Basically according to Reimann and Dexter's method, bone marrow cells of LACA mice were cultured for long term. MCA was added to the cell suspension at the final concentration of 3.3μg/ml and /or 60 Co γ-ray irradiation was performed with 300 rads in vitro. The following results were obtained.
Malignant transformaton began to emerge at 10~11 weeks after the beginning of exposure to γ-ray and/or MCA. On observation, the biological characteristics of the malignant-transformed cells were demonstrated as follows:
1. The plating efficiency was 40.3%, and the malignant colony-formation rate was 1.3~1.7%.
2. The maximum saturation density was 0.98~2.46×104/cm2, and that of control cells was 0.14×104/cm2. The former was 7~17.6 times greater than the latter.
3. The transformed cells were agglutinated by concanavalin A within 30 minutes in the room temperature.
4. The transformed cells were able to grow and proliferate in medium with low serum (2%) or without serum.
5. They had the ability of growing and proliferating unlimitedly.
6. They were capable of growing and proliferating notwithstanding the presence of ouabain in the growth medium.
7. There appeared chromosomes abnormal in number and morphological structure.
8. When inoculated, the transformed cells developed successfully fibrosarcomas in the sites of injection. No synergistic effect between radiation and chemical carcinogen was observed. We suggested that the transformed cells might derive from the interstitial cells of the bone marrow.
