Fig. 4.
Mutation within the F-MLV ISD confers protective activity and enhances immunogenicity. (A) Protection of mice immunized with DM F-MLV and challenged with WT F-MLV. Swiss mice were injected with 8 × 108 RNA copies of DM F-MLV (white and gray circles) or with PBS (black circles), and the absence of viremia was checked 4 weeks later (day −35). Nine weeks after infection, mice were challenged with 4 × 107 RNA copies of WT F-MLV (gray and black circles) or injected with PBS (white circles), and postchallenge sera samples were collected at the indicated time points. Each circle corresponds to one individual mouse, with the lines connecting the geometric means of eight mice; data are representative of more than three independent experiments, with no significant departure from full control of viremia by the vaccinated mice in all cases. (B and C) Compared immunogenicity of WT and DM UV-inactivated F-MLV. C57BL/6 mice were injected three times with a 1-week interval with 109 RNA copies of UV-inactivated WT or DM F-MLV in the presence of 50 μg of CpG ODN. (B) One week after the last injection, mice were blood-sampled and serially diluted serum was used to detect TM-specific (Left) and Gag-specific (Right) IgG by ELISA. Results are the mean ± SD of five mice and are representative of three independent experiments. (C) Ten days after the last injection, mice were killed and splenocytes were restimulated in vitro for 72 h in the presence or absence of the I-Ab-restricted H19 Env peptide (Left) or Kb-restricted Gag peptide (Right). Specific IFN-γ secretion by CD4 or CD8 T cells was detected in culture supernatants by standardized sandwich ELISA. Data are the mean ± SD of three independent experiments performed with three to four mice per group.