Retroviral pseudo-virus carrying the envelope proteins of neurotropic Friend murine leukemia virus effectively transferred retroviral vector into glial cells

We isolated the neurotropic Friend murine leukemia virus, FrC6 and its molecular clone A8, which proliferated in rat glial cell lines in vitro and in the rat brain in vivo. To investigate the contribution of viral envelope proteins to the neurotropism of A8 virus, the retroviral pseudo-virus carrying the envelope proteins of A8 virus and Moloney murine leukemia virus (MoMLV) was produced by transfecting the env gene of A8 virus (A8env) in the MoMLV based packaging cell, ΨCRE. The phenotypically mixed pseudo-virus infected the rat glial cell lines as well as NIH 3T3 cells, whereas the ΨCRE-produced pure pseudo-virus without A8env expression infected the glial cells at lower efficiency. Furthermore, the ΨCRE cells with A8env expression produced pseudo-virus at a higher titer than normal ΨCRE cells. The infectivity of the phenotypically mixed pseudo-virus to the glial cells was abolished by a neutralizing antibody against A8 virus, which did not reduce the ability of the ΨCRE-produced pure pseudo-virus to infect NIH 3T3 cells. These results indicated that the envelope protein of A8 virus is assembled into the pseudo-viral particles and that it contributes to glial cell infection by the A8 virus.