Targeting gut microbiota to overcome immunotherapy resistance in hepatocellular carcinoma: from mechanisms to clinical practice

Abstract

Hepatocellular carcinoma (HCC) remains one of the leading causes of cancer-related mortality worldwide. Despite significant improvements in the treatment landscape for advanced HCC in recent years through combination therapies centered on immune checkpoint inhibitors (ICIs), only approximately 20%-30% of patients achieve durable clinical responses. Primary and acquired resistance remain critical bottlenecks limiting broader efficacy. Traditionally, investigations into resistance mechanisms have predominantly focused on the tumor microenvironment (TME), emphasizing the formation of an immune-“cold” niche, the compensatory upregulation of alternative immune checkpoints [e.g., lymphocyte-activation gene 3 (LAG-3), T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), T-cell immunoreceptor with Ig and ITIM domains (TIGIT)], and dynamic metabolic reprogramming. However, this tumor-centric perspective fails to fully account for the observed inter-patient heterogeneity in treatment efficacy, suggesting the critical involvement of systemic regulatory factors. Grounded in the unique anatomical and physiological connectivity of the “gut-microbiota-liver axis”, the gut microbiota, as a critical extrahepatic regulatory system, is increasingly recognized for its role in influencing hepatic immune homeostasis and anti-tumor responses. This provides a novel breakthrough for systemically understanding and overcoming immunotherapy resistance in HCC. The gut microbiota systemically regulates immune surveillance in the liver and the immune status of the tumor microenvironment through various mechanisms, including metabolites (such as short-chain fatty acids, secondary bile acids, and tryptophan metabolites), the activation of pattern recognition receptors, and antigen cross-reactivity. Clinical evidence indicates significant differences in gut microbial community structure between responders and non-responders, while antibiotic use may impair the efficacy of ICIs by disrupting microbial homeostasis. Consequently, microbiota-targeted interventions have emerged as promising strategies to reverse immunosuppression and re-sensitize tumors to immunotherapy. Modalities such as fecal microbiota transplantation (FMT), next-generation probiotics/synbiotics, metabolite-based therapies, and engineered bacteria have progressed from concept to early-stage clinical practice, demonstrating initial safety and feasibility. This article systematically reviews the mechanisms and clinical evidence regarding the role of the gut microbiota in immunotherapy resistance for HCC, and discusses its translational prospects as a personalized combination therapeutic strategy, aiming to provide new insights for overcoming bottlenecks in HCC immunotherapy.

Keywords

Hepatocellular carcinoma / immunotherapy resistance / gut microbiota / immune checkpoint inhibitors / tumor microenvironment

References

[1] Liu Y,Liu L. Changes in the epidemiology of hepatocellular carcinoma in Asia Cancers. 2022 14 4473 PMC9496757

[2] Sung H,Ferlay J,Siegel RL.et al. Global cancer statistics 2020: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries CA Cancer J Clin. 2021 71 209 49

[3] Abboud Y,Ismail M,Khan H.et al. Hepatocellular carcinoma incidence and mortality in the usa by sex, age, and race: a nationwide analysis of two decades J Clin Transl Hepatol. 2024 12 172 81 PMC10851066

[4] Chon YE,Lee J,Yoon EL.et al. Changes in antiviral treatment rate for hepatitis B virus before hepatocellular carcinoma diagnosis: a nationwide Korean study Eur J Gastroenterol Hepatol. 2025 37 1166 72 PMC12382718

[5] Facciorusso A,Tartaglia N,Villani R.et al. Lenvatinib versus sorafenib as first-line therapy of advanced hepatocellular carcinoma: a systematic review and meta-analysis. Am J Transl Res. 2021;13:2379-87 PMC8129234

[6] Kudo M,Finn RS,Qin S.et al. Lenvatinib versus sorafenib in first-line treatment of patients with unresectable hepatocellular carcinoma: a randomised phase 3 non-inferiority trial Lancet. 2018 391 1163 73

[7] Llovet JM,Ricci S,Mazzaferro V.et al. ; SHARP Investigators Study Group. Sorafenib in advanced hepatocellular carcinoma N Engl J Med. 2008 359 378 90

[8] Zhu AX,Finn RS,Edeline J.et al. ; KEYNOTE-224 investigators. Pembrolizumab in patients with advanced hepatocellular carcinoma previously treated with sorafenib (KEYNOTE-224): a non-randomised, open-label phase 2 trial Lancet Oncol. 2018 19 940 52

[9] Yau T,Park JW,Finn RS.et al. Nivolumab versus sorafenib in advanced hepatocellular carcinoma (CheckMate 459): a randomised, multicentre, open-label, phase 3 trial Lancet Oncol. 2022 23 77 90

[10] Finn RS,Qin S,Ikeda M.et al. ; IMbrave150 Investigators. Atezolizumab plus Bevacizumab in Unresectable Hepatocellular Carcinoma N Engl J Med. 2020 382 1894 905

[11] Rimassa L,Chan SL,Sangro B.et al. Five-year overall survival update from the HIMALAYA study of tremelimumab plus durvalumab in unresectable HCC J Hepatol. 2025 83 899 908

