TSLP as a Potential Therapy in the Treatment of CRLF2 B Cell Acute Lymphoblastic Leukemia

Cytokine receptor-like factor 2 B-cell acute lymphoblastic leukemia (CRLF2 B-ALL) is a high-risk subtype characterized by CRLF2 overexpression with poor survival rates in children and adults. CRLF2 and interleukin-7 receptor alpha (IL-7Rα) form a receptor for the cytokine thymic stromal lymphopoietin (TSLP), which induces JAK/STAT and PI3K/AKT/mTOR pathway signals. Previous studies from our group showed that low TSLP doses increased STAT5, AKT, and S6 phosphorylation and contributed to CRLF2 B-ALL cell survival. Here we investigated the role of TSLP in the survival and proliferation of CRLF2 B-ALL cells in vitro and in vivo. We hypothesized that high doses of TSLP increase CRLF2 signals and contribute to increased proliferation of CRLF2 B-ALL cells in vitro and in vivo. Interestingly, we observed the opposite effect. Specifically, high doses of TSLP induced apoptosis in human CRLF2 B-ALL cell lines in vitro, prevented engraftment of CRLF2 B-ALL cells, and prolonged the survival of +TSLP patient-derived-xenograft mice. Mechanistically, we showed that high doses of TSLP induced loss of its receptor and loss of CRLF2 signals in vitro. These results suggest that high doses of TSLP could be further investigated as a potential therapy for the treatment of CRLF2 B-ALL.

Mechanism of biologic therapy for pre B-cell acute lymphoblastic leukemia with CRLF2 overexpression

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Background: Acute lymphoblastic leukemia (ALL) is the most common childhood cancer, of which pre B-cell ALL with CRLF2 overexpression is a high risk subtype. CRLF2 B-ALL is associated with poor outcome, increased rate of relapse, and health disparities in Hispanic children. Together with IL-7 receptor alpha (IL-7Rα), CRLF2 makes up a receptor complex that is activated by the cytokine, thymic stromal lymphopoetin (TSLP). Activation of the receptor complex leads to JAK2/STAT5 and PI3/AKT/mTOR signals that promote leukemia cell survival and proliferation. To study the role of TSLP in CRLF2 B-ALL, we developed a patient-derived xenograft (PDX) model of CRLF2 B-ALL that allows us to alter circulating levels of human TSLP (hTSLP). We generated PDX from CRLF2 B-ALL cells harvested from patient samples and compared leukemia burden in mice with varying levels of hTSLP. In PDX models with hTSLP levels at or below physiological levels in pediatric cancer patients, CRLF2 B-ALL cells grew robustly. However, in PDX with elevated levels of hTSLP, leukemia cells were essentially eliminated. Our objective is to elaborate on the mechanism of high dose hTSLP’s antileukemic effect. Methods: We performed TSLP dose response studies and used flow cytometry to evaluate the effect of TSLP on SOCS protein expression, CRLF2 signaling shutdown, and loss of TSLP receptor components. Results: CRLF2 B-ALL cells cultured with hTSLP 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-7Rα, and maintained for 24-48 hours following a pulse of high-dose, but not low-dose, hTSLP. The loss of signaling and surface IL-7Rα could be prolonged if high-dose hTSLP levels were maintained. Flow cytometry analysis showed that high-dose hTSLP upregulated SOCS1 and SOCS3 proteins in CRLF2 B-ALL cells. Whole genome microarray showed that SOCS1, SOCS2, SOCS3 and CISH mRNA were upregulated in primary CRLF2 B-ALL cells cultured with high dose hTSLP. Conclusions: These data support the hypothesis that TSLP exerts its anti-leukemia effects through shutdown of CRLF2-mediated signals and that these effects are at least partially mediated by the loss of the IL-7Rα component, and potentially through SOCS family proteins. These studies elucidate the mechanism of the human TSLP cytokine as a potential biologic therapy to treat CRLF2 B-ALL. Supported in part by 1R01CA209829 (KJP), 1R43CA224723 (KJP), ASH HONORS Award 2018-2019 (WBW), and Alpha Omega Alpha Carolyn L. Kuckein Student Research Fellowship 2018-2019 (WBW).

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.

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

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.

