Semi-Replication-Competent Retroviral Vectors Expressing Gibbon Ape Leukemia Virus Fusogenic Membrane Glycoprotein (GALV FMG) Gene for Cancer Gene Therapy

ƒThis is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ license/by-nc/3.0/). A semi-replication-competent retroviral (s-RCR) vector system in which the gag-pol and env (GALV FMG, gibbon ape leukemia virus fusogenic membrane glycoprotein) genes were split into two separate packageable vectors was developed. These vectors are more efficient than replication-defective retroviral (RDR) vectors in gene delivery and have a higher transgene capacity than replication-competent retroviral (RCR) vectors. For the gag-pol vector construction, internal ribosomal entry site-enhanced green fluorescent protein (IRES-EGFP) was introduced downstream of the gag-pol sequence of the previously constructed MoMLV-10A1-EGFP vector to generate MoMLV-gag-pol-IRES-EGFP. For env vector construction, GALV FMG was inserted into the pCLXSN vector to generate pCLXSN-GALV FMG-IRES-EGFP. MoMLV-gag-pol-IRES-EGFP and pCLXSN-GALV FMG-IRES-EGFP were co-transfected into 293T cells to generate s-RCR viruses. These viruses propagated EGFP and induced syncytium formation due to the cytotoxicity of GALV FMG. To improve the cytotoxicity of s-RCR vector system, GALV FMG or the fusogenic envelope G glycoprotein of the vesicular stomatitis virus (VSV-G) was inserted into gag-pol vector. Co-transfection of MoMLV-gag-pol-IRES-GALV FMG + MoMLV-EGFP or MoMLV-VSV-G + pCLXSN-GALV FMG-IRES-EGFP in 293T cells induced stronger syncytium formation than s-RCR vectors (MoMLV-gag-pol-IRES-EGFP + pCLXSN-GALV FMG-IRES-EGFP). In addition, s-RCR stocks collected from transfected 293T cells induced syncytium formation in the human cancer cell lines HT1080 and TE671. Hence, the s-RCR vector systems developed in this study are useful tools for cancer gene therapy.