Enhanced activation of T cells by dendritic cells engineered to hyperexpress a triad of costimulatory molecules

Background: Activation and proliferation of T cells are essential for a suc cessful cellular immune response to an antigen, Antigen-presenting cells (A PCs) activate T cells through a two-signal mechanism. The first signal is a ntigen specific and causes T cells to enter the cell cycle. The second sign al involves a costimulatory molecule that interacts with a ligand on the T- cell surface and leads to T-cell cytokine production and their proliferatio n. Dendritic cells express several costimulatory molecules and are believed to be the most potent APCs, Two recombinant poxvirus vectors (replication- defective avipox [fowlpox; rF] and a replication-competent vaccinia [rV]) h ave been engineered to express a triad of costimulatory molecules (B7-1, in tercellular adhesion molecule-1, and leukocyte function-associated antigen- 3; designated TRICOM), This study was designed to determine if dendritic ce lls infected with these vectors would have an enhanced capacity to stimulat e T-cell responses. Methods: Murine dendritic cells (of both intermediate m aturity and full maturity) were infected with rF-TRICOM or rV-TRICOM I and were used in vitro to stimulate naive T cells with the use of a pharmacolog ic agent as signal 1, to stimulate T cells in allospecific mixed lymphocyte cultures, and to stimulate CD8(+) T cells specific for a peptide from the ovalbumin (OVA) protein, In addition, dendritic cells infected with TRICOM vectors were pulsed with OVA peptide and used to vaccinate mice to examine T-cell responses in vivo. All statistical tests were two-sided, Results: De ndritic cells infected with either rF-TRICOM or rV-TRICOM were found to gre atly enhance naive T-cell activation (P<.001), allogeneic responses of T ce lls (P<.001), and peptide-specific T-cell stimulation in vitro (P<.001), Pe ptide-pulsed dendritic cells infected with rF-TRICOM or rV-TRICOM induced c ytotoxic T-lymphocyte activity in vivo to a markedly greater extent than pe ptide-pulsed dendritic cells (P = .001 in both). Conclusions: The ability o f dendritic cells to activate both naive and effector T cells in vitro and in vivo can be enhanced with the use of poxvirus vectors that potentiate th e hyperexpression of a triad of costimulatory molecules. Use of either rF-T RICOM or rV-TRICOM vectors significantly improved the efficacy of dendritic cells in priming specific immune responses. These studies have implication s in vaccine strategies for both cancer and infectious diseases.