The antigen-specific T cell responses are initiated by professional antigen-presenting cells (APCs). Dendritic cells (DCs) are known to represent such specialized antigen-presenting cell.

Any protein in the tumor cell is a potential tumor antigen. These antigen are released by secretion, shedding, or tumor lysis and captured by DCs. Uptaken antigens are processed and presented by HLA (human leukocyte antigen) class ¥° and class ¥± molecules for priming and activation of CD8+ and CD4+ T cells. Activated CD4+ T cells provide important costimulation via cytokine secretion, which can initiate and also amplify the CD8+ T cell response. In addition, memory CD4+ T cells play a critical role in maintaining the protective immunity. Activated antigen-specific CD8+ T cells become cytotoxic and lyse tumor cells.