[12] Abou-alfa GK,Lau G,Kudo M.et al. Tremelimumab plus durvalumab in unresectable hepatocellular carcinoma NEJM Evid. 2022 1 EVIDoa2100070

[13] El-Khoueiry AB,Sangro B,Yau T.et al. Nivolumab in patients with advanced hepatocellular carcinoma (CheckMate 040): an open-label, non-comparative, phase 1/2 dose escalation and expansion trial Lancet. 2017 389 2492 502 PMC7539326

[14] Ren Z,Xu J,Bai Y.et al. ; ORIENT-32 study group. Sintilimab plus a bevacizumab biosimilar (IBI305) versus sorafenib in unresectable hepatocellular carcinoma (ORIENT-32): a randomised, open-label, phase 2-3 study Lancet Oncol. 2021 22 977 90

[15] Llovet JM,Kelley RK,Villanueva A.et al. Hepatocellular carcinoma Nat Rev Dis Primers. 2021 7 6

[16] Sharma P,Hu-Lieskovan S,Wargo JA,Ribas A. Primary, adaptive, and acquired resistance to cancer immunotherapy Cell. 2017 168 707 23 PMC5391692

[17] Sia D,Jiao Y,Martinez-Quetglas I.et al. Identification of an immune-specific class of hepatocellular carcinoma, based on molecular features Gastroenterology. 2017 153 812 26 PMC12166766

[18] Spranger S,Bao R,Gajewski TF. Melanoma-intrinsic β-catenin signalling prevents anti-tumour immunity Nature. 2015 523 231 5

[19] Luke JJ,Bao R,Sweis RF,Spranger S,Gajewski TF. WNT/β-catenin pathway activation correlates with immune exclusion across human cancers Clin Cancer Res. 2019 25 3074 83 PMC6522301

[20] Gettinger S,Choi J,Hastings K.et al. Impaired HLA Class I antigen processing and presentation as a mechanism of acquired resistance to immune checkpoint inhibitors in lung cancer Cancer Discov. 2017 7 1420 35 PMC5718941

[21] Koyama S,Akbay EA,Li YY.et al. Adaptive resistance to therapeutic PD-1 blockade is associated with upregulation of alternative immune checkpoints Nat Commun. 2016 7 10501 PMC4757784

[22] Chauvin JM,Zarour HM. TIGIT in cancer immunotherapy J Immunother Cancer. 2020 8 e000957 PMC7477968

[23] De Palma M,Biziato D,Petrova TV. Microenvironmental regulation of tumour angiogenesis Nat Rev Cancer. 2017 17 457 74

[24] Zaretsky JM,Garcia-diaz A,Shin DS.et al. Mutations associated with acquired resistance to PD-1 blockade in melanoma N Engl J Med. 2016 375 819 29 PMC5007206

[25] Mariathasan S,Turley SJ,Nickles D.et al. TGFβ attenuates tumour response to PD-L1 blockade by contributing to exclusion of T cells Nature. 2018 554 544 8 PMC6028240

[26] Lu Y,Yang A,Quan C.et al. A single-cell atlas of the multicellular ecosystem of primary and metastatic hepatocellular carcinoma Nat Commun. 2022 13 4594 PMC9357016

[27] Zheng Y,Wang T,Tu X.et al. Gut microbiome affects the response to anti-PD-1 immunotherapy in patients with hepatocellular carcinoma J Immunotherapy Cancer. 2019 7 193 PMC6651993

[28] Mao J,Wang D,Long J.et al. Gut microbiome is associated with the clinical response to anti-PD-1 based immunotherapy in hepatobiliary cancers J Immunother Cancer. 2021 9 e003334 PMC8650503

[29] Dizman N,Meza L,Bergerot P.et al. Nivolumab plus ipilimumab with or without live bacterial supplementation in metastatic renal cell carcinoma: a randomized phase 1 trial Nat Med. 2022 28 704 12 PMC9018425

[30] Mager LF,Burkhard R,Pett N.et al. Microbiome-derived inosine modulates response to checkpoint inhibitor immunotherapy Science. 2020 369 1481 9

[31] Baruch EN,Youngster I,Ben-Betzalel G.et al. Fecal microbiota transplant promotes response in immunotherapy-refractory melanoma patients Science. 2021 371 602 9

[32] Smith M,Dai A,Ghilardi G.et al. Gut microbiome correlates of response and toxicity following anti-CD19 CAR T cell therapy Nat Med. 2022 28 713 23 PMC9434490

[33] Bian CF,Wang Y,Yu A.et al. Gut microbiota changes and biological mechanism in hepatocellular carcinoma after transarterial chemoembolization treatment Front Oncol. 2022 12 1002589 PMC9577458

[34] Chowdhury S,Castro S,Coker C,Hinchliffe TE,Arpaia N,Danino T. Programmable bacteria induce durable tumor regression and systemic antitumor immunity Nat Med. 2019 25 1057 63 PMC6688650

[35] Finn RS,Ryoo BY,Merle P.et al. ; KEYNOTE-240 investigators. Pembrolizumab as second-line therapy in patients with advanced hepatocellular carcinoma in KEYNOTE-240: a randomized, double-blind, Phase III trial J Clin Oncol. 2020 38 193 202