Abstract 5829: Targeting TSLP-induce upregulation of Mcl-1 for the treatment of Ph-like ALL with CRLF2 alterations

B cell precursor acute lymphoblastic leukemia (B-ALL) is the most common childhood cancer. The subset of pediatric B-ALL patients at greatest risk for relapse and death have a gene expression profile similar to Philadelphia chromosome positive ALL. Approximately half of these Ph-like B-ALL are defined by genetic alterations that result in overexpression of the cytokine receptor, CRLF2. Stimulation of the CRLF2 receptor by the cytokine, TSLP, causes downstream activation of the JAK/STAT5 and PI3/AKT/MTOR pathways. Activation of these pathways has been associated with oncogenesis and chemoresistance. A gene target of activated STAT5 in B cell precursors is Mcl-1, a Bcl2 family pro-survival molecule. Further, Mcl-1 protein levels are increased through post-transcriptional mechanisms induced by activation of the mTOR pathway. We hypothesized that circulating TSLP cytokine contributes to chemoresistance by increasing CRLF2 activation leading to increased Mcl-1 expression and that targeting Mcl-1 could be an effective strategy for treating Ph-like B-ALL with overexpression of CRLF2 (CRLF2 B-ALL). To test this hypothesis we cultured human CRLF2 B-ALL cell lines (MUTZ5 and CALL4) with and without TSLP for 3 days and evaluated expression of Mcl-1 by flow cytometry. We found that TSLP induced significant increases in Mcl-1 proteins in both cell lines. To determine if these results are reflective of what happens in patients, primary CRLF2 B-ALL cells from pediatric patients were cultured with physiological levels of TSLP (~20 pg/ml) and similarly evaluated. Physiological TSLP significantly increased Mcl-1 protein in primary CRLF2 B-ALL cells, including those with activating JAK mutations. Our next question was whether TSLP-induced increases in Mcl-1 could be effectively targeted with Mcl-1 inhibitors (MIM-1 or Maritcolax). CRLF2 B-ALL cells were incubated with and without TSLP and treated with increasing doses of Mcl-1 inhibitor. Dose responses were evaluated by flow cytometry after 2 or 3 days. Mcl-1 inhibitors induced dose-dependent decreases in cell count and increases in caspase-3 activation and apoptosis (Annexin V/7-AAD). These corresponded with dose-dependent decreases in Mcl-1 protein, suggesting that both inhibitors target Mcl-1 for degradation. MIM-1 and Maritoclax showed efficacy against both CRLF2 B-ALL cell lines and primary patient samples, including those with activating JAK mutations, although cells cultured with TSLP typically required twice the dose of Mcl-1 inhibitor to achieve the same effect observed without TSLP. These data provide evidence that TSLP can contribute to leukemia cell survival and identify Mcl-1 inhibitor as a candidate therapy for CRLF2 B-ALL. Ongoing studies are evaluating the efficacy of the Mcl-1 inhibitor, Maritoclax, in novel patient-derived xenograft models of CRLF2 B-ALL that provide physiological levels of human TSLP.

Citation Format: Cornelia Stoian, Nathaniel George Mambo, Pierce McCarthy, Veriah Vidales, Jacqueline S. Coats, Ineavely Baez, Sinisa Dovat, Shadi Farzin Gohar, Dhimant Desai, Muhammad Kamal, Kimberly J. Payne. Targeting TSLP-induce upregulation of Mcl-1 for the treatment of Ph-like ALL with CRLF2 alterations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5829. doi:10.1158/1538-7445.AM2017-5829

Expression of Exogenous Cytokine in Patient-derived Xenografts via Injection with a Cytokine-transduced Stromal Cell Line

Patient-derived xenograft (PDX) mice are produced by transplanting human cells into immune deficient mice. These models are an important tool for studying the mechanisms of normal and malignant hematopoiesis and are the gold standard for identifying effective chemotherapies for many malignancies. PDX models are possible because many of the mouse cytokines also act on human cells. However, this is not the case for all cytokines, including many that are critical for studying normal and malignant hematopoiesis in human cells. Techniques that engineer mice to produce human cytokines (transgenic and knock-in models) require significant expense before the usefulness of the model has been demonstrated. Other techniques are labor intensive (injection of recombinant cytokine or lentivirus) and in some cases require high levels of technical expertise (hydrodynamic injection of DNA). This report describes a simple method for generating PDX mice that have exogenous human cytokine (TSLP, thymic stromal lymphopoietin) via weekly intraperitoneal injection of stroma that have been transduced to overexpress this cytokine. Use of this method provides an in vivo source of continuous cytokine production that achieves physiological levels of circulating human cytokine in the mouse. Plasma levels of human cytokine can be varied based on the number of stromal cells injected, and cytokine production can be initiated at any point in the experiment. This method also includes cytokine-negative control mice that are similarly produced, but through intraperitoneal injection of stroma transduced with a control vector. We have previously demonstrated that leukemia cells harvested from TSLP-expressing PDX, as compared to control PDX, exhibit a gene expression pattern more like the original patient sample. Together the cytokine-producing and cytokine-negative PDX mice produced by this method provide a model system that we have used successfully to study the role of TSLP in normal and malignant hematopoiesis.

