Are the tumor cells of the G2 period of the cell cycle sensitive to the immune pressure?

The present work was aimed at analysing as to whether the cell loss is random within the cell cycle or not. In order to verify the former statement two regressing tumor systems: Ehrlich ascites carcinoma transplated into rats (heterologous graft) and BN/b lymphoma implanted into immunized BN/b mice (syngeneic graft), were used. Both tumor lines were examined by means of double labeling method coupled with short colcemide block. In the case of regressing tumors the cell flux into DNA synthesis was found to be at the same level as for the growing tumors. On the contrary, the flux into mitosis was much lower for regressing tumors than for growing ones. The above results suggest the immune attack on tumor cells while in the G2 phase of the cell cycle.