Enhancing the potency of peptide-pulsed antigen presenting cells by vector-driven hyperexpression of a triad of costimulatory molecules

Recombinant orthopox vectors (both replication-defective fowlpox [rF]. and replication competent vaccinia [rV] have been developed that simultaneously express three T-cell costimulatory molecule transgenes. The constituents o f this, triad of costimulatory molecules (designated TRICOM) are B7-1, ICAM -1, and LFA-3. We have previously shown that infection of murine dendritic cells (DCs) with TRICOM vectors increases their level of expression of the triad of costimulatory molecules and enhances the efficacy of DCs to activa te T cells. While DCs are arguably the most potent antigen presenting cell (APC), limitations clearly exist in their use due to the level of effort an d cost for their generation. The studies reported here demonstrate that a g eneric APC population, murine splenocytes, can be made markedly more effici ent as APCs by infection with either rF-TRICOM or rV-TRICOM vectors. Infect ion of splenocytes with either TRICOM vector led to significant improvement of APC capabilities in terms of: (a) enhancement of mixed lymphocyte react ions, (b) a reduction in the amount of signal 1 to activate naive T cells; and (c) a reduction in the amount of APCs required to activate T cells usin g a constant amount of signal 1. TRICOM-enhanced T-cell activation was show n to correspond to increases in type-1 cytokines and a reduced level of apo ptosis. compared with T cells activated with uninfected or control vector-i nfected splenocytes. In vitro and in vivo experiments compared DCs with TRI COM-infected splenocytes. Infection of splenocytes with TRICOM vectors mark edly enhanced their ability to activate T cells to levels approaching that of DCs. These studies thus demonstrate for the first time that an abundant and accessible population of APCs obtainable without lengthy culture or the use of costly exogenous cytokines tin contrast to that of DCs) can be made more potent as APCs with the use of vectors that express a triad of costim ulatory molecules. Published by Elsevier Science Ltd.