This work was supported by funding received from the National Institutes of Health (1R01AI083269).

The murine studies were approved by the Institutional Animal Care and Use Committee (IACUC) of the University of North Carolina Chapel Hill and all animal care was in accordance with the IACUC guidelines.
1. Preparation of Newborn and Adult Thymi
<ol>
	<li>Prepare all reagents and equipment prior to euthanizing donor mice.</li>
	<li>Sterilize surgical instruments by autoclaving or other appropriate methods. All surgical procedures must be performed under a laminar flow hood to maintain sterile conditions and avoid contamination. Assemble the tools needed for extraction of thymi from donor mice.</li>
	<li>Fill a 60 mm dish with sterile 1x PBS (pH 7.4) and place on ice inside the hood. This will be used to briefly store thymi excised from donor mice prior to transplantation.</li>
	<li>As per ethical guidelines, euthanize newborn donor mice by decapitation and adult donor mice by CO2 asphyxiation followed by cervical dislocation.</li>
	<li>For removal of the thymus: Lay the mouse in a dorsal recumbent position on a sterile absorbent paper towel and spray with 70% ethanol prior to making an incision.</li>
	<li>Expose the abdominal and thoracic cavity by making a midline incision through the skin. Fold the skin over the chest and forelimbs to reveal the thoracic cavity.</li>
	<li>Make two lateral incisions through the diaphragm and ribcage to expose the superior mediastinum and anterior thoracic cavity. The thymus should be visible as two white lobes immediately above and adjacent to the heart.</li>
	<li>Tease apart the connective tissue surrounding the thymus with fine forceps, making certain not to disrupt the capsule. While holding back the ribcage with forceps, use a second pair of forceps to extract the two lobes of the thymus by positioning curved forceps underneath the organ and pulling vertically. This can be done using a dissecting scope for extracting thymi from newborn mice.</li>
	<li>Place the thymus in the 60 mm dish containing sterile 1x PBS (pH 7.4) on ice and separate thymic lobes by cutting through the connective isthmus. Remove any debris from the thymic lobes making certain not to damage the capsule, and cut the thymus into the appropriate number of sections for transplantation.</li>
	<li>Do not manipulate the thymi obtained from newborn mice. 
	NOTE: Used for a maximum of two recipient mice (1 lobe per recipient).</li>
	<li>Transplant the thymi obtained from adult mice into a maximum of 4-6 recipient mice. Using a pair of forceps, carefully grasp one adult thymic lobe, as shown in Figure 1, cut the thymus into three equal sections using surgical scissors.</li>
	<li>Repeat steps 1.3-1.4 for each donor mouse. In order to limit the time thymi are exposed, prepare 1 donor thymus at a time.</li>
</ol>
2. Thymus Implantation Under the Kidney Capsule
<ol>
	<li>Assemble the pre-sterilized equipment listed in Table 1. Proper aseptic technique should be utilized during the course of the procedure to prevent exposing transplant-recipients to contaminated tools or reagents.</li>
	<li>Prior to transplantation, weigh and tag each recipient mouse.</li>
	<li>Set up the dissecting microscope and anesthesia circuit in the laminar flow hood.</li>
	<li>Using an electric razor, shave the left side of the recipient mouse and ensure no hair remains around the area used to make the incision.</li>
	<li>Turn on isofluorane vaporizer and anesthetize the mouse using a dose of between 1-2%. Ascertain proper anesthetization prior to starting the surgical procedure by checking for an absence of reflex following toe pinch.</li>
	<li>After the mouse is properly anesthetized, apply veterinary ointment to the eyes of the mouse to prevent dryness and prepare the mouse for transplantation as follows:</li>
	<li>Position the mouse under the dissecting microscope in a right lateral recumbent position so that the shaved side is facing up. Starting in the center of the surgical area, dispense in a circular motion using a disposable transfer pipette 70% ethanol, followed by povidone-iodine (betadine). Repeat the ethanol/betadine treatment 3 times prior to making an incision.</li>
	<li>Using dissecting scissors make a 1-2 cm flank incision directly above the kidney.</li>
	<li>Using medium forceps grasp connective tissue adjacent to the kidney and gently lift the kidney so that it lies atop the musculature. To keep the kidney exposed and in place over the musculature, insert one arm of medium forceps underneath the kidney, paying special attention not to disrupt the renal ilium.</li>
	<li>In order to prevent tissue desiccation, irrigate the kidney with sterile 1x PBS (pH 7.4) during each step until manipulation of the kidney and kidney capsule is complete.</li>
	<li>Using fine forceps pinch and lift the capsule near the edge of the kidney most distal to the adrenal glands to separate it from the kidney.</li>
	<li>Use an 18 gauge needle to make an incision large enough to insert the prepared piece of donor thymus (Figure 2A). Make certain to keep the capsular incision as small as possible to prevent dislocation of the graft over time.</li>
	<li>While keeping the capsule pulled away from the kidney, use a second pair of fine forceps to insert the graft underneath the capsule and push the thymus as far forward from the capsular incision as possible (Figure 2B).</li>
	<li>Remove the forceps from underneath the kidney, and gently return the kidney back into place through the incision.</li>
	<li>Close the musculature by suturing the peritoneal wall and applying betadine once closed. After suturing is complete, apply wound clips to close the dermis and apply betadine to the surrounding area.</li>
	<li>Return the mouse to a cage that has been warmed using a heat lamp.</li>
	<li>Monitor each post-operative mouse until it regains full consciousness and mobility and do not place mice that have not recovered following anesthesia into a cage with other animals.</li>
	<li>Treat mice with post-operative pain management drugs as needed. Provide mice with post-operative analgesics such as acetaminophen in the drinking water at a concentration of 1.6 mg/ml.</li>
	<li>Repeat steps 2.3-2.9 for each recipient mouse.</li>
	<li>Ensure that mice return to normal activity within 1 hr post-surgery. Monitor post-operative weight, motor skills, as well as the drinking and feeding activity of each mouse to determine complications arising as a result of the transplant procedure. 
	NOTE: Post-operative weight loss, when compared to pre-operative weight, as well as altered mobility or failure to eat or drink may indicate complications.</li>
	<li>Monitor T cell reconstitution in peripheral blood by bleeding mice via tail nick followed by separation of lymphocytes using Lympholyte cell separation media according to the manufacturer&#8217;s specifications. Accomplish T cell characterization by staining lymphocytes with&#160;fluorescently conjugated antibodies specific for&#160;T cell markers CD3, CD4, and CD8, as well as a live dead discriminator such as a fluorescently activated succinimidyl ester8. Analysis as shown in Figure 3 can be accomplished via gating on singlets, live cells, and CD3 positive cells.</li>
</ol>

