Tumor-associated macrophages (TAMs) arise from monocytes and represent major contributors to the immunosuppressive microenvironment of solid tumors. However, the environmental cues that govern TAM differentiation and immunosuppressive activity remain incompletely understood. Here we demonstrate that hepatocellular carcinoma (HCC) cells secrete extracellular vesicles (EVs) that are preferentially taken up by monocytes, inducing their differentiation to TAMs characterized by a distinct immune-inhibitory signature. Mechanistically, HCC-derived EVs encapsulate the lipogenic enzyme ATP-citrate lyase (ACLY), promote palmitate biosynthesis in targeted monocytes, thereby enhancing the S-palmitoylation and stability of multiple immune checkpoint proteins. To validate this, we synthesized liposomal vesicles (LVs) decorated with an EV-marker protein CD81, which mimicked the targeting specificity of endogenous EVs for monocytes and differentiated macrophages. When loaded with ACLY proteins as interior cargo, these LVs were sufficient to induce immunosuppressive TAMs and promote HCC progression. Conversely, CD81-decorated LVs encapsulating the ACLY inhibitor SB204990 markedly reduced the TAM-mediated immunosuppressive activity, leading to restrained HCC progression. Importantly, we further demonstrated that targeting EV-transferred, TAM-specific ACLY represents a promising strategy to enhance immunotherapeutic efficacy without notable side effects, particularly when combined with anti-PD-1/PD-L1 antibodies for HCC treatment.
Liu et al. (Fri,) studied this question.
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