CD4 and neoplasm: TCRs on the surface of CD8+ T cells interact with TAAs presented by major histocompatibility complex (MHC) class I molecules on the surface of tumor cells, while TCRs on the surface of CD4+ T cells interact with TAAs presented by MHC class II molecules on the surface of antigen-presenting cells (APCs, such as dendritic cells, macrophages, and B cells).