017;Somech et al, 2017;Volpi et al, 2019).…”