Abstract 3097: TSLP regulates expression of genes involved in cell survival in a preclinical xenograft model of CRLF2 B-ALL

Abstract

Abstract A subset of children with B cell precursor acute lymphoblastic leukemia (B-ALL) are at high risk for relapse and death. Gene expression profiles in these high-risk B-ALLs is similar to that of Philadelphia chromosome-positive ALL. Approximately half of these Ph-like B-ALL are characterized by genetic defects resulting in overexpression of CRLF2. This defect occurs 5 times more commonly in Hispanic children than others and thus is a significant biological component of pediatric cancer health disparities. CRLF2, together with the IL-7Rα, forms a receptor complex that is activated by the cytokine, TSLP. Receptor complex activation leads to JAK-STAT5 phosphorylation. The activating JAK mutations found in some CRLF2 B-ALL led to speculation that TSLP stimulation is not a factor in CRLF B-ALL. However, we and others have found that TSLP increases STAT5 phosphorylation in CRLF2 B-ALL cells, including those with JAK defects. Our next step was to evaluate the role of TSLP-CRLF2 interactions in vivo in the human-mouse xenograft model. However, mouse TSLP is species-specific and does not activate the human TSLP receptor complex that includes CRLF2. Thus, traditional xenograft models do not provide the TSLP-CRLF2 interactions that may contribute to high risk CRLF2 B-ALL. We engineered immune-deficient NOD/SCID IL-2Rγ null (NSG) mice to express human TSLP (hTSLP+ mice), as well as control mice that lack the TSLP cytokine (hTSLP- mice). Then we used this hTSLP+/- xenograft model system to evaluate the in vivo effects of TSLP on transplanted CRLF2 B-ALL cells harboring a JAK defect (MUTZ5 cell line). Transplanted mice were euthanized at 5 weeks and bone marrow (BM) was harvested. Evaluation of BM by flow cytometry showed that approximately half of the human leukemia cells were apoptotic in mice without TSLP while apoptosis was virtually absent in CRLF2 B-ALL cells harvested from hTSLP+ mice. Next we used Ingenuity Pathway Analysis to identify functions and pathways regulated by TSLP. Primary CRLF2 B-ALL cells were transplanted into hTSLP+ and hTSLP- mice. Whole genome microarray performed on primary human leukemia cells isolated from BM of xenograft mice identified 280 genes that were upregulated and 281 genes that were downregulated (> 2 fold up or downregulated; p<.05) in leukemia cells from hTSLP+ as compared to hTSLP- mice. Ingenuity Pathway Analysis of changes in gene expression identified “Cell Death and Survival” as the “Molecular and Cellular Function” most impacted by TSLP (34 genes differentially regulated).These data suggest that TSLP-induced CRLF2 signaling may contribute to leukemia cell survival in vivo in CRLF2 B-ALL. Current studies are aimed at identifying TSLP-regulated genes that can be therapeutically targeted as a part of combination therapy to successfully treat CRLF2 B-ALL and reduce the cancer health disparities for children with this disease. Citation Format: Olivia L. Francis, Ruijun Su, Shannalee R. Martinez, Ineavely Baez, Terry-Ann Milford, Ross Fisher, Christopher L. Morris, Xiaobing Zhang, Valeri Filippov, Sinisa Dovat, Kimberly J. Payne. TSLP regulates expression of genes involved in cell survival in a preclinical xenograft model of CRLF2 B-ALL. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3097. doi:10.1158/1538-7445.AM2014-3097