<ol>
	<li>Kappler, J. W., Roehm, N., Marrack, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=T+cell+tolerance+by+clonal+elimination+in+the+thymus.">T cell tolerance by clonal elimination in the thymus.</a> Cell. 49 (2), 273-280 (1987).</li><li>Takahama, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Journey+through+the+thymus:+stromal+guides+for+T-cell+development+and+selection.">Journey through the thymus: stromal guides for T-cell development and selection.</a> Nat. Rev. Immunol. 6, 127-135 (2006).</li><li>Klein, L., Kyewski, B., Allen, P. M., Hogquist, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Positive+and+negative+selection+of+the+T+cell+repertoire:+what+thymocytes+see+(and+don&#8217;t+see).">Positive and negative selection of the T cell repertoire: what thymocytes see (and don&#8217;t see).</a> Nat. Rev. Immunol. 14 (6), 377-391 (2014).</li><li>Schwartz, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acquisition+of+immunologic+self-tolerance.">Acquisition of immunologic self-tolerance.</a> Cell. 57 (7), 1073-1081 (1989).</li><li>Kishimoto, H., Sprent, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+defect+in+central+tolerance+in+NOD+mice.">A defect in central tolerance in NOD mice.</a> Nat. Immunol. 2 (11), 1025-1031 (2001).</li><li>Anderson, G., Jenkinson, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigating+central+tolerance+with+reaggregate+thymus+organ+cultures.">Investigating central tolerance with reaggregate thymus organ cultures.</a> Methods. Mol. Biol. 380, 185-196 (2007).</li><li>He, 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=Thymic+development+of+autoreactive+T+cells+in+NOD+mice+is+regulated+in+an+age-dependent+manner.">Thymic development of autoreactive T cells in NOD mice is regulated in an age-dependent manner.</a> J. Immunol. 191 (12), 5858-5866 (2013).</li><li>Stewart, C. C., Stewart, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+6.+Immunophenotyping.">Chapter 6. Immunophenotyping.</a> Current Protocols in Cytometry. , (2001).</li><li>Rice, H. E., 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=Thymic+transplantation+for+complete+DiGeorge+syndrome:+medical+and+surgical+considerations.">Thymic transplantation for complete DiGeorge syndrome: medical and surgical considerations.</a> J. Pediatr. Surg. 39 (11), 1607-1615 (2004).</li><li>Markert, M. L., 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=Transplantation+of+thymus+tissue+in+complete+DiGeorge+Syndrome.">Transplantation of thymus tissue in complete DiGeorge Syndrome.</a> N. Engl. J. Med. 341, 1180-1189 (1999).</li><li>Market, M. L., Devlin, B. H., McCarthy, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thymus+transplantation.">Thymus transplantation.</a> Clin. Immunol. 135 (2), 236-246 (2010).</li><li>Wells, A. D., Li, X., Strom, T. B., Turka, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+peripheral+T-cell+depletion+in+transplantation+tolerance.">The role of peripheral T-cell depletion in transplantation tolerance.</a> Philos. Trans. R. Soc. Lond. B. Biol. Sci. 356 (1409), 617-623 (2001).</li><li>Albuquerque, A. 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=Human+FOXN1-Deficiency+is+associated+with+ab+double-negative+and+FoxP3++T-cell+expansions+that+are+distinctly+modulated+upon+thymic+transplantation.">Human FOXN1-Deficiency is associated with ab double-negative and FoxP3+ T-cell expansions that are distinctly modulated upon thymic transplantation.</a> PLoS One. 7 (5), e37042 (2012).</li><li>Chinn, I. K., Milner, J. D., Scheinberg, P., Douek, D. C., Markert, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thymus+transplantation+restores+the+repertoires+of+forkhead+box+protein+3+(FoxP3)++and+FoxP3-+T+cells+in+complete+DiGeorge+anomaly.">Thymus transplantation restores the repertoires of forkhead box protein 3 (FoxP3)+ and FoxP3- T cells in complete DiGeorge anomaly.</a> Clin Exp Immunol. 173 (1), 140-149 (2013).</li><li>Savino, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+thymus+is+a+common+target+organ+in+infectious+diseases.">The thymus is a common target organ in infectious diseases.</a> PLoS Pathog. 2 (6), e62 (2006).</li></ol>

The authors do not have any competing financial interests to disclose.

