Abstract 3295: A novel patient-derived xenograft model for evaluating the role of TSLP in CRLF2 B-ALL

B-cell acute lymphoblastic leukemia (B-ALL) with genetic alterations leading to overexpression of CRLF2 (CRLF2 B-ALL) is associated with poor outcomes. CRLF2 B-ALL is 5 times more common in Hispanic children than others making it a significant biological component of pediatric cancer health disparities. CRLF2 is a component of the receptor complex that is activated by the cytokine, TSLP. Receptor signaling induces Jak/STAT5 and PI3/AKT/mTOR pathway activation and plays a role in the proliferation and differentiation B cell precursors. We found that primary human bone marrow (BM) stroma express TSLP providing an in vivo source of TSLP to stimulate CRLF2 B-ALL cells. Our goal was to develop patient-derived xenograft (PDX) models of CRLF2 B-ALL for studies to understand disease mechanisms and identify therapies to treat CRLF2 B-ALL and reduce the health disparities for Hispanic children with this disease. PDX models are possible because many cytokines produced in the mouse show cross species activity on human cells. However, available data suggests that mouse TSLP does not activate human CRLF2-mediated signals. Using phospho flow cytometry we show that mouse TSLP was unable to induce increases in pSTAT5, pAKT and pS6 observed in CRLF2 B-ALL cells stimulated with human TSLP. We developed a human TSLP +/- PDX model system by transplanting immune deficient NSG mice with HS-27 stroma transduced to express human hTSLP (hTSLP+ mice) or with control vector (hTSLP- mice). Human TSLP was present at normal human serum levels in hTSLP+ mice but undetectable in hTSLP- mice. To identify genes targeted by TSLP in CRLF2 B-ALL and verify pathway activation, we transplanted primary leukemia cells from a Hispanic patient into hTSLP+ and hTSLP- mice. Whole genome microarray was performed on CRLF2 B-ALL cells isolated from the BM of the hTSLP+ and hTSLP- PDX mice. Microarray identified 280 genes that are upregulated and 281 genes that are downregulated in vivo in leukemia cells from hTSLP+ as compared to hTSLP- PDX mice. Evaluation of microarray data by Gene Set Enrichment Analysis (GSEA) and Ingenuity Pathway Analysis showed that genes downstream of mTOR pathway activation were upregulated in hTSLP+ as compared to hTSLP- mice, confirming hTSLP activity in the hTSLP+ PDX mice. Our next question was whether cells expanded in hTSLP+ vs. hTSLP- mice would exhibit changes in their ability to respond to TSLP. When we subjected PDX-expanded primary CRLF2 B-ALL cells to ex vivo TSLP st