CX3CR1 distinguishes three antigen-experienced CD8 T cell subsets with distinct migratory, functional and homeostatic properties

Abstract

Abstract Following infection, pathogen-specific T cells differentiate into diverse short-lived effectors (TEff) that give rise to long-lived memory (TMem) subsets. These T cell fate decisions and lineage relationships are poorly understood, in part, because available subset-defining markers do not adequately reflect existing heterogeneities. Here, we report that CX3CR1 identifies three distinct CD8+ TEff and TMem subsets. CX3CR1 expression levels on TEff were indicative of TEff differentiation, and predictive of the magnitude and type of memory progeny. Classical central memory (TCM) and effector memory cells (TEM) were CX3CR1– and CX3CR1high, respectively. In addition, we identified a hitherto unrecognized CX3CR1int population. The fraction of CX3CR1int cells among antigen-experienced TMem was remarkably stable over the course of a year, while TEM gradually declined and TCM increased to be the largest subset by 10 months. Interestingly, CX3CR1int TMem had the highest proliferation rate of the three TMem subsets. While TCM and TEM were phenotypically stable over >10 weeks at steady state, CX3CR1int TMem not only self-renewed, but also gave rise to bonafide TCM. This suggests that CX3CR1int TMem may contribute to the gradual increase in TCM. In contrast, re-infection resulted in unidirectional differentiation from TCM to CX3CR1int TMem to TEM. The newly identified CX3CR1int TMem displayed unique migratory properties. Unlike CX3CR1high TEM, CX3CR1int gradually acquired lymph node homing capability. Moreover, parabiosis experiments and analysis of recirculating memory cells in thoracic duct lymph revealed that CX3CR1int TMem, not TEM, are the predominant T cell subset surveying non-lymphoid peripheral tissues.