[36] Zhang L,Chen C,Chai D.et al. The association between antibiotic use and outcomes of HCC patients treated with immune checkpoint inhibitors Front Immunol. 2022 13 956533 PMC9429218

[37] Wang Z,Wang Y,Gao P,Ding J. Immune checkpoint inhibitor resistance in hepatocellular carcinoma Cancer Lett. 2023 555 216038

[38] Pfister D,Núñez NG,Pinyol R.et al. NASH limits anti-tumour surveillance in immunotherapy-treated HCC Nature. 2021 592 450 6 PMC8046670

[39] Fukumura D,Kloepper J,Amoozgar Z,Duda DG,Jain RK. Enhancing cancer immunotherapy using antiangiogenics: opportunities and challenges Nat Rev Clin Oncol. 2018 15 325 40 PMC5921900

[40] Routy B,Le Chatelier E,Derosa L.et al. Gut microbiome influences efficacy of PD-1–based immunotherapy against epithelial tumors Science. 2018 359 91 7

[41] Pomej K,Frick A,Scheiner B.et al. Study protocol: Fecal Microbiota Transplant combined with atezolizumab/bevacizumab in patients with hepatocellular carcinoma who failed to achieve or maintain objective response to atezolizumab/bevacizumab - the FAB-HCC pilot study PLoS ONE. 2025 20 e0321189 PMC11999108

[42] Gilbert JA,Blaser MJ,Caporaso JG,Jansson JK,Lynch SV,Knight R. Current understanding of the human microbiome Nat Med. 2018 24 392 400 PMC7043356

[43] Tripathi A,Debelius J,Brenner DA.et al. The gut-liver axis and the intersection with the microbiome Nat Rev Gastroenterol Hepatol. 2018 15 397 411 PMC6319369

[44] Seki E,Schnabl B. Role of innate immunity and the microbiota in liver fibrosis: crosstalk between the liver and gut J Physiol. 2012 590 447 58 PMC3379693

[45] Tilg H,Cani PD,Mayer EA. Gut microbiome and liver diseases Gut. 2016 65 2035 44

[46] Albillos A,de Gottardi A,Rescigno M. The gut-liver axis in liver disease: Pathophysiological basis for therapy J Hepatol. 2020 72 558 77

[47] Szabo G,Petrasek J. Inflammasome activation and function in liver disease Nat Rev Gastroenterol Hepatol. 2015 12 387 400

[48] Jia W,Xie G,Jia W. Bile acid-microbiota crosstalk in gastrointestinal inflammation and carcinogenesis Nat Rev Gastroenterol Hepatol. 2018 15 111 28 PMC5899973

[49] Chiang JYL,Ferrell JM. Bile acid receptors FXR and TGR5 signaling in fatty liver diseases and therapy Am J Physiol Gastrointest Liver Physiol. 2020 318 G554 73 PMC7099488

[50] Tilg H,Adolph TE,Trauner M. Gut-liver axis: Pathophysiological concepts and clinical implications Cell Metab. 2022 34 1700 18

[51] Wahlström A,Sayin SI,Marschall HU,Bäckhed F. Intestinal crosstalk between bile acids and microbiota and its impact on host metabolism Cell Metab. 2016 24 41 50

[52] Juneja P,Tripathi DM,Kaur S. Revisiting the gut-liver axis: gut lymphatic system in liver cirrhosis and portal hypertension Am J Physiol Gastrointest Liver Physiol. 2022 322 G473 9

[53] Yang X,Lu D,Zhuo J,Lin Z,Yang M,Xu X. The gut-liver axis in immune remodeling: new insight into liver diseases Int J Biol Sci. 2020 16 2357 66 PMC7378637

[54] Lee PC,Wu CJ,Hung YW.et al. Gut microbiota and metabolites associate with outcomes of immune checkpoint inhibitor-treated unresectable hepatocellular carcinoma J Immunother Cancer. 2022 10 e004779 PMC9226985

[55] Chua HH,Chen YH,Wu LL.et al. Antagonism between gut Ruminococcus gnavus and Akkermansia muciniphila modulates the progression of chronic hepatitis B Cell Mol Gastroenterol Hepatol. 2024 17 361 81 PMC10821531

[56] Zhang N,Gou Y,Liang S.et al. Dysbiosis of gut microbiota promotes hepatocellular carcinoma progression by regulating the immune response J Immunol Res. 2021 2021 4973589 PMC8551979

[57] Ma H,Yang L,Liang Y.et al. B. thetaiotaomicron-derived acetic acid modulate immune microenvironment and tumor growth in hepatocellular carcinoma Gut Microbes. 2024 16 2297846 PMC10813637

[58] Yang J,Lim J,Kim EH.et al. Prognostic Role of Short-Chain Fatty Acid-Producing Gut Microbiota and Gut Microbial Dynamics in Patients with Hepatocellular Carcinoma Receiving Chemoembolization: A Prospective Study J Hepatocell Carcinoma. 2025 12 1991 2004 PMC12413548

