Abstract 5027: In vivo effects of TSLP in a human-mouse xenograft model of CRLF2 B-ALL.

Pediatric CRLF2 B-cell Acute Lymphoblastic Leukemia (CRLF2 B-ALL) is a high-risk form of leukemia that is associated with relapse and poor patient survival outcomes. This leukemia occurs five times more frequently among children of Hispanic/Latino ethnicity than others and represents the most significant biological component of childhood cancer health disparities identified to date. CRLF2 B-ALL arises from genetic alterations that result in overexpression of the CRLF2 gene. CRLF2, together with the IL-7 receptor α, forms a receptor complex that is activated by the cytokine, TSLP. The JAK-STAT5 pathway is phosphorylated downstream of receptor activation. The activating JAK mutations found in some CRLF2 B-ALL have led to speculation that TSLP stimulation is not a factor in CRLF B-ALL. However, we found that TSLP increases STAT5 phosphorylation, even in CRLF2 B-ALL cells with JAK mutations. Our studies of normal B cell development show that TSLP stimulation increases cellular proliferation in early human B lineage cells. We also find that pediatric bone marrow (BM) stromal cells express TSLP and thus provide an in vivo source of TSLP that can act on CRLF2 B-ALL cells. We proposed to evaluate the role of TSLP in human CRLF2 B-ALL using a human-mouse xenograft model. However, TSLP is different from most other cytokines produced in the mouse in that it is species-specific and therefore does not activate the human TSLP receptor complex that contains CRLF2. Thus, traditional xenograft models do not provide the TSLP-CRLF2 interactions that we believe to be a contributing factor in CRLF2 B-ALL. To overcome this hurdle we engineered immune deficient mice to express human TSLP (hTSLP+ mice) as well as control mice that lack the human TSLP cytokine (hTSLP- mice). We used this hTSLP+/- xenograft model system to evaluate the in vivo effects of TSLP on survival and proliferation of transplanted CRLF2 B-ALL cells harboring a JAK defect (MUTZ5 cell line). Mice were euthanized at 5 weeks and BM was harvested. Evaluation of BM disease by flow cytometry showed that the percentage of viable human leukemia cells in hTSLP+ mice was twice that observed in hTSLP-mice. Evaluation of cell cycle progression in human CRLF2 B-ALL cells isolated from xenograft BM showed that the percentage of cycling cells in hTSLP+ mice was 2.5 fold higher than in hTSLP- mice. These preliminary data suggest that TSLP may contribute to CRLF2 B-ALL by increasing the survival and proliferation of CRLF2-B-ALL cells. Ongoing studies are focused on evaluating in vivo effects of TSLP in primary CRLF2 B-ALL from Hispanic patients. The identification of genes downstream of TSLP-CRLF2 signaling has the potential of providing drug targets for combination therapy to effectively treat CRLF2 B-ALL and reduce cancer health disparities in Hispanic childhood B-ALL.This work is supported by NIH R21R21CA162259, a St. Baldrick's Foundation Research Grant, and a LLU GCAT award (KJP)Citation Format: Rui-jun Su, Olivia L. Francis, Shannalee R. Martinez, Ineavely Baez, Terry-Ann Milford, Christopher L. Morris, Ross O. Fisher, Xiao-Bing Zhang, Sinisa Dovat, Kimberly J. Payne. In vivo effects of TSLP in a human-mouse xenograft model of CRLF2 B-ALL. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5027. doi:10.1158/1538-7445.AM2013-5027