The average volume of the C1498-mWT1 tumor mass was significantly smaller in the B. longum 420 group than in the B. longum 2012 group on days 17, 19, and 21 after leukemia cell inoculation (P < 0.01, P < 0.001, and P < 0.001, respectively; Fig. 1a); hence, the antitumor activity of B. longum 420 was shown to be caused by WT1-specific immune responses. Here, WT1 is linked to neoplasm.