Immune rejection of metastases arising from intraocular tumors in mice

The role of the immune response in the elimination of spontaneous metastases arising from intraocular tumors was examined in a syngeneic intraocular murine tumor model. P91 mastocytoma (DBA/2 origin) expresses strong tumor-specific transplantation antigens and grows transiently in the eyes of syngeneic hosts before undergoing spontaneous rejection. An organ culture technique was used to detect spontaneous metastases in the lungs, spleens, brains, and thymus of intraocular tumor-bearing mice. Metastatic tumor cells were detected in all organs of immunodeficient mice (i.e., athymic, nude, or x-irradiated DBA/2 mice) within 14 days of intraocular transplantation, and grew progressively thereafter. By contrast, metastatic tumors were rejected in 100% of the immunocompetent DBA/2 mice examined on day 15. Timed enucleation experiments demonstrated that the immune rejection of disseminated tumor cells occurred within 24-48 hr of their arrival at the various organs. The immune rejection of spontaneous metastases could be adoptively transferred to immunodeficient tumor-bearing mice using spleen cells, but not immune serum, from intraocular tumor-bearing immunocompetent donors. Selective cell depletion experiments revealed that the immune spleen cell effecting immunity was an Lyt 1+, 2+ T cell. The results indicate that the immune rejection of the spontaneous metastases arising from primary intraocular tumors is a T cell-dependent, radiosensitive process that rapidly eliminates metastases within the lungs, brain, thymus, and the spleen of the immunocompetent host.