Syngeneic spleen cells do not mediate an anti-leukemia effect in IL-12–treated mice. Results of two experiments that gave similar results are combined. B10 mice were treated with 10.25 Gy WBI and received 5 × 10⁶ TCD B10 BMC, 15 or 18 × 10⁶ B10 spleen cells plus 500 EL4 cells with no further treatment (•; n = 10) or with 4,900 IU IL-12 intraperitoneally on day 0 (○; n = 9). Nonleukemic control mice received similar inocula without EL4 cells with no further treatment (□; n = 6) or with 4,900 IU intraperitoneally (▪; n = 6).