Enhanced Therapeutic Efficacy of Tumor RNA-Pulsed Dendritic Cells after Genetic Modification with Lymphotactin

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Abstract
Pulsing dendritic cells (DCs) with tumor cell-derived mRNA is regarded as an attractive alternative in the development of DC-based tumor vaccines. Our aim is to improve the therapeutic efficacy of DC-based tumor RNA vaccines by augmenting the preferential chemotaxis of DCs to T cells. Mouse bone marrow-derived DCs were genetically modified with lymphotactin (Lptn) by adenovirus vector, which conferred on DCs preferential chemotaxis to CD4+ and CD8+ T cells (Cao et al., 1998). Lptn gene-modified DCs (Lptn-DCs) were pulsed with tumor mRNA and used for vaccination in the tumor models of 3LL lung carcinoma and B16 melanoma. In both tumor models, immunization with 4 x 10 4 tumor RNA-pulsed Lptn-DCs induced more potent CTL activity, compared with their counterparts, specifically against tumor cells and Mut1 or tyrosinase-related protein 2 (TRP-2) peptide-pulsed RMA-S cells, and rendered the immunized mice resistant to tumor challenge much more effectively. CD8+ T cells were necessary and sufficient to generate the protection of LptnDC-based RNA tumor vaccines, and CD4+ T cells were required for the induction of tumor rejection. In the preestablished 3LL and B16 tumor models, vaccination with DC-based or LacZ-DC-based tumor RNA vaccines (2 x 10 5 cells) could reduce pulmonary metastasis and extend survival of tumor-bearing mice, but was less effective than the Lptn-DC counterpart (with 60-80% mice surviving). When the immunizing dose was decreased to 4 x 10 4 cells, Lptn-DC-based tumor vaccines rather than their counterparts were still significantly effective. Our studies provide a potential strategy to improve the efficacy of DC-based vaccines, and a new approach to immunological intervention by chemokines.