Fig. 3

Leukemia cell-mediated IL-15 therapy leads to long-term immunity and protection against 70Z/3-L for IL-15sol but not IL-15Rc. a, b Mice were initially injected with 10⁶ cells of either a LV15sol clones, or b LV15Rc clones. After 100 days surviving mice were re-challenged with 10⁶ 70Z/3-L cells to test whether immunity was established. A naïve control group received 10⁶ 70Z/3-L cells to control for the efficiency to cause leukemia. a p = 0.0062 for all 3 surviving groups vs 70Z/3-L controls; b p = 0.0246 (LV15Rc.3-primed), p = 0.9876 (LV15Rc.4-primed) vs 70Z/3-L controls; c-e Both T-cell subsets are required for leukemia cell-mediated IL-15 therapy. Mice were depleted of certain cell populations prior to challenging them with either c 10⁶ LV15sol.1 cells; or d 10⁶ LV15Rc.4 cells. In both instances, CD4⁺ and CD8⁺ T-cell subsets were required. e In order to establish whether the same T-cell populations are necessary in the secondary challenge, we immunized 55 mice with the IL-15sol clone LV15sol.1. After 100 days (all 55 mice survived) they were depleted of various cell populations and then re-challenged with the parent strain. Again, both T-cell subsets were required. In all instances, a control group (naïve mice) received 10⁶ 70Z/3-L cells to control for their efficiency to cause leukemia. In the re-challenge experiment one group of not re-challenged (NR) mice was included. Depletion of NK-cells did not have an effect in any of the experiments