Memory CD8⁺T-cell heterogeneity associated with TCF1 expression. (A) Characterization of T-cell subsets in peripheral blood of healthy and chronically infected humans. CD4⁺/CD8⁺ T-cell ratios in donor subjects (top left). Identification of CD8⁺ T-cell subsets in peripheral blood: naive (CCR7⁺CD45RA⁺), TCM (CCR7⁺CD45RA⁻), TEM (CCR7⁻CD45RA⁻), and TEMRA (CCR7⁻CD45RA⁺) (bottom left). Distribution of naive and memory CD8⁺ T-cell subsets (top right). Subset frequencies were not significantly associated with infection status (2-way analysis of variance [ANOVA]). Steady-state expression (mean fluorescence intensity [MFI]) of TCF1 by CD8⁺ T cell subsets (bottom right). (B) Hierarchical expression of TCF1. Identification of TCF1-hi, TCF1-int, and TCF1-lo subsets within the bulk CD8⁺ T-cell compartment (left). Distribution of TCF1-subsets within traditional naive, TCM, TEM, and TEMRA populations (right). (C) Expression of transcription factors Eomes, LEF1, and T-bet by TCF1-hi, TCF1-int, and TCF1-lo populations in healthy donors. *P < .05. **P < .01. ***P < .001. Repeated measures 1-way ANOVA with Sidak correction. (D) Reciprocal expression of TCF1 and CD57 across CD8⁺ T-cell populations in healthy donors. Gate denotes frequency of the TCF1-lo CD57⁺ population. Results are representative of 5 independent donors. (E) Quiescent phenotype of TCF1-hi cells. Expression of CD127 (IL7-R), CD27 (costimulatory receptor), and CD57 (senescence marker) by TCF1 subsets in healthy donors. *P < .05; ***P < .001; n.s., not significant (repeated-measures 1-way ANOVA with Sidak correction). HCV, hepatitis C virus.