Fig. 2

Increasing levels of leukemia cell-mediated IL-15 positively correlates with improved survival. a IL-15 levels of LV15sol clones (for both (A) and (B) secretion levels are mean + SEM calculated from 2 to 4 individual ELISAs with duplicate wells). b IL-15 levels of LV15Rc clones; Correlation of survival with IL-15 output: a LV15sol clones; (p <  0.005, LV15sol.1–.7 vs 70Z/3-L, Log-rank, Mantel-Cox test); b LV15Rc clones; (p <  0.0001 for LV15Rc.1–.4, p <  0.003 for LV15Rc.5–.7 vs 70Z/3-L, Log-rank, Mantel-Cox test); Mice were injected ip with 10⁶ cells of either the parent line, or one of the transduced clones and monitored for onset of disease. Based on the secretion levels of IL-15 a theoretical threshold was established (arrow indicates the threshold), below which the protective effect of IL-15 was not observed. Multiple experiments were pooled for survival curves for some clones (n numbers are indicated in brackets). c Side by side comparison of the survival rates of the two IL-15 models using clones LV15sol.1 and LV15Rc.4 in an extended 250-day experiment. P-values: p <  0.001 for both IL-15 groups vs 70Z/3-L controls; p = 0.0003 LV-15Rc vs LV-15sol (Log-rank, Mantel-Cox test); d H³-Thymidin incorporation and e total live cell counts demonstrate that the representative LV15Rc and LV15sol clones used throughout this study grow at a similar rate as the 70Z/3-L parent strain. Results are mean + SEM calculated from 2 to 4 individual experiments with triplicate wells