MHV-nsp1Δ99-GP33-GFP and MHV-GP33-GFP Elicit Strong CTL Responses and Protect Mice from Homologous and Heterologous Viral Infections

(A, B) Groups of three C57BL/6 mice were immunized with the indicated doses of MHV-nsp1Δ99-GP33-GFP or MHV-GP33-GFP. IFN-γ–secreting CD8⁺ splenocytes were determined 8 d post immunization following short-term in vitro restimulation with GP33 or S598 peptide. Values in (A) represent the percentage ±SD of IFN-γ–secreting CD8⁺ T cells restimulated with GP33 or S598; values in (B) represent the absolute numbers of CD8⁺ IFN-γ⁺ cells ±SD (n = 6 for GP33, n = 3 for S598). Pooled data from two separate experiments are shown.

(C, D) Groups of three mice were immunized with 5,000 pfu of the indicated virus or PBS-treated and 14 d later challenged with 5,000 pfu of wild-type MHV-A59. At 5 d post challenge, viral titers in liver and spleen were determined (C) and ALT values (D) were measured. Data in graphs (C) and (D) represent means ±SD from one representative experiment. n.d., not detected.

(E) Protection against heterologous viral challenge. Groups of four C57BL/6 mice have been immunized with the indicated viral doses or PBS-treated and 28 d later challenged with 200 pfu of LCMV-WE. At 4 d post challenge, viral titers in spleens were determined. Data in graph represent means ±SD from two pooled experiments with a total of eight mice per group. Statistical analysis was performed using Student's t-test (***, p < 0.001; **, p < 0.01; n.s., p > 0.05).