Mouse mammary carcinoma E 0771 of C57BL/6 origin, known to yield XYZ factors, was inoculated into 30 C57BN/cd as well as 30 BALB/c mice. Eight to 15 days later these animals, as well as an additional 30 C57BR/cd and 76 BALB/c mice, received an injection of viable E 0771 tumor cells. No significant difference in tumor development was noted when animals receiving only a single injection of E 0771 tumor cells were compared to mice receiving a double inoculation of the same tumor.

Similarly, the prior inoculation of fresh Brown-Pearce rabbit epithelioma cells failed to alter the malignant process in recipient hosts receiving a second implant of the same tumor administered at a different site 14–21 days later. This was made known in a series of experiments utilizing 78 rabbits of mixed breeds. Of these animals, 40 served as recipients of a double inoculum of viable Brown-Pearce tumor cells, while the remainder received only a single injection and served as controls. These results are in sharp contrast to the XYZ phenomenon observed when frozen Brown-Pearce tumor tissue is given prior to challenge transplantation with fresh homologous tumor tissue.

Thus, for these two mammalian tumors, the E 0771 mammary carcinoma of mice and the Brown-Pearce epithelioma of rabbits, the inoculation of test animals with fresh viable cancerous tissue, followed by a second implantation of the same tumor, does not alter significantly the malignant process in the recipient hosts, although potent XYZ factors are known to be demonstrable when these tumors are subjected to prolonged frozen storage, lyophilization, or centrifugation.

That this phenomenon may be applicable to other experimental neoplasms is made apparent when the data of Jobling and Flexner concerning a rat carcinoma and the data of Rous and Murphy based on experiments with a fowl tumor are reviewed. Although the prior injection of heated rat carcinoma cells resulted in an enhancement of a subsequent transplant of tumor cells, the prior injection of fresh unheated tumor cells did not significantly alter the progress of a subsequent transplant with homologous cancer tissue. Similarly, although the Rous fowl sarcoma appears capable of exhibiting the XYZ phenomenon when supernatant fluid derived from the tumor is utilized, no enhancement of tumor transplant growth occurred when an injection of viable Rous tumor cells preceded challenge with the same tumor tissue.

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The work was aided by grants from the American Cancer Society, the Damon Runyon Fund through the Committee on Growth of the National Research Council, and by the International Cancer Research Foundation. Mr. Dryadale is a graduate student in enzyme chemistry at the University of Wisconsin and Mr. Shear a graduate student in bacteriology and immunology at the University of Minnesota.

Two of the experiments with the rabbits were done in the laboratories of Drs. Wade H. Brown and Louise Pearce at the Rockefeller Institute many years ago, and the experiments with the mice in the laboratories of Drs. George Snell and Nathan Kaliss at the Jackson Laboratory. The assistance of William Fenn, R. R. Davis, M. L. Wrenn, Erma Salter, Gordon L. Ross, and Ward Talley of the Baptist Hospital Laboratory Staff and of Priscilla Smith, Freddy Gabrielson, Dianne Kelton, Joane Byron, and Judy Fielder of the Jackson Laboratory is gratefully acknowledged.

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