Inhibition of Acetyl-CoA Carboxylase Enhances Antitumor Immunity of Tumor-Infiltrating CD8+ T Cells

Background and Objective

In recent years, the impact of metabolic changes in the Tumor Microenvironment (TME) on the function of Tumor-Infiltrating Lymphocytes (TILs) has become a hot topic in immunological research. Although T cells possess strong antitumor capabilities, their functions are often impaired in the TME, limiting their ability to inhibit cancer. One of the main reasons for this functional loss is the scarcity of nutritional resources in the TME, leading to competition between tumor cells and immune cells for nutrients, especially glucose. This study aims to investigate how Acetyl-CoA Carboxylase (ACC) regulates lipid utilization in CD8+ TILs in the TME, thereby exploring whether limiting ACC can improve the antitumor immunity of CD8+ T cells by enhancing Fatty Acid Oxidation (FAO).

Source

This research paper was authored by Elizabeth G. Hunt, Katie E. Hurst, Brian P. Riesenberg, and others, published on May 7, 2024, in “Cell Metabolism,” Volume 36, Pages 969 to 983. The authors are primarily from the Lineberger Comprehensive Cancer Center and the Department of Cell Biology and Physiology at the University of North Carolina at Chapel Hill.

Research Process

The study was conducted through multiple steps to comprehensively understand the impact of ACC on lipid metabolism in CD8+ T cells. Here is a detailed procedure of the entire research:

Step 1: Impact of TME on Lipid Metabolism of CD8+ TILs

The study first utilized RNA sequencing (RNA-seq) to detect CD8+ TILs in the MCA-205 fibrosarcoma mouse model and found that these T cells are significantly enriched with genes related to aberrant lipid cycling. Subsequently, through Ultra-Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS) lipidomics analysis, it was confirmed that the lipid content in CD8+ TILs significantly increases compared to splenic CD8+ T cells. Specifically, neutral lipids such as triglycerides (TAG) and diacylglycerides (DAG) were enriched in tumor-infiltrating CD8+ T cells and significant accumulation of lipid droplets (LDs) in these cells was observed through confocal microscopy.

Step 2: Role of ACC in CD8+ T Cells

The study further explored the specific role of ACC in CD8+ T cells and found that the expression of ACC1 is significantly upregulated in CD8+ TILs. Through whole-genome differential expression analysis and proteomics screening, it was found that ACC1 is induced in both murine and human CD8+ TILs, accompanied by steatosis. Using CRISPR-Cas9 technology to delete the ACC1 gene, it was discovered that ACC directly promotes the storage of triglycerides in cytoplasmic LDs.

Step 3: Effects of Limiting ACC on Lipid Metabolism and Physiological Function of T Cells

Through metabolomics research, it was found that limiting ACC activity reprograms the metabolism of CD8+ T cells, prompting these cells to use FAO more for energy production. Mitochondrial stress testing confirmed that limiting ACC activity significantly enhances the oxidative metabolic capacity of T cells, as evidenced by increased levels of oxidative intermediates in the tricarboxylic acid (TCA) cycle such as acetyl-CoA and fumarate. Moreover, using lipid labeling experiments observed that, under restricted ACC activity, free fatty acids (FFA) are more directed towards mitochondria rather than stored as LDs.

Step 4: Impact of ACC on Antitumor Function of T Cells

In in vivo experiments, OT-1 CD8+ T cells treated with limited ACC activity were infused into B16F1-OVA metastatic tumor mouse models. The study found these treated T cells exhibited stronger tumor control ability and endurance. Flow cytometry and fluorescence confocal microscopy analyses confirmed that these cells displayed phenotypic markers associated with stem cell characteristics, such as CD62L, TCF-1, and Bcl-2. Additionally, these T cells showed enhanced multifunctionality and reduced exhaustion markers.

Step 5: Impact of ACC Inhibitors on Human CD8+ T Cells

The study also explored the application potential of ACC inhibitors in human CD8+ T cells, finding that ACC inhibitor treatment significantly increased the proportion of central memory T cells (T_CM) and decreased the proportion of effector memory T cells (T_EM) in human CD8+ T cells. This result suggests that ACC inhibitors could be a strategy to modulate human T cell metabolism and function, thereby improving the efficacy of immunotherapy.

Research Findings

a) Across various tumor models, including MCA-205 fibrosarcoma, MC-38 colon adenocarcinoma, and B16 melanoma, it was found that tumor-infiltrating CD8+ T cells typically accumulate neutral lipids. These accumulated lipids are primarily represented by triglycerides and diacylglycerides and are stored in cytoplasmic lipid droplets. b) In vitro experiments indicated that under hypoxia and nutrient deprivation conditions, lipid droplet accumulation in CD8+ T cells significantly increases, accompanied by the loss of cell function. c) Through genetic editing and chemical inhibition methods, it was demonstrated that ACC1 regulates lipid synthesis and storage in CD8+ T cells, and restricting ACC activity significantly enhances fatty acid oxidative metabolism, improving energy synthesis capacity under nutritional stress. d) In in vivo experiments, CD8+ T cells treated with limited ACC activity better controlled tumor growth and exhibited greater resilience and multifunctionality.

Conclusion and Significance

The study indicates that in the tumor microenvironment, acetyl-CoA carboxylase (ACC) in CD8+ T cells inhibits fatty acid oxidative metabolism by promoting lipid synthesis and storage, thereby weakening their antitumor function. Limiting ACC activity can significantly improve the metabolism and function of CD8+ T cells, allowing them to maintain robust antitumor immune responses for a longer time in the tumor microenvironment. This discovery provides new strategies and theoretical support for future immunotherapy, particularly cell therapy based on CD8+ T cells.

Highlights

1. Discovery of the profound impact of metabolic conditions in the tumor microenvironment on the lipid metabolism of CD8+ T cells.
2. Confirmation that ACC inhibits FAO in CD8+ T cells through lipid synthesis and storage, thereby limiting T cell antitumor capability.
3. Proposal of a new strategy to reprogram T cell metabolism by limiting ACC activity to enhance their survival and function in the tumor microenvironment.
4. Research findings are validated not only in mouse models but also show potential for application in regulating human CD8+ T cells.

Additional Valuable Information

This research utilizes various complex experimental techniques, including UPLC-MS lipidomics analysis, RNA-seq, CRISPR-Cas9 gene editing, flow cytometry, and confocal microscopy, to comprehensively analyze the crucial role of ACC in lipid metabolism of tumor-infiltrating CD8+ T cells. The study also investigates the application of ACC inhibitors in human immune cells, which lays the foundation for more targeted tumor immunotherapy in the future.

This research provides significant theoretical and experimental basis for enhancing CD8+ T cell antitumor immune functions through metabolic regulation strategies. Future studies will further explore the potential and effects of these metabolic regulation strategies in clinical tumor immunotherapy.