This work was supported by Reithera, by MIUR project 2017K55HLC_006, and by 5&#160;&#215; 1000 grant from Associazione Italiana Ricerca sul Cancro (AIRC).&#160;The following tetramer was obtained through the NIH Tetramer Facility: APC-conjugated H-2K (d) HIV gag 197-205 AMQMLKETI.

<ol>
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E., Schoenberger, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Na&#239;ve+CTLs+require+a+single+brief+period+of+antigenic+stimulation+for+clonal+expansion+and+differentiation.">Na&#239;ve CTLs require a single brief period of antigenic stimulation for clonal expansion and differentiation.</a> Nature Immunology. 2 (5), 423-429 (2001).</li><li>Kaech, S. M., Wherry, E. J., Ahmed, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effector+and+memory+T-cell+differentiation:+implications+for+vaccine+development.">Effector and memory T-cell differentiation: implications for vaccine development.</a> Nature Review Immunology. 2 (4), 251-262 (2002).</li><li>Beverley, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primer:+making+sense+of+T-cell+memory.">Primer: making sense of T-cell memory.</a> Nature Clinical Practice Rheumatology. 4 (1), 43-49 (2008).</li><li>Parretta, 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=CD8+cell+division+maintaining+cytotoxic+memory+occurs+predominantly+in+the+bone+marrow.">CD8 cell division maintaining cytotoxic memory occurs predominantly in the bone marrow.</a> Journal of Immunology. 174 (12), 7654-7664 (2005).</li><li>Di Rosa, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maintenance+of+memory+T+cells+in+the+bone+marrow:+survival+or+homeostatic+proliferation.">Maintenance of memory T cells in the bone marrow: survival or homeostatic proliferation.</a> Nature Review Immunology. 16 (4), 271 (2016).</li><li>Di Rosa, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two+niches+in+the+bone+marrow:+a+hypothesis+on+life-long+T+cell+memory.">Two niches in the bone marrow: a hypothesis on life-long T cell memory.</a> Trends in Immunology. 37 (8), 503-512 (2016).</li><li>Di Rosa, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Commentary:+Memory+CD8(+)+T+cells+colocalize+with+IL-7(+)+stromal+cells+in+bone+marrow+and+rest+in+terms+of+proliferation+and+transcription.">Commentary: Memory CD8(+) T cells colocalize with IL-7(+) stromal cells in bone marrow and rest in terms of proliferation and transcription.</a> Frontiers in Immunology. 7, 102 (2016).</li><li>Simonetti, 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=Antigen-specific+CD8+T+cells+in+cell+cycle+circulate+in+the+blood+after+vaccination.">Antigen-specific CD8 T cells in cell cycle circulate in the blood after vaccination.</a> Scandinavian Journal of Immunology. 89 (2), 12735 (2019).</li><li>Wilson, 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=c-Myc+controls+the+balance+between+hematopoietic+stem+cell+self-renewal+and+differentiation.">c-Myc controls the balance between hematopoietic stem cell self-renewal and differentiation.</a> Genes &amp; Development. 18 (22), 2747-2763 (2004).</li><li>Hirche, 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=Systemic+virus+infections+differentially+modulate+cell+cycle+state+and+functionality+of+long-term+hematopoietic+stem+cells+in+vivo.">Systemic virus infections differentially modulate cell cycle state and functionality of long-term hematopoietic stem cells in vivo.</a> Cell Report. 19 (11), 2345-2356 (2017).</li><li>Colloca, 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=Vaccine+vectors+derived+from+a+large+collection+of+simian+adenoviruses+induce+potent+cellular+immunity+across+multiple+species.">Vaccine vectors derived from a large collection of simian adenoviruses induce potent cellular immunity across multiple species.</a> Science Translational Medicine. 4 (115), (2012).</li><li>Di Lullo, 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=Marker+gene+swapping+facilitates+recombinant+Modified+Vaccinia+Virus+Ankara+production+by+host-range+selection.">Marker gene swapping facilitates recombinant Modified Vaccinia Virus Ankara production by host-range selection.</a> Journal of Virological Methods. 156 (1-2), 37-43 (2009).</li><li>Di Lullo, 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=The+combination+of+marker+gene+swapping+and+fluorescence-activated+cell+sorting+improves+the+efficiency+of+recombinant+modified+vaccinia+virus+Ankara+vaccine+production+for+human+use.">The combination of marker gene swapping and fluorescence-activated cell sorting improves the efficiency of recombinant modified vaccinia virus Ankara vaccine production for human use.</a> Journal of Virological Methods. 163 (2), 195-204 (2010).</li><li>. Mouse phenotype Available from: <a target="_blank" href="https://www.mousephenotype.org/data/secondaryproject/3i">https://www.mousephenotype.org/data/secondaryproject/3i</a> (2020)</li><li>Yoon, H., Kim, T. S., Braciale, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+cell+cycle+time+of+CD8++T+cells+responding+in+vivo+is+controlled+by+the+type+of+antigenic+stimulus.">The cell cycle time of CD8+ T cells responding in vivo is controlled by the type of antigenic stimulus.</a> PLoS One. 5 (11), 15423 (2010).</li><li>Pauklin, S., Vallier, 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+cell-cycle+state+of+stem+cells+determines+cell+fate+propensity.">The cell-cycle state of stem cells determines cell fate propensity.</a> Cell. 155 (1), 135-147 (2013).</li><li>Vignon, 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=Flow+cytometric+quantification+of+all+phases+of+the+cell+cycle+and+apoptosis+in+a+two-color+fluorescence+plot.">Flow cytometric quantification of all phases of the cell cycle and apoptosis in a two-color fluorescence plot.</a> PLoS One. 8 (7), 68425 (2013).</li></ol>

A. Folgori and S. Capone are employees of Reithera Srl. A. Nicosia is named inventor on patent application WO 2005071093 (A3) &#34;Chimpanzee adenovirus vaccine carriers.&#34; The other authors have nothing to disclose.