[59] Mcculloch JA,Davar D,Rodrigues RR.et al. Intestinal microbiota signatures of clinical response and immune-related adverse events in melanoma patients treated with anti-PD-1 Nat Med. 2022 28 545 56 PMC10246505

[60] Gong J,Chehrazi‐Raffle A,Placencio‐Hickok V,Guan M,Hendifar A,Salgia R. The gut microbiome and response to immune checkpoint inhibitors: preclinical and clinical strategies Clin Transl Med. 2019 8 e9 PMC6423251

[61] Kiziltas S. Toll-like receptors in pathophysiology of liver diseases World J Hepatol. 2016 8 1354 69 PMC5114472

[62] Ghosh SS,Wang J,Yannie PJ,Ghosh S. Intestinal barrier dysfunction, LPS translocation, and disease development. J Endocr Soc. 2020;4:bvz039 PMC7033038

[63] Sepich-Poore GD,Zitvogel L,Straussman R,Hasty J,Wargo JA,Knight R. The microbiome and human cancer. Science. 2021;371:eabc4552 PMC8767999

[64] Yao J,Ning B,Ding J. The gut microbiota: an emerging modulator of drug resistance in hepatocellular carcinoma Gut Microbes. 2025 17 2473504 PMC11901387

[65] Choi YH,Yu AM. ABC transporters in multidrug resistance and pharmacokinetics, and strategies for drug development Curr Pharm Des. 2014 20 793 807 PMC6341993

[66] de Groot RA,Reedijk D,Faucher Q,Mihăilă SM,Masereeuw R. Strategies for overcoming ABC transporter-mediated multidrug resistance in colorectal cancer Am J Physiol Cell Physiol. 2025 329 C699 717

[67] Wu D,Fan Y,Zhang M.et al. Tumor-suppressing multi-enterobacteria and PD-1/PD-L1 immune checkpoint inhibitor combination improves the outcome of hepatocellular carcinoma therapy Front Immunol. 2025 16 1598436 PMC12226584

[68] Lu Y,Yuan H,Liang S.et al. Microbial metabolite-driven immune reprogramming in tumor immunotherapy: mechanisms and therapeutic perspectives Front Immunol. 2025 16 1603658 PMC12575249

[69] Wang J,Hao Y,Yang Y,Zhang Y,Xu C,Yang R. Gut microbiota derived indole-3-acetic acid ameliorates precancerous inflammatory intestinal milieu to inhibit tumorigenesis through IL-35 J Immunother Cancer. 2025 13 e011155 PMC12020765

[70] Jia B,Jeon CO. Promotion and induction of liver cancer by gut microbiome-mediated modulation of bile acids PLoS Pathog. 2019 15 e1007954 PMC6728016

[71] Park J,Kim M,Kang SG.et al. Short-chain fatty acids induce both effector and regulatory T cells by suppression of histone deacetylases and regulation of the mTOR-S6K pathway Mucosal Immunol. 2015 8 80 93 PMC4263689

[72] Donohoe DR,Collins LB,Wali A,Bigler R,Sun W,Bultman SJ. The warburg effect dictates the mechanism of butyrate-mediated histone acetylation and cell proliferation Mol Cell. 2012 48 612 26 PMC3513569

[73] Lai MW,Chu YD,Hsu CW,Chen YC,Liang KH,Yeh CT. Multi-omics analyses identify signatures in patients with liver cirrhosis and hepatocellular carcinoma Cancers. 2022 15 210 PMC9818216

[74] Yang Q,He Y,Tian L.et al. Anti-tumor effect of infant-derived Enterococcus via the inhibition of proliferation and inflammation as well as the promotion of apoptosis Food Funct. 2023 14 2223 38

[75] Yang Y,Bo Z,Wang J.et al. Machine learning based on alcohol drinking-gut microbiota-liver axis in predicting the occurrence of early-stage hepatocellular carcinoma BMC Cancer. 2024 24 1468 PMC11606210

[76] Gopalakrishnan V,Helmink BA,Spencer CN,Reuben A,Wargo JA. The influence of the gut microbiome on cancer, immunity, and cancer immunotherapy Cancer Cell. 2018 33 570 80 PMC6529202

[77] Wang J,Xu W,Wang R,Cheng R,Tang Z,Zhang M. The outer membrane protein Amuc_1100 of Akkermansia muciniphila promotes intestinal 5-HT biosynthesis and extracellular availability through TLR2 signalling Food Funct. 2021 12 3597 610

[78] Chelakkot C,Choi Y,Kim DK.et al. Akkermansia muciniphila-derived extracellular vesicles influence gut permeability through the regulation of tight junctions Exp Mol Med. 2018 50 e450 PMC5903829

[79] Depommier C,Everard A,Druart C.et al. Supplementation with Akkermansia muciniphila in overweight and obese human volunteers: a proof-of-concept exploratory study Nat Med. 2019 25 1096 103 PMC6699990

[80] Hsieh CY,Osaka T,Moriyama E,Date Y,Kikuchi J,Tsuneda S. Strengthening of the intestinal epithelial tight junction by Bifidobacterium bifidum Physiol Rep. 2015 3 e12327 PMC4393161

