Effective therapeutic anticancer vaccines based on precision guiding of cytolytic T lymphocytes

In natural immune responses CD4(+) T helper (Th) cells, reactive with peptide antigens presented by major histocompatibility complex (MHC) class II molecules on dendritic cells (DC), can drive the maturation of DC that is required for induction of CD8(+) cytolytic T-lymphocyte (CTL) immunity. Proper induction, expansion and maintenance of CTL responses are achieved through delicate interactions between CD4(+) T cells, DC and CD8(+) T cells involving several ligand-receptor pairs. Th cells to a large extent operate through up-regulation of CD40L, which then interacts with CD40 on DC to cause DC maturation. Subsequent CTL induction by activated DC requires CD80/CD86 on the DC to interact with the CD28 costimulatory receptor on CD8(+) T cells. For maintenance and full expansion of CTL, interaction of the DC-expressed 4-1BB ligand with its receptor 4-1BB on CTL is also important. Alternative molecular triggers of DC activation that can support induction of powerful CTL responses include agonistic anti-CD40 antibody or ligands of Toll-like receptors (TLR) such as LPS (TLR4 ligand) or oligodeoxynucleotides containing CpG-motifs (TLR9 ligand). The combination of CpG adjuvant with a 35 amino acid long synthetic peptide comprising both tumor-specific CTL and Th epitopes proved to be a highly effective vaccine formulation capable of inducing therapeutic immunity against human papillomavirus-induced mouse tumors. The recently acquired insights into antigen presentation and costimulatory signals have made possible the development of a new generation of therapeutic anticancer vaccines.