Figure 1.

Vaccine-stimulated T cells encounter many immunosuppressive pathways within the tumor microenvironment. Immunogenic tumor vaccines will stimulate tumor-reactive T cells to expand within lymphoid tissue and migrate through the vasculature to the tumor bed. Within malignant tissue, T cells can potentially encounter many immunosuppressive pathways. Tumor cells can express inhibitory molecules, such as PD-L1 and IDO, which suppress T cell effector function and allow tumor immunoevasion. At the same time, many tumors promote the accumulation of regulatory immune cells, such as myeloid-derived suppressor cells (MDSCs) and Tregs to further inhibit effector T cell function locally. Therapies targeting these local immunoevasive pathways may allow vaccine-stimulated T cells to maintain full functionality within a hostile tumor microenvironment.