Although T cell clonal expansion has been intensively studied, some aspects remain unknown, mostly because the tools available to investigate it are few and have their own drawbacks. From this perspective, we set up a highly sensitive flow cytometric method to analyze cell cycle of antigen-specific CD8 T cells at early times after vaccination in a mouse model. The protocol is based on a combination of Ki67 and DNA staining, which was previously used to analyze the cell cycle of BM hematopoietic cells in mice13,14. To adapt the protocol to antigen-specific CD8 T cells, we had to consider a few critical issues, including the choice of the DNA dye, the appropriate conditions to obtain comparable DNA staining across different samples, and the gating strategy for data analysis.
Many dyes are available for DNA staining, including propidium Iodide and 7-aminoactinomycin D; we chose Hoechst because it was compatible with membrane staining and the mild fixation / permeabilization protocol required for Ki67 staining. At the same time, staining with Hoechst allowed us to obtain a DNA histogram of excellent quality, i.e., the G0/G1 and G2/M DNA peaks had a much lower coefficient of variation (CV) than DNA peaks usually obtained with other DNA dyes, e.g., DRAQ519. Indeed, Hoechst can stain DNA even in live cells20.
Some strategies were used to avoid the fluctuation in Hoechst intensity in different samples of the same experiment. Hoechst staining was performed just before sample acquisition at the flow cytometer to minimize the decline of dye intensity during time. For those interested in reproducing the protocol in big experiments with numerous samples, we recommend performing Hoechst staining on a few samples at a time. One other drawback is that Hoechst intensity can be heavily influenced by cell number during incubation with the dye. For this reason, we strongly recommend always using the same number of cells and the same volume per sample for DNA staining. If a high number of cells is required for acquisition at the flow cytometer, we recommend preparing two or more identical samples and then merging them just before the Hoechst staining step.
A key point of the protocol is the gating strategy for data analysis. We recently published a novel strategy for T cell analysis at early times of the immune response, which allowed us to increase the sensitivity of detection of antigen-specific T cells12. We applied this strategy to the data shown here as follows. First, we excluded cell aggregates in the DNA-A/W plot. Second, after gating out dead cells, we used a fairly large lymphocyte gate in the FSC/SSC plot (&#34;relaxed gate&#34;). By this strategy, we were able to include highly activated antigen-specific CD8 T cells in S-G2/M that are usually missed by current gating strategies, as these cells have high FSC-A and SSC-A. In summary, the data analysis represents a critical part of the method, which is essential to obtain a sensitive detection of activated /proliferating antigen-specific T cells.
The method prevents the possibility of missing critical T cell data at early phases of immune response and opens new perspectives for T cell immuno-monitoring. A future improvement might be to include staining for phospho-histone 3 that would allow differentiation between G2 and M21. A current limitation is that cells have to be fixed and permeabilized to stain for the nuclear marker, Ki67. Thus, cells cannot be used for other types of analysis such as sorting and subsequent functional analysis. Moreover, DNA dyes, including Hoechst, usually interfere with the genomic DNA analysis and are not suitable for this type of evaluation. Identification of membrane markers that correlate with different cell cycle phases and that can be stained on live cells could overcome this limitation. In conclusion, the method has great potential for the evaluation of activated/proliferating T cells in several contexts such as vaccination, infection, immuno-mediated diseases, and immuno-therapy.

