The Effect of Low-Dose Chemotherapy on the Tumor Microenvironment and its Antitumor Activity Combined with Anti-PD-1 Antibody

Aim: This study aimed to explore the effects of low-dose chemotherapy in the tumor microenvironment (TME) on a gastric cancer xenograft and its antitumor activity combined with the anti-PD-1 antibody. Materials & methods: Mice with gastric cancer were divided into four groups. The body weight and tumor volume of the mice were recorded. The TME was analyzed using flow cytometry. Results: Low-dose paclitaxel increased the PD-L1 expression level and the number of CD8+ T cells, but not the CD4+ T and myeloid-derived suppressor cells or PD-1+ CD8+ T cells in the TME. Low-dose 5-fluorouracil reduced the number of myeloid-derived suppressor cells and PD-1+ CD8+ T cells, but the PD-L1 expression level and the number of CD4+ T and CD8+ T cells did not change in the TME. The anti-PD-1 antibody inhibited tumor growth, but the combination therapy did not show superior antitumor activity. Conclusion: Low-dose chemotherapy altered the TME but failed to improve the responses to the anti-PD-1 antibody.