Immune cells display an abnormal maturation and a pro-inflammatory profile in telomere biology disorders.

Pathogenic germline variants causing excessive telomere shortening may result in bone marrow failure, hematopoietic malignancy, and extramedullary complications, such as pulmonary fibrosis, liver cirrhosis, and solid tumors. Patients with short telomeres also develop immunodeficiency with low CD4+ T cells and impaired general immunosurveillance, particularly against solid neoplasms. We investigated a broad spectrum of lymphocyte subsets and myeloid immune cells from human patients with telomere biology disorders (TBDs) and matched healthy volunteers to understand further how the immune system is affected by telomere dysfunction. We employed mass cytometry (CyTOF) for deep-immunophenotyping peripheral blood mononuclear cells (PBMCs), followed by high-dimensional data analysis. Cytokines, chemokines, and growth factors were assessed in serum. Our results showed profound immune alterations in TBD beyond those observed in aging, with low naïve lymphocytes and thymic hypofunction. We further observed that T helper subsets were markedly skewed, with an inverted TH2/TH1 ratio and low TH17 and TH17.1 levels. T cell activation and exhaustion markers were upregulated, whereas circulating mucosal-associated invariant T (MAIT) cells were significantly decreased and overactivated. Several serum cytokine levels were positively correlated with telomere length and blood counts, suggesting an association with marrow function. In aggregate, these findings suggest a pro-inflammatory profile in TBDs. Our data provide new details on how TBD affects immune cells, particularly lymphocytes, which may contribute to the clinical phenotypes.