Effects of vaccinia virus-expressed interleukin 2 on the immune system of sublethally irradiated mice.

Vaccinia virus that expressed interleukin 2 (IL 2) was cleared from immunodeficient irradiated mice more efficiently than virus that did not express interleukin 2. These results extend the previously observed protection from nude mice to another model of immunodeficiency. No antibody or cytotoxic T lymphocyte response could be detected in sublethally irradiated mice that had been inoculated with IL 2-expressing vaccinia virus, but levels of splenic natural killer cell activity were elevated. Sublethally irradiated mice that had recovered from IL 2-plus hemagglutinin-expressing vaccinia virus were partially protected against both influenza virus and vaccinia virus. These results indicate that vaccinia virus-expressed IL 2 mediates clearance of primary viral infection via a mechanism that does not involve antibody or cytotoxic T lymphocytes. They also indicate that inclusion of lymphokine genes in live recombinant viral vaccine vectors may increase vaccine safety.