Antitumor activity of T cells in lymphoid organs induced by interferon in tumor-bearing mice

Administration of human hybrid interferon-alpha A/D (IFN) for 5 consecutive days induced antitumor activity in spleen of Meth A fibrosarcoma-bearing mice 9-10 days after cessation of IFN administration. Antitumor activity assayed by the in vivo neutralization test was found in the spleen of responding mice but not in that of progressive mice. This activity was T-cell-dependent and tumor-selective. However, tumor-neutralizing activity was not found in spleen recovered as early as 3 days after cessation of IFN administration when many tumor cells are still surviving in tumor nodules and being attacked by the host. Instead, T-cell-dependent and tumor-selective tumor-neutralizing activity was found in the lymph node of tumor-bearing mice at this early stage. Furthermore, the tumor-neutralizing activity was already detected in the lymph nodes during the course of IFN administration, although there was no difference in the cell composition of the lymph nodes of IFN- and placebo-administered mice. Since IFN-alpha is apparently not a direct modifier of T cells, these results indicate that IFN probably did not directly increase the number of antitumor T cells but instead modified the host-tumor interaction in such a way that, as an early event, the enhanced T-cell response to tumor cells occurred, resulting in an increase in the antitumor T-cell population in lymph nodes. We supposed that, as the tumor regressed, these antitumor T cells would eventually leave the lymph node and migrate to the spleen.