Events regulating thymic selection are poorly understood. Recent studies have demonstrated ontogenic changes in the efficiency of selection. Coupling this approach with different transgenic thymus donor and recipient mice will further facilitate studies to identify the events and parameters that regulate thymic selection. Notably, thymic transplantation is used for the treatment and management of T cell and thymic disorders seen for instance in athymic infants lacking functional T cells and in patients with DiGeorge syndrome, characterized by thymic hypoplasia or thymic aplasia9-10. Thymus transplantation, like most organ transplantation, is not free of complications, which are mostly due to transplant tolerance-related complications12 and development of autoimmune pathologies11. These issues, coupled with the need to better understand and characterize mechanisms involved in thymocyte tolerance induction led to the development of this method. The protocol described herein experimentally models thymic transplantation and demonstrates that efficient T cell reconstitution is obtained in recipients.
There are several key points to note in the protocol. It is necessary to be adept at surgery and aseptic technique prior to performing the transplantation surgery. Adherence to this will help minimize trauma, the time the mouse is anesthetized, and recovery time so that 100% post-surgery survival rate can be readily obtained. When preparing the donor thymus, it is imperative that the organ is kept on wet ice to minimize cell death. In addition the thymic lobes need to be cut to appropriate sized fragments to permit implantation without tearing the kidney capsule. Similarly, care is required to prevent any injury to the kidney upon making the incision of the renal capsule. Placement of the thymic graft underneath the kidney capsule is another important step in the process. Injury to the kidney or tearing of the renal capsule can be avoided with gentle handling, using appropriate fine-tipped surgical tools, and sufficient practice. One possibility to note is that successful T cell engraftment may also be achieved by implanting thymic lobes at sites other than under the kidney capsule, for instance at a subcutaneous site. The kidney however provides an ideal environment to receive thymic grafts due to a high level of vascularization, which promotes both graft survival as well as efficient T cell trafficking following thymic selection.
A distinct advantage of the above thymus transplant protocol is the technical ease in determining T cell engraftment. Using flow cytometry, success of the procedure is qualitatively and quantitatively assessed by measuring the frequency of T cells in peripheral blood. In addition to observing mature T cells in the blood, T cell engraftment is detected in various lymphoid organs. The latter permits further study of the expansion, activation, and differentiation of peripheral T cells in various host genetic environments under physiological conditions. One caveat that investigators may consider when interpreting results is that following thymic engraftment into an immunodeficient recipient, newly selected T cells will undergo lymphopenic expansion in the periphery. Although this rapid expansion will not alter thymic selection events, it may lead to preferential expansion of distinct T cell subsets in peripheral tissues. 
This protocol is widely applicable for studying mechanisms regulating T cell development and homeostasis in a variety of pathologies. For example, this approach can be used to study FoxP3 regulatory T cell generation and development7,13-14, as well as T cell renewal and export from the thymus in in vivo models of persistent viral, fungal, or bacterial infection15. In summary, this article describes a method of thymus transplantation that entails minimal manipulation of donor tissue, and a high success rate once the technique has been mastered.

The thymus is an organ in which critical events in T cell development occur1. Resident thymocytes, upon rearrangement of the T cell receptor (TCR) &#945; and &#946; genes, undergo a series of interactions with lymphostromal and antigen presenting cells (APC) in the cortical and medullary regions of the thymus2. Thymic positive selection is mediated by cortical thymic epithelial cells (TEC) to produce thymocytes that recognize antigenic peptides in the context of host major histocompatibility complex (MHC) class I and II molecules2-3. Subsequent thymic negative selection entails purging of autoreactive thymocytes, driven by an interaction with medullary TEC or dendritic cells (DC) that present peptides derived from self-proteins bound by MHC class I and II molecules3. The end result of these processes is the establishment of a pool of mature CD4+ and CD8+ T cells able to respond to a broad spectrum of foreign antigens while exhibiting minimal reactivity to self-proteins4.
The efficiency of thymic selection events is influenced by a host of factors, including thymic maturation, frequency of medullary and cortical TEC, subset composition of thymic DC, and the source of thymic precursors3. Notably, aberrant thymic selection can result in autoimmune5 or immunodeficient pathologies, which arise from impaired negative or positive selection, respectively. The molecular events regulating thymic selection, however, are poorly understood. In vitro approaches such as reaggregate thymic organ cultures (RTOC)6, have proven to be useful for analyzing basic events associated with thymic selection, but fail to fully recapitulate the dynamics of ongoing in vivo events. As a result, this thymic transplantation-based approach was established to better study thymocyte selection events in vivo7.
This protocol describes transplanting thymi from newborn and adult donor mice into immunodeficient scid recipient mice. This technique permits the study of mechanisms that regulate positive and negative thymic selection, as well as thymic output of various T cell subsets during ontogeny. Most recently, this approach has been used to demonstrate that the efficiency of thymic selection is limited early after birth in mice leading to increased development of autoreactive T cells, and a reduced T cell repertoire specific for foreign antigens7.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Ethanol&#160;</td>
			<td>Decon Laboratories</td>
			<td>2705HC</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>GIBCO</td>
			<td>14190-144</td>
			<td>pH 7.2</td>
		</tr>
		<tr>
			<td>Betadine Solution</td>
			<td>Purdue Products</td>
			<td>67618-150-17</td>
			<td></td>
		</tr>
		<tr>
			<td>18 gauge needle</td>
			<td>BD</td>
			<td>305195</td>
			<td></td>
		</tr>
		<tr>
			<td>Sutures (1.0 metric)</td>
			<td>Ethicon</td>
			<td>J493G</td>
			<td>18&#34; (45cm)</td>
		</tr>
		<tr>
			<td>AUTOCLIP Wound Clips (9mm)</td>
			<td>Clay Adams&#174; Brand</td>
			<td>427631</td>
			<td></td>
		</tr>
		<tr>
			<td>Transfer pipette</td>
			<td>Fisher Scientific</td>
			<td>13-711-20</td>
			<td>Sterile, disposable</td>
		</tr>
		<tr>
			<td>Mouse anti-CD3 Ab</td>
			<td>eBioscience</td>
			<td>11-0031-85</td>
			<td>Clone: 1452C11</td>
		</tr>
		<tr>
			<td>Mouse anti-CD4 Ab</td>
			<td>eBioscience</td>
			<td>48-0042-82</td>
			<td>Clone: RM4-5</td>
		</tr>
		<tr>
			<td>Mouse anti-CD8 Ab</td>
			<td>eBioscience</td>
			<td>25-0081-82</td>
			<td>Clone: 53-6.7</td>
		</tr>
		<tr>
			<td>Lancet</td>
			<td>Medipoint</td>
			<td>Goldenrod 4mm</td>
			<td></td>
		</tr>
		<tr>
			<td>Pacific Orange Succinimidyl Ester, Triethylammonium Salt</td>
			<td>Invitrogen</td>
			<td>P30253</td>
			<td></td>
		</tr>
		<tr>
			<td>96-well round botton polypropylene plates</td>
			<td>Corning</td>
			<td>3365</td>
			<td></td>
		</tr>
		<tr>
			<td>1.2mL polypropylene cluster tubes</td>
			<td>Corning</td>
			<td>4401</td>
			<td></td>
		</tr>
		<tr>
			<td>5mL polypropylene round-bottom tubes</td>
			<td>BD</td>
			<td>352002</td>
			<td></td>
		</tr>
		<tr>
			<td>40uM Nylon Cell Strainer</td>
			<td>Falcon</td>
			<td>352340</td>
			<td></td>
		</tr>
		<tr>
			<td>16% Paraformaldehyde Solution, EM Grade</td>
			<td>Electron Microscopy Services</td>
			<td>15710</td>
			<td>Hazardous</td>
		</tr>
		<tr>
			<td>Puralube Optical Ointment</td>
			<td>Fisher Scientific</td>
			<td>NC0138063</td>
			<td></td>
		</tr>
		<tr>
			<td>Lympholyte</td>
			<td>Cedarlane</td>
			<td>CL5030</td>
			<td></td>
		</tr>
		<tr>
			<td>60 mm cell culture dish</td>
			<td>Corning</td>
			<td>430196</td>
			<td>60mm x 15mm, Sterile</td>
		</tr>
	</tbody>
</table>

