Glycosylation of B7-H3 Promotes CD8+ T Cell Exhaustion by Inhibiting the Endosome-Lysosome Pathway in HCC.

A pivotal factor in the immune evasion of hepatocellular carcinoma (HCC) is the excessive exhaustion of CD8+ T cells; however, the molecular drivers of this phenomenon remain incompletely understood. In this study, we discovered that B7-H3 is markedly overexpressed in HCC and actively promotes CD8+ T cell exhaustion. Through high-resolution mass spectrometry and site-directed mutagenesis, we identified asparagine 215 (N215) as a critical N-linked glycosylation site of B7-H3. By employing dual orthogonal strategies-pharmacological inhibition via tunicamycin and targeted genetic ablation (N215Q mutation)-we provided strong evidence that, upon N215 glycosylation, B7-H3 maintains its cell-surface abundance through RAB11-mediated recycling of the endosomal pathway. Conversely, when glycosylation is impeded through either intervention, B7-H3 undergoes accelerated degradation via the endosome-lysosome route, thereby enhancing the cytotoxic activity of CD8+ T cells. Finally, murine experiments confirmed that both the specific genetic disruption of N215 and systemic blockade with tunicamycin enhance the antitumor effects of anti-PD-1, anti-PD-L1, and anti-CTLA-4 antibodies. Collectively, our data reveal that the "B7-H3 Glycosylation-RAB11 Axis" preserves membrane expression of B7-H3, constituting an intrinsic mechanism of immune evasion in HCC, and uncover the intricate crosstalk between B7-H3 glycosylation and the immunosuppressive tumor microenvironment.