Delayed-type hypersensitivity to tumor antigens co-expressed with immunogenic determinants induced by xenogenization.

Previous work has shown that murine lymphoma cells antigenically altered ("xenogenized") by drug treatment elicit strong in vivo resistance to the original cells. Moreover, splenocytes immune to a drug-treated variant (L5178Y/DTIC) of a murine lymphoma exert anti-parental tumor activity in an adoptive transfer system, an effect mediated by L3T4+ lymphocytes and associated with the detection of an anti-L5178Y delayed-type hypersensitivity (DTH) response. We now report that the in vivo activity of the tumor-immune L3T4+ lymphocytes is a radio-sensitive (2,500 rad in vitro) phenomenon that requires collaboration with radio-resistant, silica-sensitive syngeneic cells in the host, and is inhibited by treatment of recipient mice with monoclonal antibodies (MAbs) to the L3T4 antigen or murine interferon-gamma (IFN-gamma). In vitro, the tumor-immune L3T4+ lymphocytes produce interleukin 2 (IL-2), lymphotoxin (LT) and IFN-gamma activities on incubation with L5178Y cells and spleen-adherent cells. These results suggest that the mechanisms of anti-parental tumor protection by xenogenized cells involve specific induction of a DTH response mediated by the "inflammatory" (THI) subset of L3T4+ T lymphocytes and IFN-gamma activated macrophages.