isolation and transplantation of different aged murine thymic grafts.

The mechanisms that regulate the efficacy of thymic selection remain ill-defined. The method presented here allows in vivo analyses of the development and selection of T cells specific for self and foreign antigens. The approach entails implantation of thymic grafts derived from various aged mice into immunodeficient scid recipients. Over a relatively short period of time the recipients are fully reconstituted with T cells derived from the implanted thymus graft. Only thymocytes seeding the thymus at the time of isolation undergo selection and develop into mature T cells. As such, changes in the nature and specificity of the engrafted T cells as a function of age-dependent thymic events can be assessed. Although technical expertise is required for successful thymic transplantation, this method provides a unique strategy to study in vivo a wide range of pathologies that are due to or a result of aberrant thymic function and/or homeostasis.

The success of this procedure is dependent on minimal surgical trauma as well as the accurate positioning of the graft underneath the kidney capsule. The thymic graft should be cut to ensure appropriately sized thymic sections for subsequent transplantation as shown in Figure 1. Following the schematic in Figure 1, thymi from newborn or adult mice can be used for successful subcapsular transplantation with consistent and reproducible T cell engraftment results. As mentioned, appropriate positioning of the graft under the kidney capsule is important in maintaining long-term survival, function, and vascularization of the graft. As seen in Figure 2, the thymic graft should be placed atop the kidney, closest to the adrenal glands (anterior of kidney), on the opposite end from the capsular incision (posterior of kidney). A successful thymic transplant, when coupled with an appropriate hematopoietic environment, can remain productive in excess of 30 weeks7.
Following transplantation, engraftment is assessed by flow cytometric analyses of T cells obtained from peripheral blood. Figure 3 and Table 2 demonstrate the typical level of T cell engraftment observed in organs and peripheral blood in a transplant recipient 6 weeks post-transplantation. Using this technique, our group has previously shown the kinetics of CD4+ and CD8+ T cell reconstitution in peripheral blood over time in transplant recipients of newborn and adult thymi. Briefly, circulating T cells can be observed in the periphery within one week post-surgery and CD4+ and CD8+ T cell numbers continue to increase until the peripheral T cell compartment is fully reconstituted at 5-6 weeks post transplantation7.
<img alt="Figure 1" src="/files/ftp_upload/52709/52709fig1.jpg" /> 
Figure 1: Preparation of thymic lobes and sections from donor newborn and adult mice. Donor thymi are excised from 1 day-old (N.B.) and 4 week-old (Adult). Dashed lines are presented as a guide for preparing the maximum number of sections from one donor organ for subsequent transplantation.
<img alt="Figure 2" src="/files/ftp_upload/52709/52709fig2.jpg" /> 
Figure 2: Position of capsular incision and placement of thymic graft. An appropriately sized section prepared from the donor thymus is inserted into the subcapsular space created by a small incision in the renal capsule at the posterior end of the kidney (A). Anterior to the kidney, closest to the adrenal glands (not pictured) and at the opposite end from the capsular incision, is the optimal position for the graft that is inserted underneath the capsule as shown in (B).
<img alt="Figure 3" src="/files/ftp_upload/52709/52709fig3.jpg" /> 
Figure 3. Determining successful engraftment via T cell reconstitution in peripheral blood and lymphoid organs. Flow cytometric data are representative of T cell reconstitution observed 6 weeks post-transplantation in a scid recipient of a N.B. thymic graft. Similar levels of T cell engraftment are observed in peripheral blood, spleen, pancreatic lymph node (PLN), and the mesenteric lymph node (MLN) following successful transplantation of a thymic graft.
<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Fine Dissecting forceps</td>
		</tr>
		<tr>
			<td>Medium Dissecting forceps (2)</td>
		</tr>
		<tr>
			<td>Fine dissecting forceps (curved tip)</td>
		</tr>
		<tr>
			<td>Betadine Solution</td>
		</tr>
		<tr>
			<td>70% Ethanol&#160;</td>
		</tr>
		<tr>
			<td>18 gauge needle</td>
		</tr>
		<tr>
			<td>Dissecting microscope w/light source</td>
		</tr>
		<tr>
			<td>Disposable transfer pipettes (2)</td>
		</tr>
		<tr>
			<td>Drugs for pain management: Acetaminophen</td>
		</tr>
		<tr>
			<td>Sterile wipes&#160;</td>
		</tr>
		<tr>
			<td>Heat lamp</td>
		</tr>
		<tr>
			<td>Electric razor</td>
		</tr>
		<tr>
			<td>Isoflurane and isoflurane vaporizer</td>
		</tr>
		<tr>
			<td>Sutures (fast absorbing, plain gut)</td>