Abstract B46: A novel patient-derived xenograft model for evaluating therapies that target the CRLF2 signaling pathway to reduce health disparities for Hispanic children with leukemia

The purpose of the studies described here was to identify drug targets and develop a preclinical model for testing therapies that can reduce health disparities for Hispanic children with high-risk acute lymphoblastic leukemia (ALL). Hispanic children are 1.24 times more likely to develop ALL than non-Hispanic whites and that number rises to 2.09 by adolescence and early adulthood. A major contributor to this health disparity is a type high-risk B-cell ALL called CRLF2 B-ALL. 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. CRLF2 B-ALL is caused by genetic alterations that result in over expression of the cytokine receptor, CRLF2. The CRLF2 receptor is activated by the cytokine, TSLP, causing downstream activation of the JAK/STAT5 and PI3/AKT/MTOR pathways. A gene target of activated STAT5 in B cell precursors is Mcl-1, a Bcl2 family pro-survival molecule. In addition, Mcl-1 protein levels are known to be increased through post-transcriptional mechanisms by activation of the mTOR pathway. We hypothesized that the normal level of circulating TSLP cytokine could induce CRLF2 activation leading to increased Mcl-1 expression in CRLF2 B-ALL cells. Our data show that TSLP increases phosphorylation of STAT5, as well as AKT and S6 (downstream of mTOR) in primary CRLF2 B-ALL cells from Hispanic pediatric patients, even when activating JAK mutations are present. When CRLF2 B-ALL cells from Hispanic pediatric patients were cultured for 3 days with and without physiological levels of TSLP, flow cytometry showed that expression of the Mcl-1 protein was significantly increased in cultures with TSLP as compared to cultures without TSLP. CRLF2 B-ALL cells treated in vitro with Mcl-1 inhibitor showed dose-dependent increases in caspase 3 activation and apoptosis as indicated by flow cytometry. These data provide evidence that TSLP can contribute to leukemia cell survival and identify Mcl-1 inhibitor as a candidate therapy for CRLF2 B-ALL. Our next step was to develop a preclinical model for testing therapies that target genes, such as Mcl-1, that are regulated by TSLP-induced CRLF2 signals in this disease. Patient-derived xenograft (PDX) models produced by transplanting leukemia cells from patients into immune deficient mice provide an in vivo model of disease that includes contributions of the background genetic landscape that can influence disease progression or treatment outcome in health disparities diseases. PDX models are possible because most cytokines produced in the mouse are active on human cells, however mouse TSLP is species-specific. Thus classic PDX models do not provide TSLP that can activate the CRLF2 receptor that is overexpressed in CRLF2 B-ALL. To address this issue we engineered PDX mice to express physiological levels of human TSLP (+T PDX mice) and control -T mice that lacked human TSLP. In vivo TSLP activity was validated and +T PDX were successfully generated using leukemia cells from two Hispanic pediatric patients with CRLF2 B-ALL. To determine whether +T PDX mice provide a preclinical model of B-ALL that more closely mirrors patients than -T PDX mice, we compared RNAseq gene expression profiles of leukemia cells isolated from +T PDX and -T PDX mice to that from the original patient sample. The gene expression pattern in leukemia cells from +T mice was significantly closer to primary patient sample than that from -T mice. The +T PDX mice described here provide a novel in vivo preclinical model for evaluating efficacy of drugs, such as Mcl-1 inhibitor, in context of the background genetic landscape and physiological human TSLP present in patients.

Citation Format: Kimberly J. Payne, Cornelia Stoian, Jacqueline S. Coats, Olivia Francis, Terry-Ann M. Milford, Ineavely Baez, Pierce J. McCarthy, George Mambo, Anna V.C. White, Mariah M.Z. Jackson, Juliette M. Personius, Veriah Vidales, Muhammad Omair Kamal, Shadi Farzin Gohar, Sinisa Dovat. A novel patient-derived xenograft model for evaluating therapies that target the CRLF2 signaling pathway to reduce health disparities for Hispanic children with leukemia. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr B46.

