Abstract
Naïve CD8(+) T cells are key players of adaptive immunity, but their heterogeneity and age-related changes are not fully understood. This study aimed to compare naïve CD8(+) T cell subsets defined by different combinations of markers, namely, N(CCR7) (CD45RA(+)CCR7(+)), N(CD28) (CD45RA(+)CD28(+)), N(CD27) (CD45RA(+)CD27(+)), and phenotypically most "true-naïve"-like, N(TN) (CD45RA(+)CCR7(+)CD28(+)CD27(+)CD57(-)). Peripheral blood was harvested from donors of various ages and the phenotype of the four subsets of naïve CD8(+) T cells was analyzed. N(CD27) and N(TN) cells showed similar phenotypes with low expression of differentiation markers, pro-inflammatory cytokines, and effector molecules. Furthermore, they exhibited optimal mitochondrial fitness, low senescence markers, reduced apoptosis, and high proliferation potential. Hierarchical clustering identified cluster one including N(CD27) and N(TN), with lower expression of differentiation markers and pro-inflammatory molecules, and cluster 2, including N(CCR7) and N(CD28) cells, in which these parameters were more expressed. Age-related changes were observed in all subsets, although they were less pronounced for the N(CD27) and N(TN) subsets. Taken together, this study demonstrates significant heterogeneity among naïve CD8(+) T cell subsets, with N(TN) cells representing the most bona fide naïve phenotype and N(CD27) showing a partially similar phenotype. These findings significantly enhance our understanding of naïve CD8(+) T cell biology and function.