ABSTRACT
In 1979 the author developed a murine model of tumor-dormancy (1-3). The protocol used to establish the tumor-dormant state and to treat individual tumor-dormant mice. He presents the concept of how the immune response that maintains L5178Y cells in a tumor-dormant state is regulated. The cytokine network which regulates the cellular immune mechanisms which maintain L5178Y cells in a tumor-dormant state is extremely sensitive to the down-regulatory effects of Prostaglandin E2, which is produced by activated macrophages. The repeating cycles of tumor cell proliferation, immune lysis and tumor cell escape result in the selection of an L5178Y phenotype which is relatively resistant to immune lysis and poorly immunogenic. He also tested the supernatants of pure L5178Y cell cultures for immunomodulatory activities and found 5 different activities. These are Immunosuppressive Factor, Macrophage-triggering Factor, Interleukin-1-beta, Thymocyte-stimulating Factor and Tumor Growth-stimulating Factor. L5178Y cells may produce these immunomodulatory factors by virtue of their T-cell origin, and non T-cell derived tumors may behave differently.