		</tr>
		<tr>
			<td>Dissecting Scissors&#160;</td>
		</tr>
		<tr>
			<td>9 mm Stainless Steel Wound clips</td>
		</tr>
		<tr>
			<td>Wound clip removal tool</td>
		</tr>
		<tr>
			<td>Sterile 1x PBS</td>
		</tr>
		<tr>
			<td>60 mm Dish</td>
		</tr>
	</tbody>
</table>
Table 1: Materials needed during surgical thymic transplantation. List of necessary materials used to implant the thymus underneath the kidney capsule of the recipient mouse. The quantity of specified materials is listed in parenthesis.
<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td></td>
			<td>Total Number of CD4 T cells</td>
			<td>Total Number of CD8 T cells</td>
		</tr>
		<tr>
			<td>Blood</td>
			<td>1,652 cells/&#965;l</td>
			<td>351 cells/&#965;l</td>
		</tr>
		<tr>
			<td>Spleen</td>
			<td>11,546,617</td>
			<td>4,203,299</td>
		</tr>
		<tr>
			<td>PLN</td>
			<td>1,241,789</td>
			<td>364,918</td>
		</tr>
		<tr>
			<td>MLN</td>
			<td>2,182,266</td>
			<td>532,059</td>
		</tr>
	</tbody>
</table>
Table 2. Total number of T cells present in peripheral blood and lymphoid organs of a thymic transplant recipient. Total numbers of CD4+ and CD8+ T cells recovered from the organs as well as peripheral blood of a newborn thymic transplant recipient 6 weeks post-transplantation. These numbers are representative of CD4+ and CD8+ T cell cellularity that is typically observed in successful newborn and adult thymic transplant recipients.

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Isolation and Transplantation of Different Aged Murine Thymic Grafts.

This report provides a detailed description of transplanting murine thymi from different aged donor mice under the kidney capsule of immunodeficient mouse recipients. The goal of this approach is to model T cell development and thymic selection events in vivo.

The mechanisms that regulate the efficacy of thymic selection remain ill-defined. The method presented here allows in vivo analyses of the development and ...

isolation-and-transplantation-of-different-aged-murine-thymic-grafts

Nanyang Technological University

Research

JoVE Journal

Immunology and Infection

13.7K Views.  University of North Carolina at Chapel Hill. This report provides a detailed description of transplanting murine thymi from different aged donor mice under the kidney capsule of immunodeficient mouse recipients. The goal of this approach is to model T cell development and thymic selection events in vivo. 

Video: Isolation and Transplantation of Different Aged Murine Thymic Grafts.

Murine Model of CD40-activation of B cells

Research on B cells has shown that CD40 activation improves their antigen presentation capacity. When stimulated with interleukin-4 and CD40 ligand (CD40L), human B cells can be expanded without difficulties from small amounts of peripheral blood within 14 days to very large amounts of highly-pure CD40-B cells (&gt;109 cells per patient) from healthy donors as well as cancer patients1-4. CD40-B cells express important lymph node homing molecules and can attract T cells in vitro5. Furthermore they efficiently take up, process and present antigens to T cells6,7. CD40-B cells were shown to not only prime na&iacute;ve, but also expand memory T cells8,9. Therefore CD40-activated B cells (CD40-B cells) have been studied as an alternative source of immuno-stimulatory antigen-presenting cells (APC) for cell-based immunotherapy1,5,10. In order to further study whether CD40-B cells induce effective T cell responses in vivo and to study the underlying mechanism we established a cell culture system for the generation of murine CD40-activated B cells. Using splenocytes or purified B cells from C57BL/6 mice for CD40-activation, optimal conditions were identified as follows: Starting from splenocytes of C57BL/6 mice (haplotype H-2b) lymphocytes are purified by density gradient centrifugation and co-cultured with HeLa cells expressing recombinant murine CD40 ligand (tmuCD40L HeLa)11. Cells are recultured every 3-4 days and key components such as CD40L, interleukin-4, -Mercaptoethanol and cyclosporin A are replenished. In this protocol we demonstrate how to obtain fully activated murine CD40-B cells (mCD40B) with similar APC-phenotype to human CD40-B cells (Fig 1a,b). CD40-stimulation leads to a rapid outgrowth and expansion of highly pure (&gt;90%) CD19+ B cells within 14 days of cell culture (Fig 1c,d). To avoid contamination with non-transfected cells, expression of the murine CD40 ligand on the transfectants has to be controlled regularly (Fig 2). Murine CD40-activated B cells can be used to study B-cell activation and differentiation as well as to investigate their potential to function as APC in vitro and in vivo. Moreover, they represent a promising tool for establishing therapeutic or preventive vaccination against tumors and will help to answer questions regarding safety and immunogenicity of this approach12.

