INCREASED PROPORTION OF CD8-CELLS AFTER IMMUNIZATION WITH TUM(-) VERSUS TUM(+) RAT GLIOMA( TUMOR RESPONSIVE T)

Previously established immunogenic (tum(-)) clones of an ENU (ethyl-N- nitrosourea)-induced rat glioma, N32, were compared to the original tu mor concerning their capacity to induce T lymphocyte responses after i n vivo immunization and in vitro restimulation of responder spleen cel ls in mixed lymphocyte tumor culture (MLTC) assays. Quite unexpectedly , original N32 (tum(+)) in vivo primed spleen cells proliferated to th e same extent in vitro in response to tum(+) stimulator cells as did t um(-) in vivo primed spleen cells. However, flow-cytometric analysis o f parallel cultures showed a greatly increased proportion of CD3(+)CD8 (+) lymphocytes in the proliferating responder cell population from tu m(-) immunized hosts, contrary to a CD3(+)CD4(+) lymphocyte dominance after tum(+) immunization. Although the original tum(+) N32 tumor cell s are not capable of inducing a clearly demonstrable isograft rejectio n response, they induce a strong T cell response readily detectable in MLTC assays. We propose that the increased CD8(+) lymphocyte prolifer ation could be an essential feature of the isograft rejection response induced by tum(-) tumor variants. Possible mechanisms of the augmente d CD8(+) T cell response are discussed. (C) 1995 Academic Press, Inc.