An erratum was issued for:&#160;<a href="https://www.jove.com/t/61867">A DNA/Ki67-Based Flow Cytometry Assay for Cell Cycle Analysis of Antigen-Specific CD8 T Cells in Vaccinated Mice</a>. The Authors section and a figure were&#160;updated.
The authors section was updated from:
Sonia Simonetti*1,2, Ambra Natalini*1,2, Giovanna Peruzzi3, Alfredo Nicosia4, Antonella Folgori5, Stefania Capone5, Angela Santoni2, Francesca Di Rosa1 
1Institute of Molecular Biology and Pathology, National Research Council of Italy (CNR), 
2Department of Molecular Medicine, University of Rome &#8220;Sapienza&#8221;, 
3Center for Life Nano Science, Istituto Italiano di Tecnologia, 
4Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, 
5Reithera Srl 
* These authors contributed equally
To:
Sonia Simonetti*1,2, Ambra Natalini*1,2, Giovanna Peruzzi3, Alfredo Nicosia4, Antonella Folgori5, Stefania Capone5, Angela Santoni2,6, Francesca Di Rosa1 
1Institute of Molecular Biology and Pathology, National Research Council of Italy (CNR), 
2Department of Molecular Medicine, University of Rome &#8220;Sapienza&#8221;, 
3Center for Life Nano Science, Istituto Italiano di Tecnologia, 
4Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, 
5Reithera Srl 
6IRCCS, Neuromed 
* These authors contributed equally
Figure 1 was updated from:
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61867/61867fig1v2.jpg" /> 
Figure 1: Scheme of the protocol for cell cycle analysis of antigen-specific CD8 T cells.&#160;<a href="https://www.jove.com/files/ftp_upload/61867/61867fig1v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
To:
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61867/61867fig1v4.jpg" /> 
Figure 1: Scheme of the protocol for cell cycle analysis of antigen-specific CD8 T cells.&#160;<a href="https://www.jove.com/files/ftp_upload/61867/61867fig1v4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

An erratum was issued for:&#160;<a href="https://www.jove.com/t/61867">A DNA/Ki67-Based Flow Cytometry Assay for Cell Cycle Analysis of Antigen-Specific CD8 T Cells in Vaccinated Mice</a>. The Authors section and a figure were&#160;updated.

Erratum: A DNA/Ki67-Based Flow Cytometry Assay for Cell Cycle Analysis of Antigen-Specific CD8 T Cells in Vaccinated Mice

An erratum was issued for:&#160;<a href="https://www.jove.com/t/61867">A DNA/Ki67-Based Flow Cytometry Assay for Cell Cycle Analysis of Antigen-Specific CD8 T Cells in Vaccinated Mice</a>. The Protocol, Representative Results, and Discussion sections have been&#160;updated.
Step 9.5 of the Protocol was updated from:
Double click on the fully stained sample in the group to open the graph window.
to:
Double click on the fully stained sample in the group to open the graph window and display the ungated events in a dot plot. Note that the x-and y-axis are labelled as in the fcs files, according to the Flow Cytometer settings (Table 2).
Step 9.6 of the Protocol was updated from:
Display the total events acquired for this sample in a dot plot with DNA-A on the x axis and DNA-W on the y-axis.
to:
Check that a sufficient number of ungated events is displayed for appropriate visualization. If necessary, open Preferences by clicking on the &#8220;heart&#8221; icon in the Workspace ribbon, select Graphs, then Dot Plot as graph type, and indicate the number of dots drawn in the corresponding box. Display ungated events in the graph window as a dot plot with DNA-A on the x-axis and DNA-W on the y-axis. Use linear scale for both axes. If necessary, change scale from logarithmic to linear by clicking on the box indicated with a &#8220;T&#8221; (Transform Data Display) close to each axis in the graph window.
Step 9.12 of the Protocol was updated from:
Double click in the center of the &#34;relaxed&#34; gate to display the cells in a dot plot with CD3 on the x-axis and CD8 on the y-axis.
to:
Double click in the center of the &#34;relaxed&#34; gate to display the cells in a dot plot with CD3 on the x-axis and CD8 on the y-axis. Use appropriate axis scale for visualization in the graph window. If necessary, modify x- and/or y-scale by clicking on the box indicated with a &#8220;T&#8221; (Transform Data Display) close to each axis, choose Customize axis function, and modify Extra Neg. decades, Width basis and Positive decades, as necessary.
