This article examines the molecular regulation of bystander activation in human memory CD8+ T cells that is induced by Interleukin-15 (IL-15). The authors, Lee et al., found that while IL-15 causes these T cells to exhibit NK-like cytotoxicity and elevated expression of markers like NKG2D, concurrent T cell receptor (TCR) signaling suppresses these specific "bystander" features. Mechanistically, this suppression is shown to rely on the Ca²⁺-calcineurin signaling pathway, which activates NFATc1, leading to NFATc1 binding to AP-1 and subsequently limiting the expression of NK-like genes. The study successfully defines an IL-15-specific gene set that characterizes this bystander activation, validating it in memory CD8+ T cells from patients with acute Hepatitis A Virus infection.

References:

• Lee H, Kim S Y, Kim S H, et al. TCR signaling via NFATc1 constrains IL-15-induced bystander activation of human memory CD8+ T cells[J]. Immunity, 2025.