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Increased Oncogenicity of the Murine Sarcoma Virus (Moloney) by Co-infection with Murine Leukemia Viruses¹

Viral Leukemia and Lymphoma Branch, National Cancer Institute, NIH, and Microbiological Associates, Inc., Bethesda, Maryland 20014

The high incidence of spontaneous regressions of primary tumors induced by the Moloney sarcoma virus in adult mice was significantly altered by co-infection with Rauscher, Moloney, and Friend leukemia viruses. Intramuscular, intraperitoneal, or subcutaneous inoculation of sarcoma extracts, prepared from progressively growing tumors obtained from dually infected animals, resulted in extensive metastases. Tumor nodules were observed in several tissues and organs. Regression of primary virus-induced tumors could be altered by low concentrations of Rauscher leukemia virus. The role of the leukemia virus, acting as "helper" or as an immunosuppressor, is discussed.

¹ Presented in part at the Third International Symposium on Comparative Leukemia Research, Paris, France, July, 1967.

² Present address: The Hebrew University of Jerusalem, Rehovoth, Israel.

³ This investigation was supported in part by the National Cancer Institute, USPHS, Contract No. PH-43-66-887 at Microbiological Associates, Inc., Bethesda, Maryland.

Received 11/ 8/67. Accepted 2/16/68.