Biologic for the Treatment of Ph-like B-Cell Acute Lymphoblastic Leukemia with Overexpression of CRLF2

Ph-like B-cell acute lymphoblastic leukemia (B-ALL) is associated with poor outcomes and high relapse rates. Approximately 50% of Ph-like B-ALL cases occur due to genetic alterations leading to overexpression of the cytokine receptor, CRLF2. B-ALL with overexpression of CRLF2 (CRLF2 B-ALL) occurs 5 times more often in Hispanic children than others, is prevalent in adolescents and young adults, and makes up ~1/3 of adult B-ALL. CRLF2, together with the IL-7Rα, forms a receptor complex that can be activated by circulating TSLP cytokine in patients. The human CRLF2 receptor is not activated by mouse TSLP so classic patient-derived xenografts (PDX) do not model TSLP-induced CRLF2 signaling that occurs in patients. CRLF2-mediated JAK/STAT and PI3/AKT/mTOR signals are believed to contribute to survival and proliferation of leukemia cells. We developed a novel PDX model of CRLF2 B-ALL that allows us to vary circulating levels of human TSLP (+T PDX). Primary CRLF2 B-ALL cells injected into +T PDX with circulating human TSLP (hTSLP) levels similar to pediatric leukemia patients (~4-10 pg/ml), engrafted well and showed a gene expression pattern that was more similar to the original patient sample than when injected into classic PDX. To our surprise, when +T PDX expressed physiological, but elevated levels of hTSLP (> 40 pg/ml, upper end of range reported in healthy children), CRLF2 B-ALL cells were essentially eliminated, but grew robustly in PDX without hTSLP (-T PDX). These results have been observed in 4 independent experiments for a total of 17 +T PDX and 12 -T PDX mice produced using CRLF2 B-ALL cells from two different Hispanic pediatric patients with CRLF2 B-ALL. We hypothesize that anti-leukemia effects observed at hTSLP concentrations above 40 pg/ml are mediated via TSLP-induced upregulation of the Suppressor of Cytokine Signaling (SOCS) genes. SOCS genes encode a family of proteins that regulate cytokine signaling via negative feedback through multiple mechanisms including ubiquitin-mediated degradation of JAKs and cytokine receptor components. Using the CRLF2 B-ALL cell lines, MUTZ5 and CALL-4, we found that SOCS family proteins encoded by the SOCS1 and SOCS3 genes were upregulated following culture with 15 ng/ml hTSLP, as compared to controls without hTSLP. Similarly, primary CRLF2 B-ALL cells from Hispanic pediatric patients cultured with TSLP showed upregulation of SOCS1 and SOCS3 mRNA and proteins. Next, we determined whether the upregulation of SOCS proteins was accompanied by a loss of CRLF2-mediated signals. We found that CRLF2 B-ALL cell lines and primary cells cultured with hTSLP lost the ability to upregulate STAT5 and S6 phosphorylation following hTSLP stimulation. Further, cells cultured with TSLP showed a loss of cytokine receptors as well as STAT5 phosphorylation levels that were below the baseline observed in leukemia cells never exposed to hTSLP. These data suggest that TSLP exerts anti-leukemia effects by shutting down CRLF2-mediated signals and that this shut down may occur through SOCS-mediated degradation of cytokine receptor components and/or degradation of the mutant JAK2 that provides constitutively low level STAT5 activation in these CRLF2 B-ALL cell lines and in a majority of patients with this disease. In summary, these results provide evidence that elevated hTSLP exerts a therapeutic effect on CRLF2 B-ALL and suggest that this occurs via SOCS-mediated suppression of the CRLF2 signaling pathway. These studies identify the human TSLP cytokine as a potential biologic therapy to treat CRLF2 B-ALL and reduce cancer health disparities for Hispanic children with CRLF2 B-ALL. Supported by 1R01CA209829.