Abstract
The structure and behavior of canine transmissible venereal tumor after repeated transplantation were studied. Ten random mongrel dogs were divided into a control group (Nos. 1-5) and an experimental group (Nos. 6-10). Before the investigation the experimental animals were sensitized repeatedly by subcutaneous injections of a tumor cell suspension. The cell suspension (cell viability=22.0-38.8%) was transplanted subcutaneously into the right and left hypogastric regions, and within 4 to 5 days after transplantation, a palpable tumor with nodules of 3-5 mm in diameter was detected. By the 18th day after transplantation, the tumors of the experimental animals were not observable. The regression of the tumor in the experimental animals showed the following pattern: firstly, the tumor cells were infiltrated by lymphocytes; secondly, the lymphocytes adhered to the surface of the tumor cells; thirdly, the tumor cells were destroyed and ultimately reabsorbed. Electron microscopy of the tumor cell destruction revealed the following: some of the lymphocytes adhered to the tumor cell at the surface of the cell membrane running parallel to it; when the lymphocytes came into contact with the tumor cell, an intedigitation of protuberances of both cells was visible; the surface of the tumor cell membrane was disturbed at the point of contact; the tumor cell appeared swollen and showed an irregular form; and the cytoplasm was vacuolated with many electron-dense granules. As above mentioned, lymphocytes are thought to have an important role in the regression of the tumor.
