Impact of ILT4 on lipid metabolism of tumor-associated macrophages to drive immunosuppression and tumor progression in NSCLC.

Abstract

e20598 Background: Tumor-associated macrophages (TAMs), as the most abundant immune cells in the tumor microenvironment (TME), are main mediators impairing anti-tumor immune response of T cells and restrict immune checkpoint blockade (ICB) efficacy. Suppressing reprogramming and enhancing phagocytosis of TAMs represent promising strategies to potentiate ICB efficacy by harnessing the dual immunoregulatory roles of TAMs. However, the key regulators for TAM reprogramming have not been fully elucidated. Immunoglobulin-like transcript 4 (ILT4) is pivotal for the immunosuppressive activity of myeloid cells. However, its critical role and specific mechanisms in reprogramming TAMs within NSCLC are poorly understood. Methods: Transcriptomic sequencing, multicolor immunofluorescence, and integrated bioinformatics analysis of public databases were used to identify the key regulators for TAMs reprogramming. Kaplan–Meier survival and clinicopathological analysis were performed to assess the clinical significance of ILT4 expression in TAMs. The role of ILT4 in TAM reprogramming and tumor progression were elucidated through in vitro and in vivo experiments. Lipidomics, lipidTOX staining, mitochondrial stress test, transcriptomic sequencing, and rescue experiments were conducted to identify the specific mechanism. Mouse tumor models and therapeutic intervention models were employed to evaluate the potential synergy of combining ILT4 knockout (via adoptive transfer of macrophages from ILT4 (PIR-B) knockout mice) with CD47 and/or PD1 antibody blockade. Results: ILT4 was enriched in TAMs of NSCLC tissues, predicting immunosuppressive TME and unfavorable clinical outcomes. Functionally, ILT4 reprogrammed TAMs towards a pro-tumoral phenotype, therefore suppressing T cell immunity and fueling tumor aggressiveness. Mechanistically, ILT4-activated PI3K/AKT signaling upregulated the expression of CD36 and fatty acid synthase (FASN), two key enzymes mediating fatty acid uptake and synthesis, led to triglyceride (TG) accumulation and energy disorder in TAMs, and sustained their pro-tumoral properties. ILT4 inhibition prevented lipid reprogram of TAMs, and reversed TAM-induced immunosuppression and tumor progression. More importantly, ILT4 (PIR-B) knockout enhanced the efficacy of anti-PD1 and anti-CD47 therapy in vivo, while the triple combination therapy showed the optimal efficacy compared to dual or monotherapy. Conclusions: ILT4 is enriched in TAMs infiltrating NSCLC and plays a key role in driving pro-tumoral polarization of TAMs, a process mediated by the PI3K-AKT-CD36/FASN-TG axis. Furthermore, ILT4 blockade synergistically enhances the efficacy of both CD47 and PD-1 antibodies, with the triple combination showing optimal therapeutic activity. These findings establish a theoretical foundation for developing novel clinical strategies.