A DNA Vaccine Targeting the Fetal Liver Kinase-1 (Flk-1) can Activate the Special CD8+ T Cell and Inhibit the Metastasis of Orthotopic Lewis Lung Cancer Model

Abstract

 Lung cancer is the leading cause of cancer related deaths and need new more effective therapies. In this study, we investigated the anti-tumor effect of recombinant orally DNA vaccine delivered by attenuated S.typhimurium strain SL3261 (aroA mutant) targeting vascular endothelial growth factor receptor (VEGFR-2), also known as fetal liver kinase-1 (Flk-1) in mouse. The cDNA of extracellular domains (ECD) of VEGFR-2 (Flk-1_ECD) was amplified by RT-PCR and cloned into the pcDNA3.1 (+) vector, then transformed to the attenuated S.typhimurium strain to construct the oral DNA vaccine. Then pcDNA3.1-Flk-1_ECD was successfully transfected into COS-7 cells and the recombinant protein was detected by Western blot. The effect of the oral DNA vaccine was analyzed by flow cytometry (FCM) analysis and cytotoxicity assay. For mimic the local and regional growth pattern seen in lung cancer patients, the effect of the oral DNA vaccine on tumor growth and metastasis was analyzed by orthotopic cancer cells challenge in vivo. The results demonstrated that the oral DNA vaccine can overcome peripheral immune tolerance, and generated Flk-1- specific CD8⁺ cytotoxic T cell response. Moreover, this oral DNA vaccine could effectively reduce tumor growth, metastasis and increase the survival. It indicated that the oral VEGFR2 DNA vaccine encoding Flk-1_ECD delivered by salmonella might act a potential strategy for immunotherapy of lung cancers.