KitV558&#916;/+ mice were genetically engineered and shared by Dr. Peter Besmer10. This work was supported by NIH grants R01 CA102613 and T32 CA251063.

All mice were housed under pathogen-free conditions at the University of Pennsylvania according to NIH guidelines and with approval of the University of Pennsylvania IACUC. Euthanasia was performed following the University of Pennsylvania Laboratory Animal Resources standard operating procedures.
1. KitV558&#916;/+ mouse breeding
<ol>
	<li>Backcross the KitV558&#916;/+ mice more than 10 times onto a C57BL/6...

<ol>
	<li>Mastrangelo, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Incidence+of+soft+tissue+sarcoma+and+beyond:+a+population-based+prospective+study+in+3+European+regions.">Incidence of soft tissue sarcoma and beyond: a population-based prospective study in 3 European regions.</a> Cancer. 118 (21), 5339-5348 (2012).</li><li>Joensuu, H., DeMatteo, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+management+of+gastrointestinal+stromal+tumors:+a+model+for+targeted+and+multidisciplinary+therapy+of+malignancy.">The management of gastrointestinal stromal tumors: a model for targeted and multidisciplinary therapy of malignancy.</a> Annual Review of Medicine. 63, 247-258 (2012).</li><li>Blanke, C. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+results+from+a+randomized+phase+II+trial+of+standard-+versus+higher-dose+imatinib+mesylate+for+patients+with+unresectable+or+metastatic+gastrointestinal+stromal+tumors+expressing+KIT.">Long-term results from a randomized phase II trial of standard- versus higher-dose imatinib mesylate for patients with unresectable or metastatic gastrointestinal stromal tumors expressing KIT.</a> Journal of Clinical Oncology. 26 (4), 620-625 (2008).</li><li>Demetri, G. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficacy+and+safety+of+regorafenib+for+advanced+gastrointestinal+stromal+tumours+after+failure+of+imatinib+and+sunitinib+(GRID):+an+international,+multicentre,+randomised,+placebo-controlled,+phase+3+trial.">Efficacy and safety of regorafenib for advanced gastrointestinal stromal tumours after failure of imatinib and sunitinib (GRID): an international, multicentre, randomised, placebo-controlled, phase 3 trial.</a> Lancet. 381 (9863), 295-302 (2013).</li><li>Gold, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Outcome+of+metastatic+GIST+in+the+era+before+tyrosine+kinase+inhibitors.">Outcome of metastatic GIST in the era before tyrosine kinase inhibitors.</a> Annals of Surgical Oncology. 14 (1), 134-142 (2007).</li><li>Huynh, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sorafenib+induces+growth+suppression+in+mouse+models+of+gastrointestinal+stromal+tumor.">Sorafenib induces growth suppression in mouse models of gastrointestinal stromal tumor.</a> Molecular Cancer Therapeutics. 8 (1), 152-159 (2009).</li><li>Na, Y. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Establishment+of+patient-derived+xenografts+from+patients+with+gastrointestinal+stromal+tumors:+analysis+of+clinicopathological+characteristics+related+to+engraftment+success.">Establishment of patient-derived xenografts from patients with gastrointestinal stromal tumors: analysis of clinicopathological characteristics related to engraftment success.</a> Scientific Reports. 10 (1), 7996 (2020).</li><li>Balachandran, V. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imatinib+potentiates+antitumor+T+cell+responses+in+gastrointestinal+stromal+tumor+through+the+inhibition+of+Ido.">Imatinib potentiates antitumor T cell responses in gastrointestinal stromal tumor through the inhibition of Ido.</a> Nature Medicine. 17 (9), 1094-1100 (2011).</li><li>Vitiello, G. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+immune+profiles+distinguish+the+mutational+subtypes+of+gastrointestinal+stromal+tumor.">Differential immune profiles distinguish the mutational subtypes of gastrointestinal stromal tumor.