Patients with TBD present a lymphocytic phenotype compatible with premature aging. T and B lymphocytes were studied regarding their functional status based on surface markers, and a skewed pattern was revealed in patients with telomeropathies. After identifying these subsets by Flow-SOM, mean frequencies were compared between groups, and revealed lower levels of CD4⁺ and B cells, decreased naïve lymphocytes, and accumulation of effector cells. (A-B) Box plots representing the percentages of CD4⁺ and CD8⁺ T cells in total CD3⁺, respectively. (C) CD4/CD8 ratio is calculated from absolute cell counts, with the expected value being ≥1.0. (D) Percentage of CD19⁺ cells in CD3^–. (E) viSNE maps for healthy controls and patients with TBD showing the naïve subsets of CD4⁺ and CD8⁺ cells. (F-H) Frequencies of naïve CD4⁺ and CD8⁺ T and B cells, respectively. (I) Percentages of CD8⁺ T effector memory/terminally differentiated effector memory CD27^loCD28⁺ cells. (J-K) Frequencies of nonclass switched memory B cells and viSNE maps highlight this population in healthy controls and patients with TBD. ∗P ≤ .05; ∗∗P ≤ .01. TBD, telomere biology disorders; TEM, T effector memory; TEMRA, T effector memory CD45RA⁺; tSNE1, t-distributed stochastic neighbor embedding.