The effect of vaccinia virus on Carcinoma 755 (Ca-755) has been investigated, and it has been shown that tumor-inhibitory activity depends on the strain and concentration of the virus used. The most significant degree of oncolysis has been produced with the IHD-T and IHD-E strains of vaccinia virus. Almost complete suppression of tumor growth was obtained when 107.0 pock-forming units of virus were incubated with tumor fragments. Increasingly less tumor-inhibitory activity was demonstrable upon dilution of virus. Inhibition of tumor growth was accompanied by extensive multiplication of virus, but virus multiplication per se did not insure an oncolytic effect. The concentration of virus initially incubated with tumor fragments was found to be more critical in this respect than the titer of virus eventually obtained in the established tumor. Regardless of the extent of virus multiplication in Ca-755, hemagglutinin-inhibiting antibodies to vaccinia virus have not been detected in the sera of tumor-bearing mice. Virus shown to persist in Ca-755 tumors for periods up to 1 month has successfully been transferred along with tumor tissue through eleven serial transplants with but minimal effect on tumor growth. The multiplication and oncolytic activity of vaccinia virus were abolished upon implantation of virus-treated tumors into vaccinia-immunized mice.

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This investigation was made possible by Contract No. SA-43-ph-3016 with the Cancer Chemotherapy National Service Center, National Cancer Institute, National Institutes of Health.

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