</a> Journal of Clinical Investigation. 129 (5), 1863-1877 (2019).</li><li>Sommer, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gastrointestinal+stromal+tumors+in+a+mouse+model+by+targeted+mutation+of+the+Kit+receptor+tyrosine+kinase.">Gastrointestinal stromal tumors in a mouse model by targeted mutation of the Kit receptor tyrosine kinase.</a> Proceedings of the National Academy of Sciences of the United States of America. 100 (11), 6706-6711 (2003).</li><li>Cavnar, M. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=KIT+oncogene+inhibition+drives+intratumoral+macrophage+M2+polarization.">KIT oncogene inhibition drives intratumoral macrophage M2 polarization.</a> Journal of Experimental Medicine. 210 (13), 2873-2886 (2013).</li><li>Medina, B. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oncogenic+kinase+inhibition+limits+Batf3-dependent+dendritic+cell+development+and+antitumor+immunity.">Oncogenic kinase inhibition limits Batf3-dependent dendritic cell development and antitumor immunity.</a> Journal of Experimental Medicine. 216 (6), 1359-1376 (2019).</li><li>Zhang, J. Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Macrophages+and+CD8(+)+T+cells+mediate+the+antitumor+efficacy+of+combined+CD40+ligation+and+imatinib+therapy+in+gastrointestinal+stromal+tumors.">Macrophages and CD8(+) T cells mediate the antitumor efficacy of combined CD40 ligation and imatinib therapy in gastrointestinal stromal tumors.</a> Cancer Immunology Research. 6 (4), 434-447 (2018).</li><li>. General Protocol for Western Blotting Available from: <a target="_blank" href="https://www.bio-rad.com/webroot/web/pdf/lsr/literature/Buttetin_6376.pdf">https://www.bio-rad.com/webroot/web/pdf/lsr/literature/Buttetin_6376.pdf</a> (2022)</li><li>Sadeghipour, A., Babaheidarian, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Making+formalin-fixed,+paraffin+embedded+blocks.">Making formalin-fixed, paraffin embedded blocks.</a> Biobanking: Methods and Protocols. , 253-268 (2019).</li><li>Sy, J., Ang, L. -. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microtomy:+Cutting+formalin-fixed,+paraffin-embedded+sections.">Microtomy: Cutting formalin-fixed, paraffin-embedded sections.</a> Biobanking: Methods and Protocols. , 269-278 (2019).</li><li>Seifert, A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PD-1/PD-L1+blockade+enhances+T-cell+activity+and+antitumor+efficacy+of+imatinib+in+gastrointestinal+stromal+tumors.">PD-1/PD-L1 blockade enhances T-cell activity and antitumor efficacy of imatinib in gastrointestinal stromal tumors.</a> Clinical Cancer Research. 23 (2), 454-465 (2017).</li><li>Liu, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oncogenic+KIT+modulates+Type+I+IFN-mediated+antitumor+immunity+in+GIST.">Oncogenic KIT modulates Type I IFN-mediated antitumor immunity in GIST.</a> Cancer Immunology Research. 9 (5), 542-553 (2021).</li><li>Rossi, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oncogenic+Kit+signaling+and+therapeutic+intervention+in+a+mouse+model+of+gastrointestinal+stromal+tumor.">Oncogenic Kit signaling and therapeutic intervention in a mouse model of gastrointestinal stromal tumor.</a> Proceedings of the National Academy of Sciences of the United States of America. 103 (34), 12843-12848 (2006).</li></ol>

The KitV558&#916;/+&#160;mouse model is a powerful research tool in the molecular and immunologic analysis of GIST. Although the breeding strategy requires a single cross, using KitV558&#916;/+ mouse cohorts in experiments analyzing tumor response requires extensive breeding. Mice should be age- and sex-matched to ensure similar tumor weights, and 10% of mice die before 8 weeks of age when tumors are established. Less extensive breeding strategies are possible if using advanced ima...

