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Studies on the HST (Hamazaki)^* Virus Isolated from Yoshida Tumor

( Department of Pathology, the Okayama University Medical School, Okayama, Japan)

It has been recognized that immunity to tumor transplantation may exist; it may be either spontaneous or produced by certain definite means. The existence of an antibody comparable to those in bacterial infections has been demonstrated only in connection with the filtrable tumors and with transplantable tumors which produce concomitant immunity. It has been hitherto believed that there are only three types of tumors which are definitely caused by a specific virus: namely, the Rous fowl sarcoma, the Shope infectious rabbit papilloma, and the kidney tumor in frogs. Opinions are divided at the present time concerning the viral nature of the milk factor of mice bearing mammary cancer (2).

We have succeeded in isolating the virus in question from the tumor ascites. This isolation has been successful in our hands in every instance. The antisera produced by the application of our virus actually inhibited the growth of the ascites tumor whenever the virus in the tumor cell was neutralized by corresponding antisera. It should be stressed that these inhibited tumor cells completely regained their malignant characteristics when the virus in question was re-introduced. If all these facts are taken into consideration, it appears permissible to conclude that the virus isolated from the ascites tumor is an indispensable agent of the tumor ascites. Reproduction of the ascites tumor by means of the administration of our virus to rats unfortunately has been unsuccessful so far, although the HST virus after about 40 successive transmissions acquired a progressively more viscerotropic character and caused, to a marked degree, a chronic inflammation of the granulation type in the omentum, the liver, the spleen, the lymph nodes, the lungs, etc. Mice inoculated with the virus often showed anaplastic growth of peritoneal serous cells and produced an ascites which occasionally produced an ascites tumor containing neoplastic cells derived from the peritoneum. On the whole, the mouse ascites tumor resembles very closely that of rats from which the virus has been isolated. Further details of these findings will be given in a future report.

^* The HST virus was named by Y. Hamazaki, the director of the Department of Pathology, the "HST" being derived from the initials of the main investigators: Y. Hamazaki, J. Sato, T. Sasaki, M. Takahashi, and H. Tani.

This work was supported by grants-in-aid of the Brasilian Japanese Society for the support of Japanese science.

Received 10/18/51.