Inhibition of experimental and spontaneous lung metastases of highly metastatic syrian hamster sarcoma cells by non‐activated bone marrow and peritoneal exudate cells

The possibility of inhibiting local tumor growth (experimental and spontaneous lung metastases) of the selected highly‐metastatic Syrian hamster sarcoma of STHE‐LM 8 subline by means of non‐activated syngeneic and allogeneic spleen, bone marrow (BMC) and peritoneal exudate (PEC) cells was studied. Retroorbital inoculation of Syrian hamsters with native, or lethally irradiated allogeneic BMC and PEC, but not spleen cells, or hamster embryo cells effectively inhibited the development of experimental and spontaneous lung metastases induced by STHE‐LM 8 cells in the animals. Spontaneous lung metastases were effectively inhibited in about 50 % of STHE‐LM 8 tumor‐bearing animals (with or without tumor excision) inoculated with BMC five times at 5‐ to 7‐day intervals beginning from 1 ‐10 days after subcutaneous palpable tumor appearance. Experimental lung metastases were inhibited in 20‐80 % of animals inoculated with BMC or PEC once 5‐7 days before the tumor cells, simultaneously with them, or during the 5‐7 days following the inoculation of tumor cells, thus demonstrating that BMC metastasis‐inhibiting activity was expressed during 10‐14 days against single tumor cells, or small clusters of tumor cells, and was not effective at the stage of micro‐, or macrometastasis formation. BMC and PEC of normal allogeneic donors were significantly more active in metastasis inhibition than the same cells of tumor‐bearing animals. BMC of inbred normal Syrian hamsters of the ICV line were significantly less active, or did not inhibit experimental lung metastases either in syngeneic or in randombred allogeneic hamsters, thus apparently demonstrating an unknown genetic defect of their NR system.