Adoptive immunotherapy of a syngeneic murine leukemia with a tumor-specific cytotoxic T cell clone and recombinant human interleukin 2: Correlation with clonal IL 2 receptor expression

The successful adoptive immunotherapy of the syngeneic Friend virus-induced murine leukemia FLB-3 was mediated by a proliferative MHC-restricted, tumor-specific CTL clone in combination with recombinant human IL 2. This clone was previously shown to express the L3T4^-, Lyt-1⁺, Lyt-2⁺ surface phenotype. Activation of the clone for 48 hr in vitro with irradiated tumor cells induced the expression of IL 2 receptors and markedly increased clonal proliferation in response to recombinant IL 2. Intravenous injection of 2 x 10⁷ 48 hr in vitro-activated cloned cells, followed by 6 days of systemic (i.p.) administration of IL 2 resulted in the complete regression of tumors and the cure of 50% of the treated mice. IL 2 alone had no effect on tumor growth, whereas the injection of nonactivated (resting) clone plus IL 2 or activated clone without IL 2 had small but insignificant effects on tumor growth and survival. These results indicated that the in vivo effector functions of cloned T cells may be markedly enhanced by the concurrent systemic administration of recombinant IL 2 and by the induction of optimal IL 2 receptor expresson on the cloned T cells at the time of cell administration.