[81] Zheng D,Liwinski T,Elinav E. Interaction between microbiota and immunity in health and disease Cell Res. 2020 30 492 506 PMC7264227

[82] Horvath A,Leber B,Schmerboeck B.et al. Randomised clinical trial: the effects of a multispecies probiotic vs. placebo on innate immune function, bacterial translocation and gut permeability in patients with cirrhosis Aliment Pharmacol Ther. 2016 44 926 35 PMC5053220

[83] Gur C,Ibrahim Y,Isaacson B.et al. Binding of the Fap2 protein of Fusobacterium nucleatum to human inhibitory receptor TIGIT protects tumors from immune cell attack Immunity. 2015 42 344 55 PMC4361732

[84] Wang X,Fang Y,Liang W.et al. Gut-liver translocation of pathogen Klebsiella pneumoniae promotes hepatocellular carcinoma in mice Nat Microbiol. 2025 10 169 84 PMC11726454

[85] Zhang M,Huang X,Zhang Y.et al. Gut microbial metabolite butyrate suppresses hepatocellular carcinoma growth via CXCL11-dependent enhancement of natural killer cell infiltration Gut Microbes. 2025 17 2519706 PMC12218501

[86] Arpaia N,Campbell C,Fan X.et al. Metabolites produced by commensal bacteria promote peripheral regulatory T-cell generation Nature. 2013 504 451 5 PMC3869884

[87] Sun M,Wu W,Chen L.et al. Microbiota-derived short-chain fatty acids promote Th1 cell IL-10 production to maintain intestinal homeostasis Nat Commun. 2018 9 3555 PMC6120873

[88] He Y,Fu L,Li Y.et al. Gut microbial metabolites facilitate anticancer therapy efficacy by modulating cytotoxic CD8⁺ T cell immunity Cell Metab. 2021 33 988 1000.e7

[89] Singh N,Gurav A,Sivaprakasam S.et al. Activation of Gpr109a, receptor for niacin and the commensal metabolite butyrate, suppresses colonic inflammation and carcinogenesis Immunity. 2014 40 128 39 PMC4305274

[90] He J,Zhang P,Shen L.et al. Short-Chain fatty acids and their association with signalling pathways in inflammation, glucose and lipid metabolism Int J Mol Sci. 2020 21 6356 PMC7503625

[91] Chang PV,Hao L,Offermanns S,Medzhitov R. The microbial metabolite butyrate regulates intestinal macrophage function via histone deacetylase inhibition Proc Natl Acad Sci U S A. 2014 111 2247 52 PMC3926023

[92] Nomura M,Nagatomo R,Doi K.et al. Association of short-chain fatty acids in the gut microbiome with clinical response to treatment with nivolumab or pembrolizumab in patients with solid cancer tumors JAMA Netw Open. 2020 3 e202895 PMC7163404

[93] Parada Venegas D,De la Fuente MK,Landskron G.et al. Short chain fatty acids (SCFAs)-mediated gut epithelial and immune regulation and its relevance for inflammatory bowel diseases Front Immunol. 2019 10 277 PMC6421268

[94] Nastasi C,Candela M,Bonefeld CM.et al. The effect of short-chain fatty acids on human monocyte-derived dendritic cells Sci Rep. 2015 5 16148 PMC4635422

[95] Ma C,Han M,Heinrich B.et al. Gut microbiome-mediated bile acid metabolism regulates liver cancer via NKT cells. Science. 2018;360:eaan5931 PMC6407885

[96] Yamada S,Takashina Y,Watanabe M.et al. Bile acid metabolism regulated by the gut microbiota promotes non-alcoholic steatohepatitis-associated hepatocellular carcinoma in mice Oncotarget. 2018 9 9925 39 PMC5839411

[97] Sydor S,Best J,Messerschmidt I.et al. Altered microbiota diversity and bile acid signaling in cirrhotic and noncirrhotic NASH-HCC Clin Transl Gastroenterol. 2020 11 e00131 PMC7145043

[98] Petrick JL,Florio AA,Koshiol J.et al. Prediagnostic concentrations of circulating bile acids and hepatocellular carcinoma risk: REVEAL‐HBV and HCV studies Int J Cancer. 2020 147 2743 53 PMC7529994

[99] Thomas CE,Luu HN,Wang R.et al. Association between pre-diagnostic serum bile acids and hepatocellular carcinoma: The Singapore Chinese Health Study Cancers. 2021 13 2648 PMC8198655

[100] Colosimo S,Tomlinson JW. Bile acids as drivers and biomarkers of hepatocellular carcinoma World J Hepatol. 2022 14 1730 8 PMC9521453

[101] Guo C,Chen WD,Wang YD. TGR5, not only a metabolic regulator Front Physiol. 2016 7 646 PMC5183627

[102] Yang Z,Zhou F,Zhan D,Li P,Pan J. Levels of bile acid metabolism are associated with alterations of gut microbes in hepatocellular carcinoma Mol Carcinog. 2025 64 543 51

[103] Yang R,Qian L. Research on gut microbiota-derived secondary bile acids in cancer progression. Integr Cancer Ther. 2022;21:15347354221114100 PMC9421216

