CD8 memory T cells have a bioenergetic advantage that underlies their rapid recall ability

Abstract

A characteristic of memory T (T M ) cells is their ability to mount faster and stronger responses to reinfection than naïve T (T N ) cells do in response to an initial infection. However, the mechanisms that allow this rapid recall are not completely understood. We found that CD8 T M cells have more mitochondrial mass than CD8 T N cells and, that upon activation, the resulting secondary effector T (T E ) cells proliferate more quickly, produce more cytokines, and maintain greater ATP levels than primary effector T cells. We also found that after activation, T M cells increase oxidative phosphorylation and aerobic glycolysis and sustain this increase to a greater extent than T N cells, suggesting that greater mitochondrial mass in T M cells not only promotes oxidative capacity, but also glycolytic capacity. We show that mitochondrial ATP is essential for the rapid induction of glycolysis in response to activation and the initiation of proliferation of both T N and T M cells. We also found that fatty acid oxidation is needed for T M cells to rapidly respond upon restimulation. Finally, we show that dissociation of the glycolysis enzyme hexokinase from mitochondria impairs proliferation and blocks the rapid induction of glycolysis upon T-cell receptor stimulation in T M cells. Our results demonstrate that greater mitochondrial mass endows T M cells with a bioenergetic advantage that underlies their ability to rapidly recall in response to reinfection. In addition, several intrinsic aspects of T M cells have been suggested to contribute to their ability to respond more efficiently, such as increased activity of proximal TCR signaling components, an "open" chromatin conformation of cytokine genes, and altered transcriptional profiles (1, 2, 5-9). However, whether bioenergetic differences contribute to this process is not clear.Resting cells like T N and T M cells interchangeably use glucose, amino acids, and lipids to fuel the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) for ATP production (10-12). However, proliferating cells like activated T cells promote aerobic glycolysis, which supports cell growth, proliferation, and effector functions (13-16). Although T N and T M cells both have a similar metabolism, there are metabolic differences between these cells (17). T M cells from Listeria monocytogenes-infected mice have more mitochondria than T N cells, which is consistent with our finding that T M cells but not T N cells have considerable spare respiratory capacity (SRC) (17). Because SRC is important for cellular survival and function (17)(18)(19) and T M cells are characterized by their ability to respond vigorously to Ag reencounter (20), we investigated whether bioenergetic differences between T M and T N cells contribute to the ability of T M cells to rapidly recall in response to reinfection. We show here that T M cells have more mitochondria and ATP than T N cells and that, upon activation, secondary T E cells proliferate faster, produce cytokines more quickly, and maintain more ATP ...

The Tumor Microenvironment Represses T Cell Mitochondrial Biogenesis to Drive Intratumoral T Cell Metabolic Insufficiency and Dysfunction

“…To confirm the phenotype we were observing was due to loss of mitochondrial mass and not only mitochondrial depolarization, we employed both Mito-Tracker Green FM (another carbocyanine-based dye) and antibodies to the mitochondrial outer membrane protein Voltage Dependent Anion Channel (VDAC), revealing similar losses ( Figure S1B). T cells of various effector and memory phenotypes have been shown to have distinct mitochondrial masses (van der Windt et al, 2013), which we confirmed with our dyes; however, these differences are substantially smaller than those observed within the tumor microenvironment ( Figure S1C). For clarity, throughout this study we primarily gate solely on CD8 + T cells and without further subdivision unless explicitly stated.…”

“…We believe our corollary data employing MitoTracker Green and VDAC antibodies indeed confirm that T cells infiltrating tumors exhibit losses of mitochondrial function and total mass, consistent with repressed PGC1α-mediated mitochondrial biogenesis. Whereas effector T cells have been shown to possess fewer mitochondria than their memory counterparts (van der Windt et al, 2012;van der Windt et al, 2013), it is unclear how chronic stimulation might alter this fate. Our data suggest that the continued, inflammatory activation of T cells in cancer promotes a defect in mitochondrial biogenesis, mediated in part by Akt-controlled inhibition of Foxo-programmed PGC1α transcription.…”

“…The precise contributions of this pathway and its teleology remain the subject of much study, but nevertheless the mitochondria remain an essential component of T cell metabolism. Effector T cells significantly upregulate oxidative activity and memory T cell precursors become increasingly dependent on mitochondria to mediate fatty-acid oxidation over time (van der Windt et al, 2012;van der Windt et al, 2013). Furthermore, the mitochondria remain important organelles for biosynthesis, calcium buffering, and mediating programmed cell death (Rizzuto et al, 2012;Wenner, 2012).…”

Friends Not Foes: CTLA-4 Blockade and mTOR Inhibition Cooperate during CD8+ T Cell Priming To Promote Memory Formation and Metabolic Readiness

“…Metabolic changes regulated by the mTOR pathway have recently been described to be important for memory CD8 + T cell differentiation and function (8,12,25), and our data corroborate a role for fatty acid metabolism in the combination anti-CTLA-4/rapamycin-mediated enhancement of memory CD8 + T cell formation and functional efficacy. In a recent study, CD8 + T cells exhibited increased mitochondrial biogenesis, fatty acid oxidation, and spare respiratory capacity in vitro in the presence of the memory-inducing cytokine IL-15 (17), and these changes have been shown to contribute to the ability of memory CD8 + T cells to rapidly respond to rechallenge (26). Given the differential expression of metabolism genes we encountered in CD8 + T cells primed in the presence of anti-CTLA-4 and rapamycin, we next specifically investigated changes in expression of mitochondrial transcription factor A (TFAM) and mitochondrial transporter carnitine palmitoyltransferase 1 (CPT1a).…”

TLR-Mediated Innate Production of IFN-γ by CD8+ T Cells Is Independent of Glycolysis

“…This can be generated through oxidative phosphorylation (OXPHOS) and/or aerobic glycolysis (41,42). Memory T cells have an increased glycolytic capacity compared with naive T cells (42,43), and the PI3K-Akt and mTORC2 pathway was found to drive the immediate glycolytic switch upon TCR-mediated activation of memory T cells to produce the required energy (43). We therefore questioned whether TLR triggering of Ag-experienced T cells also resulted in an immediate switch toward aerobic glycolysis.…”