Supported by the Pasteur Institute, INSERM, Agence Nationale de Recherche ANR (Grant &#8216;Lymphopoiesis&#8217;), the REVIVE Future Investment Program and &#8220;La Ligue contre le Cancer&#8221;.

Ethics statement: all experiments were performed according to the Pasteur Institute Ethic Charter, approved by the French Agriculture Ministry, and to the EU guidelines. A manipulator with training on small rodent surgery, certified by the French Ministry of Agriculture, performs all surgical interventions. 
NOTE: See in annex Table 1 showing the 5-step plan procedure.
1. Selection of the Embryos
<ol>
	<li>Use 36 C57BL/6 CD45.2 females, 12 females CD45.1, 12 C57BL/6 CD4...

<ol>
	<li>Rodewald, H. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thymus+organogenesis.">Thymus organogenesis.</a> Annu Rev Immunol. 26, 355-388 (2008).</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>Anderson, G., Jenkinson, E. J., Moore, N. C., Owen, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MHC+class+II-positive+epithelium+and+mesenchyme+cells+are+both+required+for+T-cell+development+in+the+thymus.">MHC class II-positive epithelium and mesenchyme cells are both required for T-cell development in the thymus.</a> Nature. 362, 70-73 (1993).</li><li>Douagi, I., Andre, I., Ferraz, J. C., Cumano, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+T+cell+precursor+activity+in+the+murine+fetal+thymus:+evidence+for+an+input+of+T+cell+precursors+between+days+12+and+14+of+gestation.">Characterization of T cell precursor activity in the murine fetal thymus: evidence for an input of T cell precursors between days 12 and 14 of gestation.</a> Eur J Immunol. 30, 2201-2210 (2000).</li><li>Calderon, L., Boehm, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synergistic,+context-dependent,+and+hierarchical+functions+of+epithelial+components+in+thymic+microenvironments.">Synergistic, context-dependent, and hierarchical functions of epithelial components in thymic microenvironments.</a> Cell. 149, 159-172 (2012).</li><li>Adolfsson, 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=Identification+of+Flt3++lympho-myeloid+stem+cells+lacking+erythro-megakaryocytic+potential+a+revised+road+map+for+adult+blood+lineage+commitment.">Identification of Flt3+ lympho-myeloid stem cells lacking erythro-megakaryocytic potential a revised road map for adult blood lineage commitment.</a> Cell. 121, 295-306 (2005).</li><li>Kondo, M., Weissman, I. L., Akashi, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+clonogenic+common+lymphoid+progenitors+in+mouse+bone+marrow.">Identification of clonogenic common lymphoid progenitors in mouse bone marrow.</a> Cell. 91, 661-672 (1997).</li><li>Bhandoola, A., von Boehmer, H., Petrie, H. T., Zuniga-Pflucker, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Commitment+and+developmental+potential+of+extrathymic+and+intrathymic+T+cell+precursors:+plenty+to+choose+from.">Commitment and developmental potential of extrathymic and intrathymic T cell precursors: plenty to choose from.</a> Immunity. 26, 678-689 (2007).</li><li>Ramond, C., 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=Two+waves+of+distinct+hematopoietic+progenitor+cells+colonize+the+fetal+thymus.">Two waves of distinct hematopoietic progenitor cells colonize the fetal thymus.</a> Nat Immunol. 15, 27-35 (2014).</li><li>Allison, J. P., Havran, W. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+immunobiology+of+T+cells+with+invariant+gamma+delta+antigen+receptors.">The immunobiology of T cells with invariant gamma delta antigen receptors.</a> Annu Rev Immunol. 9, 679-705 (1991).</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=Fetal+thymus+organ+culture.">Fetal thymus organ culture.</a> CSH Protoc. , (2007).</li><li>Schmitt, T. M., Zuniga-Pflucker, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Induction+of+T+cell+development+from+hematopoietic+progenitor+cells+by+delta-like-1+in+vitro.">Induction of T cell development from hematopoietic progenitor cells by delta-like-1 in vitro.</a> Immunity. 17, 749-756 (2002).</li><li>Barbee, S. 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=Skint-1+is+a+highly+specific,+unique+selecting+component+for+epidermal+T+cells.">Skint-1 is a highly specific, unique selecting component for epidermal T cells.</a> Proc Natl Acad Sci U S A. 108, 3330-3335 (2011).</li><li>Douagi, I., Colucci, F., Di Santo, J. P., Cumano, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+the+earliest+prethymic+bipotent+T/NK+progenitor+in+murine+fetal+liver.">Identification of the earliest prethymic bipotent T/NK progenitor in murine fetal liver.</a> Blood. 99, 463-471 (2002).</li><li>Malissen, 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=Altered+T+cell+development+in+mice+with+a+targeted+mutation+of+the+CD3-epsilon+gene.">Altered T cell development in mice with a targeted mutation of the CD3-epsilon gene.</a> EMBO J. 14, 4641-4653 (1995).</li></ol>

The authors declare that they have no competing financial interests.

