Expression of metastatic potential of allogenic and xenogeneic neoplasms in young nude mice.

Several different mouse and rat tumors were injected s.c. or i.v. into specific-pathogen-free young (3-week-old) and adult (6-week-old) nude mice. All tumors grew s.c.; however, following i.v. injections, only metastatic neoplasms produced visible pulmonary tumor foci in the 3-week-old (but not in the 6-week-old) nude mice. The quantitative differences in metastatic potential among tumor lines and clones observed in syngeneic hosts were maintained also when 3-week-old nude mice were used. The enhanced survival of tumor cells in the lungs and the large numbers of visible pulmonary metastases observed in the young nude recipients correlated closely with the low levels of natural killer cell activity detected in 3-week-old (but not in 6-week-old) nude mice. In vivo activation of natural killer cells by treatment of mice with polyinosinic-polycytidylic acid or Corynebacterium parvum, 24 hr prior to tumor challenge rendered th 3-week-old nude mice resistant to development of metastases. We conclude that specific-pathogen-free 3-week-old nude mice, which lack functional T-lymphocytes and demonstrate low natural killer cell activity, could serve as an in vivo model to ascertain the metastatic potential of allogeneic and xenogeneic tumors.