Effect of coexpression of interleukin-2 by recombinant respiratory syncytial virus on virus replication, immunogenicity, and production of other cytokines

We constructed rRSV/mIL-2, a recombinant respiratory syncytial virus (rRSV) containing the coding sequence of murine interleukin-2 (mIL-2) in a transc ription cassette inserted into the G-F intergenic region, The recovered vir us (rRSV/mIL-2) expressed high levels (up to 2.8 mu g/ml) of mIL-2 in cell culture. Replication of rRSV/mIL-2 in vitro was reduced up to 13.6-fold fro m that of wild-type (wt) rRSV, an effect that was due to the presence of th e foreign insert but was not specific to mIL-2, Replication of the rRSV/mIL -2 virus in the upper and lower respiratory tracts of BALB/c mice was reduc ed up to 6.3-fold, an effect that was specific to mIL-2, The antibody respo nse, including the levels of RSV-specific serum immunoglobulin G1 (IgG1), I gG2a, IgA, and total IgG, and the level of protective efficacy against wt R SV challenge were not significantly different from those of wt rRSV, Analys is of total pulmonary cytokine mRNA isolated 1 and 4 days following infecti on with rRSV/mIL-2 revealed elevated levels of mRNA for IL-2, gamma interfe ron (IFN-gamma), IL-4, IL-5, IL-6, IL-10, IL-13, and IL-12 p40 compared to those for,vt rRSV. Flow cytometry of total pulmonary mononuclear cells isol ated 10 days following infection with rRSV/mIL-2 revealed increased levels of CD4(+) T lymphocytes expressing either IFN-gamma or IL-4 compared to tho se of wt rRSV. These elevations in cytokine mRNA or cytokine-expressing CD4 (+) cells relative to those of wt rRSV-primed animals were not observed fol lowing challenge with wt RSV on day 28, Thus, the expression of mIL-2 by rR SV was associated with a modest attenuation of virus growth in vivo, induct ion of serum antibodies at levels comparable to that of wt rRSV, and transi ent increases in both the Th1 and Th2 CD4(+) lymphocytes and cytokine mRNAs compared to those of wt rRSV.