Myeloid-derived suppressor cells (MDSCs) play a pivotal role in cancer. To overcome the problem of the MDSCs in the tumor microenvironment in this study, a combination of immunotherapy and chemotherapy was used. For this purpose, a liposomal formulation of P5 peptide and PEGylated liposomal doxorubicin (Doxil®) was utilized to treat mice bearing HER2+ tumor model. The results revealed that Doxil® administration before immunotherapy had not only reduced the population and functions of the MDSCs in the spleen (P < 0.001) and the tumor microenvironment (P < 0.05) but had also supported further immunotherapy including enhanced CD4+ (P < 0.01) and CD8+ lymphocyte (P < 0.001) population and IFN-γ production (P < 0.001). This effect was also more pronounced with a liposomal P5 and Doxil® compared with free peptide and doxorubicin. In conclusion, the results demonstrated that Doxil® plus liposomal P5 could have a decreasing effect on MDSCs and tumor growth, and it could be beneficial in breast cancer treatment.
Keywords: Breast cancer; Chemoimmunotherapy; Doxil®; Liposomal HER2/neu-derived peptide; MDSC.
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