In this video, we demonstrate the procedure of CD40-activation and expansion of murine B cells from splenocytes of C57BL/6 mice, which can be used as a model antigen-presenting cell (APC) to study induction of immunity.

Research on B cells has shown that CD40 activation improves their antigen presentation capacity. When stimulated with interleukin-4 and CD40 ligand ...

RNA Isolation of Pseudomonas aeruginosa Colonizing the Murine Gastrointestinal Tract

Pseudomonas aeruginosa (PA) infections result in significant morbidity and mortality in hosts with compromised immune systems, such as patients with leukemia, severe burn wounds, or organ transplants1. In patients at high-risk for developing PA bloodstream infections, the gastrointestinal (GI) tract is the main reservoir for colonization2, but the mechanisms by which PA transitions from an asymptomatic colonizing microbe to an invasive, and often deadly, pathogen are unclear. Previously, we performed in vivo transcription profiling experiments by recovering PA mRNA from bacterial cells residing in the cecums of colonized mice 3 in order to identify changes in bacterial gene expression during alterations to the host&#x2019;s immune status.
As with any transcription profiling experiment, the rate-limiting step is in the isolation of sufficient amounts of high quality mRNA. Given the abundance of enzymes, debris, food residues, and particulate matter in the GI tract, the challenge of RNA isolation is daunting. Here, we present a method for reliable and reproducible isolation of bacterial RNA recovered from the murine GI tract. This method utilizes a well-established murine model of PA GI colonization and neutropenia-induced dissemination4. Once GI colonization with PA is confirmed, mice are euthanized and cecal contents are recovered and flash frozen. RNA is then extracted using a combination of mechanical disruption, boiling, phenol/chloroform extractions, DNase treatment, and affinity chromatography. Quantity and purity are confirmed by spectrophotometry (Nanodrop Technologies) and bioanalyzer (Agilent Technologies) (Fig 1). This method of GI microbial RNA isolation can easily be adapted to other bacteria and fungi as well.

RNA Isolation of Pseudomonas aeruginosa Colonizing the Murine Gastrointestinal Tract

A reliable method for the RNA isolation of Pseudomonas aeruginosa recovered from murine cecums is described. The RNA recovered is of sufficient quantity and quality for subsequent qPCR, transcription profiling, and RNA Seq experiments. This technique can be adapted for RNA isolation of other intestinal microbes.

Pseudomonas aeruginosa (PA) infections result in significant morbidity and mortality in hosts with compromised immune systems, such as patients with ...

Examination of Thymic Positive and Negative Selection by Flow Cytometry

A healthy immune system requires that T cells respond to foreign antigens while remaining tolerant to self-antigens. Random rearrangement of the T cell receptor (TCR) &alpha; and &beta; loci generates a T cell repertoire with vast diversity in antigen specificity, both to self and foreign. Selection of the repertoire during development in the thymus is critical for generating safe and useful T cells. Defects in thymic selection contribute to the development of autoimmune and immunodeficiency disorders1-4. 
T cell progenitors enter the thymus as double negative (DN) thymocytes that do not express CD4 or CD8 co-receptors. Expression of the &alpha;&beta;TCR and both co-receptors occurs at the double positive (DP) stage. Interaction of the &alpha;&beta;TCR with self-peptide-MHC (pMHC) presented by thymic cells determines the fate of the DP thymocyte. High affinity interactions lead to negative selection and elimination of self-reactive thymocytes. Low affinity interactions result in positive selection and development of CD4 or CD8 single positive (SP) T cells capable of recognizing foreign antigens presented by self-MHC5.
Positive selection can be studied in mice with a polyclonal (wildtype) TCR repertoire by observing the generation of mature T cells. However, they are not ideal for the study of negative selection, which involves deletion of small antigen-specific populations. Many model systems have been used to study negative selection but vary in their ability to recapitulate physiological events6. For example, in vitro stimulation of thymocytes lacks the thymic environment that is intimately involved in selection, while administration of exogenous antigen can lead to non-specific deletion of thymocytes7-9. Currently, the best tools for studying in vivo negative selection are mice that express a transgenic TCR specific for endogenous self-antigen. However, many classical TCR transgenic models are characterized by premature expression of the transgenic TCR&alpha; chain at the DN stage, resulting in premature negative selection. Our lab has developed the HYcd4 model, in which the transgenic HY TCR&alpha; is conditionally expressed at the DP stage, allowing negative selection to occur during the DP to SP transition as occurs in wildtype mice10.
Here, we describe a flow cytometry-based protocol to examine thymic positive and negative selection in the HYcd4 mouse model. While negative selection in HYcd4 mice is highly physiological, these methods can also be applied to other TCR transgenic models. We will also present general strategies for analyzing positive selection in a polyclonal repertoire applicable to any genetically manipulated mice.

We present a flow cytometry-based method to examine T cell development in vivo using genetically manipulated mice on a wildtype or T cell receptor transgenic background.

A healthy immune system requires that T cells respond to foreign  antigens while remaining tolerant to self-antigens. Random rearrangement of the  T cell ...

