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

Efficiency of Neural Differentiation of Mouse P19 Embryonal Carcinoma Cells is Dependent on the Seeding Density

Serum-free culture conditions for retinoic acid-induced neural differentiation of mouse P19 embryonal carcinoma cells were determined for future ex vivo retroviral gene transfer and brain transplantation studies. Neural differentiation of P19 cells was dependent on the seeding densities, and both neurons and astroglia differentiated efficiently at high seeding densities (2 × 104 and 5 × 104 cells/cm2) but not at low seeding density (1 × 104 cells/cm2). In addition, P19 cells cultured at 5 × 104 cells/cm2 showed neural differentiation whether or not they were infected with Friend leukemia virus FrC6-V, which inhibited neural differentiation at 2 × 104 cells/cm2. These results indicate that FrC6-V-infected P19 embryonal carcinoma cells should be seeded at high density to achieve efficient neural differentiation in vitro for ex vivo gene transfer with a FrC6-V–derived retroviral vector system.

Neuropathology induced by infection with Friend murine leukemia viral clone A8-V depends upon the level of viral antigen expression

A8-V is a neuropathogenic clone isolated from the Friend murine leukemia virus which causes spongiosis in the rat brain after infection at birth. Serial studies using chimeric viruses derived from the A8-V and the 57 virus (57-V), which is a non-neuropathogenic strain of Friend murine leukemia virus, proved that the long terminal repeat (LTR) and 5' leader (LTR-leader/A8) derived from A8-V, in addition to the env gene (env/A8) of A8-V, are necessary for the neuropathogenesis of A8-V. The enhancer element within the LTR of A8-V (LTR/A8) has been supposed to contribute to the severe manifestation of spongiosis by inducing high levels of viral production in the brain after A8-V infection. However, the recombinant viruses R7c and R7f, which lack the enhancer element of A8-V, induced spongiosis with high incidence rates, although the isolated viral titers of the infected brain display very low levels, which are even comparable to the 57-V infection. Immunohistochemical studies demonstrated that infection with neuropathogenic chimerae, R7c and R7f, induced increased expression of viral antigens than that produced by infection with non-neuropathogenic chimeric virus, Rec5, despite the fact that R7c, R7f and Rec5 all exhibited similar levels of viral proliferation in the brain postinfection. Thus, neuropathology induced by A8 infection is not dependent upon the viral proliferation rate but rather the level of viral antigen expression.