Abstract In recent years, the incidence of hepatocellular carcinomas (HCC) associated with MASLD (Metabolic dysfunction-associated steatotic liver disease) and MASH (Metabolic dysfunction-associated steato-hepatitis), has continued to rise, although that of viral HCC declines because of the development of anti-viral drugs. However, combination therapy with atezolizumab plus bevacizumab in non-viral liver cancers, including MASLD-related cases, has shown no clear clinical benefit (Cheng et al., J Hepatol 2022), and monotherapy with anti-PD-1/PD-L1 antibodies has even exacerbated disease (Pfister et al., Nature 2021). These findings suggest that mechanisms of HCC development in steatotic MASLD-related liver fundamentally differ from HCCs of other etiologies. In this study, we sought to elucidate the unique mechanisms driving MASLD-associated hepatocarcinogenesis, with a focus on how exhausted T cells arise within the highly steatotic tumor microenvironment. We employed chemical carcinogenesis mouse models of MASLD-associated liver cancer previously established by our group (Yoshimoto et al., Nature 2013), alongside patient-derived samples. Multiplex assay for plasma profiling of healthy controls, MASLD/MASH patients, and MASLD/MASH-related liver cancer patients revealed a high level of CXCL9 specifically in the MASLD/MASH-related cancer group. Consistently, CXCL9 levels were increased in samples of our MASLD-related mouse models. Notably, blockade of the CXCL9-CXCR3 axis reduced T-cell trafficking from lymph nodes to the liver and, surprisingly, markedly suppressed tumor formation. Pharmacologic inhibition of lymphocyte migration revealed similar effects. Because CXCL9 expression was predominantly upregulated in liver sinusoidal endothelial cells (LSECs) in the MASLD-HCC model, we generated LSEC-specific CXCL9-knockout mice, which also consistently exhibited reduced tumorigenesis. Although CXCL9 is generally considered a favorable chemokine that recruits cytotoxic T cells to enhance anti-tumor immunity in other cancer types, it plays a detrimental role in MASLD-associated HCC. Our results suggest that LSEC-derived CXCL9 recruits T cells from lymph nodes, but these T cells rapidly undergo exhaustion in the steatotic microenvironment, ultimately promoting cancer progression. To further dissect this process, we performed single-cell TCR sequencing of CD8+ T cells from lymph nodes and liver tissues. We will present the pseudotime analysis of the clonal trajectory, which may suggest the unique mechanisms underlying MASLD-associated HCC development. Citation Format: Naoko Ohtani, Tomonori Kamiya, Kanae Echizen, Yoshiki Nonaka, Yoshimi Yukawa-Muto, Hideki Fujii, Shinji Itoh, Norifumi Kawada. Unique mechanism of MASLD-associated hepatocarcinogenesis: LSEC-derived CXCL9 facilitates T-cell exhaustion in steatotic tumor microenvironment abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4079.
Ohtani et al. (Fri,) studied this question.