Tests were made to learn whether an anaplastic, epidermal carcinoma, the Vx2, which had originated more than 8 years previously from a virus papilloma in a domestic rabbit, still rendered its hosts immune to the virus. It had done so in the first 22 successive groups of animals to which it was transferred during a period of 3½ years, its growth regularly eliciting a blood antibody that neutralized the Shope virus and fixed complement in mixture with it; and on the assumption that this would continue to be the case no further observations were made for nearly 4½ years more. Then direct inoculation of animals carrying the tumor in its 46th Generation showed them to be as susceptible to the virus as normal rabbits; and sera procured from hosts of the 46th, 47th, 48th, and 50th Generations failed to neutralize the virus or fix complement with it. Tests of this last sort, repeated at intervals since,—most recently with sera from animals carrying the tumor in its 73rd Generation,—have yielded consistently negative findings.
Loss of the power to immunize against the papilloma virus was not attended by any perceptible change in the Vx2 carcinoma. Manifestly the antigen responsible for the immunity cannot, as such, have been the actuating cause of the tumor.
Attempts were made to infect the cells providing 48th Generation cancers, by mixing them with a suspension of the papilloma virus at time of implantation, or by injecting this agent into the blood stream of rabbits in which the tumog had already begun to proliferate. Its morphology and rate of growth remained unaltered; but tests of the animals to which transfers were next made yielded what appeared to be evidence of some slight immunity to the virus.