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Organoid modeling of cancer cells and the tumor immune microenvironment.We have successfully established primary 3D organoid cultures of diverse tissues and used them to achieve the first in vitro conversion of primary intestine, stomach and pancreas tissue to adenocarcinoma (Ootani et al, Nat Med 2009; Li et al, Nat Med 2014) amongst others. These organoid systems comprise an robust in vitro system which we are exploiting for the functional validation of putative oncogenic loci which are identified in whole-genome cancer surveys such as TCGA. In a new direction, we have developed organoid methods to preserve tumor cells along with a diversity of endogenous infiltrating immune cells (T, B, NK, macrophages) and demonstrated that such organoids are responsive to checkpoint inhibitor therapy (Neal et al, Cell 2018). Further, we have established large biobanks of organoids from clinical cancer biopsies with relevance to tumor modeling and predication of patient responses to therapeutics. Organoids for regenerative medicine.We are also interested in using organoids as a method to grow mini-organs that can be transplanted into recipients for regenerative medicine purposes. We are establishing proof-of-principle for human or mouse organoid transplantation, ultimately to effect phenotypic correction of diseases. Intestinal stem/progenitor biology.The complete regeneration of the epithelial lining of the intestine every 5-7 days renders the intestine a model system for studying stem cell behaviors. We are investigating the regulation of the intestinal stem cell (ISC) compartment by extracellular signals such as Wnts, using adenoviral and conditional knockout approaches. We have defined R-spondins as dominant regulators of the ISC niche with Wnts playing a more permissive role using lineage tracing, bioengineered Wnts and single cell RNA-seq approaches (Yan et al., Nature, 2017a; Janda et al, Nature 2017b). We have found that Bmi1+ ISC are strongly injury-inducible versusthe homeostatic function of Lgr5+ ISC (c.f. Yan et al, PNAS 2012, Barry et al, Nature 2013) and have enteroendocrine characteristics (Yan et al., Stem Cell, 2017). Further, we have derived robust organoid methods for prolonged culture of and ex vivo expansion of primary intestine and other GI organs, with preservation of ISCs and recapitulation of the Wnt- and Notch-dependent ISC niche, even allowing peristalsis (Ootani et al, Nat Med 2009; Li et al Nat Med 2014).Angiogenesis and the blood-brain barrier.We are interested in determining functions of novel molecules regulating angiogenesis including receptors such as GPCRs, microRNAs and secreted molecules. We found that GPR124 is essential for developmental brain angiogenesis (Kuhnert et al, Science 2010) that GPR124 is critical for maintaining blood-brain barrier integrity during stroke and brain tumor growth (Chang et al, Nat Med 2017) and that the GPR124-associated protein RECK is a Wnt7 receptor (Vallon et al, Cell Reports, 2018). We have several active projects in stroke and blood-brain barrier (BBB) basic biology and therapeutic development. We have previously exploring the functions of the endothelial miRNA miR-126 in adults using conditional ko mice (Kuhnert et al, Development 2008) and have extensive interests in pharmacologic inhibition of novel targets for anti-angiogenic therapy of cancer and ocular disorders.