Current hepatocellular carcinoma (HCC) immunotherapy trials only yield modest outcome, suggesting that possibly strong intrinsic immunosuppressive network needed to be tackled. Conventional chemotherapies are found to exert immunomodulatory effect on the tumor microenvironment (TME). Our study investigated anti-tumor activity of 5-FU in combination with anti-PD-L1, using pre-clinical HCC mouse model, and evaluated the immunomodulation in TME after drug treatments.
For the orthotopic HCC in vivo experiment, 6-8-week-old male C57BL/6 mice were injected intrahepatically with 5x10^5 RIL-175 luc+ cells. In order to assess its immunomodulatory effect on HCC TME rather than on direct tumor-killing effect, 5-FU was administrated (i.p.) 3 times per week at a relative low dose—20mg/kg. Whilst, anti-PD-L1(10mg/kg) was delivered (i.p.) every 5 days. Tumor growth was monitored via in vivo imaging. Tumor, liver, spleen and blood was collected afterwards, followed by immune profiling analysis via flow cytometry.
In terms of in vivo imaging results, mice with single anti-PD-L1 treatment showed significant response in tumor growth amongst other groups. Meanwhile 5-FU monotherapy and combined treatment group showed no difference with vehicle group. We found an increased amounts of T lymphocytes and NK cells in the tumor site after anti-PD-L1 single treatment, suggesting that these immune active cells contributed to the anti-tumor effect. Tumor-infiltrating myeloid cells, particularly P-MDSC, elevated upon 5-FU treatment in both single and combined group, suggesting that they may play a role in mediating immunosuppression.
This study illustrated that anti-PD-L1 monotherapy enriched tumor-infiltrating T lymphocytes and NK cells, possibly accounting for the deferred tumor growth. However, the accumulation of myeloid cells in 5-FU treated mice hinders the anti-tumor activity of anti-PD-L1 from this orthotopic HCC mouse model. Therefore, low dose of 5-FU may initiate immunosuppressive mechanism to alter the effectiveness of anti-PD-L1 in HCC.
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All authors have declared no conflicts of interest.