TSLP or IL-7 provide an IL-7Rα signal that is critical for human B lymphopoiesis

Thymic stromal lymphopoietin (TSLP) and IL-7 are cytokines that signal via the IL-7 receptor alpha (IL-7Rα) to exert both overlapping and unique functions during early stages of mouse B-cell development. In human B lymphopoiesis, the requirement for IL-7Rα signaling is controversial and the roles of IL-7 and TSLP are less clear. Here, we evaluated human B-cell production using novel in vitro and xenograft models of human B-cell development that provide selective IL-7 and human TSLP (hTSLP) stimulation. We show that in vitro human B-cell production is almost completely blocked in the absence of IL-7Rα stimulation, and that either TSLP or IL-7 can provide a signal critical for the production and proliferation of human CD19(+) PAX5(+) pro-B cells. Analysis of primary human bone marrow stromal cells shows that they express both IL-7 and TSLP, providing an in vivo source of these cytokines. We further show that the in vivo production of human pro-B cells under the influence of mouse IL-7 in a xenograft scenario is reduced by anti-IL-7 neutralizing antibodies, and that this loss can be restored by hTSLP at physiological levels. These data establish the importance of IL-7Rα mediated signals for normal human B-cell production.

Abstract A07: A novel patient-derived xenograft model to define the role of TSLP-induced CRLF2 signals and identify therapies for Ph-like B-ALL

A subset of high-risk B cell acute lymphoblastic leukemia (ALL) shows a gene expression profile similar to Philadelphia chromosome positive (Ph+) ALL and has been described as Ph-like ALL. Approximately 50% of Ph-like B-ALL is characterized by genetic alterations leading to overexpression of CRLF2 (CRLF2 B-ALL). CRLF2 B-ALL occurs 5 times more often in Hispanic and Native American children than others and is prevalent in adolescents and young adults. Biologically, CRLF2 acts as a receptor component for the cytokine, TSLP, which induces JAK2-STAT5 and PI3/AKT/mTOR pathway activation downstream of binding to CRLF2. While activating JAK mutations are associated with CRLF2 B-ALL, over half of CRLF2 B-ALL lack such mutations. Our data show that primary human bone marrow (BM) stromal cells express TSLP. Thus TSLP is present in the tumor microenvironment to provide TSLP-induced CRLF2 signals that could play a role in the initiation, maintenance and/or progression of CRLF2 B-ALL. Consistent with this, TSLP has been reported to increase in vitro production of human fetal B cell precursors. However studies of TSLP in B lymphopoiesis have been conducted almost exclusively in mice which show low homology (~40%) with respect to human TSLP and CRLF2. Further, phospho flow cytometry assays show that human, but not mouse TSLP activates CRLF2 signals in primary human CRLF2 B-ALL cells and cell lines as indicated by increased pSTAT5, pAKT and pS6. These data indicate that the mouse TSLP present in classic patient derived xenograft models (PDX) does not produce the TSLP-induced CRLF2 signals present in the patient. To address this challenge we engineered PDX mice to produce human TSLP (hTSLP) by transplanting them with stromal cells transduced to express hTSLP (+T mice). Control (T) mice were produced by transplantation with stroma transduced with a control vector. Supernatant from engineered +T stroma, but not T stroma, induced JAK/STAT5 and PI3K/AKT/mTOR pathway activation in human CRLF2 B-ALL cells. ELISA assays showed that serum levels of hTSLP in mice was proportional to numbers of stromal cells injected at weekly time points. Normal human serum levels of hTSLP (12-32 pg/ml) could be achieved in +T mice, while hTSLP was undetectable in T mice. Because TSLP has been shown to increase in vitro production of human B cell precursors, we evaluated the in vivo functionality of our model by comparing the production of normal B cell precursors in the BM of +T and T PDX mice generated with human umbilical cord blood CD34+ cells. Data from 3 different cord blood donors showed that production of B cell precursors is 3-5 fold increased in +T as compared to T mice. TSLP-induced increases were specific to B lineage cells, initiated in the earliest CD19+ B cell precursors, and maintained through later stages of B cell development. Next we evaluate the in vivo functionality of our model using primary CRLF2 B-ALL leukemia cells. Human CRLF2 B-ALL cells were isolated from the BM of PDX mice and whole genome microarray was performed. 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 +T as compared to T PDX mice, confirming hTSLP activity in the +T PDX mice. To determine whether +T PDX mice provide a preclinical model of B-ALL that more closely mirrors patients than T PDX mice, we compared RNAseq gene expression profiles of leukemia cells from +T and T PDX mice to that from original patient sample. The gene expression pattern in +T mice was significantly closer to primary patient sample than that from T mice. The +T and T PDX mice described here provide a novel preclinical model for studying the role of TSLP in the initiation, progression and maintenance of CRLF2 B-ALL and for evaluating drug efficacy in an in vivo model that more closely mirrors the in vivo environment present in patients.

