Antitumor Immunity in the Shope Papilloma-Carcinoma Complex of Rabbits. Ill. Response to Reinfection With Viral Nucleic Acid2

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Abstract
Challenge inoculation with infectious viral nucleic acid was used to assess the antitumor immunity of rabbits previously infected with Shope papilloma virus. Each animal was inoculated at 5 sites. Papillomas developed on all 6 carcinomatous animals and on 9 of 10 animals with persistent papillomas. Primary papillomas on 2 rabbits regressed soon after nucleic acid inoculation and no tumors developed at challenge sites on them. No papillomas appeared on 15 regressor animals, although the interval from regression of the primary papilloma to challenge was as long as 5 months. Results were the same whether the regression of the primary tumor had occurred as early as 5 weeks or as late as 6 months after the initial virus inoculation. In round numbers, the proportion of inoculated sites at which tumors developed was: normal rabbits—90 percent, carcinomatous rabbits—90 percent, rabbits with persistent papillomas—75 percent, and regressor rabbits—0 percent. In 10 normal animals inoculated with nucleic acid, all tumors regressed in 4 within 7 weeks after inoculation and all tumors regressed in one by the 10th week. No nucleic acid-induced tumors regressed on any animal with persistent papillomas or carcinomas during an observation period of 16 weeks. It is concluded thatviral nucleic acid induces infection and tumor development in animals bearing persistent papillomas or carcinomas with a frequency close to the infection rate in normal animals, in spite of the known presence of neutralizing antibody in previously infected rabbits. Substantial resistance to tumor development persists for many months after regression of a papilloma.

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