Antitumor immune response is generally suppressed in different ways in many types of tumors. In fact, a variety of immunosuppressive cells, such as regulatory T cells, myeloid-derived suppressor cells, and tumor-associated macrophages, surround the tumor modulate antigen-presenting cells and effector T cells. The strategy to abreact the immunosuppressive conditions is necessary for a successful immunotherapy against cancers. Particularly, the improvement of the tumor microenvironment (TME) from this point is important for cancer immunotherapy. The checkpoint blockade as the representative success of the cancer immunotherapy can reactive the suppressed T cells. However, the efficacy of this treatment is limited. Therefore, it is necessary to evaluate the TME to establish more valid cancer immunotherapies. In addition, we need to pay attention to the relation of the therapy to immune responses. When tumor cells are killed by the antitumor agents, such as anticancer drugs, it is important that the cell death guides a secondary immune response by the antigen-presenting cells, particularly dendritic cells. Here, we discuss how the positive and negative effects by immune regulatory cells or stimulatory cells influence the subsequent immune dynamics in the TME. This will also lead to the development of new therapies to activate immunosuppressive conditions in the TME.