Two main assays can be used to analyze T cell differentiation ex vivo. The most recently reported is the co-culture of hematopoietic progenitors with BM stromal cells, OP9, expressing the ligands of Noth1, delta like 1 or 412. This 2-D assay is easy to perform, highly efficient and sensitive, allowing analysis at the single cell level. However, it neither supports T cell development beyond the stage of DP nor the generation of &#947;&#948; DETC13, both of which require direct interactions w...

T lymphocytes, bearing the &#945;&#946; or the &#947;&#948; T cell receptor (TcR), differentiate in a specialized organ, the thymus. The fully developed thymus is organized into two distinct regions: the cortex, where thymic progenitors develop and where thymocytes that productively rearrange the TcR &#946; and &#945; chain genes are rescued from programmed death (a process known as positive selection); and the medulla, where selected thymocytes with too strong reactivity to self-ligands are deleted (negative selection)1,2. The thymus originates from the endodermal layer of the third pharyngeal pouch that is later surrounded by mesenchymal cells3. It is colonized by hematopoietic progenitors starting at embryonic day E12 and, thereafter, continuous recruitment is required for normal T cell development4. Thymic immigrants evolve through successive developmental stages, orchestrated by a tightly regulated program, initiated and maintained by the activation of the Notch signaling pathway on thymocytes upon interaction with its ligand, delta like 4, expressed on thymic epithelial cells (TECs)5.
Thymocyte development starts at the so-called CD4-CD8- double negative (DN) stages. DN thymocytes can be further subdivided according to the expression of CD25 and CD44 into DN1 (CD25-CD44+), DN2 (CD25+CD44+), DN3 (CD25+CD44-) and DN4 (CD25-CD44-). CD24 (HSA) and CD117 (c-Kit) further subdivides the DN1 compartment into 5 subsets where DN1a and b correspond to early thymic progenitors (ETP). Thymocytes rearrange the TcR &#948;, &#946; and &#945; chains at the DN stage and undergo pre-TcR selection (DN3-DN4 stages). They further transit to the CD4+CD8+ double positive (DP) compartment where the TcR &#945; chain rearranges prior to positive and negative selection. At this stage most thymocytes are eliminated and only a small percentage (3-5%) reach the CD4+ or CD8+ mature T cell compartment.
The lymphoid differentiation pathway progresses through the stages of HSCs that generate multipotent progenitors (MPP) and lymphoid-primed multipotent progenitors (LMPP) that lost the erythrocyte and megakaryocyte potential6. LMPP are phenotypically defined by the absence of differentiated blood cell markers (lineage negative, Lin-), the expression of c-Kit (CD117), Sca-1 and Flt3/Flk2 (CD135) and the absence of detectable levels of the interleukin (IL)-7 receptor &#945; chain (IL-7r&#945; or CD127). LMPPs further differentiate into common lymphoid progenitors (CLP)7 that by that stage have lost the capacity to generate myeloid cells. CLP retain lymphocyte (B and T cell), NK cell, DC and innate lymphoid cell (ILC) potential, and differ from LMPP by the expression of CD127 and the absence of high levels of Sca-1.
Although the nature of the thymic settling progenitors (TSP) has been extensively debated8, it became recently clear that TSP change phenotype, differentiation potential and function, throughout development9. We performed in vitro and in vivo assays to characterize the TSP, isolated by FACS cell sorting from either E13 (first wave) or E18 (second wave). Fetal thymic organ cultures (FTOC) with irradiated thymic lobes colonized by equal numbers of E13 and E18 progenitors, bearing different allotypic markers, allowed following their progeny in a similar developmental environment and revealed cell intrinsic properties, different between both types of progenitors. Thymic lobes colonized by either E13 or E18 TSP allowed development without selection due to competition between both progenitors. In vivo transplantation of the colonized thymic lobes further showed that also the mature progeny of E13 and E18 TSP have different biologic properties in vivo. TSPs from the first wave rapidly generate T cells but give rise to low numbers of &#945;&#946; and &#947;&#948; T cells. Among the latter we detected V&#947;5V&#948;1 dendritic epithelial T cells (DETC), that have an invariant TcR, migrate to the epidermis where they exert a function in wound healing and are only produced during embryonic development10. In contrast, TSP from the second wave take longer time to generate high numbers of TcR+ T cells and are unable to generate DETC.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>90 x 15 mm and 35 x 15 mm plastic tissue culture petri dishes.</td>
