Single-cell metabolic analysis by mass cytometry reveals distinct transitional states of CD8 T cell differentiation

Memory T cells conventionally rely on oxidative phosphorylation and short-lived effector T cells on glycolysis. Here, we investigate how T cells arrive at these states during an immune response. In order to understand the metabolic state of rare, early activated T cells, we adapted mass cytometry to quantify metabolic regulators at single-cell resolution in parallel with cell signaling, proliferation, and effector function. We interrogated CD8 T cell activation in vitro as well as the trajectory of CD8 T cells responding to Listeria monocytogenes infection, a well-characterized in vivo model for studies of T cell differentiation. This approach revealed a unique metabolic state in early activated T cells characterized by maximal expression of glycolytic and oxidative metabolic proteins. Peak utilization of both pathways was confirmed by extracellular flux analysis. Cells in this transient state were most abundant five days post-infection before rapidly downregulating metabolic protein expression. This approach should be useful for mechanistic investigations of metabolic regulation of immune responses.