The roles of plasmacytoid dendritic cells on the tumor immune microenvironment and surgical stress-induced tumor recurrence in hepatocellular carcinoma

Abstract

Background & aims Patients with hepatocellular carcinoma (HCC) confront a high incidence of tumor recurrence after curative tumor resection. Plasmacytoid dendritic cells (pDCs) exert regulatory roles in both tumor microenvironment (TME) and hepatic ischemia-reperfusion injury (IRI) during liver surgery. It is highly believed that immunosuppression of TME fosters tumor growth and metastasis. Surgical stress drives tumor relapse after surgery through disturbing immunological, metabolic, and neuroendocrine systems. However, the mechanisms of pDCs on immunosuppression of HCC and surgical-stress-induced HCC recurrence remain elusive. Methodology The pDC phenotypes were analyzed by flow cytometry and immunohistochemistry. The correlation of pDCs and clinicopathologic parameters were studied in 117 patients. pDC migration was examined in the 3D-hanging drop co-culture model. The roles of pDCs on tumor immunity and progression were investigated in co-culture systems and HCC mouse models. The multiplex array was applied to screen the cytokine/chemokine candidates related to cancer recurrence of HCC patients after liver resection. The prognostic values of IFN-α and pDCs were analyzed in two independent clinical cohorts. The role and mechanism of pDCs on MDSC recruitment were explored through in vitro transwell assay and in vivo mouse IRI model. Hydrodynamic tail vein injection was used to achieve CX3CL1 or IRF1 knockdown in hepatocytes in vivo. Therapeutic interventions were investigated in the mouse liver tumor models. Results Part I: pDCs were accumulated in tumor tissue and ascetic fluid of the patients with HCC. High infiltration of pDCs in the tumor was correlated with dismal prognostic outcomes. Hypoxia-induced extracellular adenosine (eADO) profoundly enhanced pDC recruitment into tumors via adenosine A1 receptor (ADORA1). Mechanistically, HIF-1α transcriptionally upregulated the expression of ectonucleotidases CD39 and CD73 in HCC cells, where both enzymes are essential for generating eADO. eADO-stimulated pDCs promoted Foxp3 expression in CD4+ T cells and suppressed the cytotoxicity and proliferation of CD8+ T cells. Depletion of pDCs significantly improved tumor-killing immunity of CD8+ T cells and suppressed HCC growth in the immunocompetent HCC mouse model. Part II: Clinically, postsurgical IFN-α was an independent risk factor for tumor recurrence. IFN-α-producing pDCs were activated and correlated with poor disease-free survival after surgery. In the animal study, IFN-α and pDCs were responsible for MDSC mobilization following hepatic IRI. Conditioned medium from IFN-α treated hepatocytes, but not IFN-α itself mediated the migration of MDSCs. Mechanistically, among all the elevated chemokines in hepatocytes, CX3CL1 was validated to mediate the recruitment of monocytic MDSCs. IRF1 transcriptionally regulated CX3CL1 expression. In vivo knockdown of IRF1 or CX3CL1 in hepatocytes significantly inhibited the accumulation of monocytic MDSCs. Therapeutically, blockades of pDCs, IFN-α, or CX3CR1 restored tumor-killing immunity, limiting tumor growth and metastasis following hepatic IRI. Conclusions Part I: The accumulation of pDCs via HIF-1α/eADO/ADORA1 was correlated to poor prognosis due to its immunosuppressive role. Targeting pDC recruitment could serve as a potential adjuvant strategy for immunotherapies of HCC. Part II: IFN-α-producing pDCs drive MDSC recruitment via hepatocyte IRF1/CX3CL1 signaling, leading to poor clinical outcomes after surgery. Targeting pDC-IFN-α/CX3CL1/CX3CR1 axis could serve as therapeutics for surgical-stress-induced HCC recurrence.