A Triad of Costimulatory Molecules Synergize to Amplify T‐‐Cell Activation in Both Vector‐‐Based and Vector‐‐Infected Dendritic Cell Vaccines

Abstract

The activation of a T cell has been shown to require two signals via molecules present on professional antigen presenting cells: signal 1, via a peptide//MHC complex, and signal 2, via a costimulatory molecule. Here, the role of three costimulatory molecules in the activation of T cells was examined. Poxvirus ((vaccinia and avipox)) vectors were employed because of their ability to efficiently express multiple genes. Murine cells provided with signal 1 and infected with either recombinant vaccinia or avipox vectors containing a TRIad of COstimulatory Molecules ((B7‐‐1//ICAM‐‐1//LFA‐‐3, designated TRICOM)) induced the activation of T cells to a far greater extent than cells infected with vectors expressing any one or two costimulatory molecules. Despite this T‐‐cell “hyperstimulation” using TRICOM vectors, no evidence of apoptosis above that seen using the B7‐‐1 vector was observed. Results employing the TRICOM vectors were most dramatic under conditions of either low levels of first signal or low stimulator cell to T‐‐cell ratios. Experiments employing a four‐‐gene construct also showed that TRICOM recombinants could enhance antigen‐‐specific T‐‐cell responses in vivo. These studies thus demonstrate the ability of vectors to introduce three costimulatory molecules into cells, thereby activating both CD4⁺⁺ and CD8⁺⁺ T‐‐cell populations to levels greater than those achieved with the use of only one or two costimulatory molecules. This new threshold of T‐‐cell activation has broad implications in vaccine design and development.Dendritic cells infected with TRICOM vectors were found to greatly enhance naïve T‐‐cell activation, and peptide‐‐specific T‐‐cell stimulation. In vivo, peptide‐‐pulsed DCs infected with TRICOM vectors induced cytotoxic T lymphocyte activity markedly and significantly greater than peptide‐‐pulsed DCs.

• Vaccines
• Cancer vaccine
• Cancer
• Costimulation
• T cells