Antitumor Effect of Recombinant Human Interleukin‐2 on the Growth of Murine Hemangioendothelioma D14 in Nude Mice: Occurrence of Large Granular Cells in the Tumor

The antitumor effect of recombinant human interleukin-2 (rIL-2) on murine hemangioendothelioma D14 (D14) in female BALB/c-nu/nu mice was examined histologically. D14 cells which had been maintained in vitro were transplanted subcutaneously into nude mice on day 0 (1 × 107 cells/mouse). The mice with established tumor on day 28 received rIL-2 subcutaneously at a dose of 20 μg/mouse/ day for 35 days. On day 63, the mice were killed, and the tumor, spleen and bone marrow were examined histologically. In the mice that had received rIL-2, tumor growth was significantly suppressed. Histologically, there was marked infiltration of large granular cells (about 15-30 μ in diameter) in the tumors. In the adjacent areas, there was a significant increase in the number of tumor cells showing karyorrhexis. The large granular cells (LGC) contained periodic acid Schiff-positive round granules in the cytoplasm and were stained positively for Thy-1.2 surface antigen. The LGC were also positive for asialo GM1 surface antigen but not for Lyt-1, Lyt-2 or IgG surface antigens. This evidence suggests that the LGC are lymphokine-activated killer-like cells which were derived from a natural killer cell lineage. The concomitant increases in the number of LGC and the number of cells showing karyorrhexis in the tumors of the mice treated with rIL-2 suggest that LGC play an important role in the destruction of tumor cells.