In recent years, growing understanding of the structural and immune microenvironmental features of hepatocellular carcinoma (HCC) has placed immunotherapy at the forefront of HCC research and treatment. The emergence of immune checkpoint inhibitors (ICIs) and adoptive cell therapy (ACT) has opened new avenues of hope for patients with HCC. ACT, in particular, is a promising approach that involves the infusion of ex vivo activated and expanded autologous or allogeneic immune effector cells, and has shown potential in the treatment of infections, autoimmune disorders, and malignancies.

Cell-based immunotherapy has rapidly evolved as a novel modality for cancer treatment and has yielded encouraging results in clinical settings. In light of the progress of chimeric antigen receptor (CAR) T-cell therapy in solid tumors and the potential of CAR-NK cells, researchers have recently turned their attention toward the development of CAR-engineered macrophages (CAR-M) for solid tumor treatment. The sources of CAR-M cells primarily include peripheral blood mononuclear cells (PBMCs), induced pluripotent stem cells (iPSCs), and monocytic leukemia cell lines such as THP-1. To date, CAR-M therapies have been explored in the context of various cancer types.

The liver, a highly vascularized organ, is rich in innate immune cells, particularly macrophages. These include monocyte-derived macrophages (MDMs) and tissue-resident macrophages (TRMs), both of which play critical roles in phagocytosis and cytotoxic responses to limit intrahepatic tumor spread. Therefore, macrophage-targeted cell therapy holds great promise in HCC treatment. However, several challenges remain. One major limitation is the insufficient number of cells available for therapy. Given the low proliferative capacity of macrophages, the number of cells obtainable from patients is often inadequate, potentially compromising therapeutic efficacy. Another pressing challenge is their limited phagocytic capacity. Enhancing macrophage phagocytosis remains a key hurdle to overcome.

Publication Highlight

On June 5, 2025, Gut published a study led by Dr. Shuang Li from the 302 Clinical Medical College of Peking University (Fifth Medical Center of the PLA General Hospital), with Dr. Yinying Lu as corresponding author. The study employed immunofluorescence staining on patient samples and established various HCC mouse models—including spontaneous, orthotopic, and subcutaneous tumor models. Experiments were conducted using wild-type, Nlrp6 knockout, and macrophage-specific Nlrp6-deficient mice. The research included RNA sequencing, flow cytometry, and immunohistochemistry.

To evaluate phagocytic function, the team assessed the ability of macrophages to engulf particles or tumor cells. Using multi-omics analysis, immunoprecipitation-mass spectrometry, Western blotting, and co-immunoprecipitation assays, the researchers explored the molecular interactions between the PYD domain of NLRP6 and the SMP domain of E-Syt1. Their findings reveal that NLRP6 interacts with E-Syt1 via these domains to suppress macrophage infiltration and phagocytosis, thereby promoting HCC progression. Notably, adoptive transfer of Nlrp6-deficient macrophages emerged as a promising therapeutic strategy capable of significantly inhibiting tumor growth in vivo.

Conclusion

This study elucidates the mechanism by which NLRP6 suppresses macrophage infiltration and phagocytic activity through its interaction with E-Syt1—specifically between the PYD domain of NLRP6 and the SMP domain of E-Syt1—thereby contributing to the progression of hepatocellular carcinoma. From a therapeutic perspective, adoptive transfer of Nlrp6⁻/⁻ macrophages markedly inhibited tumor growth in vivo, offering a new direction for the development of macrophage-targeted immunotherapies for HCC.