The effect of pre-treatment of syngeneic mice with tumour cells cultured in vitro on the induction of a transplantable tumour.

The pre-treatment with in vitro cultured mammary adenocarcinoma (ADK-1t) cells strongly protects syngeneic Balb/c mice against the challenge with the same non-cultured tumour cells. If the cultured cells were detached with sodium versenate, 50-60% protection was given, whereas if trypsin was used only 20-30% protection was achieved. That in vitro culture considerably reduces the oncogenic potential of ADK-1t cells was shown by the fact that very many more cultured than non-cultured cells were required to induce tumours.