CXCL16-driven CD4+ T cells orchestrate immunosurveillance against MHC-I-deficient hepatocellular tumors

Background: Major histocompatibility complex class I (MHC)-I loss is a prevalent mechanism for immune evasion and resistance to immunotherapy. However, how MHC-I loss shapes the tumor microenvironment and influences immune cell interactions, ultimately affecting tumor growth, remains largely unknown. Methods: We established B2m knockout (MHC-I-deficient) tumor cells using CRISPR/Cas9 and evaluated their growth in subcutaneous and orthotopic mouse models. Immune profiling was performed using flow cytometry and single-cell RNA sequencing. Antibody-mediated cell depletion was used to assess the functional contributions of specific immune subsets. Chemokine expression was analyzed by bulk RNA sequencing, quantitative PCR, ELISA and western blotting, and its functional relevance was determined using knockout or overexpression in tumor cells implanted in vivo. Signaling pathways were interrogated using pharmacological inhibition, RNA interference and western blotting. Results: MHC-I loss promoted tumor growth in MC38, AKR, and LLC1 models, but unexpectedly suppressed Hepa1-6 and orthotopic MYC;Trp53 -/- hepatocarcinoma growth. This differential effect correlated with changes in immune infiltrates. CD4+ T cells, natural killer (NK) cells, and macrophages were required for suppression of MHC-I-deficient Hepa1-6 tumors. CD4+ T cells were essential for recruiting NK cells and monocytes/macrophages and for inducing their tumoricidal phenotypes, including iNOS (inducible nitric oxide synthase) expression in macrophages. The differential infiltration of CD4+ T cells was driven by opposite regulation of CXCL16 on B2m knockout: upregulation in Hepa1-6 cells and downregulation in other models. CXCL16 exerted potent antitumor effects by recruiting CD4+ T cells. Mechanistically, B2M loss regulated CXCL16 via suppression of Akt in MC38 and AKR cells, but via activation of NF-κB in Hepa1-6 cells. Conclusion: CXCL16-driven CD4+ T cells are central regulators of antitumor immunity against MHC-I-deficient tumors. The context-dependent regulation of CXCL16 by MHC-I loss determines the immune landscape and tumor outcome, highlighting a potential therapeutic avenue for targeting MHC-I-deficient cancers.