			<td>TPP</td>
			<td>T93100/T9340</td>
			<td>Sampling</td>
		</tr>
		<tr>
			<td>26GA 3/8 IN 0.45x10mm syringes with needles Beckton-Dickinson Plastipak.</td>
			<td>BD Plastipak</td>
			<td>300015</td>
			<td>Cell suspension</td>
		</tr>
		<tr>
			<td>Nylon mesh bolting cloth sterilized 50/50 mm pieces.</td>
			<td>SEFAR NITEX</td>
			<td>03-100/32</td>
			<td>Filtration of cells</td>
		</tr>
		<tr>
			<td>Ethanol 70%.</td>
			<td>VWR</td>
			<td>83801.36</td>
			<td>Sterility Actions</td>
		</tr>
		<tr>
			<td>Iodide Povidone 10% (Betadine)&#160;</td>
			<td>MEDA Pharma</td>
			<td>314997.8</td>
			<td>Sterility Actions</td>
		</tr>
		<tr>
			<td>Ketamine 100mg/ml (stock solution)</td>
			<td>MERIAL</td>
			<td>&#160;-</td>
			<td>Anesthesic</td>
		</tr>
		<tr>
			<td>Xylazine 100mg/ml in PBS (stock solution)</td>
			<td>Sigma</td>
			<td>X1251-1G</td>
			<td>Anesthesic and muscle relaxant</td>
		</tr>
		<tr>
			<td>Buprenorphin 0.3mg/ml stock solution</td>
			<td>AXIENCE</td>
			<td>&#160;-</td>
			<td>Morphinic analgesic</td>
		</tr>
		<tr>
			<td>Ophtalmic gel (0.2% cyclosporin)</td>
			<td>Schering-Plough Animal Health</td>
			<td>&#160;-</td>
			<td>Eyes protection</td>
		</tr>
		<tr>
			<td>DPBS (+ CaCl2, MgCl2)</td>
			<td>GIBCO Life Technology</td>
			<td>14040-174</td>
			<td>to isolate embryos</td>
		</tr>
		<tr>
			<td>HBSS Hanks&#39; Balanced Salt Solution (+ CaCl2, MgCl2)</td>
			<td>GIBCO Life Technology</td>
			<td>24020-091</td>
			<td>to wash out the blood and dissect the embryos</td>
		</tr>
		<tr>
			<td>OPTI-MEM I GlutaMAX I</td>
			<td>GIBCO Life Technology</td>
			<td>51985-026</td>
			<td>Medium for cultures</td>
		</tr>
		<tr>
			<td>F&#339;tal Calf serum</td>
			<td>EUROBIO</td>
			<td>CVFSVF00-0U</td>
			<td>additive for cultures</td>
		</tr>
		<tr>
			<td>Penicilin and Streptomycin</td>
			<td>GIBCO Life Technology</td>
			<td>15640-055</td>
			<td>Antibiotics for cultures</td>
		</tr>
		<tr>
			<td>2 b mercapto ethanol</td>
			<td>GIBCO Life Technology</td>
			<td>31350010</td>
			<td>additive for cultures</td>
		</tr>
		<tr>
			<td>LEICA MZ6 Dissection microscope</td>
			<td>LEICA</td>
			<td>MZ6 10445111</td>
			<td>Occular W-Pl10x/23</td>
		</tr>
		<tr>
			<td>Cold lamp source</td>
			<td>SCHOTT VWR</td>
			<td>KL1500 compact</td>
			<td>Two goose neck fibers adapted</td>
		</tr>
		<tr>
			<td>Silicone elastomer</td>
			<td>World Precision Instruments</td>
			<td>SYLG184</td>
			<td>Dissecting Pad</td>
		</tr>
		<tr>
			<td>Spoon, round and perforated</td>
			<td>Fine Science Tools</td>
			<td>10370-18</td>
			<td>Dissection tools</td>
		</tr>
		<tr>
			<td>Fine Iris Scissors</td>
			<td>Fine Science Tools</td>
			<td>14090-09</td>
			<td>Dissection tools</td>
		</tr>
		<tr>
			<td>Vannas spring Scissors</td>
			<td>Fine Science Tools</td>
			<td>15018-10</td>
			<td>Dissection tools</td>
		</tr>
		<tr>
			<td>Forceps : Dumont #5/45 Inox 11 cm</td>
			<td>F.S.T.</td>
			<td>11253-25</td>
			<td>Dissection tools</td>
		</tr>
		<tr>
			<td>Two pairs of fine straight watchmakers&#8217; forceps Dumont #5 11 cm fine tips.</td>
			<td>Fine Science Tools</td>
			<td>11295-20</td>
			<td>Dissection tools</td>
		</tr>
		<tr>
			<td>Polyamid thread with needle 6-0&#160;&#160; C-3 3/8c</td>
			<td>ETHICON</td>
			<td>F2403</td>
			<td>for sutures</td>
		</tr>
		<tr>
			<td>Needle-holder</td>
			<td>MORIA/F.S.T.</td>
			<td>12060-02</td>
			<td>for sutures</td>
		</tr>
		<tr>
			<td>Heating pad</td>
			<td>VWR</td>
			<td>100229-100</td>
			<td>To maintain mouse temperature during anesthesy</td>
		</tr>
		<tr>
			<td>Membrane Isopore RTTPO2500</td>
			<td>DUTSCHER</td>
			<td>44210</td>
			<td>For FTOC</td>
		</tr>
		<tr>
			<td>Terasaki 60 wells plates</td>
			<td>FISHER</td>
			<td>1x270 10318801</td>
			<td>For hanging drop technique</td>
		</tr>
		<tr>
			<td>Gauze swabs steriles 7.5cmx7.5cm</td>
			<td>Hydrex</td>
			<td>11522</td>
			<td>To apply disinfecting solution</td>
		</tr>
		<tr>
			<td>Fluorescence or biotin labelled antibodies</td>
			<td>BD Biosciences, Biolegend or e-Biocsiences&#160;</td>
			<td>Clone Number see table below</td>
			<td>Staining cells</td>
		</tr>
		<tr>
			<td>MACS Columns/Streptavidin Microbeads&#160;</td>
			<td>Miltenyi Biotec</td>
			<td>130-042-401/130-048-101</td>
			<td>Cell depletion&#160;</td>
		</tr>
		<tr>
			<td>Mice</td>
			<td>Charles Rivers Laboratories (CD45.1) and Janvier Labs&#160; (CD45.2)</td>
			<td>C57BL/6 CD45.1 OR CD45.2</td>
			<td>Source of cells and thymic lobes&#160;</td>
		</tr>
		<tr>
			<td>Mice</td>
			<td>CDTA Orl&#233;ans, France</td>
			<td>CD 3 epsilon Ko CD45.2</td>
			<td>&#160;Grafting experiment</td>
		</tr>
	</tbody>
</table>