Citation Format: Olivia L. Francis, Terry-Ann Milford, Ineavely Baez, Jacqueline S. Coats, Christopher L. Morris, Ross Fisher, Ben Van Handel, Ruijun Su, Batul Suterwala, Muhammad Kamal, Shadi Farzin Gohar, Sinisa Dovat, Kimberly J. Payne. A novel patient-derived xenograft model to define the role of TSLP-induced CRLF2 signals and identify therapies for Ph-like B-ALL. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr A07.

A novel xenograft model to study the role of TSLP-induced CRLF2 signals in normal and malignant human B lymphopoiesis

Thymic stromal lymphopoietin (TSLP) stimulates in-vitro proliferation of human fetal B-cell precursors. However, its in-vivo role during normal human B lymphopoiesis is unknown. Genetic alterations that cause overexpression of its receptor component, cytokine receptor-like factor 2 (CRLF2), lead to high-risk B-cell acute lymphoblastic leukemia implicating this signaling pathway in leukemogenesis. We show that mouse thymic stromal lymphopoietin does not stimulate the downstream pathways (JAK/STAT5 and PI3K/AKT/mTOR) activated by the human cytokine in primary high-risk leukemia with overexpression of the receptor component. Thus, the utility of classic patient-derived xenografts for in-vivo studies of this pathway is limited. We engineered xenograft mice to produce human thymic stromal lymphopoietin (+T mice) by injection with stromal cells transduced to express the cytokine. Control (-T) mice were produced using stroma transduced with control vector. Normal levels of human thymic stromal lymphopoietin were achieved in sera of +T mice, but were undetectable in -T mice. Patient-derived xenografts generated from +T as compared to -T mice showed a 3-6-fold increase in normal human B-cell precursors that was maintained through later stages of B-cell development. Gene expression profiles in high-risk B-cell acute lymphoblastic leukemia expanded in +T mice indicate increased mTOR pathway activation and are more similar to the original patient sample than those from -T mice. +T/-T xenografts provide a novel pre-clinical model for understanding this pathway in B lymphopoiesis and identifying treatments for high-risk B-cell acute lymphoblastic leukemia with overexpression of cytokine-like factor receptor 2.

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 stimulation ∼1/3 fewer gene targets were up- and downregulated in the leukemia cells expanded in hTSLP- mice as compared to cells from hTSLP+ mice. This suggests that CRLF2 B-ALL cells expanded in xenograft without TSLP lose some of their ability to respond to TSLP. The hTSLP+ CRLF2 B-ALL PDX mice described here provide a novel preclinical model for studying disease mechanisms and identifying therapies to target signaling pathways activated by TSLP in CRLF2 B-ALL and reduce cancer health disparities for this disease.

Citation Format: Olivia L. Francis, Parveen Shiraz, Terry-Ann Milford, Ineavely Baez, Jacqueline S. Coats, Karina Mayagoitia, Elizabeth Ginelli, Katherine R. Salcedo-Concepcion, Shannalee Martinez, Xiaobing Zhang, Valeri Filippov, Ruijun J. Su, Ross Fisher, Christopher L. Morris, Sinisa Dovat, Kimberly J. Payne. A novel patient-derived xenograft model for evaluating the role of TSLP in CRLF2 B-ALL. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3295. doi:10.1158/1538-7445.AM2015-3295

Infratentorial strokes for posterior circulation folks: clinical correlations for current translational therapeutics

Approximately 20 percent of all strokes will occur in the Infratentorial brain. This is within the vascular territory of the posterior vascular circulation. Very few clinical specifics are known about the therapeutic needs of this patient sub-population. Most evidence-based practices are founded from research about the treatment of anterior circulatory stroke. As a consequence, little is known about how stroke in the Infratentorial brain region would require a different approach. We characterized the neurovascular features of Infratentorial stroke, pathophysiological responses, and experimental models for further translational study.