Step 9.19 of the Protocol was updated from:
Repeat step 9.5 to 9.18 for the &#34;b-LN group.
to:
Copy the entire gating strategy from the &#8220;a-LN&#8221; to the &#34;b-spleen&#8221; group. Copy the first 3 gates of the gating strategy from the &#8220;a-LN&#8221; to the &#8220;c-BM&#8221; group (Figure 2A).
The fourth paragraph of the Representative Results was&#160;updated from:
Notably, the protocol allowed us to have an extremely low background in the antigen-specific CD8 T cell gate of LNs and spleen&#160;of untreated mice (usually 0.00% and at maximum 0.02%). The overlay of gag-specific CD8 T cells onto total CD8 T cells in the FSC-A / SSC-A plot showed that the gag-specific cells had high SSC-A and FSC-A (Figure 3D), confirming the need to use a &#34;relaxed&#34; FSC-A/ SSC-A gating to capture these cells. We then evaluated the percentages of gag-specific CD8 T cells in different cell cycle phases (Figure 4A). We found that gag-specific CD8 T cells in the spleen and even more in the draining LNs contained a high proportion of cells in S-G2/M phases at day 3 post-boost (18.60% and 33.52%, respectively)
to:
Notably, the protocol allowed us to have an extremely low background in the antigen-specific CD8 T cell gate of LNs and spleen&#160;of untreated mice (usually 0.00% and at maximum 0.02%). The&#160;comparison of gag-specific and not gag-specific FSC-A / SSC-A plots&#160;showed that the gag-specific cells had high SSC-A and FSC-A (Figure 3D), confirming the need to use a &#34;relaxed&#34; FSC-A/ SSC-A gate&#160;to capture these cells. We then evaluated the percentages of gag-specific CD8 T cells in different cell cycle phases (Figure 4A). We found that gag-specific CD8 T cells in the spleen and even more in the draining LNs contained a high proportion of cells in S-G2/M phases at day 3 post-boost (18.60% and 33.52%, respectively)
The fourth paragraph of the Discussion was&#160;updated from:
A key point of the protocol is the gating strategy for data analysis. We recently published a novel strategy for T cell analysis at early times of the immune response, which allowed us to increase the sensitivity of detection of antigen-specific T cells12. We applied this strategy to the data shown here as follows. First, we excluded cell aggregates in the DNA-A/W plot. Second, after gating out dead cells, we used a fairly large lymphocyte gate in the FSC/SSC plot (&#34;relaxed gate&#34;). By this strategy, we were able to include highly activated antigen-specific CD8 T cells in S-G2/M that are usually missed by current gating strategies, as these cells have high FSC-A and SSC-A. In summary, the data analysis represents a critical part of the method, which is essential to obtain a sensitive detection of activated /proliferating antigen-specific T cells.
to:
A key point of the protocol is the gating strategy for data analysis. We recently published a novel strategy for T cell analysis at early times of the immune response, which allowed us to increase the sensitivity of detection of antigen-specific T cells12. We applied this strategy to the data shown here as follows. First, we excluded cell aggregates in the DNA-A/W plot. Second, after gating out dead cells, we used a fairly large lymphocyte gate in the FSC/SSC plot (&#34;relaxed gate&#34;). Then, we gated on CD8 T cells, and on antigen-specific cells among them. We analyzed cell cycle by evaluating the DNA/ Ki67 staining profile of the antigen-specific CD8 T cells. By this strategy, we were able to include highly activated antigen-specific CD8 T cells in S-G2/M that are usually missed by current gating strategies, as these cells have high FSC-A and SSC-A. In summary, the data analysis represents a critical part of the method, which is essential to obtain a sensitive detection of activated /proliferating antigen-specific T cells.

An erratum was issued for:&#160;<a href="https://www.jove.com/t/61867">A DNA/Ki67-Based Flow Cytometry Assay for Cell Cycle Analysis of Antigen-Specific CD8 T Cells in Vaccinated Mice</a>. The Protocol,&#160;Representative Results, and Discussion&#160;sections have been&#160;updated.

Na&#239;ve T cells undergo clonal expansion and differentiation upon antigen-priming. Differentiated T cells display effector functions that are essential for antigen clearance and for the maintenance of antigen-specific memory, which is key for long-lasting protection. During the first steps of the primary response, na&#239;ve T cell interaction with antigen-presenting cells (APCs) within specialized niches in lymphoid organs is critical to induce the huge T cell proliferation that characterizes the clonal expansion phase1,2,3. T cell-APC interaction is finely regulated by concentration and persistence of antigen, co-stimulatory signals, and soluble factors (cytokines and chemokines) that influence the quantity and quality of the T cell clonal progeny4,5,6,7.
