Dendritic cells (DC) can provide all the known costimulatory signals required for activation of unprimed T cells and are the most efficient and perhaps the critical antigen presenting cells in the induction of primary T cell-mediated immune responses. It is now shown that mouse cell lines with many of the features of DC can be generated using the MIB phi 2-N11 retroviral vector transducing a novel envAKR-mycMH2 fusion gene. The immortalized dendritic cell line (CB1) displays most of the morphologic, immunophenotypic, and functional attributes of DC, including constitutive expression of major histocompatibility complex (MHC) class II molecules, costimulatory molecules B7/BB1, heat stable antigen, intracellular adhesion molecule 1, and efficient antigen-presenting ability. Granulocyte/macrophage colony-stimulating factor (GM-CSF) proved to be effective in increasing MHC class II molecule expression and in enhancing presentation of native protein antigens. In comparison with macrophages, CB1 dendritic cells did not exhibit phagocytic and chemotactic activity in response to various stimuli and lipopolysaccharide activation was ineffective in inducing tumor necrosis factor alpha or interleukin 1 beta production. CB1 cells, pulsed with haptens in vitro and injected into naive mice were able to induce delayed-type hypersensitivity responses, further increased with pretreatment with GM-CSF, indicating that these cells may represent an immature, rather than a mature DC. The ability of CB1 to prime T cells in vivo could provide a tool to design novel immunization strategies.

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