XIAP inhibition augments personalized neoantigen vaccine-driven antitumor immunity in orthotopic hepatocellular carcinoma

Background Personalized neoantigen vaccines offer a rational immunotherapeutic strategy for hepatocellular carcinoma (HCC), but their efficacy is limited by insufficient tumor immunogenicity and an immunosuppressive tumor microenvironment. Tumor-intrinsic factors that constrain vaccine-induced immune responses in HCC are not well defined. X-linked inhibitor of apoptosis protein (XIAP) is frequently overexpressed in HCC and has been linked to immune evasion, raising the possibility that targeting XIAP may improve the effectiveness of neoantigen-based vaccination.Methods XIAP expression is examined in human HCC specimens using transcriptomic analysis and multiplex immunofluorescence. A personalized neoantigen vaccine (NeoVAC) is generated and evaluated in combination with Birinapant, a clinically investigated second mitochondria-derived activator of caspases (SMAC) mimetic, and IAP antagonist, in orthotopic HCC and KPC-OVA-ICC mouse models. Antitumor efficacy is assessed by bioluminescence imaging and survival analysis. Immune landscapes are characterized by flow cytometry, immunohistochemistry, multiplex immunofluorescence, and single-cell RNA sequencing. Neoantigen-specific immune responses are further assessed using functional assays.Results XIAP is markedly upregulated in human HCC and inversely associates with intratumoral CD8+T cell infiltration and recurrence-free survival. Birinapant treatment increases major histocompatibility complex class I (MHC-I) expression, reduces PD-L1 levels, and facilitates immune-cell infiltration, but only has modest antitumor effects as monotherapy. In contrast, combining Birinapant with NeoVAC substantially improves tumor control. A notable proportion of treated mice achieves complete tumor regression, accompanied by durable protection against tumor rechallenge and metastatic dissemination. These effects are associated with the expansion of neoantigen-specific Ly6C +CD8+ T cells exhibiting effector-memory features, strong cytotoxic capacity, and limited exhaustion, together with enhanced dendritic-cell antigen presentation and a shift of tumor-associated macrophages toward a pro-inflammatory M1-like phenotype.Conclusions These data identify XIAP expression as a clinical correlate of an immune-refractory HCC phenotype and show that pharmacological IAP antagonism with Birinapant enhances tumor immunogenicity and supports antigen-specific T-cell immunity. The findings provide a preclinical rationale for combining the SMAC mimetic Birinapant with neoantigen vaccine-based immunotherapy in HCC.