GIST is the most common sarcoma in humans with an incidence of about 6,000 cases in the United States of America1. GIST appears to originate from the gastrointestinal pacemaker cells named the interstitial cells of Cajal, and is typically driven by a single mutation in the tyrosine kinase KIT or PDGFRA2. Surgery is the mainstay of treatment for GIST and can be curative, but patients with advanced disease may be treated with the tyrosine kinase inhibitor (TKI), imatinib. Since its introduction over 20 years ago, imatinib has transformed the treatment paradigm in GIST, improving the survival in advanced disease from 1 to over 5 years3,4,5. Unfortunately, imatinib is rarely curative due to acquired KIT mutations, so new treatments are needed for this tumor.
Mouse models are an important research tool in the investigation of novel therapies in cancer. Multiple subcutaneous xenograft and patient-derived xenograft models have been developed and investigated in GIST6,7. However, immunodeficient mice do not fully represent human GIST since GISTs harbor differential immune profiles depending on their oncogenic mutation, and altering the gastrointestinal tumor microenvironment improves upon the effects of TKI therapy8,9. The KitV558&#916;/+&#160;mouse has a heterozygous germline deletion in Kit exon 11, which encodes the juxtamembrane domain, the most commonly mutated site in human GIST10. KitV558&#916;/+&#160;mice develop a single cecal GIST with 100% penetrance, and tumors have similar histology, molecular signaling, immune infiltration, and response to therapy as human GIST8,11,12,13. Here, we describe breeding, treatment, and specimen isolation and processing in KitV558&#916;/+&#160;mice for use in molecular and immunologic research in GIST.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>100 micron filter</td>
			<td>EMSCO</td>
			<td>1194-2360</td>
			<td></td>
		</tr>
		<tr>
			<td>1x RBC lysis buffer</td>
			<td>Life Technologies</td>
			<td>00-4333-57</td>
			<td></td>
		</tr>
		<tr>
			<td>3mL syringe</td>
			<td>Thermo Fisher Scientific/BD Biosciences</td>
			<td>14823435</td>
			<td></td>
		</tr>
		<tr>
			<td>4&#8211;15% Mini-PROTEAN TGX Precast Protein Gels, 10-well, 30 &#181;l</td>
			<td>Bio-Rad</td>
			<td>4561083</td>
			<td></td>
		</tr>
		<tr>
			<td>4% Paraformaldehyde Solution</td>
			<td>Thermo Fisher Scientific</td>
			<td>AAJ19943K2</td>
			<td></td>
		</tr>
		<tr>
			<td>40 micron filter</td>
			<td>EMSCO</td>
			<td>1194-2340</td>
			<td></td>
		</tr>
		<tr>
			<td>5M NaCl</td>
			<td>Sigma Aldrich</td>
			<td>S6546</td>
			<td></td>
		</tr>
		<tr>
			<td>70 micron filter</td>
			<td>EMSCO</td>
			<td>1194-2350</td>
			<td></td>
		</tr>
		<tr>
			<td>AKT antibody (C67E7)</td>
			<td>Cell Signaling</td>
			<td>4691</td>
			<td></td>
		</tr>
		<tr>
			<td>C57BL/6J mice</td>
			<td>The Jackson Laboratory</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase IV</td>
			<td>Sigma Aldrich</td>
			<td>C5138</td>
			<td></td>
		</tr>
		<tr>
			<td>Complete mini edta free protease inhibitor</td>
			<td>Thomas Scientific</td>
			<td>C852A34</td>
			<td></td>
		</tr>
		<tr>
			<td>Countess II Automated Cell Counter</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable Scalpels</td>
			<td>Thermo Fisher Scientific/Exel International</td>
			<td>14-840-00</td>
			<td></td>
		</tr>
		<tr>
			<td>Dnase I</td>
			<td>Thomas Scientific</td>
			<td>C756V81</td>
			<td></td>