Despite intensive studies of T cell clonal expansion, it is still not known whether antigen-primed T cells complete their entire cell cycle at the site of antigen recognition, or whether they migrate to other organs during cell cycle progression. This lack of knowledge is due to the properties of available tools&#160;for cell cycle analysis. These include monoclonal antibodies (mAbs) specific for the nuclear marker, Ki67, and cell dyes that either identify cells that have undergone the S-phase of the cell cycle (e.g.,&#160;Bromodeoxyuridine&#160;&#160;(BrdU)) or discriminate among daughter cells and their ancestors (e.g., carboxyfluorescein succinimidyl ester (CFSE)).
However, cell-labeling dyes, such as CFSE and BrdU, do not allow the determination as to whether cells found in a particular organ proliferated locally or rather migrated to this site after division8,9. Moreover, the intranuclear protein, Ki67, is only able to distinguish cells in G0 (Ki67-negative cells) from those in any other cell cycle phase (Ki67-positive cells). Thus, Ki67 analysis does not distinguish cells in active proliferation (i.e., in S, G2, or M) from those in G1, which may either quickly progress to division or stay for long periods in G1 or revert to quiescence10,11.
Here, we describe a new flow cytometric method for cell cycle analysis of antigen-specific CD8 T cells12 from the spleen and lymph nodes (LNs) of vaccinated mice (Figure 1). The method exploits a combination of Ki67 and DNA staining that was previously used to analyze the cell cycle of mouse bone marrow (BM) hematopoietic cells13,14. Here, we successfully applied Ki67 plus DNA staining, together with the recently published innovative gating strategy12, to the analysis of CD8 T cell clonal expansion. We were able to clearly discriminate between antigen-specific CD8 T cells in G0, in G1, and in S-G2/M phases in the spleen&#160;and draining LNs of vaccinated mice.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
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			<td >1-200 &#956;L universal fit bulk packed pipet tips</td>
			<td >Corning&#160;</td>
			<td >CLS4866-1000EA</td>
			<td ></td>
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		<tr >
			<td >2.4G2 anti-Fc&#947;R mAb&#160;</td>
			<td >BD</td>
			<td >553141</td>
			<td>10 &#956;g/ml final concentration</td>
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		<tr >
			<td >5 ml syringe plunger</td>
			<td>BD Emerald&#160;</td>
			<td >307733</td>
			<td></td>
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		<tr >
			<td >15 ml conical tubes</td>
			<td >MercK Millipore&#160;</td>
			<td >SBHA025SB</td>
			<td></td>
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			<td >60 mm TC-treated Cell Culture Dish</td>
			<td >Falcon</td>
			<td >353002</td>
			<td></td>
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		<tr >
			<td >70 &#956;m cell strainer&#160;</td>
			<td >Falcon</td>
			<td >352097</td>
			<td></td>
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			<td >96-well Clear Round Bottom TC-treated Culture Microplate</td>
			<td >Falcon&#160;</td>
			<td >353077</td>
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			<td >Anti-Rat/Hamster Ig,k/Negative Control Compensation Particles</td>
			<td >BD- Bioscience</td>
			<td >552845</td>
			<td></td>
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		<tr >
			<td >Beta-mercaptoethanol&#160;&#160;</td>
			<td >Sigma</td>
			<td >M3148</td>
			<td></td>
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		<tr >
			<td >Bovine Serum Albumin</td>
			<td >Sigma</td>
			<td >A07030</td>
			<td></td>
		</tr>
		<tr >
			<td >BUV805 Rat Anti-Mouse CD8a&#160;</td>
			<td >BD- Bioscience</td>
			<td>564920</td>
			<td>4 &#956;g/ml final concentration</td>
		</tr>
		<tr >
			<td >Dulbecco&#39;s Phosphate Buffer Saline w/o Calcium w/o Magnesium&#160;</td>
			<td >Euroclone</td>
			<td >ECB4004L&#160;</td>
			<td></td>
		</tr>
		<tr >
			<td >Eppendorf Safe-Lock Tubes, 1.5 mL</td>