[104] Shen R,Ke L,Li Q.et al. Abnormal bile acid-microbiota crosstalk promotes the development of hepatocellular carcinoma Hepatol Int. 2022 16 396 411 PMC9013324

[105] Song X,Sun X,Oh SF.et al. Microbial bile acid metabolites modulate gut RORγ⁺ regulatory T cell homeostasis Nature. 2019 577 410 5 PMC7274525

[106] Roager HM,Licht TR. Microbial tryptophan catabolites in health and disease Nat Commun. 2018 9 3294 PMC6098093

[107] Platten M,Nollen EAA,Röhrig UF,Fallarino F,Opitz CA. Tryptophan metabolism as a common therapeutic target in cancer, neurodegeneration and beyond Nat Rev Drug Discov. 2019 18 379 401

[108] Luo W,Li R,Pan C,Luo C. Gut microbiota-derived metabolites in immunomodulation and gastrointestinal cancer immunotherapy Front Immunol. 2025 16 1710880 PMC12678330

[109] Huo R,Xu QG,You YQ.et al. Bifidobacterium boosts anti-PD-1 effectiveness through JAK pathway in hepatocellular carcinoma NPJ Precis Oncol. 2025 9 251 PMC12287312

[110] Round JL,Mazmanian SK. Inducible Foxp3+ regulatory T-cell development by a commensal bacterium of the intestinal microbiota Proc Natl Acad Sci U S A. 2010 107 12204 9 PMC2901479

[111] Mazmanian SK,Liu CH,Tzianabos AO,Kasper DL. An immunomodulatory molecule of symbiotic bacteria directs maturation of the host immune system Cell. 2005 122 107 18

[112] Mazmanian SK,Round JL,Kasper DL. A microbial symbiosis factor prevents intestinal inflammatory disease Nature. 2008 453 620 5

[113] Xiong H,Han X,Cai L,Zheng H. Natural polysaccharides exert anti-tumor effects as dendritic cell immune enhancers Front Oncol. 2023 13 1274048 PMC10593453

[114] Yano JM,Yu K,Donaldson GP.et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis Cell. 2015 161 264 76 PMC4393509

[115] Sarrouilhe D,Clarhaut J,Defamie N,Mesnil M. Serotonin and cancer: what is the link? Curr Mol Med. 2015;15:62-77

[116] Seki E,De Minicis S,Österreicher CH.et al. TLR4 enhances TGF-β signaling and hepatic fibrosis Nat Med. 2007 13 1324 32

[117] Soares JB,Pimentel-Nunes P,Roncon-Albuquerque R,Leite-Moreira A. The role of lipopolysaccharide/toll-like receptor 4 signaling in chronic liver diseases Hepatol Int. 2010 4 659 72 PMC2994611

[118] Vatanen T,Kostic AD,d’hennezel E.et al. ; DIABIMMUNE Study Group. Variation in microbiome LPS immunogenicity contributes to autoimmunity in humans Cell. 2016 165 842 53 PMC4950857

[119] Zhou Z,Xu MJ,Gao B. Hepatocytes: a key cell type for innate immunity Cell Mol Immunol. 2015 13 301 15 PMC4856808

[120] Dapito DH,Mencin A,Gwak G.et al. Promotion of hepatocellular carcinoma by the intestinal microbiota and TLR4 Cancer Cell. 2012 21 504 16 PMC3332000

[121] Netea MG,Domínguez-Andrés J,Barreiro LB.et al. Defining trained immunity and its role in health and disease Nat Rev Immunol. 2020 20 375 88 PMC7186935

[122] Weiskirchen R,Tacke F. Cellular and molecular functions of hepatic stellate cells in inflammatory responses and liver immunology Hepatobiliary Surg Nutr. 2014 3 344 63 PMC4273119

[123] Yan H,Zhong M,Yang J.et al. TLR5 activation in hepatocytes alleviates the functional suppression of intrahepatic CD8⁺ T cells Immunology. 2020 161 325 44 PMC7692256

[124] Shepard CR. TLR9 in MAFLD and NASH: at the intersection of inflammation and metabolism Front Endocrinol. 2021 11 613639 PMC7880160

[125] Li X,Zhang Q,Ding Y.et al. Methyltransferase Dnmt3a upregulates HDAC9 to deacetylate the kinase TBK1 for activation of antiviral innate immunity Nat Immunol. 2016 17 806 15

[126] Harrington KJ,Brody J,Ingham M.et al. LBA15 - Preliminary results of the first-in-human (FIH) study of MK-1454, an agonist of stimulator of interferon genes (STING), as monotherapy or in combination with pembrolizumab (pembro) in patients with advanced solid tumors or lymphomas Ann Oncol. 2018 29 ⅷ712

[127] Zitvogel L,Kroemer G. Cross-reactivity between microbial and tumor antigens Curr Opin Immunol. 2022 75 102171

[128] Lee CH,Salio M,Napolitani G,Ogg G,Simmons A,Koohy H. Predicting cross-reactivity and antigen specificity of T cell receptors Front Immunol. 2020 11 565096 PMC7642207