characterization of thymic settling progenitors in the mouse embryo using in vivo and in vitro assays

Characterizing thymic settling progenitors is important to understand the pre-thymic stages of T cell development, essential to devise strategies for T cell replacement in lymphopenic patients. We studied thymic settling progenitors from murine embryonic day 13 and 18 thymi by two complementary in vitro and in vivo techniques, both based on the &#8220;hanging drop&#8221; method. This method allowed colonizing irradiated fetal thymic lobes with E13 and/or E18 thymic progenitors distinguished by CD45 allotypic markers and thus following their progeny. Colonization with mixed populations allows analyzing cell autonomous differences in biologic properties of the progenitors while colonization with either population removes possible competitive selective pressures. The colonized thymic lobes can also be grafted in immunodeficient male recipient mice allowing the analysis of the mature T cell progeny in vivo, such as population dynamics of the peripheral immune system and colonization of different tissues and organs. Fetal thymic organ cultures revealed that E13 progenitors developed rapidly into all mature CD3+ cells and gave rise to the canonical &#947;&#948; T cell subset, known as dendritic epithelial T cells. In comparison, E18 progenitors have a delayed differentiation and were unable to generate dendritic epithelial T cells. The monitoring of peripheral blood of thymus-grafted CD3-/- mice further showed that E18 thymic settling progenitors generate, with time, larger numbers of mature T cells than their E13 counterparts, a feature that could not be appreciated in the short term fetal thymic organ cultures.

In order to choose a method to deplete thymic lobes of endogenous thymocytes allowing the best development of colonizing progenitors, we compared the levels of T cell reconstitution in thymic lobes colonized after irradiation or a 5-day deoxy-guanosine (d-Gua) treatment. The results show that while there is no difference at day 9 of culture, irradiated lobes contained more T cells than those treated with d-Gua, at day 12. Thus, irradiation is more appropriate than d-Gua treatment to obtain T cell development after thymic...

Watch this Scientific Journal Video about Characterization of Thymic Settling Progenitors in the Mouse Embryo Using In Vivo and In Vitro Assays at JoVE.com

Characterization of Thymic Settling Progenitors in the Mouse Embryo Using In Vivo and In Vitro Assays

This article describes in vivo and in vitro methodology to characterize the thymic settling progenitors by the analysis of the kinetics of generation, phenotype and numbers of their T cell progeny.

Characterization of Thymic Settling Progenitors in the Mouse Embryo Using In Vivo and In Vitro Assays

Characterizing thymic settling progenitors is important to understand the pre-thymic stages of T cell development, essential to devise strategies for T ...

characterization-thymic-settling-progenitors-mouse-embryo-using-vivo

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8.2K Views.  Institut Cochin. This article describes in vivo and in vitro methodology to characterize the thymic settling progenitors by the analysis of the kinetics of generation, phenotype and numbers of their T cell progeny. 