			<td >Eppendorf</td>
			<td >30120159</td>
			<td></td>
		</tr>
		<tr >
			<td >Ethanol</td>
			<td >Sigma</td>
			<td >34852-1L-M</td>
			<td></td>
		</tr>
		<tr >
			<td >Ethylenediaminetetraacetic Acid Disodium Salt solution (EDTA)&#160;</td>
			<td >Sigma&#160;</td>
			<td >E7889</td>
			<td></td>
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		<tr >
			<td >Fetal Bovine Serum</td>
			<td >Corning</td>
			<td >35-079-CV</td>
			<td></td>
		</tr>
		<tr >
			<td >Filcon, Sterile, Syringe-Type 70 &#956;m</td>
			<td >Falcon&#160;</td>
			<td >352350</td>
			<td></td>
		</tr>
		<tr >
			<td >Fixable Viability Dye eFluor 780</td>
			<td >eBioscience</td>
			<td >65-0865-14</td>
			<td>1:1000 final concentration</td>
		</tr>
		<tr >
			<td >Foxp3 / Transcription Factor Staining Buffer Set</td>
			<td >eBioscience</td>
			<td >00-5523-00</td>
			<td>This Set contains fixation/permeabilization concentrate and diluent, and permeabilization buffer 10x</td>
		</tr>
		<tr >
			<td >H-2k(d) AMQMLKETI allophycocyanin (APC)-labelled tetramer</td>
			<td >provided by NIH Tetramer Core Facility</td>
			<td ></td>
			<td>6 &#956;g/ml final concentration</td>
		</tr>
		<tr >
			<td >H-2k(d) AMQMLKETI phycoerythrine (PE) labelled pentamer</td>
			<td >Proimmune&#160;</td>
			<td >F176-2A-E - 176</td>
			<td>10 &#956;L / sample&#160;</td>
		</tr>
		<tr >
			<td >Hoechst 33342, Trihydrochloride, Trihydrate - 10 mg/mL Solution in Water</td>
			<td >ThermoFisher</td>
			<td >H3570</td>
			<td></td>
		</tr>
		<tr >
			<td >Ki-67 Monoclonal Antibody (SolA15), FITC</td>
			<td >eBioscience</td>
			<td >11-5698-82</td>
			<td>5 &#956;g/ml final concentration</td>
		</tr>
		<tr >
			<td >L-Glutamine 100X (200 mM)</td>
			<td >Euroclone</td>
			<td >ECB3000D&#160;</td>
			<td></td>
		</tr>
		<tr >
			<td >Millex-HA Filters 0,45 &#181;m</td>
			<td>BD</td>
			<td >340606</td>
			<td></td>
		</tr>
		<tr >
			<td >Penicillin/Streptomycin 100X</td>
			<td >Euroclone</td>
			<td >ECB3001D&#160;</td>
			<td></td>
		</tr>
		<tr >
			<td >PE/Cyanine7 anti-mouse CD62L Antibody</td>
			<td >Biolegend&#160;</td>
			<td >104418</td>
			<td>0.2 &#956;g/ml final concentration</td>
		</tr>
		<tr >
			<td >PerCP-Cy&#8482;5.5 Hamster Anti-Mouse CD3e&#160;</td>
			<td >BD- Bioscience</td>
			<td >551163</td>
			<td>4.4 &#956;g/ml final concentration</td>
		</tr>
		<tr >
			<td >Red Blood Cell Lysis Buffer</td>
			<td >Sigma</td>
			<td >R7757</td>
			<td></td>
		</tr>
		<tr >
			<td >Round-Bottom Polystyrene Tubes, 5 mL</td>
			<td >Falcon&#160;</td>
			<td >352058</td>
			<td></td>
		</tr>
		<tr >
			<td >RPMI 1640 Medium without L-Glutamine with Phenol Red</td>
			<td >Euroclone</td>
			<td >ECB9006L&#160;</td>
			<td></td>
		</tr>
		<tr >
			<td >Software package for analyzing flow cytometry data</td>
			<td >FlowJo</td>
			<td>v.10</td>
			<td></td>
		</tr>
		<tr >
			<td >Software for acquisition of samples at flowcytometer</td>
			<td >BD FACSDiva&#160;</td>
			<td>v 6.2</td>
			<td></td>
		</tr>
		<tr >
			<td >Trypan Blue Solution</td>
			<td >Euroclone</td>
			<td >ECM0990D</td>
			<td></td>
		</tr>
	</tbody>
</table>

a dna/ki67-based flow cytometry assay for cell cycle analysis of antigen-specific cd8 t cells in vaccinated mice

The cell cycle of antigen-specific T cells in vivo has been examined by using a few methods, all of which possess some limitations. Bromodeoxyuridine (BrdU) marks cells that are in or recently completed S-phase, and carboxyfluorescein succinimidyl ester (CFSE) detects daughter cells after division. However, these dyes do not allow identification of the cell cycle phase at the time of analysis. An alternative approach is to exploit Ki67, a marker that is highly expressed by cells in all phases of the cell cycle except the quiescent phase G0. Unfortunately, Ki67 does not allow further differentiation as it does not separate cells in S-phase that are committed to mitosis from those in G1 that can remain in this phase, proceed into cycling, or move into G0.