[129] Boesch M,Baty F,Rothschild SI.et al. Tumour neoantigen mimicry by microbial species in cancer immunotherapy Br J Cancer. 2021 125 313 23 PMC8329167

[130] Zheng Z,Wieder T,Mauerer B,Schäfer L,Kesselring R,Braumüller H. T cells in colorectal cancer: unravelling the function of different T cell subsets in the tumor microenvironment Int J Mol Sci. 2023 24 11673 PMC10380781

[131] Vétizou M,Pitt JM,Daillère R.et al. Anticancer immunotherapy by CTLA-4 blockade relies on the gut microbiota Science. 2015 350 1079 84 PMC4721659

[132] Leventhal DS,Sokolovska A,Li N.et al. Immunotherapy with engineered bacteria by targeting the STING pathway for anti-tumor immunity Nat Commun. 2020 11 2739 PMC7264239

[133] Zheng JH,Nguyen VH,Jiang SN.et al. Two-step enhanced cancer immunotherapy with engineeredSalmonella typhimurium secreting heterologous flagellin Sci Transl Med. 2017 9 eaak9537

[134] Ghosh SS,Wang J,Yannie PJ,Ghosh S. Intestinal barrier function and metabolic/liver diseases Liver Research. 2020 4 81 7

[135] Guerville M,Boudry G. Gastrointestinal and hepatic mechanisms limiting entry and dissemination of lipopolysaccharide into the systemic circulation Am J Physiol Gastrointest Liver Physiol. 2016 311 G1 15

[136] Papadakos SP,Arvanitakis K,Stergiou IE.et al. The role of TLR4 in the immunotherapy of hepatocellular carcinoma: can we teach an old dog new tricks? Cancers. 2023;15:2795 PMC10216531

[137] Veglia F,Sanseviero E,Gabrilovich DI. Myeloid-derived suppressor cells in the era of increasing myeloid cell diversity Nat Rev Immunol. 2021 21 485 98 PMC7849958

[138] Li Z,Luo J,Peng L,Wu B,Yu Z. Prognostic significance of systemic immune-inflammation index in hepatocellular carcinoma: a meta-analysis Clin Transl Oncol. 2026 28 601 16

[139] Park SR,Kim G,Kim Y.et al. Fecal microbiota transplantation combined with anti-PD-1 inhibitor for unresectable or metastatic solid cancers refractory to anti-PD-1 inhibitor J Clin Oncol. 2023 41 105

[140] Pomej K,Frick A,Scheiner B.et al. Fecal microbiota transplant combined with atezolizumab plus bevacizumab in patients with hepatocellular carcinoma who progressed on atezolizumab plus bevacizumab - interim analysis of the FAB-HCC phase II pilot study Z Gastroenterol. 2024 62 e479 80

[141] Kim Y,Kim G,Kim S.et al. Fecal microbiota transplantation improves anti-PD-1 inhibitor efficacy in unresectable or metastatic solid cancers refractory to anti-PD-1 inhibitor Cell Host Microbe. 2024 32 1380 93.e9

[142] Huang J,Zheng X,Kang W.et al. Metagenomic and metabolomic analyses reveal synergistic effects of fecal microbiota transplantation and anti-PD-1 therapy on treating colorectal cancer Front Immunol. 2022 13 874922 PMC9336524

[143] Lin A,Jiang A,Huang L.et al. From chaos to order: optimizing fecal microbiota transplantation for enhanced immune checkpoint inhibitors efficacy Gut Microbes. 2025 17 2452277 PMC12716052

[144] Li Z,Zhang Y,Hong W.et al. Gut microbiota modulate radiotherapy-associated antitumor immune responses against hepatocellular carcinoma via STING signaling Gut Microbes. 2022 14 2119055 PMC9467592

[145] Rauber C,Roberti MP,Vehreschild MJ.et al. Protocol: faecal microbiota transfer in liver cancer to overcome resistance to atezolizumab/bevacizumab - a multicentre, randomised, placebo-controlled, double-blind phase II trial (the FLORA trial) BMJ Open. 2025 15 e097802 PMC12421604

[146] Abenavoli L,Montori M,Svegliati Baroni G.et al. Perspective on the role of gut microbiome in the treatment of hepatocellular carcinoma with immune checkpoint inhibitors Medicina. 2023 59 1427 PMC10456509

[147] Thilakarathna WPDW,Rupasinghe HPV,Ridgway ND. Mechanisms by which probiotic bacteria attenuate the risk of hepatocellular carcinoma Int J Mol Sci. 2021 22 2606 PMC7961993

[148] Gao G,Ma T,Zhang T.et al. Adjunctive probiotic lactobacillus rhamnosus Probio-M9 administration enhances the effect of Anti-PD-1 antitumor therapy via restoring antibiotic-disrupted gut microbiota Front Immunol. 2021 12 772532 PMC8712698

[149] Lau HC,Zhang X,Ji F.et al. Lactobacillus acidophilus suppresses non-alcoholic fatty liver disease-associated hepatocellular carcinoma through producing valeric acid EBioMedicine. 2024 100 104952 PMC10801313

[150] Tanoue T,Morita S,Plichta DR.et al. A defined commensal consortium elicits CD8 T cells and anti-cancer immunity Nature. 2019 565 600 5

