CD4 and neoplasm: On the other hand, type I tumors are affected by adaptive resistance, which suggests that inflammatory signals such as interferons secreted by CD4+ T helper cells and CD8+ T cells in the tumor microenvironment induce upregulation of PD-L1 expression by tumor cells and TIICs, including macrophages, myeloid suppressor cells, dendritic cells, and even lymphocytes.