Here, we describe a flow cytometric method for capturing a &#34;snapshot&#34; of T cells in different cell cycle phases in mouse secondary lymphoid organs. The method combines Ki67 and DNA staining with major histocompatibility complex (MHC)-peptide-multimer staining and an innovative gating strategy, allowing us to successfully differentiate between antigen-specific CD8 T cells in G0, in G1 and in S-G2/M phases of the cell cycle in the spleen&#160;and draining lymph nodes of mice after vaccination with viral vectors carrying the model antigen gag of human immunodeficiency virus (HIV)-1.
Critical steps of the method were the choice of the DNA dye and the gating strategy to increase the assay sensitivity and to include highly activated/proliferating antigen-specific T cells that would have been missed by current criteria of analysis. The DNA dye, Hoechst 33342, enabled us to obtain a high-quality discrimination&#160;of the G0/G1 and G2/M DNA peaks, while preserving membrane and intracellular staining. The method has great potential to increase knowledge about T cell response in vivo and to improve immuno-monitoring analysis.

The cell cycle phases of cells from spleen, LNs, and BM of Balb/c mice were analyzed using the fluorescent DNA dye, Hoechst, and an anti-Ki67 mAb, according to the protocol summarized in Figure 1. This staining allowed the differentiation of cells in the following phases of cell cycle: G0 (Ki67neg, with 2N of DNA defined as DNAlow), G1 (Ki67pos, DNAlow), and S-G2/M (Ki67pos, with a DNA content comprised between 2N and 4N, or equal to 4N of DNA defined as DNAintermediate/high).
We first performed cell cycle analysis of BM cells to reproduce previously published results13,14 and then analyzed the cells of interest, i.e., CD8 T cells. Figure 2 shows a typical example of cell cycle analysis of BM cells (Figure 2A). The protocol yielded a low coefficient of variation (CV) of G0/G1 and G2/M DNA peaks, indicating the excellent quality of the DNA staining (Figure 2B, showing an example with CV &#60; 2.5; CV was always &#60; 5 in all the experiments).
We then applied the same protocol to antigen-specific CD8 T cells from vaccinated mice. BALB/c mice were vaccinated against the antigen gag of HIV-1 by using Chad3-gag for priming and MVA-gag for boosting, both engineered to carry HIV-1 gag. At day (d) 3 post-boost, we analyzed the frequency of gag-specific CD8 T cells from the spleen and draining LNs. We took advantage of the newly defined gating strategy for T cells in the early phase of immune response, which in contrast to the conventional strategy, is appropriate for detecting highly activated antigen-responding CD8 T cells12. We executed the novel strategy in five subsequent steps. In step 1, we excluded doublets or aggregates by DNA-A/ -W gate, and in step 2, we identified live cells by dead cell marker exclusion. In step 3, we identified the population of interest using a non-conventional &#34;relaxed&#34; FSC-A/ SSC-A gate (Figure 3A) instead of the canonical narrow lymphocyte gate12. After gating on CD3+CD8+ cells (step 4 of Figure 3A), we identified gag-specific CD8 T cells by using two different MHC multimers, i.e., Pent-gag and Tetr-gag (step 5 of Figure 3A). We used two multimers instead of one to improve the sensitivity of gag-specific CD8 T cell detection in vaccinated mice, without increasing the staining background in untreated mice (Figure 3B and C, step 5). Thus, we successfully distinguished untreated mice (0.00% and 0.00% antigen-specific CD8 T cells in LNs and spleen, respectively) from vaccinated mice (0.46% and 0.29% antigen-specific CD8 T cells in LNs and spleen, respectively, Figure 3B&#160;and C).
Notably, the protocol allowed us to have an extremely low background in the antigen-specific CD8 T cell gate of LNs and spleen&#160;of untreated mice (usually 0.00% and at maximum 0.02%). The comparison&#160;of gag-specific and not gag-specific&#160;FSC-A / SSC-A plots showed that the gag-specific cells had high SSC-A and FSC-A (Figure 3D), confirming the need to use a &#34;relaxed&#34; FSC-A/ SSC-A gate to capture these cells. We then evaluated the percentages of gag-specific CD8 T cells in different cell cycle phases (Figure 4A). We found that gag-specific CD8 T cells in the spleen and even more in the draining LNs contained a high proportion of cells in S-G2/M phases at day 3 post-boost (18.60% and 33.52%, respectively).
