Dendritic cells (DC) represent the first line of body's defenses against pathogens and provide a critical link between the innate and acquired arms of the immune system. Because of their unique capacity to present antigens and to initiate powerful immune responses, DC carry tremendous clinical potential as vaccines against infections and cancer. However, the progress in DC research and therapeutic applications is hampered by the lack of essential genetic tools, such as reliable systems for DC-specific gene expression or gene inactivation in vivo. The goal of this proposal is to generate and characterize such genetic systems for gene manipulation in DC. As Specific Aim 1, we propose to generate a system for Cre/LoxP-mediated gene manipulation in murine DC. Recently, we created a mouse strain expressing Cre recombinase specifically in DC. We will characterize the efficiency and specificity of Cre/LoxP recombination in this strain, and test its utility for DC- specific gene inactivation. In addition, novel Cre-expressing strains will be generated to facilitate both constitutive and inducibe gene targeting in DC. As Specific Aim 2, we propose to create a robust system for targeting gene expression specifically to DC in vivo. To this end, we will characterize the distal regulatory elements of the DC-specific CD11c gene, and test their utility for DC-specific transgene expression. Altogether, these studies might facilitate the basic research of DC development and function, as well as pave the way for their clinical applications as vaccines and immunomodulatory agents. [unreadable] [unreadable] [unreadable] [unreadable]