Understanding immunoactinopathies: A decade of research on WAS gene defects

L-plastin associated syndrome of immune deficiency and hematologic cytopenia

BACKGROUND

LCP1 encodes L-plastin, an actin-bundling protein primarily expressed in hematopoietic cells. In mouse and fish models, LCP1 deficiency has been shown to result in hematologic and immune defects.

OBJECTIVE

This study aimed to determine the nature of a human inborn error of immunity resulting from a novel genetic variant of LCP1.

METHODS

We performed genetic, protein, and cellular analysis of PBMCs from a kindred with apparent autosomal dominant immune deficiency. We identified a candidate causal mutation in LCP1, which we evaluated by engineering the orthologous mutation in mice and Jurkat cells.

RESULTS

A splice-site variant in LCP1 segregated with lymphopenia, neutropenia, and thrombocytopenia. The splicing defect resulted in at least 2 aberrant transcripts, producing an in-frame deletion of 24 nucleotides, and a frameshift deletion of exon 8. Cellular analysis of the kindred revealed a proportionate reduction of T and B cells and a mild expansion of transitional B cells. Similarly, mice carrying the orthologous genetic variant exhibited the same in-frame aberrant transcript, reduced expression Lcp1 and gene dose-dependent leukopenia, mild thrombocytopenia, and lymphopenia, with a significant reduction of T-cell populations. Functional analysis revealed that LCP1c740-1G>A confers a defect in platelet development and function with aberrant spreading on collagen. Immunologic analysis revealed defective actin organization in T cells, reduced migration of PBMCs from patients, splenocytes from mutant mice, and a mutant Jurkat cell line in response to CXCL12; impaired germinal center B-cell expansion after immunization; and reduced cytokinesis during T cell proliferation.

CONCLUSIONS

We describe a unique human hematopoietic defect affecting neutrophils, lymphocytes, and platelets arising from partial LCP1 deficiency.

Controlled WASp activity regulates the proliferative response for Treg cell differentiation in the thymus

The Wiskott-Aldrich syndrome protein (WASp) regulates actin cytoskeletal dynamics and function of hematopoietic cells. Mutations in the WAS gene lead to two different syndromes; Wiskott-Aldrich syndrome (WAS) caused by loss-of-function mutations, and X-linked neutropenia (XLN) caused by gain-of-function mutations. We previously showed that WASp-deficient mice have a decreased number of regulatory T (Treg) cells in the thymus and the periphery. We here evaluated the impact of WASp mutations on Treg cells in the thymus of WAS and XLN mouse models. Using in vitro Treg differentiation assays, WAS CD4 single-positive thymocytes have decreased differentiation to Treg cells, despite normal early signaling upon IL-2 and TGF-β stimulation. They failed to proliferate and express CD25 at high levels, leading to poor survival and a lower number of Foxp3+ Treg cells. Conversely, XLN CD4 single-positive thymocytes efficiently differentiate into Foxp3+ Treg cells following a high proliferative response to IL-2 and TGF-β, associated with high CD25 expression when compared with WT cells. Altogether, these results show that specific mutations of WASp affect Treg cell development differently, demonstrating a critical role of WASp activity in supporting Treg cell development and expansion.

Wiskott-Aldrich syndrome: A new synonym mutation in the WAS gene

Wiskott-Aldrich syndrome (WAS) is a rare X-linked recessive primary immunodeficiency disorder. Mutations in the WAS gene are considered to be the primary cause of WAS. In this work, we report a boy who presented with intracranial hemorrhage (ICH) as an initial symptom and detects a novel pathogenic synonymous mutation in his WAS gene. His mother was a carrier of the mutant gene. The mutation, located at position c.273 (c.273 G>A) in exon 2, is a synonym mutation and predicted to affect protein expression by disrupting gene splicing. This study summarizes the diagnosis and treatment process of the patient and expands the genetic spectrum of WAS.

Severe eczema in Wiskott-Aldrich syndrome-related disorder successfully treated with dupilumab

Treatment of severe eczema in patients with primary immunodeficiencies can be particularly challenging as there are no guidelines with regards to these conditions. Dupilumab is an interleukin (IL)-4Rα antagonist that inhibits both IL-4 and IL-13 and is approved for the treatment of atopic dermatitis in pediatric patients. In this report, we describe a patient with a case of severe eczema in the context of Wiskott-Aldrich syndrome-related disorder, who was successfully treated with dupilumab.

Recent advances in hematopoietic gene therapy for genetic disorders

Hematopoietic gene therapy is based on the transplantation of gene-modified autologous hematopoietic stem cells and since the inception of this approach, many technological and medical improvements have been achieved. This review focuses on the clinical studies that have used hematopoietic gene therapy to successfully treat several rare and severe genetic disorders of the blood or immune system as well as some non-hematological diseases. Today, in some cases hematopoietic gene therapy has progressed to the point of being equal to, or better than, allogeneic bone marrow transplant. In others, further improvements are needed to obtain more consistent efficacy or to reduce the risks posed by vectors or protocols. Several hematopoietic gene therapy products showing both long-term efficacy and safety have reached the market, but economic considerations challenge the possibility of patient access to novel disease-modifying therapies. © 2023 Published by Elsevier Masson SAS on behalf of French Society of Pediatrics.