Posttraumatic reduction of edema with aquaporin-4 RNA interference improves acute and chronic functional recovery

Traumatic brain injury (TBI) is common in young children and adolescents and is associated with long-term disability and mortality. The neuropathologic sequelae that result from juvenile TBI are a complex cascade of events that include edema formation and brain swelling. Brain aquaporin-4 (AQP4) has a key role in edema formation. Thus, development of novel treatments targeting AQP4 to reduce edema could lessen the neuropathologic sequelae. We hypothesized that inhibiting AQP4 expression by injection of small-interfering RNA (siRNA) targeting AQP4 (siAQP4) after juvenile TBI would decrease edema formation, neuroinflammation, neuronal cell death, and improve neurologic outcomes. The siAQP4 or a RNA-induced silencing complex (RISC)-free control siRNA (siGLO) was injected lateral to the trauma site after controlled cortical impact in postnatal day 17 rats. Magnetic resonance imaging, neurologic testing, and immunohistochemistry were performed to assess outcomes. Pups treated with siAQP4 showed acute (3 days after injury) improvements in motor function and in spatial memory at long term (60 days after injury) compared with siGLO-treated animals. These improvements were associated with decreased edema formation, increased microglial activation, decreased blood-brain barrier disruption, reduced astrogliosis and neuronal cell death. The effectiveness of our treatment paradigm was associated with a 30% decrease in AQP4 expression at the injection site.

Tissue vulnerability is increased following repetitive mild traumatic brain injury in the rat

Repetitive mild traumatic brain injury (rmTBI) is an important medical concern for active sports and military personnel. Multiple mild injuries may exacerbate tissue damage resulting in cumulative brain injury and poor functional recovery. In the present study, we investigated the time course of brain vulnerability to rmTBI in a rat model of mild cortical controlled impact. An initial mild injury was followed by a second injury unilaterally at an interval of 1, 3, or 7 days. RmTBI animals were compared to single mTBI and sham treated animals. Neuropathology was assessed using multi-modal magnetic resonance imaging (MRI), followed by ex vivo tissue immunohistochemistry. Neurological and behavioral outcomes were evaluated in a subset of animals receiving rmTBI 3 days apart and shams. RmTBI 1 or 3 days apart but not 7 days apart revealed significantly exacerbated MRI-definable lesion volumes compared to single mTBI and shams. Increases in cortical tissue damage, extravascular iron and glial activation assessed by histology/immunohistochemistry correlated with in vivo MRI findings where shorter intervals (1 or 3 days apart) resulted in greater tissue pathology. There were no neurological deficits associated with rmTBI 3 day animals. At 1 mo post-injury, animals with rmTBI 3 days apart showed reduced exploratory behaviors and subtle spatial learning memory impairments were observed. Collectively, our findings suggest that the mildly-impacted brain is more vulnerable to repetitive injury when delivered within 3 days following initial mTBI.

Non-elective intra-coronary stenting: are the clinical outcomes comparable to elective stenting at 6 months?

The aim of this study was to compare prospectively the clinical outcome of patients treated with intra-coronary stents as a non-elective/bailout procedure for acute or threatened vessel closure, with those undergoing elective stenting at 6 months. Sixty-four patients (60.2+/-11.7 y) who underwent non-elective stenting for abrupt or threatened vessel closure and/or sub-optimal results were prospectively compared with 68 patients (62+/-10.0 y) who were stented electively. All patients had broadly similar pre-procedural clinical profiles. However, patients in the elective group had a higher incidence of previous PTCA (10.2% vs. 0%, P = 0.01) and bypass surgery (30.9% vs. 6.3%, P = 0.0003) compared with the non-elective group. A total of 158 stents (1.19 per patient) were implanted in 132 patients with a procedural success rate of 99.3%. At 6 months follow-up there was no statistical difference in the primary composite end-point of death, myocardial infarction and the need of repeat revascularisation (10.9% vs. 5.8%, P = 0.35) between the two groups. However, patients in the non-elective group showed a higher incidence of unstable angina compared with the elective group (25% vs. 1.4%, P = 0.0004). The findings of this study suggest that stents (single or multiple) can be effectively implanted in non-elective situations with no increase in the incidence of death, non-fatal myocardial infarction, and the need of repeat revascularisation at 6 months compared with elective stenting.