STC1 encapsulated in small extracellular vesicles from laryngeal squamous cell carcinoma cells induces CD8+ T cell dysfunction by reprogramming tumor-associated macrophages into M2-like macrophages

Background: Tumor-derived small extracellular vesicles (sEVs) play an essential role in reprogramming the tumor microenvironment. Metabolic reprogramming is an essential prerequisite for M2 polarization of tumor-associated macrophages (TAMs). This M2 phenotype is closely related to the immune dysfunction of CD8⁺ T cells and subsequent tumor progression. This study evaluates the role of laryngeal squamous cell carcinoma cell-derived small extracellular vesicles (LSCC-sEVs) in M2 polarization of TAMs and CD8⁺ T cell dysfunction, and delineates the underlying mechanisms.

Methods: Human leukemia monocyte cell line (THP-1) was induced to differentiate into M0 macrophages using phorbol 12-myristate 13-acetate. M0 macrophages were incubated with sEVs derived from LSCC cells TU212. CD8⁺T cells, extracted from peripheral blood mononuclear cells of healthy volunteer donors, were co-cultured with the LSCC-sEV-treated M0 macrophages to evaluate their proliferation, and immune function. The role of LSCC-sEVs was investigated in macrophage tumor-bearing mouse models.

Results: LSCC-sEVs promoted TAM M2 polarization and impaired CD8⁺ T cell function, attributing to PD-L1 expression upregulation. In addition, suppression of metabolic reprogramming could partially reverse LSCC-sEV-induced CD8⁺ T cell dysfunction. STC-1 was found highly enriched in LSCC-sEVs. Knockdown of STC1 abrogated metabolic reprogramming of TAMs into M2-like macrophages and restored CD8⁺ T cell function. Importantly, in vivo results showed that LSCC-sEVs transform TAMs into M2 phenotype by mediating metabolic reprogramming and induce CD8⁺ T cell dysfunction, ultimately accelerating tumor growth.

Conclusion: Our data reveal a previously undescribed role for LSCC-sEVs in the regulation of M2 polarization of TAMs and immune cell function through STC1 mediated metabolic reprogramming.

CD8+ T cell dysfunction; Laryngeal squamous cell carcinoma; M2 polarization; Metabolic reprogramming; STC1; Small extracellular vesicles; Tumor-associated macrophages.