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Alveologenesis is the culmination of lung development and involves the correct temporal and spatial signals to generate the delicate gas exchange interface required for respiration. Using a novel Wnt signaling reporter system, we demonstrate the emergence of a Wnt-responsive alveolar epithelial cell sublineage that arises during alveologenesis called the axin2+ alveolar type 2 cell or AT2Axin2. The number of AT2Axin2 cells increases substantially during late lung development, correlating with a wave of Wnt signaling during alveologenesis. Transcriptome analysis, in vivo clonal analysis, and ex vivo lung organoid assays reveal that AT2sAxin2 promote enhanced AT2 cell growth during generation of the alveolus. Activating Wnt signaling results in expansion of AT2s whereas inhibition of Wnt signaling inhibits AT2 cell development and shunts alveolar epithelial development towards the alveolar type 1 cell lineage. These findings reveal a wave of Wnt-dependent AT2 expansion required for lung alveologenesis and maturation.

CRLF2 rearrangements, JAK1/2 point mutations, and JAK2 fusion genes have been identified in Philadelphia chromosome (Ph)-like acute lymphoblastic leukemia (ALL), a recently described subtype of pediatric high-risk B-precursor ALL (B-ALL) which exhibits a gene expression profile similar to Ph-positive ALL and has a poor prognosis. Hyperactive JAK/STAT and PI3K/mammalian target of rapamycin (mTOR) signaling is common in this highrisk subset. We, therefore, investigated the efficacy of the JAK inhibitor ruxolitinib and the mTOR inhibitor rapamycin in xenograft models of 8 pediatric B-ALL cases with and without CRLF2 and JAK genomic lesions. Ruxolitinib treatment yielded significantly lower peripheral blast counts compared with vehicle (P < .05) in 6 of 8 human leukemia xenografts and lower splenic blast counts (P < . IntroductionSurvival rates for childhood B-precursor acute lymphoblastic leukemia (B-ALL) approach 90% with current combination chemotherapy regimens. 1 Intensification of chemotherapy regimens has largely been responsible for dramatic improvements in survival; however, recent modifications have yielded diminishing returns, particularly in a subset of leukemias that are relatively resistant to conventional cytotoxic chemotherapy. The identification of underlying genetic alterations in chemotherapy-resistant subtypes, particularly lesions that drive leukemogenesis and can be targeted with novel therapies, remains an urgent need.Genome-wide analyses and next-generation sequencing approaches have advanced our understanding of potential leukemogenic mutations in pediatric ALL. [2][3][4][5][6][7] Recently, these analyses identified a cohort of clinically high-risk pediatric B-precursor ALL with gene expression profiles similar to those of Philadelphia chromosome-positive ALL (Ph ϩ ALL, also termed BCR-ABL1-positive ALL). 2,4,8 This Ph-like cohort suffers high rates of relapse and mortality. The similarity to Ph ϩ ALL suggests that aberrant kinase activity may also drive this subset of ALL. Indeed, several lesions affecting kinase activity and cytokine signaling have recently been identified in Ph-like ALL. 9 Rearrangements in CRLF2 (cytokine receptor-like factor 2), leading to overexpression of this component of the heterodimeric cytokine receptor for thymic stromal lymphopoietin (TSLP), are present in up to 7% of childhood B-precursor ALL overall, 10-12 represent approximately half of Ph-like ALLs, 8 and are highly associated with point mutations in Janus kinase (JAK) family members. 11,13-15 Moreover, CRLF2 overexpression is an independent negative prognostic factor in high-risk pediatric B-ALL. 16 The frequency of genetic alterations in CRLF2 and JAK2 in high-risk B-ALL and Down syndrome-associated ALL 10,17 suggests that these lesions may be key events in leukemogenesis. Consistent with its role in early B-cell development, we have previously demonstrated that TSLP stimulates proliferation of precursor B-ALL cell lines. 18,19 Similarly, JAK signaling has been implicated in BCR-ABL1-mediated transform...

