On page 3063 in the April 15, 2010, issue, there is potentially an error in the data shown in Figure 2C and 2D. The authors used 7 cell lines to confirm the expression of CD137L on AML cells, which was detected on primary patient AML cells. They observed CD137L surface expression in 5 of 7 and mRNA expression in all 7 cell lines they believed to be of AML origin. They recently discovered that the putative THP-1 cells used for the original experiments, one of the 7 cell lines investigated, may have been contaminated with RAJI cells, a lymphoma cell line. The authenticity of the other cell lines was confirmed by an independent third party (DSMZ, Germany). It is unclear whether the contamination of the THP-1 cells had already occurred at the time the experiments were performed. For this reason, the experiments shown in Figure 2C and 2D of the paper were repeated using THP-1 cells with confirmed authenticity. In agreement with the published data, the authors observed substantial CD137L surface and mRNA expression on THP-1 cells. These data are shown in the updated figures included in this erratum. Thus, the conclusions resulting from the analyses with AML cell lines in the paper are fully supported by valid data.