		</tr>
		<tr>
			<td>Dog1 antibody</td>
			<td>abcam</td>
			<td>ab64085</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Sigma Aldrich</td>
			<td>E9884</td>
			<td></td>
		</tr>
		<tr>
			<td>ERK antibody (p44/42)</td>
			<td>Cell Signaling</td>
			<td>9102</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Thomas Scientific</td>
			<td>C788U23</td>
			<td></td>
		</tr>
		<tr>
			<td>FIJI software</td>
			<td>FIJI</td>
			<td></td>
			<td>https://imagej.net/software/fiji</td>
		</tr>
		<tr>
			<td>Fisherbrand 850 Homogenizer</td>
			<td>Thermo Fisher Scientific</td>
			<td>15-340-169</td>
			<td></td>
		</tr>
		<tr>
			<td>HBSS</td>
			<td>University of Pennsylvania Cell Center</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Imatinib mesylate</td>
			<td>Selleck Chemicals</td>
			<td>S1026</td>
			<td></td>
		</tr>
		<tr>
			<td>KIT antibody (D13A2)</td>
			<td>Cell Signaling</td>
			<td>3074</td>
			<td></td>
		</tr>
		<tr>
			<td>KitV558&#916;/+ Genotyping</td>
			<td>Transnetyx</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge tubes (1.5mL)</td>
			<td>Thermo Fisher Scientific</td>
			<td>05-408-129</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse on Mouse Immunodetection Kit, Basic</td>
			<td>Vector Laboratories</td>
			<td>BMK-2202</td>
			<td></td>
		</tr>
		<tr>
			<td>Nitrocellulose Membrane, Precut, 0.45 &#181;m</td>
			<td>Rio-Rad</td>
			<td>1620145</td>
			<td></td>
		</tr>
		<tr>
			<td>Nonfat Dry Milk</td>
			<td>Thermo Fisher Scientific</td>
			<td>NC9121673</td>
			<td></td>
		</tr>
		<tr>
			<td>Nonidet P 40 Substitute</td>
			<td>Sigma Aldrich</td>
			<td>74385</td>
			<td></td>
		</tr>
		<tr>
			<td>p-AKT antibody (S473)</td>
			<td>Cell Signaling</td>
			<td>4060</td>
			<td></td>
		</tr>
		<tr>
			<td>p-ERK antibody (p44/42)</td>
			<td>Cell Signaling</td>
			<td>9101</td>
			<td></td>
		</tr>
		<tr>
			<td>p-KIT antibody (Y719)</td>
			<td>Cell Signaling</td>
			<td>3391</td>
			<td></td>
		</tr>
		<tr>
			<td>PMSF Protease Inhibitor</td>
			<td>Thermo Fisher Scientific</td>
			<td>36978</td>
			<td></td>
		</tr>
		<tr>
			<td>Proeinase K</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP170050</td>
			<td></td>
		</tr>
		<tr>
			<td>Round-Bottom Polystyrene Test (FACS) Tubes</td>
			<td>Falcon/Thermo Fisher Scientific</td>
			<td>14-959-2A</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI</td>
			<td>University of Pennsylvania Cell Center</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium fluoride (NaF)</td>
			<td>Sigma Aldrich</td>
			<td>201154</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium orthovanadate (Na3VO4)</td>
			<td>Sigma Aldrich</td>
			<td>S6508</td>
			<td></td>
		</tr>
		<tr>
			<td>SuperSignal West Dura Extended Duration Substrate</td>
			<td>Thermo Fisher Scientific</td>
			<td>34076</td>
			<td></td>
		</tr>
		<tr>
			<td>TBS buffer (10x)</td>
			<td>University of Pennsylvania Cell Center</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue culture dish (100mm2)</td>
			<td>Thermo Fisher Scientific/Falcon</td>
			<td>08-772E</td>
			<td></td>
		</tr>
		<tr>
			<td>TrisHCL</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP1757500</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td>Rio-Rad</td>
			<td>1706531</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;vivaCT 80 platform</td>
			<td>Scanco medical</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

