Combined TIM-3 and PD-1 blockade restrains hepatocellular carcinoma development by facilitating CD4+ and CD8+ T cell-mediated antitumor immune responses

Abstract

BACKGROUND Immune checkpoint inhibitors (ICIs) targeting programmed cell death protein 1 (PD-1) and T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) are beneficial to the resumption of anti-tumor immunity response and hold extreme potential as efficient therapies for certain malignancies. However, ICIs with a single target exhibit poor overall response rate in hepatocellular carcinoma (HCC) patients due to the complex pathological mechanisms of HCC. AIM To investigate the effects of combined TIM-3 and PD-1 blockade on tumor development in an HCC mouse model, aiming to identify more effective immunotherapies and provide more treatment options for HCC patients. METHODS The levels of PD-1 and TIM-3 on CD4+ and CD8+ T cells from tumor tissues, ascites, and matched adjacent tissues from HCC patients were determined with flow cytometry. An HCC xenograft mouse model was established and treated with anti-TIM-3 monoclonal antibody (mAb) and/or anti-PD-1 mAb. Tumor growth in each group was measured. Hematoxylin and eosin staining and immunohistochemical staining were used to evaluate T cell infiltration in tumors. The percentage of CD4+ and CD8+ T cells in tissue samples from mice was tested with flow cytometry. The percentages of PD-1+CD8+, TIM-3+CD8+, and PD-1+TIM-3+ CD8+ T cells was accessed by flow cytometry. The levels of the cytokines including tumor necrosis factor alpha (TNF-α), interferon-γ (IFN-γ), interleukin (IL)-6, and IL-10 in tumor tissues were gauged with enzyme-linked immunosorbent assay kits. RESULTS We confirmed that PD-1 and TIM-3 expression was substantially upregulated in CD4+ and CD8+ T cells isolated from tumor tissues and ascites of HCC patients. TIM-3 mAb and PD-1 mAb treatment both reduced tumor volume and weight, while combined blockade had more substantial anti-tumor effects than individual treatment. Then we showed that combined therapy increased T cell infiltration into tumor tissues, and downregulated PD-1 and TIM-3 expression on CD8+ T cells in tumor tissues. Moreover, combined treatment facilitated the production of T cell effector cytokines TNF-α and IFN-γ, and reduced the production of immunosuppressive cytokines IL-10 and IL-6 in tumor tissues. Thus, we implicated that combined blockade could ameliorate T cell exhaustion in HCC mouse model. CONCLUSION Combined TIM-3 and PD-1 blockade restrains HCC development by facilitating CD4+ and CD8+ T cell-mediated antitumor immune responses.