Summary
In vivo and in vitro treatment of Ehrlich cancer cells with diphtheria toxin resulted in loss of oncogenicity and in immunization against these tumor cells in mice.
The animals that survived a 1st i.p. transplantation of virulent cancer cells treated with diphtheria toxin failed to develop an ascites tumor after a 2nd transplantation up to 200 days later.
Ehrlich cancer cells lost oncogenicity also by prolonged incubation in phosphate-buffered saline in the presence of diphtheria toxin. This loss of oncogenicity was time dependent and influenced by the pH. Cells incubated for 8 hr with diphtheria toxin failed to induce an ascites tumor in both normal and immunosuppressed mice. Incubations performed at 5 pH's ranging from 6.5 to 7.5 demonstrated that the lower values were more effective in inhibiting oncogenicity than were the higher ones.
Eighty % of the normal mice that survived an i.p. transplantation of 1 × 106 cancer cells incubated with diphtheria toxin became resistant to a challenge with 1 × 106 virulent cancer cells. Only 50% of the immunized mice survived a challenge with 2 × 106 cancer cells, while the survival rate fell to nearly 0% after a challenge with 5 × 106 cells.
In Swiss albino mice immunized with Ehrlich cancer cells, a cross-resistance against ascites Sarcoma 180 was observed, while all Ehrlich tumor-immunized DBA/2 mice died within 10 days after a challenge with L1210 tumor.
