Rewiring mitochondrial metabolism to counteract exhaustion of CAR-T cells

Abstract

Short persistence and early exhaustion of T cells are major limits to the efficacy and broad application of immunotherapy. Exhausted T and chimeric antigen receptor (CAR)-T cells upregulate expression of genes associated with terminated T cell differentiation, aerobic glycolysis and apoptosis. Among cell exhaustion characteristics, impaired mitochondrial function and dynamics are considered hallmarks. Here, we review the mitochondrial characteristics of exhausted T cells and particularly discuss different aspects of mitochondrial metabolism and plasticity. Furthermore, we propose a novel strategy of rewiring mitochondrial metabolism to emancipate T cells from exhaustion and of targeting mitochondrial plasticity to boost CAR-T cell therapy efficacy.

Keywords: CAR-T cell exhaustion; Metabolism; Mitochondria; Single-cell techniques.

Fig. 1

Features of T cell exhaustion and mitochondrial alterations. During persistent antigen stimulation and under hypoxia during chronic virus infection or cancer, CD8⁺ T cells enter a state of exhaustion. Tonic signaling in CAR-T cells is induced by autologous physical interactions between CAR receptors. Exhausted T cells and CAR-T cells exhibit decreased cytokine production and reduced proliferation capability; persistently high expression of multiple inhibitory receptors, such as PD-1, TIM-3, LAG-3 and CTLA4; and altered transcriptional landscapes, such as changes in changes in NR4A, TOX, TCF1 and NFAT transcription. Mitochondrial reprogramming characteristics in T cells include both functional and structural alterations. Mitochondria in exhausted cells are swollen and undergo increased fission. The mitochondrial cristae are slightly wider and more loosely organized in intermembrane regions. Functional alterations are characterized by an increased ADP/ATP ratio, decreased ATP generation and mitochondrial biogenesis, and decelerated fatty acid oxidation (FAO) and oxidative phosphorylation (OXPHOS)

Fig. 2

Cell signaling associated with mitochondrial metabolism and strategies to counteract CAR-T cell exhaustion. A variety of signaling pathways, such as the mTOR, AMPK, and MAPK signaling pathways, and inhibiting pathways, such as the PD-1 signaling pathway, are involved in T cell activation and mitochondrial metabolism. When activated, metabolic switching mediated by the PI3K–PKB (AKT)–mTOR pathway supports the differentiation of effector T cells (T_E) cells. The AMPK pathway drives long-chain fatty acid oxidation (FAO) and mitochondrial biogenesis through phosphorylation of ACC2 and PGC-1α activity. PGC-1α activates NRF1/2, which activate Tfam. Tfam drives the transcription and replication of mitochondrial DNA (mtDNA). In addition, 4-1BB signaling upregulates PGC-1α expression through stimulation of the p38-MAPK pathway, resulting in mitochondrial fusion and biogenesis. Increased PD-1 inhibitory receptor expression induces Blimp-1 expression, a critical exhaustion-related transcription factor, to exacerbate NFAT activity. NFAT activates the transcription factor TOX, which is associated with cell exhaustion and suppresses the expression of transcription factor Tcf7, which is related to oxidative phosphorylation (OXPHOS)

Fig. 3

Metabolic analysis of T and CAR-T cells based on single-cell techniques