Human ASXL1 Deficiency Causes Epigenetic Dysfunction, Combined Immunodeficiency and EBV–Associated Hodgkin Lymphoma

Abstract

ABSTRACTInborn errors of immunity (IEI) are a group of disorders caused by deleterious variants in immune-related genes, including some that function as epigenetic regulators. Additional sex combs-like 1 (ASXL1) is an epigenetic modifier that has not previously been linked to an IEI. SomaticASXL1variants are found in clonal hematopoiesis and hematologic neoplasms, while heterozygous germline variants cause Bohring–Opitz syndrome. We present a new IEI caused by biallelic germline variants inASXL1. The patient had a complex and unusual history of disease progression notable for persistent cutaneous vaccine-strain rubella granulomas initially manifesting in early childhood, chronic macrocytosis and mild bone marrow cellular hypoplasia, and Epstein Barr virus– associated Hodgkin lymphoma in adolescence. Detailed immunophenotyping revealed progressive loss of B-cells, hypogammaglobinemia, and T-cell lymphopenia with severe skewing toward a memory phenotype and elevated expression of T-cell exhaustion and senescence markers. Molecular investigations confirmed ASXL1 protein deficiency in the patient’s T-cells and fibroblasts. The T-cells exhibited marked loss of DNA methylation, increased epigenetic aging, and CD8 T-cell dysfunction. These aberrations were ameliorated by lentivirus-mediated transduction with wild-typeASXL1, confirming the pathogenicity ofASXL1variants. This study defines a novel human IEI caused by ASXL1 deficiency, a diagnosis that should be considered in individuals with chronic viral infections, virus-associated hematologic malignancies, and combined immunodeficiency. Furthermore, our findings provide fresh insights into the mechanisms underlying the roles of human ASXL1 in T-cell function as well as in the development and maintenance of lymphomas.