We prepared the murine myeloma cell line NS-1, which stably expressed the human T lymphotropic virus type I (HTLV-I) env gene. The plasmid BCMGEnv was constructed from the episomal vector BCMGSNeo, which was primarily derived from bovine papilloma virus. Transfected env expression was detected by Northern blotting, as well as by flow cytometry using envelope protein-specific monoclonal antibodies (mAb). Expression was detectable for at least seven months. The env transfectants induced syncytium formation which is characteristic of HTLV-I-infected cells, in the human uterine cervical cancer line, HeLa, and the rat cell line, XC. The requirement of envelope proteins for syncytium formation was confirmed by an inhibition assay with envelope protein-specific mAb. Therefore, env transfectants are not only stable, but also have its specific biological function. This system may be useful to analyze the initial steps of viral attachment to the cell surface and to search for the HTLV-I receptor.
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