ICSBP-mediated immune protection against BCR-ABL-induced leukemia requires the CCL6 and CCL9 chemokines

Interferon is effective at inducing complete remissions in patients with Chronic Myelogenous Leukemia (CML), and evidence supports an immune mechanism. Here we show that the Type I Interferons (alpha and beta) regulate expression of the Interferon consensus sequence binding protein (ICSBP) in bcr-abl transformed cells and as shown previously for ICSBP, induce a vaccine-like immunoprotective effect in a murine model of bcr-abl induced leukemia. We identify the chemokines CCL6 and CCL9 as genes prominently induced by the Type I Interferons and ICSBP, and demonstrate that these immunomodulators are required for the immunoprotective effect of ICSBP expression. Insights into the role of these chemokines in the anti-leukemic response of interferons suggest new strategies for immunotherapy of CML. Total RNA was isolated from parental BaF3 cells as well as BaF3 cells expressing BCR-ABL, ICSBP, or both BCR-ABL and ICSBP. Using standard Affymetrix protocols the RNA samples were analyzed for gene expression using Affymetrix mouse 430_2 whole genome microarrays arrays. A threshold value of 50 was set for all genes and the list of genes filtered to include only those that had at least one Present flag ("P" flag) in one of the 4 conditions. For each gene, the ratio of its expression in a particular condition and its expression in parental BaF3 cells was determined. Only genes that had at least a 3-fold up or down change in expression were considered, leaving a set of 1431 genes for further analysis. K-means clustering with Gene cluster 3.0 was used to group these 1431 genes into 15 clusters and JavaTree was used to visualize the results.