molecular and immunologic techniques in a genetically engineered mouse model of gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST) is the most common human sarcoma and is typically driven by a single mutation in the KIT receptor. Across tumor types, numerous mouse models have been developed in order to investigate the next generation of cancer therapies. However, in GIST, most in vivo studies use xenograft mouse models which have inherent limitations. Here, we describe an immunocompetent, genetically engineered mouse model of gastrointestinal stromal tumor harboring a KitV558&#916;/+ mutation. In this model, mutant KIT, the oncogene responsible for most GISTs, is driven by its endogenous promoter leading to a GIST which mimics the histological appearance and immune infiltrate seen in human GISTs. Furthermore, this model has been used successfully to investigate both targeted molecular and immune therapies. Here, we describe the breeding and maintenance of a KitV558&#916;/+ mouse colony. Additionally, this paper details the treatment and procurement of GIST, draining mesenteric lymph node, and adjacent cecum in KitV558&#916;/+ mice, as well as sample preparation for molecular and immunologic analyses.

The KitV558&#916;/+ mouse model allows for the investigation of therapeutics in an immunocompetent mouse model. KitV558&#916;/+ mice have an average lifespan of 8 months due to progressive bowel obstruction (Figure 4). Tumors from KitV558&#916;/+ mice express canonical markers of GIST including the tyrosine kinase KIT and the transmembrane channel DOG1 (Figure 5...

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Molecular and Immunologic Techniques in a Genetically Engineered Mouse Model of Gastrointestinal Stromal Tumor

The goal of this manuscript is to describe the KitV558&#916;/+&#160;mouse model and techniques for successful dissection and processing of mouse specimens.

Gastrointestinal stromal tumor (GIST) is the most common human sarcoma and is typically driven by a single mutation in the KIT receptor. Across tumor ...

