Source: Liang Z, Long X, Wong PP, et al. Tumor cells metabolically resist immune-checkpoint therapy by macrophage efferocytosis-mediated fatty acid recycling. Cancer Cell. 2026;44(6):1235-1254.e11. doi:10.1016/j.ccell.2026.05.005
A research team led by Prof. Zheng Shile and Prof. Chen Lin from the Faculty of Medicine at The Chinese University of Hong Kong has revealed that tumor cells resist immune checkpoint therapy through macrophage-mediated efferocytosis-driven fatty acid recycling.
Key Findings
Tumor cells adapt metabolically to cope with the nutrient-deprived tumor microenvironment (TME), yet the mechanisms underlying metabolic plasticity behind immune checkpoint blockade (ICB) resistance remain poorly understood. This study reveals the following: TREM2+ LAMs (lipid-associated macrophages) recycle fatty acids via efferocytosis to support tumor adaptive responses to ICB. These fatty acid-containing extracellular vesicles fuel acetyl-CoA-dependent H3K36 modifications. Acetylation activates MYC and TGF-β signaling pathways. Genetic or pharmacological inhibition of TREM2 restores therapeutic sensitivity through epigenetic remodeling of the immunosuppressive TME.
Figure 1. TREM2+ LAMs recycle fatty acids via efferocytosis to support tumor immune checkpoint therapy adaptation
Research Highlights
1. ICB-resistant HCC cells depend on fatty acids for energy production in the lipid-rich TME;
2. TREM2+ LAMs deliver fatty acids to tumor cells via efferocytosis-derived extracellular vesicles (EVs);
3. TREM2+ LAMs activate tumor MYC and TGF-β signaling pathways through acetyl-CoA-mediated H3K36ac modifications;
4. TREM2 blockade restores HCC sensitivity to ICB at the metabolic level through epigenetic TME remodeling.
Key Research Points
1. Tumor Cells from ICB-Resistant HCC Patients Exhibit Enhanced Fatty Acid Uptake Activity
Single-cell sequencing of hepatitis B-associated HCC patients treated with pembrolizumab (anti-PD-1) revealed that fatty acid uptake and fatty acid oxidation pathways were significantly enriched in non-responder tumor cells, while the responder group primarily showed cholesterol metabolism. The proportion of TREM2+ LAMs in the TME of non-responders was markedly elevated, and TREM2+ LAM abundance positively correlated with tumor cell fatty acid uptake flux. Since tumor cells from ICB-resistant TME displayed higher FAU (fatty acid uptake) activity, the authors hypothesized that macrophages, as key immune cells, might be involved in this process.
2. Murine ICB-Resistant Liver Cancer Model
PD-1-resistant tumors accumulated large quantities of lipid droplets. Single-cell energy metabolism profiling via translational inhibition mapping confirmed that resistant tumors preferentially utilized fatty acids as their primary energy source, while immune cells consistently relied on glucose. Following myeloid-specific Trem2 knockout, tumor lipid droplet and free fatty acid levels decreased substantially, tumor cell fatty acid dependency was significantly reduced and shifted toward glucose metabolism, and overall protein translation declined. In vitro co-culture tracing experiments demonstrated that only when macrophages efferocytosed apoptotic tumor cells could they transport fatty acids to viable tumor cells via CD63+ EVs; simple viable cell co-culture showed no lipid transfer. The fatty acid synthesis inhibitor TOFA did not reverse this effect, confirming that the lipid supply was of exogenous origin.
3. Molecular Mechanism: The Lipid–Acetyl-CoA–Epigenetic Axis
After TREM2+ LAMs phagocytose apoptotic cells, they secrete large quantities of CD63+ extracellular vesicles enriched in long-chain free fatty acids. Knockout or blockade of Trem2 significantly reduced FFA content in EVs. 13C-palmitic acid isotope tracing revealed that apoptotic cell-derived carbon was transported via macrophages and preferentially incorporated into tumor H3K36 acetylation sites. Both the fatty acid oxidation inhibitor etomoxir and Trem2 deficiency downregulated tumor H3K36ac.
