Introduction: The objective of this study is to use a non-invasive method to quantify and qualify the growth of tissue-engineered intestine in a new murine model. Lack of gastrointestinal tissue in children such as long gap esophageal atreia or short bowel syndrome leads to severe morbidities and mortality. Current therapies do not offer adequate palliation. In previous work, we used tissue engineering to create living replacement gastrointestinal tissues in the Lewis rat. These tissues had identical architecture to native structures including muscle, nerve, ganglion cells, and mucosa. The mechanism and kinetics of the formation of engineered intestine have not been defined. Methods: Organoid units (OU), mesenchymal cell cores surrounded by a polarized epithelia, were derived from full-thickness small intestine from P4 mice that were either wildtype (Control group) or B6;C3-Tg(TettTALuc)1Dgs/J mice (Luciferase + group), which constitutively express luciferase in the absence of tetracycline. OU were obtained using a variation of the previous protocol reported for tissue-engineered colon in Lewis rats. OU were implanted on a biodegradable polymer scaffold in the omentum of wildtype C57Bl/6 mice (n=2 Control groupl, n=2 Luciferase + group). Initial measurements were made at 24 hour time points, then every 72 hours for three weeks until harvest. Imaging was performed 12 minutes after the injection of the substrate for the luciferase, D-Luciferin Firefly, potassium salt (synthetic). 4,5-Dihydro-2-(6-hydroxy-2-benzothiazolyl)-4-thiazolecarboxylic acid potassium salt, and performed simultaneously using the Xenogen IVIS 200, under inhaled anesthetic. Living Image 3.0 software was used for data analysis. Hematoxylin and eosin staining and immunohistochemistry were performed after sacrifice of the animals, at 3 weeks. Results: in the Luciferase + group, luciferase signal was identified on postoperative day 0 through 14, with an increasing intensity until day 10, then slight decrease until Day 13, when it abruptly vanished (Figure shows Day 6, representative). Tissue-engineered intestine did not form in the Luciferase + group. Luciferase signal was not identified in the control group, but tissue-engineered intestine formed with a mucosa with well-formed villi and a muscularis in one of the two control animals. One of the control animals died during the experiment from a retroperitoneal injury from luciferin injection. Conclusions: The delayed extinguishing of the luciferase signal and the formation of tissue-engineered intestine in the control group suggests the cause of an immune response secondary to the mismatched genetic backgrounds of the B6;C3-Tg(TettTALuc)1Dgs/J donor and the wildtype hosts. We plan to repeat this experiment in an immunocompromised host. Future study of the persistent cell population prior to the loss of luciferase signal may indicate the necessary cell population for the formation of engineered intestine.