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 telomere biology disorders.

• Immunodeficiency in TBD is associated with 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 less characterized within the broader TBD spectrum. We collected complete blood counts, lymphocyte subsets, and infection history from 88 consecutive TBD patients with a median age of 37 years (range 6-76). Most patients were >18 years old (80/88; 90%) and harbored either a TERT (45%) or TERC (32%) germline mutation. Thirty-two patients (36%) experienced significant infections (opportunistic, recurrent, and/or requiring hospitalization); 47% had lymphopenia, and 3% severe neutropenia. Absolute lymphocyte counts (ALC) <0.96 and <1.1 x103/µL, but not severe neutropenia, associated with increased infection risk and lower overall survival, respectively. Decreased CD3+ T-cells, both CD4+ and CD8+, associated with BMF, increased infection risk, and reduced survival. Low CD3+ and CD4+ 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 lymphopenia, possibly a consequence of accelerated aging in the hematopoietic compartment. An ALC cut-off of <1.1 x103/µL may be a useful biomarker to identify patients with an increased risk of infection, a major cause of death of TBD patients.