Selenium nanoparticles enhance the anti-tumor immune responses of anti-4-1BB antibody and alleviate the adverse effects on mice

4-1BB agonists for cancer immunotherapy have shown good preliminary efficacy in clinical trials, but several of the first-generation 4-1BB agonistic antibodies entering the clinic have failed due to safety issues. Selenium nanoparticles (SeNPs) exhibit anti-inflammatory, anti-tumor, antioxidant, and immune-modulating properties. In addition, they have been shown to have detoxifying effects and prevent oxidative liver damage. In this study, we used an anti-4-1BB antibody in combination with SeNPs to evaluate the anti-lung cancer effects in in vitro and in vivo experiments and explore the underlying mechanisms by pathological analyses, quantitative PCR, and enzyme-linked immunoassay. We found that 5 μmol·L^–1 anti-4-1BB antibody combined with 1 μmol·L^–1 SeNPs increased the expression of IFN-γ and promoted the killing effects of peripheral blood mononuclear cells on Lewis lung carcinoma cells, with a lethality rate up to 56.88 %. Experiments in tumor-bearing mice showed that the tumor inhibition rate was 58.61 % after treatment with 3.5 mg/kg anti-4-1BB antibody combined with 0.25 mg/kg SeNPs, and the liver function index returned to normal. When the combined treatment was compared with the antibody treatment alone, detection of immune relevant factors demonstrated that the expression of FOXP3, IL-2, IL-12, and TNF-α in the spleen was downregulated, whereas the expression of IFN-γ in the spleen, serum, and tumor was upregulated, accompanied by increased Fas ligand expression in the tumor tissues. Based on these findings, we get the conclusion that anti-4-1BB antibody combined with SeNPs may alleviate the immunosuppression of regulatory T cells, promote the immune cell proliferation and metastasis to synergistically kill tumor cells. This combination also reduces the inflammatory damage to normal tissues and slows overstimulation of the splenic immune response.