HPV-induced tumors control by CD8+ cells and MDSC depletion

Active anti-cancer immunotherapeutic approaches have been shown to induce cellular or humoral immune responses in patients, but thus far, the observed outcomes did not ensure their recommendation for clinical use. The induction of tumor-specific CD8+ T cells, although required for the clearance of most solid tumors, showed to be insufficient for the development of a successful immunotherapeutic approach. The suppressive immune environment triggered by tumors, including the expansion of myeloid-derived suppressor cells (MDSCs), is detrimental to the development of antitumor immune responses and precludes the generation of more promising clinical outcomes. In the present work, we characterized the CD8+ T cell population specifically involved in the control of tumor growth and the role of MDSCs after administration of an antitumor therapeutic DNA vaccine targeting human papillomavirus type 16 (HPV-16)-associated tumors. In mice grafted with tumor cells expressing the HPV-16 oncoproteins, led to the activation of cytotoxic high-avidity CD8+ T cells with an effector memory phenotype. In addition, MDSC antibody depletion further enhanced the immunotherapeutic effects of the vaccine, resulting in the complete eradication of tumor cells. Collectively, the present results indicate that the simultaneous control of MDSCs and activation of high-avidity tumor-specific effector memory CD8+ T cells are key features for tumor protection by immunotherapeutic approaches and deserve further testing under clinical conditions.

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