Interleukin 2 gene therapy of surgical minimal residual tumour disease: Characterization of cytolytic effector cells from tumour progressors and regressors

Experiments were designed to characterize cytolytic effector cells from mic e with SMRTD treated with IL-2 gene therapy, Mice were inoculated with syng eneic murine MK16 carcinoma cells, When the tumours reached 8-12 mm in diam eter, they were excised and the operated mice were randomized into two grou ps. The first group without any further treatment was designated as operate d-only; the second group, vaccinated 3 days after the operation with IL-2-p roducing tumour vaccine, is referred to as operated-vaccinated. Tumour recu rrence rate in the operated-only mice was 90 percent; in the operated-vacci nated group the recurrence rate was 38.5 percent (progressors). The remaini ng 61.5 percent of mice were permanently protected (regressors), On day 53, the tumour progressors, regressors and healthy controls mere sacrificed, a nd their spleen cells were used for Cr-51 microcytotoxicity assay, Splenocy tes from any group of mice were not cytolytic when allowed to react with MK 16, YAC-1 (NK sensitive) and C1498 (NK resistant) targets. However, when gr own for 3 days in IL-2-containing medium, the splenocytes from all groups o f mice could develop cytolytic activity. The cytolytic activity of splenocy tes from tumour progressors and regressors was substantially lower then tha t of splenocytes from healthy controls, In addition, significantly lower cy tolytic activity was observed with IL-2-activated splenocytes from tumour p rogressors as compared to that of tumour regressors, Depletion of NK1.1(+) cells or CD4(+) plus CD8(+) cells prevented the induction of significant IL -2-stimulated cytotoxicity directed against MK16 and C1498 targets in splee n cell cultures from tumour progressors, regressors, and healthy control mi ce, indicating that both, NK1.1(+) and CD4(+) plus CD8(+), cells participat e in the antitumour effect of IL-2 gene therapy. This was further supported by the finding that after depletion of CD4(+) plus CD8(+) cells, a residua l cytolytic activity directed exclusively against NK-sensitive YAC-1 cells was observed.