The cellular microenvironment regulates CX3CR1 expression on CD8⁺ T cells and the maintenance of CX3CR1⁺ CD8⁺ T cells

Abstract

Expression levels of the chemokine receptor CX3CR1 serve as high‐resolution marker delineating functionally distinct antigen‐experienced T‐cell states. The factors that influence CX3CR1 expression in T cells are, however, incompletely understood. Here, we show that in vitro priming of naïve CD8+ T cells failed to robustly induce CX3CR1, which highlights the shortcomings of in vitro priming settings in recapitulating in vivo T‐cell differentiation. Nevertheless, in vivo generated memory CD8+ T cells maintained CX3CR1 expression during culture. This allowed us to investigate whether T‐cell receptor ligation, cell death, and CX3CL1 binding influence CX3CR1 expression. T‐cell receptor stimulation led to downregulation of CX3CR1. Without stimulation, CX3CR1+ CD8+ T cells had a selective survival disadvantage, which was enhanced by factors released from necrotic but not apoptotic cells. Exposure to CX3CL1 did not rescue their survival and resulted in a dose‐dependent loss of CX3CR1 surface expression. At physiological concentrations of CX3CL1, CX3CR1 surface expression was only minimally reduced, which did not hamper the interpretability of T‐cell differentiation states delineated by CX3CR1. Our data further support the broad utility of CX3CR1 surface levels as T‐cell differentiation marker and identify factors that influence CX3CR1 expression and the maintenance of CX3CR1 expressing CD8+ T cells.