Antitumor Activity of Host T and Non‐T Cells Recovered from Tumor Nodules after Interferon Therapy

We examined the modification of host T cells of tumor nodules by interferon (IFN) therapy in mouse models. The host cells were recovered from regressing tumor nodules of mice at Day 13 after intradermal tumor inoculation at Day 0 and administration of 5 × 10(5) U/mouse/day IFN at Day 6 to Day 10. These host cells neutralized in vivo Meth A growth in a dose‐dependent fashion. In vitro treatment of these cells with anti‐Thy 1.2 monoclonal antibody and rabbit sera as a source of complement abrogated their tumor‐neutralizing activity, but only partially, indicating that both T cells and non‐T cells were involved in tumor neutralization. The finding that host cells from regressing tumor nodules of either Meth A or Meth 1, an antigenically distinct fibrosarcoma, neutralized both Meth A and Meth 1 tumors without much selectivity was consistent with possible non‐T cell involvement. Most of these characteristics of host cells of regressing nodules of IFN‐administered mice were also noted with host cells of progressing nodules of placebo‐administered mice and there was no significant difference in neutralizing activity qualitatively or quantitatively between the two sources of host cells. There was no significant difference in host T and B cell numbers and compositions of regressing and progressing nodules either. These essentially negative findings raise the possibility, among others, that the primary target host cells to be modified by IFN were not T cells, although the therapeutic effect of IFN was dependent on the host T cells.