Our protocol describes the breeding, maintenance, dissection, and specimen processing of the only immunocompetent mouse model, GIST, currently in use. We hope that future researchers will be able to utilize this mouse model in order to further translational research in GIST. Traditional therapies in GIST involve targeted molecular therapy with tyrosine kinase inhibitors.This model enables researchers to test immunotherapies in GIST. To begin, sterilize all instruments, wear gloves throughout the procedure, and maintain a sterile field. Prepare the area of incision with 70%ethanol.Using scissors, make a two-centimeter midline vertical incision and enter the abdominal cavity. Sharply lyse any intra-abdominal adhesions. To remove the draining mesenteric lymph node, identify the cecum and lift its mesentery superiorly.Approximately midway to the base of the colonic mesentery, identify the mesenteric lymph node and sharply dissect it. As needed, divide lymph node tissue into thirds for protein isolation, histology, and single cell suspension. Place lymph node tissue in 20 milliliters of RPMI medium for single-cell suspensions and keep on ice.The cecum is mostly replaced by a GIST in the Kit558 mice. For isolation of the GIST and cecum, carefully divide the ileocolic junction from the base of the tumor. Then, divide the cecum again, two centimeters distal to the base of the tumor.In 50 to 60%of the Kit558 mice, the head of the tumor contains a cap of cecal tissue, which typically contains serous fluid, but may rarely contain pus. Sharply dissect the cap tissue away from the tumor tissue. Divide the tumor tissue and cecum into thirds for protein isolation, histology, and single-cell suspension.For single-cell suspensions, place tumor tissue or cecum in HBSS with 2%FCS, enough to cover the sample, and keep on ice. Pour RPMI media with the lymph node specimen over a 100-micrometer filter. Move the filter to a new 50-milliliter conical, and mash the lymph node with the soft end of a three-milliliter plastic syringe.Wash filter with 20 milliliters of RPMI media. Centrifuge the samples and aspirate the supernatant. Resuspend the pellet in 20 milliliters of bead buffer and pour over a 40-micrometer filter.Collect the cell filtrate. Count cells using a hemocytometer. Centrifuge the samples and discard the supernatant.Then, resuspend in bead buffer for flow cytometry. Prepare collagenase buffer as described in the text manuscript. Place GIST in a sterile dish and add 2.5 milliliters of collagenase buffer.Using a sterile scalpel and scissors, mince the tumor until it is in fine fragments. Use a large-bore pipette to aspirate the tumor and collagenase into a 50-milliliter tube. Incubate it at 37 degrees Celsius for 30 minutes at 100 rotations per minute, then quench the reaction with two milliliters of FBS.Pour collagenase with GIST specimen over a 100-micrometer filter and mash the tumor with the soft end of a three-milliliter plastic syringe and collect in a 50-milliliter tube. Wash filter with 20 milliliters of HBSS. Centrifuge the filtrate at 450 RCF for five minutes at four degrees Celsius, then discard the supernatant.Resuspend the pellet in 20 milliliters of bead buffer and pour over a 40-micrometer filter Collect the filtrate and count cells using a hemocytometer. Centrifuge and aspirate the supernatant, then resuspend in bead buffer for flow cytometry. Using scissors, split the cecum longitudinally to expose the inner mucosa.Cut it into 0.5-centimeter sections and place it in a 50-milliliter tube with five milliliters of HBSS and 2%FBS. Shake vigorously for 30 seconds and centrifuge at 450 RCF for 20 seconds. Then, discard the supernatant.Add five to 20 milliliters of HBSS with two-millimolar EDTA. Incubate it at 37 degrees Celsius at 100 rotations per minute for 15 minutes. Centrifuge and discard the supernatant, then resuspend the pellet in five to 20 milliliters of HBSS.Shake the mixture vigorously for 30 seconds, then centrifuge at 450 RCF for 20 seconds and discard the supernatant. Repeat this process once more. Resuspend the pellet in five milliliters of collagenase buffer, then incubate it at 37 degrees Celsius for 30 minutes at 100 rotations per minute.Shake vigorously every 10 minutes and quench the reaction with two milliliters of FBS. Pour collagenase with cecum specimen over a 100-micrometer filter and mash with the soft end of a three-milliliter plastic syringe. Wash the filter with 20 milliliters of HBSS and collect the filtrate.Centrifuge and discard the supernatant. Resuspend the pellet in 20 milliliters of bead buffer and pour over a 40-micrometer filter. Collect filtrate and count cells using a hemocytometer.Repeat the centrifugation process once more and resuspend the pellet in bead buffer for flow cytometry. The Kit558 mice had an average lifespan of eight months due to progressive bowel obstruction. Tumors from the Kit558 mice expressed canonical markers of GIST, including the tyrosine kinase KIT, the transmembrane channel Dog1, and the transcription factor ETV1.Tumors were studied for changes in the KIT signaling pathway such as the downstream markers ERK and AKT or immune microenvironment, which closely mimicked human GIST. MRI or CT was used to track tumor volume as an accurate measurement of tumor response. Dissecting the tumor away from the ileocolic junction and away from the cecal cap is important to capture true tumor weight and immune and molecular analysis.Within GIST, this model has allowed for the investigation of the tumor microenvironment, as well as immunotherapies.

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Research

JoVE Journal

Cancer Research

1.9K Views.  Hospital of the University of Pennsylvania. Our protocol describes the breeding, maintenance, dissection, and specimen processing of the only immunocompetent mouse model, GIST, currently in use. We hope that future researchers will be able to utilize this mouse model in order to further translational research in GIST. Traditional therapies in GIST involve targeted molecular therapy with tyrosine kinase inhibitors.This model enables researchers to test immunotherapies in GIST. To begin, sterilize all instruments, wear gloves thro...