TSLP-Induced Gene Expression Signature in Primary CRLF2 B-ALL

The cytokine TSLP stimulates in vitro proliferation of human fetal B cell progenitors. Genetic alterations that cause overexpression of the TSLP receptor component, CRLF2, lead to B cell acute lymphoblastic leukemia (CRLF2 B-ALL) with poor outcome. The in vivo role of TSLP in normal human B cell development and its contribution to CRLF2 B-ALL are unknown. In classic xenograft models CRLF2-mediated signaling is unlikely to be activated by mouse TSLP, based on data from engineered cellular models. Here, we show that mouse TSLP does not induce activation of the CRLF-2 downstream pathways (JAK/STAT and AKT/mTOR) that are induced by human TSLP (hTSLP) in CRLF2 B-ALL cells. Based on this, we developed a novel human-mouse xenograft model system comprised of mice that produce hTSLP (+T mice) to activate human CRLF2-mediated signaling and mice that lack hTSLP (–T mice). Normal serum levels of hTSLP were achieved in +T mice, while hTSLP was undetectable in –T mice. hTSLP produced by stroma induced JAK/STAT and AKT/mTOR pathway activation and showed functional in vivo effects on normal human B cell progenitors and primary CRLF2 B-ALL cells. Whole genome microarray of primary CRLF2 B-ALL showed an induction of mTOR regulated gene expression and preservation of TSLP responsiveness in cells expanded in +T mice as compared to –T mice. TSLP-induced gene expression in primary CRLF2 B-ALL cells was measured in cells that were expanded in +TSLP and -TSLP mice for 9 weeks. TSLP-induced gene expression was also measured in primary CRLF2 B-ALL cells that were harvested from the bone marrow of +TSLP and -TSLP mice and cultured for 3 days in vitro with or without commercially available exogenous human TSLP.