Stimulation of immune responses and reduction in immunosuppression of tumor microenvironment by combination therapy

Abstract

The tumor microenvironment (TME) has been recognized as a major obstacle to the use of immunotherapies to reduce cancer cells (Tan et al., 2021). As shown in past preclinical studies, therapeutic cancer vaccines have shown great promise in the treatment of solid tumors. However, the clinical effects have been indicated to be limited in cancer patients. It is thought that this effect is a result of the immunosuppressive capabilities and the prevention of the adequate infiltration of antitumor T cells in to the TME. However, recent studies have displayed the potential of combination therapies and their ability to induce an improved antitumor immune response (Rückert et al., 2021; Zhang et al., 2021). Therefore, it is important for the treatment of established tumors to develop combination therapies of vaccines with additional therapies, such as radiotherapy (RT) and PD-1 blockade (Kadam et al., 2020; Zhang et al., 2021). This review will look closer into the establishment of the immunosuppressive nature of tumor microenvironments, along with changes in immune cells in relation to monotherapy and combination therapy use. It will further discuss specific immune cells, including Tregs and effector cells and their involvement in the TME and tumor growth. Lastly, advances and limitations in this field of study of will be reviewed involving the use of combination therapies on the TME (Rückert et al., 2021; Zhang et al., 2021).