PD-L1 in Tumor-Derived Extracellular Vesicles Promotes T Cell Senescence through Lipid Metabolism Reprogramming

Academic Background

In recent years, immunotherapy has shown great promise in cancer treatment, particularly in checkpoint blockade therapies targeting PD-1/PD-L1 (programmed cell death protein 1 and its ligand) and CTLA-4 (cytotoxic T-lymphocyte-associated protein 4). However, despite the significant success of these therapies in certain cancer types, the overall success rate of cancer immunotherapy remains limited. Many patients do not respond to immunotherapy or experience only transient responses, suggesting the presence of complex immunosuppressive mechanisms within the tumor microenvironment (TME) that lead to T cell dysfunction.

Tumor-derived extracellular vesicles (TEVs) are small vesicles secreted by tumor cells that carry various bioactive molecules such as proteins, lipids, RNA, and DNA. These molecules mediate intercellular communication within the TME. TEVs have been shown to play a significant role in tumor progression and immune suppression. However, how TEVs specifically affect T cell function, particularly whether they induce T cell senescence through metabolic reprogramming, remains an unresolved question.

This study aims to elucidate how PD-L1 in TEVs induces T cell senescence and to explore the molecular mechanisms underlying this process. This research not only deepens the understanding of immunosuppressive mechanisms in the TME but also provides new insights into overcoming immunotherapy resistance.

Source of the Paper

This paper was authored by Feiya Ma, Xia Liu, Yuanqin Zhang, Yan Tao, Lei Zhao, Hazar Abusalamah, Cody Huffman, R. Alex Harbison, Sidharth V. Puram, Yuqi Wang, and Guangyong Peng, affiliated with multiple institutions including the Saint Louis University School of Medicine and the Washington University School of Medicine. The paper was published on February 12, 2025, in the journal Science Translational Medicine, titled “Tumor extracellular vesicle–derived PD-L1 promotes T cell senescence through lipid metabolism reprogramming.”

Research Process and Results

1. TEVs Induce T Cell Senescence

The study first extracted TEVs from various human tumor cell lines (e.g., melanoma A375, lung cancer A549, and breast cancer MCF7) and co-cultured them with T cells. The results showed that TEVs significantly suppressed T cell proliferation and induced T cell senescence, as evidenced by increased expression of senescence-associated β-galactosidase (SA-β-gal). Additionally, TEVs downregulated CD28 expression on the T cell surface and upregulated cell cycle regulators p16, p21, and p53.

2. The Role of PD-L1 in TEV-Induced T Cell Senescence

Through proteomic analysis, the study identified 321 core proteins in TEVs, 34 of which were associated with PD-L1 signaling. Further experiments confirmed that PD-L1 is a key molecule in TEV-induced T cell senescence. Knockout of the PD-L1 gene in tumor cells using CRISPR-Cas9 or blockade of PD-L1 function with a neutralizing antibody significantly reduced TEV-induced T cell senescence. Moreover, recombinant PD-L1 protein was found to directly induce T cell senescence, a process independent of T cell exhaustion markers such as PD-1, TIM3, and CTLA-4.

3. TEVs Induce T Cell Senescence through DNA Damage and CREB Signaling

The study further explored the molecular mechanisms by which TEVs induce T cell senescence. The results showed that TEVs activate the ATM (ataxia-telangiectasia mutated) signaling pathway, leading to a DNA damage response. Additionally, TEVs promote lipid metabolism reprogramming by activating the CREB (cAMP response element-binding protein) signaling pathway. The experiments also revealed that CREB signaling activation is a critical step in TEV-induced T cell senescence.

4. TEVs Promote T Cell Senescence through Lipid Metabolism Reprogramming

The study found that TEVs significantly upregulate the expression of genes related to cholesterol synthesis and phospholipid metabolism in T cells, and promote the accumulation of cholesterol and lipid droplets (LD). The use of cholesterol synthesis inhibitors such as simvastatin or LD formation inhibitors like avasimibe effectively prevented TEV-induced T cell senescence.

5. In Vivo Validation of TEV-Induced T Cell Senescence

In mouse models, the study confirmed that TEVs can induce T cell senescence in vivo and promote lipid accumulation. Inhibition of TEV generation using GW4869, or treatments with anti-PD-L1 antibodies, CREB inhibitor 666-15, and simvastatin significantly reduced T cell senescence and enhanced anti-tumor immune responses.

Conclusions and Significance

This study reveals that PD-L1 in tumor-derived extracellular vesicles induces T cell senescence and suppresses its function by activating DNA damage, CREB signaling, and lipid metabolism reprogramming. This research not only uncovers a novel immunosuppressive mechanism in the TME but also provides new therapeutic strategies to overcome immunotherapy resistance. By inhibiting TEV generation, blocking PD-L1 function, or modulating lipid metabolism, T cell senescence can be effectively reversed, enhancing the efficacy of tumor immunotherapy.

Highlights and Innovations

1. First to reveal the role of PD-L1 in TEVs in T cell senescence, providing new insights into the immunosuppressive mechanisms in the TME.
2. Uncovers the critical role of lipid metabolism reprogramming in T cell senescence, offering a theoretical foundation for developing cancer therapies targeting T cell metabolism.
3. Validates the therapeutic potential of modulating T cell senescence in preclinical mouse models, supporting the optimization of immunotherapy.

Additional Valuable Information

This study also developed several novel experimental methods, such as the use of CRISPR-Cas9 to knockout the PD-L1 gene and the application of GW4869 to inhibit TEV generation. These methods provide important technical tools for further research into immunosuppressive mechanisms in the TME.

This research holds significant value in the field of basic science and offers new perspectives and strategies for clinical cancer treatment, with broad application prospects.