Transplantation Immunity to Simian Virus 40-Transformed Cells in Tumor-Bearing Mice. I. Development of Cellular Immunity to Simian Virus 40 Tumor-Specific Transplantation Antigens During Tumorigenesis by Transplanted Cells2
The immune response of inbred BALB/c mice to tumor-specific transplantation antigens (TSTA) of transplanted syngeneic cells transformed by simian virus 40 (SV40) was studied throughout the period of tumorigenesis. Immune lymphoid cells, capable of specifically preventing or delaying tumor growth of admixed SV40-transformed mouse or hamster cells when inoculated into adult hosts, were detected in lymph nodes, spleens, and peritoneal exudates of mice with established tumors. Furthermore, tumor-bearing mice resisted high secondary challenges of SV40-transformed cells when inoculated at a site distant from the primary inoculation site, which thus demonstrated the presence of a functional effector mechanism for tumor rejection. By 4 days after the inoculation of 105 SV40-transformed cells, mice could resist challenges of similar doses of the virus-transformed cells. Transformed cells inoculated only a day after a previous inoculation at a distant site were delayed in developing a tumor; however, the rate of development of the tumor at the first site was unaffected. These results indicate that cellular immunity to SV40 TSTA develops early during tumorigenesis by transplanted cells; nevertheless, the tumors develop and grow progressively. It is suggested that either the level of immunity is not sufficient during early tumorigenesis to prevent the tumor from establishing or, alternatively, there is a local efferent block at the site of tumor development.