• ETP-ALL, a high-risk subtype of T-ALL, is characterized by aberrant activation of the JAK/STAT signaling pathway.• The JAK1/2 inhibitor ruxolitinib demonstrates robust activity in patientderived xenograft models of ETP-ALL.Early T-cell precursor (ETP) acute lymphoblastic leukemia (ALL) is a recently described subtype of T-ALL characterized by a unique immunophenotype and genomic profile, as well as a high rate of induction failure. Frequent mutations in cytokine receptor and Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathways led us to hypothesize that ETP-ALL is dependent on JAK/STAT signaling. Here we demonstrate aberrant activation of the JAK/STAT pathway in ETP-ALL blasts relative to non-ETP T-ALL. Moreover, ETP-ALL showed hyperactivation of STAT5 in response to interleukin-7, an effect that was abrogated by the JAK1/2 inhibitor ruxolitinib. In vivo, ruxolitinib displayed activity in 6 of 6 patient-derived murine xenograft models of ETP-ALL, with profound single-agent efficacy in 5 models. Ruxolitinib treatment decreased peripheral blast counts relative to pretreatment levels and compared with control (P < .01) in 5 of 6 ETP-ALL xenografts, with marked reduction in mean splenic blast counts (P < .01) in 6 of 6 samples. Surprisingly, both JAK/STAT pathway activation and ruxolitinib efficacy were independent of the presence of JAK/STAT pathway mutations, raising the possibility that the therapeutic potential of ruxolitinib in ETP-ALL extends beyond those cases with JAK mutations. These findings establish the preclinical in vivo efficacy of ruxolitinib in ETP-ALL, a biologically distinct subtype for which novel therapies are needed. (Blood. 2015;125(11):1759-1767 Introduction Early T-cell precursor (ETP) acute lymphoblastic leukemia (ALL) was first described in 2009 as a subtype of T-ALL with a unique immunophenotype that includes expression of myeloid and early progenitor or stem cell markers in addition to T-cell lineage markers. 1Although overall survival for the majority of T-ALL cases has improved dramatically over the last 50 years, 2 largely due to intensification of chemotherapy regimens, many published studies suggest a large percentage of ETP-ALL cases have dismal outcomes.1,3-7 More recent studies suggest that children with ETP-ALL treated on contemporary protocols that intensify therapy based on minimal residual disease response may not fare as poorly as originally thought. 8,9 ETP-ALL, which represents ;10% to 15% of new T-ALL diagnoses in children 1,4,5 and ;10% to 30% in adults, 3,6 accounts for a disproportionate fraction of T-ALL induction failures (ie, failure to achieve a morphologic remission at the end of the first month of chemotherapy). Novel therapies with alternative mechanistic approaches are urgently needed for chemotherapy-refractory subgroups of ETP-ALL.In addition to an immunophenotype with myeloid/stem cell markers, ETP-ALL cases demonstrate a similar transcriptional and mutational landscape to myeloid leukemias and hematopoietic stem ce...

High-risk subtypes of B-cell acute lymphoblastic leukemia (B-ALL) include Philadelphia chromosome-positive (Ph+) BALL driven by the BCR-ABL1 oncogene and a more recently identified subtype known as BCR-ABL-like or Ph-like BALL. A hallmark of both Ph+ and Ph-like BALL is constitutive activation of tyrosine kinase signaling that is potentially targetable with tyrosine kinase inhibitors (TKIs). BALL cells also receive extracellular signals from the microenvironment that can maintain proliferation and survival following treatment with TKIs. Therefore, there is strong rationale for combining TKIs with other therapies targeting signal transduction pathways. Here we show that combinations of the ABL-directed TKI dasatinib with mTOR kinase inhibitors (TOR-KIs) are more effective than TKI alone against patient-derived Ph-like BALL cells harboring rearrangements of ABL1 or ABL2. We also report the establishment of a new human Ph-like BALL cell line that is stromal cell-independent in vitro and can be used for xenograft experiments in vivo. These findings provide rationale for clinical testing of TKI plus TOR-KIs in children and adults with Ph-like BALL and a new experimental tool to test promising therapeutic strategies in this poor prognosis subtype of BALL. www.impactjournals.com/oncotarget/