Oncogenicity of Two Strains of Chicken Sarcoma Virus for Rats2

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Abstract
Two strains of Rous chicken sarcoma virus, one supplied by Dr. W. R. Bryan of the National Cancer Institute, Bethesda, Maryland, and the other by Dr. L. A. Zilber of the Gamaleya Institute of Epidemiology and Microbiology, Moscow, have been investigated for their oncogenicity in rats. Both virus strains were recovered in diminishing titer from tissues of newborn and “conditioned” adolescent rats, up to day 21 after inoculation with a tumor mince. Of 102 rats inoculated when newborn with the Bryan strain of virus, only 1 developed a solid tumor. Of 221 rats inoculated when 5 to 6 weeks old, with or without conditioning (X ray and cortisone, alone or combined, and 3-methylcholanthrene), 6 developed solid tumors in the cervical, axillary, or inguinal region. After injection of the Bryan material, virus was not demonstrated in any of these tumors. After the Zilber strain of chicken sarcoma was injected into 162 newborn to 7-day-old rats, 73 developed cystic hemorrhagic tumors in the cervical, axillary, and inguinal regions. Solid tumors developed in 4 rats at the site of previously cystic tumors. When rats were inoculated at 2 to 6 weeks of age, no cystic tumors developed, but solid tumors appeared in 5 of 45 rats given injections of this material at this age. Infective virus was demonstrated in the capsule of some cysts up to 11 weeks after inoculation. Older cysts and solid tumors yielded no virus. The cystic rat tumors consisted of multiple endothelium-lined cysts in a loose fibromatous or myxomatous stroma. In older cystic lesions the cyst lining was stratified, probably as a result of hypertrophy and hyperplasia of the endothelial cells. Cysts, in the early stages, were filled with a straw-colored fluid that later became hemorrhagic. Neutralization studies indicated that these two strains of chicken sarcoma were antigenically dissimilar. The solid tumors were fibromas, but in some of them small cystic lesions persisted and former cystic areas solidified by fibrosis could be detected. Conditioning had no discernible effect on the pathogenicity of the Bryan virus.

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