Abstract 1372: Macrophages impair antigen specific CD8+ T cell response against HCC in NAFLD mice
Authors: McVey John C. , Green Benjamin L. , Ruf Benjamin , Greten Tim F. , Ma Chi 
Published: June 2022

Abstract
Background: Liver cancer is a leading cause of cancer-related deaths. Non-alcoholic fatty liver disease (NAFLD) has become a burgeoning etiology of liver cancer. Emerging data shows that NAFLD alters adaptive T cell immunity and has a profound influence on both liver cancer development and efficacy of immunotherapy. Tumor antigen-specific T cells recognize tumor and are crucial for controlling malignancy. However, their populations are often low, and detection requires special tools. This study utilized a novel mouse model of HCC to investigate how the tumor antigen-specific T cell response is affected in NAFLD.
Methods: We generated a doxycycline-inducible MHC-I OVA257-264 and MHC-II OVA323-339 antigen-expressing HCC cell line which allowed us to investigate tumor antigen-specific T cell responses. The cell line was seeded orthotopically into the livers of diet-induced (methionine choline-deficient [MCD]) and genetic (Ob/Ob [Ob]) NAFLD mouse models. OVA257-264 specific CD8+ T cells were detected by flow cytometry using H-2Kb/OVA257-264 tetramer. Pharmacological depletion experiments were used to identify additional effector cells.
Results: The creation of an inducible MHC-I and -II OVA antigen-expressing HCC cell line was validated in both in-vitro and in-vivo settings. Tumor expression of highly immunogenic OVA antigens caused a strong tumor suppression which was mostly mediated by CD8+ T cells in mice fed with normal diet. The inverse correlation between percentage of OVA257-264 specific CD8+ T cells with tumor size further supported their critical role in tumor control. In contrast, in NAFLD mice fed MCD diet as well as Ob/Ob mice, tumor OVA antigens induction failed to reduce liver tumor growth. The presence of OVA257-264 specific CD8+ T cells in NAFLD mice suggested that NAFLD did not inhibit the generation of tumor antigen-specific T cells. This was supported by the finding that OVA257-264 specific CD8+ T cells from NAFLD mice had similar cytotoxic potential, activation, degranulation, PD-1 expression, and effector memory phenotype compared to controls, suggesting an indirect mechanism for the impaired anti-tumor immunity. Immunoprofiling revealed a drastic increase of macrophages in tumor-bearing NAFLD livers. Depletion of macrophages with clodronate reversed the NAFLD caused resistance to tumor-antigen dependent tumor suppression. It was observed that there were minimal changes to the amount of TAS CD8+ T cells in doxycycline-treated mice irrespective of clodronate depletion. There was, however, higher markers of activation such as CD69 and TNFα in clodronate-depleted mice compared to controls.
Conclusions: NAFLD impairs antigen-specific CD8+ T cell immunity against liver tumor. The effect was not due to reduced generation or intrinsic functional changes of tumor antigen-specific CD8+ T cells but caused by accumulated macrophages in the liver environment.
Citation Format: John C. McVey, Benjamin L. Green, Benjamin Ruf, Tim F. Greten, Chi Ma. Macrophages impair antigen specific CD8+ T cell response against HCC in NAFLD mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1372.