ChIP-seq demonstrated that H3K36ac was enriched at the promoters of MYC, TGFB1, VEGFA, and SOX4, promoting their transcription. Trem2-MKO mice exhibited significantly reduced tumor MYC, TGF-β, and VEGF secretion, relieving the suppression of lymphocyte infiltration.
4. In Vivo Therapeutic Intervention Validation
Myeloid Trem2 knockout combined with anti-PD-1 therapy significantly inhibited resistant tumor growth, whereas Trem2 knockout alone showed only modest anti-tumor effects. In a spontaneous liver cancer model (p53/c-Myc mutations), anti-TREM2 antibody combined with anti-PD-1 simultaneously reduced tumor lipids, acetyl-CoA, and H3K36ac, while enhancing anti-tumor lymphocyte infiltration and IFN-γ responses. Treatment with the efferocytosis inhibitor UNC2250 reduced tumor 13C lipid uptake to levels comparable to those in Trem2 knockout mice, directly demonstrating that efferocytosis is an essential step in lipid transfer.
Conclusions
This study employed stable isotope tracing combined with acetylome profiling to demonstrate that, following TREM2+ LAM-mediated efferocytic transport, apoptotic palmitic acid (13C-labeled)-derived carbon is preferentially incorporated into H3K36 acetylation sites in viable tumor cells. Compared with LysM-Cre control mice, Trem2 myeloid knockout (Trem2-MKO) mice treated with anti-PD-1 showed simultaneous reductions in lipid content, acetyl-CoA levels, and both global and site-specific H3K36 acetylation in liver cancer tissues.
RNA-seq and ChIP-seq joint analysis revealed that H3K36 acetylation activates multiple MYC-driven proliferative pathways. MYC serves as a core oncogene for tumor adaptation to nutrient deprivation; previous studies in triple-negative breast cancer have confirmed that MYC upregulates fatty acid uptake genes and promotes fatty acid oxidation, and high-MYC tumor cells exhibit a greater survival advantage over low-MYC cells. The mechanistic cascade identified in this study: TREM2+ LAMs increase local fatty acid supply through extracellular vesicles, upregulate total fatty acid uptake in tumor cells, and generate acetyl-CoA via fatty acid oxidation to activate MYC, ultimately selecting and enriching metabolically adapted tumor cells with high fatty acid uptake.
Clodronate Liposomes Macrophage Depletion: Methods and Results
C57BL/6 mice were subcutaneously injected with 5×105 RIL-175/PD-1R HCC tumor cells. On day 13 post-modeling, 200 μL Clodronate Liposomes (Yeasen, 40337ES) was administered, while the control group received 200 μL PBS Liposomes (Yeasen, 40338ES) simultaneously. On day 14, 13C-labeled apoptotic tumor cells were injected. On day 15, a second injection of equal-volume Clodronate Liposomes and PBS Liposomes was administered to maintain macrophage depletion. On day 16, 13C-labeled apoptotic tumor cells were injected again. On day 17, mice were euthanized and tumor cells were isolated.
Figure 2. Schematic of the in vivo 13C carbon tracing experiment using PBS liposomes or clodronate liposomes intervention
Results:
As shown below, in the PBS liposome control group, tumor cell δ13C values were significantly higher, indicating that large quantities of 13C-labeled fatty acids from apoptotic cells were transported into tumor cells via macrophage efferocytosis and EV transfer. After clodronate liposome-mediated macrophage depletion, tumor cell δ13C abundance was significantly reduced, demonstrating that macrophage deficiency directly disrupted the apoptotic cell fatty acid recycling and delivery pathway to tumor cells.
Related Product
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Cat. No. |
Product Name |
Size |
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Clodronate Liposomes Kit — Macrophage Depletion Kit (with Control Liposomes) |
2 mL+2 mL / 5 mL+5 mL / 10 mL+10 mL |