Isolation, Processing and Analysis of Murine Gingival Cells

We have developed a technique to precisely isolate and process murine gingival tissue for flow cytometry and molecular studies. The gingiva is a unique and important tissue to study immune mechanisms because it is involved in host immune response against oral biofilm that might cause periodontal diseases. Furthermore, the close proximity of the gingiva to alveolar bone tissue enables also studying bone remodeling under inflammatory conditions. Our method yields large amount of immune cells that allows analysis of even rare cell populations such as Langerhans cells and T regulatory cells as we demonstrated previously 1. Employing mice to study local immune responses involved in alveolar bone loss during periodontal diseases is advantageous because of the availability of various immunological and experimental tools. Nevertheless, due to their small size and the relatively inconvenient access to the murine gingiva, many studies avoided examination of this critical tissue. The method described in this work could facilitate gingival analysis, which hopefully will increase our understating on the oral immune system and its role during periodontal diseases.

This study describes an efficient technique to isolate and process gingival tissues from the mouse oral cavity in order to produce a single-cell culture. The resulting cells can be further used for flow cytometry analysis and molecular studies.

We have developed a technique to precisely isolate and process murine gingival tissue for flow cytometry and molecular studies. The gingiva is a unique ...

Isolation, Identification, and Purification of Murine Thymic Epithelial Cells

The thymus is a vital organ for T lymphocyte development. Of thymic stromal cells, thymic epithelial cells (TECs) are particularly crucial at multiple stages of T cell development: T cell commitment, positive selection and negative selection. However, the function of TECs in the thymus remains incompletely understood. In the article, we provide a method to isolate TEC subsets from fresh mouse thymus using a combination of mechanical disruption and enzymatic digestion. The method allows thymic stromal cells and thymocytes to be efficiently released from cell-cell and cell-extracellular matrix connections and to form a single-cell suspension. Using the isolated cells, multiparameter flow cytometry can be applied to identification and characterization of TECs and dendritic cells. Because TECs are a rare cell population in the thymus, we also describe an effective way to enrich and purify TECs by depleting thymocytes, the most abundant cell type in the thymus. Following the enrichment, cell sorting time can be decreased so that loss of cell viability can be minimized during purification of TECs. Purified cells are suitable for various downstream analyses like Real Time-PCR, Western blot and gene expression profiling. The protocol will promote research of TEC function and as well as the development of in vitro T cell reconstitution.

Here we describe an efficient method for isolation, identification, and purification of mouse thymic epithelial cells (TECs). The protocol can be utilized for studies of thymus function for normal T cell development, thymus dysfunction, and T cell reconstitution.

The thymus is a vital organ for T lymphocyte development. Of thymic stromal cells, thymic epithelial cells (TECs) are particularly crucial at multiple ...

Isolation of Murine Lymph Node Stromal Cells

Secondary lymphoid organs including lymph nodes are composed of stromal cells that provide a structural environment for homeostasis, activation and differentiation of lymphocytes. Various stromal cell subsets have been identified by the expression of the adhesion molecule CD31 and glycoprotein podoplanin (gp38), T zone reticular cells or fibroblastic reticular cells, lymphatic endothelial cells, blood endothelial cells and FRC-like pericytes within the double negative cell population. For all populations different functions are described including, separation and lining of different compartments, attraction of and interaction with different cell types, filtration of the draining fluidics and contraction of the lymphatic vessels. In the last years, different groups have described an additional role of stromal cells in orchestrating and regulating cytotoxic T cell responses potentially dangerous for the host. 
Lymph nodes are complex structures with many different cell types and therefore require a appropriate procedure for isolation of the desired cell populations. Currently, protocols for the isolation of lymph node stromal cells rely on enzymatic digestion with varying incubation times; however, stromal cells and their surface molecules are sensitive to these enzymes, which results in loss of surface marker expression and cell death. Here a short enzymatic digestion protocol combined with automated mechanical disruption to obtain viable single cells suspension of lymph node stromal cells maintaining their surface molecule expression is proposed.

Isolation of lymph node stromal cells is a multistep procedure including enzymatic digestion and mechanical disaggregation to obtain fibroblastic reticular cells, lymphatic and blood endothelial cells. In the described procedure, a short digestion is combined with automated mechanical disaggregation to minimize surface marker degradation of viable lymph node stromal cells.

Secondary lymphoid organs including lymph nodes are composed of stromal cells that provide a structural environment for homeostasis, activation and ...

Isolation and Intravenous Injection of Murine Bone Marrow Derived Monocytes

As a subtype of leukocytes and progenitors of macrophages, monocytes are involved in many important processes of organisms and are often the subject of various fields in biomedical science. The method described below is a simple and effective way to isolate murine monocytes from heterogeneous bone marrow.
Bone marrow from the femur and tibia of Balb/c mice is harvested by flushing with phosphate buffered saline (PBS). Cell suspension is supplemented with macrophage-colony stimulating factor (M-CSF) and cultured on ultra-low attachment surfaces to avoid adhesion-triggered differentiation of monocytes. The properties and differentiation of monocytes are characterized at various intervals. Fluorescence activated cell sorting (FACS), with markers like CD11b, CD115, and F4/80, is used for phenotyping. At the end of cultivation, the suspension consists of 45%&#177; 12% monocytes. By removing adhesive macrophages, the purity can be raised up to 86%&#177; 6%. After the isolation, monocytes can be utilized in various ways, and one of the most effective and common methods for in vivo delivery is intravenous tail vein injection. 
This technique of isolation and application is important for mouse model studies, especially in the fields of inflammation or immunology. Monocytes can also be used therapeutically in mouse disease models.