[151] Suez J,Zmora N,Zilberman-Schapira G.et al. Post-antibiotic gut mucosal microbiome reconstitution is impaired by probiotics and improved by autologous FMT Cell. 2018 174 1406 23.e16

[152] Liu X,Wang L,Jing N,Jiang G,Liu Z. Biostimulating gut microbiome with bilberry anthocyanin combo to enhance Anti-PD-L1 efficiency against murine colon cancer Microorganisms. 2020 8 175 PMC7074734

[153] Rong L,Ch’ng D,Jia P,Tsoi KKF,Wong SH,Sung JJY. Use of probiotics, prebiotics, and synbiotics in non‐alcoholic fatty liver disease: a systematic review and meta-analysis J Gastroenterol Hepatol. 2023 38 1682 94

[154] Nabavi S,Rafraf M,Somi MH,Homayouni-Rad A,Asghari-Jafarabadi M. Effects of probiotic yogurt consumption on metabolic factors in individuals with nonalcoholic fatty liver disease J Dairy Sci. 2014 97 7386 93

[155] Ahn SB,Jun DW,Kang BK,Lim JH,Lim S,Chung MJ. Randomized, double-blind, placebo-controlled study of a multispecies probiotic mixture in nonalcoholic fatty liver disease Sci Rep. 2019 9 5688 PMC6450966

[156] Yang M,Chen W,Gupta D.et al. Nanoparticle/Engineered bacteria based triple-strategy delivery system for enhanced hepatocellular carcinoma cancer therapy Int J Nanomedicine. 2024 19 3827 46 PMC11068060

[157] Raman V,Van Dessel N,Hall CL.et al. Intracellular delivery of protein drugs with an autonomously lysing bacterial system reduces tumor growth and metastases Nat Commun. 2021 12 6116 PMC8531320

[158] Li Y,Wang X,Ye F.et al. Acid-responsive engineered bacteria with aberrant In-Situ anti-PD-1 expression for post-ablation immunotherapy of hepatocellular carcinoma Biomed Pharmacother. 2025 186 118046

[159] Lin JH,Lin CH,Kuo YW.et al. Probiotic Lactobacillus fermentum TSF331, Lactobacillus reuteri TSR332, and Lactobacillus plantarum TSP05 improved liver function and uric acid management - a pilot study PLoS One. 2024 19 e0307181 PMC11268587

[160] Ye W,Chen Z,He Z.et al. Lactobacillusplantarum-derived postbiotics ameliorate acute alcohol-induced liver injury by protecting cells from oxidative damage, improving lipid metabolism, and regulating intestinal microbiota Nutrients. 2023 15 845 PMC9965849

[161] Guo Z,Yao Z,Chen X.et al. Mechanistic roles and intervention strategies involving gut microbiota, amino acid metabolism, and the tumor immune microenvironment in MAFLD-HCC progression Clin Exp Med. 2025 26 31 PMC12644233

[162] Hu C,Xu B,Wang X.et al. Gut microbiota-derived short-chain fatty acids regulate group 3 innate lymphoid cells in HCC. Hepatology. 2023;77:48-64 PMC9970019

[163] Hang S,Paik D,Yao L.et al. Bile acid metabolites control T_H17 and T_reg cell differentiation Nature. 2019 576 143 8 PMC6949019

[164] Ye G,Zhang H,Feng Q,Xiao J,Wang J,Liu J. Important role of bacterial metabolites in development and adjuvant therapy for hepatocellular carcinoma Curr Oncol. 2025 32 673 PMC12731634

[165] McBrearty N,Arzumanyan A,Bichenkov E,Merali S,Merali C,Feitelson M. Short chain fatty acids delay the development of hepatocellular carcinoma in HBx transgenic mice Neoplasia. 2021 23 529 38 PMC8111251

[166] Dean AE,Guzior DV,Quinn RA,Gaulke CA,Anakk S. Serum cholic acid and cecal Faecalibaculum increase in a male-specific manner in a murine hepatocellular carcinoma model J Lipid Res. 2026 67 100954 PMC12799954

[167] Pham YT,Wang R,Behari J.et al. Plant‐based diet index and risk of hepatocellular carcinoma: findings from a prospective cohort study Int J Cancer. 2025 157 2463 75

[168] Cheng K,Cai N,Yang X.et al. Short-term starvation boosts anti-PD-L1 therapy by reshaping tumor-associated macrophages in hepatocellular carcinoma Hepatology. 2025 82 1414 31 PMC12614376

[169] Li Y,Zhu T,Chen J.et al. Dual‐Targeted engineered bacterial outer membrane vesicles for hepatocellular carcinoma immunotherapy Adv Funct Mater. 2024 34 2401355

[170] Eng L,Sutradhar R,Niu Y.et al. Impact of antibiotic exposure before immune checkpoint inhibitor treatment on overall survival in older adults with cancer: a population-based study J Clin Oncol. 2023 41 3122 34

[171] Caffa I,Spagnolo V,Vernieri C.et al. Fasting-mimicking diet and hormone therapy induce breast cancer regression Nature. 2020 583 620 4 PMC7881940