Many types of tumors are known to contain functionally abnormal DCs [60-62].Furthermore, direct suppression of the proliferation and differentiation of Tcells by a tumor or its environment or suppression of DC differentiation areconsidered to be an important mechanism of tumor escape from the immune system.In this part of the review, we describe the adverse effects of a tumor and itsenvironment on the functional activity of DCs, leading to a suppression of thespecific activation of effector CD4+ and CD8+ T cells. Here, CD4 is linked to neoplasm.