Abstract B71: Biologic for the treatment of CRLF2 B-cell acute lymphoblastic leukemia to reduce pediatric cancer health disparities

B-cell acute lymphoblastic leukemia (B-ALL) with genetic alterations leading to overexpression of the cytokine receptor, CRLF2, is associated with poor outcomes. CRLF2 B-ALL occurs 5 times more often in Hispanic children than others, is prevalent in adolescents and young adults, and is associated with a high relapse rate and poor prognosis. In patients, the CRLF2 receptor is stimulated by circulating TSLP cytokine. This stimulation is not provided by classic patient-derived xenograft (PDX) models because the TSLP present in mice has low homology to human TSLP and does not activate the CRLF2 receptor. We developed a novel PDX model of CRLF2 B-ALL that allows us to vary circulating levels of human TSLP (+T PDX). When we injected primary CRLF2 B-ALL cells from Hispanic pediatric patients into +T PDX with circulating human TSLP (hTSLP) levels similar to pediatric leukemia patients (~4-10 pg/ml), they 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 physiologic 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. Our next step was to identify the mechanism through which hTSLP exerts its antileukemia effects. Binding of hTSLP to CRLF2 and associated receptor components activates the JAK-STAT5 pathway as well as the PI3K/AKT/mTOR pathway. JAK-STAT signaling is known to upregulate the Suppressor of Cytokine Signaling (SOCS) genes. SOCS genes encode a family of proteins that regulate cytokine signaling via negative feedback through multiple mechanisms. Flow cytometry analysis showed that the SOCS family proteins, SOCS1, SOCS3, and CISH, were upregulated in the CRLF2 B-ALL cell lines MUTZ5 and CALL-4 following 3 days of culture with hTSLP, as compared to controls without hTSLP. Similar results were obtained using CRLF2 B-ALL cells from two Hispanic pediatric patients. Whole-genome RNA sequencing of primary CRLF2 B-ALL cells from a Hispanic pediatric patient also showed upregulation of SOCS1, SOCS3, and CISH mRNA. Next, we determined whether the upregulation of SOCS proteins was accompanied by the deactivation of hTSLP-induced CRLF2 signaling. CRLF2 B-ALL cell lines were cultured with or without hTSLP for 3 days to allow SOCS upregulation, then harvested and assessed for their ability to activate the JAK/STAT5 and PI3/AKT/mTOR pathways following hTSLP stimulation. Leukemia cells cultured for 3 days without hTSLP retained their ability to induce phosphorylation of STAT5 and ribosomal protein S6 (downstream of PI3/AKT/mTOR). In contrast, leukemia cells cultured with hTSLP showed no phosphorylation of STAT5 or S6 following hTSLP stimulation. Similar results were seen with the CALL-4 cell line and in a primary CRLF2 B-ALL from a Hispanic pediatric patient. These results suggest that elevated hTSLP exerts a therapeutic effect on CRLF2 B-ALL via SOCS-mediated suppression of CRLF2 signaling. Our published studies show that hTSLP expands the production of normal human B cells in PDX at both low and high physiologic levels with no reduction in other immune cells. Taken together, these data suggest that the hTSLP cytokine has promising potential as a biologic therapy to reduce health disparities for Hispanic children with CRLF2 B-ALL by targeting leukemic B cells while supporting the restoration of normal B cells following chemotherapy. Supported by 1R01CA209829. Citation Format: Cornelia Stoian, Jacqueline S. Coats, Veriah Vidales, Juliette Personius, Evgeny Chirshev, Hossam Alkashgari, Ineavely Baez, Lawrence Liu, Hannah Choi, Sinisa Dovat, Kimberly Payne. Biologic for the treatment of CRLF2 B-cell acute lymphoblastic leukemia to reduce pediatric cancer health disparities [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr B71.