Abstract 3169: Mechanisms of novel cytokine therapy for Ph-like B-cell acute lymphoblastic leukemia with overexpression of CRLF2

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Abstract B-cell acute lymphoblastic leukemia with overexpression of CRLF2 (CRLF2 B-ALL) comprises ~50% of Ph-like B-ALL, a leukemia that is associated with poor outcomes, high relapse rates and leukemia health disparities in Hispanic children. CRLF2, together with the IL-7 receptor alpha (IL-7Ra), comprises a receptor complex that is activated by the cytokine, TSLP. Receptor activation induces JAK2/STAT5 and PI3/AKT/mTOR signals that are believed to contribute to survival and proliferation of leukemia cells. To study the role of TSLP in CRLF2 B-ALL, we developed a novel patient-derived xenograft (PDX) model of CRLF2 B-ALL that allows us to vary circulating levels of human TSLP (hTSLP). Primary CRLF2 B-ALL cells injected into PDX mice without hTSLP or with circulating hTSLP levels similar to pediatric leukemia patients (~4-10 pg/ml) showed engraftment and expansion of leukemia cells. In contrast, CRLF2 B-ALL cells were essentially eliminated in PDX with elevated physiologic levels of hTSLP (40-140 pg/mL). We observed these results in 5 independent experiments produced using primary CRLF2 B-ALL cells from two different Hispanic pediatric patients with CRLF2 B-ALL (N= 40 PDX). We hypothesize that the observed antileukemia effects are mediated via TSLP-induced upregulation of the Suppressor of Cytokine Signaling (SOCS) genes. SOCS genes encode a family of proteins (SOCS1-7 and CISH) that regulate cytokine signaling via negative feedback through multiple mechanisms including ubiquitin-mediated cytokine receptor degradation. Consistent with our hypothesis, SOCS1, SOCS2, SOCS3 and CISH mRNA were upregulated in primary CRLF2 B-ALL cells cultured with high-dose hTSLP. To gain mechanistic insights we evaluated the CRLF2 B-ALL cell lines, MUTZ5 and CALL4, following culture with and without hTSLP. Flow cytometry analysis showed that high-dose hTSLP upregulated SOCS1 and SOCS3 proteins in both CRLF2 B-ALL cell lines. We found that CRLF2 B-ALL cells cultured with hTSLP for 3 days showed a dose-dependent loss in the ability to induce STAT5 and S6 phosphorylation following hTSLP stimulation. This loss was correlated with the loss of IL-7Ra, and maintained for 24-48 hours following a pulse of high-dose (but not low-dose) hTSLP. The loss of signaling and surface IL-7Ra could be prolonged if high-dose hTSLP levels were maintained. These data provide evidence that TSLP exerts its antileukemia effects by shutting down CRLF2-mediated signals and suggest that these effects are at least partially mediated by the loss of the IL-7Ra component, and potentially through SOCS family proteins. 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.) Citation Format: Cornelia Stoian, Jacqueline S. Coats, Hossam Alkashgari, Veriah Vidales, Ineavely Baez, Juliette Personius, Hannah Choi, WayAnne Watson, Brandon Ng, Benjamin Becerra, Rishikesh Chavan, Muhammad Kamal, Shadi Farzin Gohar, Sinisa Dovat, Kimberly J. Payne. Mechanisms of novel cytokine therapy for Ph-like B-cell acute lymphoblastic leukemia with overexpression of CRLF2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3169.