Here we present a protocol that generates large amounts of murine monocytes from heterogeneous bone marrow for translational applications. In comparison to others, this new method helps reduce the number of sacrificed animals and lowers costs by avoiding expensive methods such as high gradient magnetic cell separation (MACS).

As a subtype of leukocytes and progenitors of macrophages, monocytes are involved in many important processes of organisms and are often the subject of ...

Isolation and Flow Cytometric Characterization of Murine Small Intestinal Lymphocytes

The intestines &#8212; which contain the largest number of immune cells of any organ in the body &#8212; are constantly exposed to foreign antigens, both microbial and dietary. Given an increasing understanding that these luminal antigens help shape the immune response and that education of immune cells within the intestine is critical for a number of systemic diseases, there has been increased interest in characterizing the intestinal immune system. However, many published protocols are arduous and time-consuming. We present here a simplified protocol for the isolation of lymphocytes from the small-intestinal lamina propria, intraepithelial layer, and Peyer&#39;s patches that is rapid, reproducible, and does not require laborious Percoll gradients. Although the protocol focuses on the small intestine, it is also suitable for analysis of the colon. Moreover, we highlight some aspects that may need additional optimization depending on the specific scientific question. This approach results in the isolation of large numbers of viable lymphocytes that can subsequently be used for flow cytometric analysis or alternate means of characterization.

There is growing interest in the quantitative characterization of intestinal lymphocytes owing to increasing recognition that these cells play a critical role in a variety of intestinal and systemic diseases. In this protocol, we describe how to isolate single cell populations from different small-intestinal compartments for subsequent flow cytometric characterization.

The intestines &#8212; which contain the largest number of immune cells of any organ in the body &#8212; are constantly exposed to foreign antigens, both ...

Preparation and Applications of Organotypic Thymic Slice Cultures

Thymic selection proceeds in a unique and highly organized thymic microenvironment resulting in the generation of a functional, self-tolerant T cell repertoire. In vitro models to study T lineage commitment and development have provided valuable insights into this process. However, these systems lack the complete three-dimensional thymic milieu necessary for T cell development and, therefore, are incomplete approximations of in vivo thymic selection. Some of the challenges related to modeling T cell development can be overcome by using in situ models that provide an intact thymic microenvironment that fully supports thymic selection of developing T cells. Thymic slice organotypic cultures complement existing in situ techniques. Thymic slices preserve the integrity of the thymic cortical and medullary regions and provide a platform to study development of overlaid thymocytes of a defined developmental stage or of endogenous T cells within a mature thymic microenvironment. Given the ability to generate ~20 slices per mouse, thymic slices present a unique advantage in terms of scalability for high throughput experiments. Further, the relative ease in generating thymic slices and potential to overlay different thymic subsets or other cell populations from diverse genetic backgrounds enhances the versatility of this method. Here we describe a protocol for the preparation of thymic slices, isolation and overlay of thymocytes, and dissociation of thymic slices for flow cytometric analysis. This system can also be adapted to study non-conventional T cell development as well as visualize thymocyte migration, thymocyte-stromal cell interactions, and TCR signals associated with thymic selection by two-photon microscopy.

We describe the preparation of thymic slices that, in combination with flow cytometry, can be used to model positive and negative selection of developing T cells. Thymic slices can also be adapted for the in situ analysis of thymocyte migration, localization, and signaling via immunofluorescence and two-photon microscopy.

Thymic selection proceeds in a unique and highly organized thymic microenvironment resulting in the generation of a functional, self-tolerant T cell ...

Isolation and Activation of Murine Lymphocytes

B and T cells, with their extremely diverse antigen-receptor repertoires, have the ability to mount specific immune responses against almost any invading pathogen1,2. Understandably, such intricate abilities are controlled by a large number of molecules involved in various cellular processes to ensure timely and spatially regulated immune responses3. Here, we describe experimental procedures that allow rapid isolation of highly purified murine lymphocytes using magnetic cell sorting technology. The resulting purified lymphocytes can then be subjected to various in vitro or in vivo functional assays, such as the determination of lymphocyte signaling capacity upon stimulation by immunoblotting4 and the investigation of proliferative abilities by 3H-thymidine incorporation or carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling5-7. In addition to comparing the functional capacities of control and genetically modified lymphocytes, we can also determine the T cell stimulatory capacity of antigen-presenting cells (APCs) in vivo, as shown in our representative results using transplanted CFSE-labeled OT-I T cells.

Lymphocytes are the major players in adaptive immune responses. Here, we present a lymphocyte purification protocol to determine the physiological functions of the desired molecules in lymphocyte activation in vitro and in vivo. The described experimental procedures are suitable for comparing functional capacities between control and genetically modified lymphocytes.

B and T cells, with their extremely diverse antigen-receptor repertoires, have the ability to mount specific immune responses against almost any invading ...

Isolation and Transplantation of Different Aged Murine Thymic Grafts.

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Murine Model of CD40-activation of B cells

RNA Isolation of Pseudomonas aeruginosa Colonizing the Murine Gastrointestinal Tract

Examination of Thymic Positive and Negative Selection by Flow Cytometry

Isolation, Processing and Analysis of Murine Gingival Cells

Isolation, Identification, and Purification of Murine Thymic Epithelial Cells

Isolation of Murine Lymph Node Stromal Cells

Isolation and Intravenous Injection of Murine Bone Marrow Derived Monocytes

Isolation and Flow Cytometric Characterization of Murine Small Intestinal Lymphocytes

Preparation and Applications of Organotypic Thymic Slice Cultures

Isolation and Activation of Murine Lymphocytes