Clinical and molecular features of immunodeficiency in patients with telomere biology disorders Available to Purchase

• T-cell lymphopenia characterizes immunodeficiency in a broad spectrum of TBDs.

• Immunodeficiency in TBD is associated with an increased risk of clinically significant infections, solid tumors, and lower overall survival.

Immunodeficiency in telomere biology disorders (TBDs) has been described in pediatric patients with severe phenotypes, but is less characterized within the broader TBD spectrum. We collected complete blood counts, lymphocyte subsets, and infection history from 88 consecutive patients with TBD with a median age of 38 years (range, 6-76). Most patients were >18 years old (80/88; 90%) and harbored either a TERT (45%) or TERC germ line mutation (32%). Thirty-two patients (36%) experienced significant infections (opportunistic, recurrent, and/or requiring hospitalization); 47% had lymphopenia, and 3% severe neutropenia. Absolute lymphocyte counts (ALCs) of <0.96 and <1.1 × 10³/μL, but not severe neutropenia, were associated with increased infection risk and lower overall survival, respectively. Decreased CD3⁺ T cells, both CD4⁺ and CD8⁺, were associated with bone marrow failure, increased infection risk, and reduced survival. Low CD3⁺ and CD4⁺ T cells were associated with solid cancers. Telomere length was shortened across the cohort without correlation with ALC or lymphocyte subsets. In a predominantly adult cohort of TBDs, immunodeficiency was marked by T-cell lymphopenia, possibly a consequence of accelerated aging in the hematopoietic compartment. An ALC cutoff of <1.1 × 10³/μL may be a useful biomarker to identify patients with an increased risk of infection, a major cause of death in patients with TBD.