Cooperation Between Early Acting Delayed-Type Hypersensitivity T-cells and Cultured Effector Cells in Tumor Rejection

Delayed-type hypersensitivity (DTH) to allogeneic tumor cells exhibits two phases, an early reaction peaking at 2 h, and a late phase at 24 h after challenge with viable tumor cells. The purpose of this study was to determine whether DTH to syngeneic tumors also displays two phases and whether either reactivity is involved in tumor rejection in vivo. When normal animals were immunized and challenged with syngeneic regressor tumors induced by UV radiation, a tumor-specific DTH exhibiting both early and late phases was seen. The cells mediating both reactivities were Thy-1⁺ and L3T4⁺, but the early DTH cells manifested their reactivity sooner after immunization than the late DTH cells. Adult-thymectomized, X-irradiated mice did not show any greater ability to reject tumors after immune-system reconstitution with either immune population than after reconstitution with normal cells. However, small numbers of the early acting DTH cells acted synergistically with small numbers of cultured T-cells, the latter capable of in vitro cytolysis, to prevent tumor growth. This indicates that the early phase of DTH may be a valuable tool for the potentiation of immunotherapy using cultured cells.