Attenuation and immunogenicity in primates of vaccinia virus recombinants expressing human interleukin-2

Vector-directed lymphokine expression represents a novel approach to the attenuation of live recombinant viruses which might be used as vaccines. Expression of interleukin-2 (IL-2) by recombinant vaccinia virus has been shown to significantly attenuate virus virulence in rodent species without diminishing immunogenicity. Skin lesion formation and immunogenicity of vaccinia/IL-2 recombinants in three species of primates was examined. IL-2 expression was associated with a 15-fold reduction in the area of induration after intradermal inoculation of recombinant viruses in patas monkeys. Wild type and a control vaccinia recombinant produced large (greater than 5000 mm2) skin ulcers in this species, but the IL-2 expressing recombinant produced no ulceration. Production of antibodies to vaccinia virus and to influenza A virus haemagglutinin expressed by recombinant vectors was examined in rhesus and squirrel monkeys. IL-2 expression accelerated the resolution of skin lesions in rhesus but not squirrel monkeys. Despite this, antibody production was equivalent in the presence or absence of IL-2. IL-2 expression can greatly reduce the skin lesions formed by live recombinant vaccinia vectors in primates, indicating significant attenuation, without reducing the immunogenicity of the vaccine.