Biological effects of recombinant vaccinia virus-expressed interleukin 4.

Recombinant vaccinia viruses expressing murine interleukin 4 (IL-4), either alone or together with interleukin 2 (IL-2) or gamma interferon (gamma-IFN), were constructed. Unlike IL-2, IL-4 expressing viruses were not cleared from immunodeficient mice and the mice died. As they died more rapidly than immunodeficient mice inoculated with a control virus, it appeared that IL-4 contributed to their death and the IL-4 mediated toxicity was confirmed in normal immunocompetent mice. The toxicity was reversed by co-expression of either IL-2 or gamma-IFN, probably due to virus clearance and therefore lower levels of circulating IL-4. Vaccinia virus-expressed IL-4 did not increase antibody or natural killer cell levels and caused a slight decrease in cytotoxic T lymphocyte levels.