Combination therapy with liposomal doxorubicin and liposomal vaccine containing E75, an HER-2/neu-derived peptide, reduces myeloid-derived suppressor cells and improved tumor therapy.

Myeloid-derived suppressor cells (MDSCs) are immunosuppressive cells causing resistance to immunotherapies in cancer tumors. In the current study, various immunogenic and therapeutic features of the combination therapies with non-liposomal Doxorubicin (Dox) and the E75 immunogenic peptide (Pep), derived from the human epidermal receptor-2 (HER-2), are investigated in parallel with their liposomal formulations (Lip-Dox (Doxil®) and Lip-Pep). Therefore, triple injection doses of Lip-Pep were preceded with Dox and Lip-Dox injections in TUBO/breast tumor-bearing BALB/c mice. Chemotherapy with either Dox or Lip-Dox reduced the frequency of MDSCs, the level of reactive oxygen species (ROS), and MDSCs-associated genes of Arg1, iNOS, S100A8, S100A9. Whereas Lip-Pep + Dox and Lip-Pep + Lip-Dox treatments synergistically potentiated the immunized splenocytes to produce INF-γ and enhanced the frequency of the anti-tumor CD8+ and CD4+ T cells as opposed to both chemotherapy and immunotherapy regimens. Chemo-immunotherapy increased the number of tumor-infiltrating lymphocytes (TILs) and reduced the level of CD25+ FoxP3+ T regulatory cells. Taken together, chemo-immunotherapy was the optimum treatment for the limitation of tumor progression as they targeted more cancer-related immune players.