The efficacy of a novel vaccine approach using tumor cells that ectopically express a codon-optimized murine GM-CSF in a murine tumor model

Granulocyte macrophage-colony stimulating factor (GM-CSF) is a potent immunomodulatory cytokine that is known to facilitate vaccine efficacy by promoting the development and prolongation of both humoral and cellular immunity. Here, we investigated a novel vaccine approach using a human papillomavirus (HPV)-16 E6/E7-transformed cell line, TC-1, that ectopically expresses a codon-optimized 26-11-2015 murine GM-CSF (cGM-CSF). Ectopically expressing cGM-CSF in TC-1 (TC-1/cGM) cells significantly increased expression of a GM-CSF that was functionally identical to wt GM-CSF by 9-fold compared with ectopically expressed wild type GM-CSF in TC-1 cells (TC-1/wt). Mice vaccinated with irradiated TC-1/cGM cells exhibited enhanced survival compared with mice vaccinated with TC-1/wt cells when both groups were subsequently injected with live TC-1. Consistently, mice vaccinated with irradiated TC-1/cGM cells exhibited stronger IFN-γ production in HPV E7-specific CD8⁺ T cells. More dendritic cells were recruited to the draining lymph nodes (dLNs) of mice vaccinated with TC-1/cGM cells than C-1/wt cells. Regarding dLN cell recall responses, both proliferation and IFN-γ production in the HPV E7-specific CD8⁺ T cells were enhanced in mice that were vaccinated with TC-1/cGM cells. Our results demonstrate that a novel practical molecular strategy utilizing a codon-optimized GM-CSF gene overcomes the limitation and improves the efficacy of tumor cell-based vaccines.