Furthermore, we found that gag-specific CD8 T cells in S-G2/M phases had high FSC-A and SSC-A, when overlaid onto the total CD8 T cells from the same organ (Figure 4B). CD62L expression by gag-specific CD8 T cells was low, as expected for activated T cells, except for a few cells in G0 in the LNs (Figure 4C). Altogether, these results confirmed that the &#34;relaxed&#34; gate (step 3 of Figure 3A, B, and C) was required to include all of the proliferating antigen-specific CD8 T cells12. The protocol was extremely valuable for a &#34;snapshot&#34; evaluation of cell cycle phases of antigen-specific CD8 T cells at the time of analysis and of CD62L expression by cells in different cell cycle phases.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61867/61867fig1v4.jpg" /> 
Figure 1: Scheme of the protocol for cell cycle analysis of antigen-specific CD8 T cells.&#160;<a href="https://www.jove.com/files/ftp_upload/61867/61867fig1v4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61867/61867fig2v2.jpg" /> 
Figure 2: Cell cycle analysis of BM cells. BM cells from untreated Balb/c mice were stained and analyzed by flow cytometry. (A) Example of gating strategy. We gated on single cells in the DNA-A/-W plot (left) and subsequently on live cells by dead cell dye exclusion (middle). Then, a &#34;relaxed&#34; FSC-A/SSC-A gate was used for all BM cells (right). (B) Example of cell cycle analysis of BM cells (left). We used a combination of Ki67 and DNA staining to identify cells in the following phases of cell cycle: G0 (bottom left quadrant, Ki67neg-DNAlow cells), G1 (top left quadrant, Ki67pos-DNAlow), S-G2/M (top right quadrant, Ki67pos-DNAintermediate/high). Fluorescence Minus One (FMO) control of Ki67 mAb (middle) and DNA histogram (right) are shown. In the DNA histogram plot, the left and right gates correspond to the G0/G1 and the G2/M DNA peak, respectively, and the numbers represent the coefficients of variation (CV) of each peak. In all the other plots, the numbers represent cell percentages in the indicated gates. The figure shows 1 representative experiment out of 5. In each experiment, we analyzed pooled BM cells from 3 mice. <a href="https://www.jove.com/files/ftp_upload/61867/61867fig2v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61867/61867fig3v2.jpg" /> 
Figure 3: Analysis of antigen-specific CD8 T cells from LNs and spleen. Balb/c mice were primed intramuscularly (i.m.) with Chad3-gag and boosted i.m. with MVA-gag. At day 3 post-boost, draining LN&#160;and spleen cells from vaccinated and untreated control mice were stained and analyzed by flow cytometry. (A) Scheme of the gating strategy in five steps to identify single cells (Step 1); live cells (Step 2); lymphocytes (Step 3); CD8 T cells (Step 4); and gag-specific cells (Step 5). (B-C) Example of plots: analysis of cells from (B) LNs and (C) spleen&#160;of untreated (top) and vaccinated (bottom) mice. We identified single cells on the DNA-A/ -W plot in Step 1. Then, in Step 2, we selected live cells by dead cell dye exclusion. In Step 3, we used a non-canonical &#34;relaxed&#34; gate for lymphocytes. In Step 4, we identified CD8 T cells by their double expression of CD3 and CD8. We then identified gag-specific cells and not gag-specific in Step 5, based on their capacity to bind fluorochrome-labelled H-2kd-gag-Pentamer (Pent-gag) and H-2kd-gag-Tetramer (Tetr-gag), or not, respectively. (D) FSC-A/SSC-A profiles of gag-specific (blue) and not gag-specific (grey) cells after gating as described above. Numbers represent cell percentages in the indicated gates. The figure shows 1 representative experiment out of 5. In each experiment, we analyzed pooled spleen and pooled LN cells from 3 vaccinated mice and 3 untreated mice. <a href="https://www.jove.com/files/ftp_upload/61867/61867fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61867/61867fig4v2.jpg" /> 
Figure 4: Cell cycle analysis of antigen-specific CD8 T cells. Mice were vaccinated as in Figure 3 and cell cycle analysis of gag-specific cells was performed at day 3 post-boost, after gating in 5 steps as in Figure 3. (A) Example of cell cycle analysis of gag-specific CD8 T cells from LNs (top) and spleen (bottom) of vaccinated mice. Cell cycle phases were identified as in Figure 2B. The panels represent cells in G0, in G1, and in S-G2/M (left) and Fluorescence Minus One (FMO) control of Ki67 mAb (right). Numbers represent cell percentages in the indicated gates. (B) FSC-A/SSC-A dot plots showing gag-specific CD8 T cells in S-G2/M phases (in red) overlaid onto total CD3+CD8+ T cells (in grey) from LNs (top) and spleen (bottom) of vaccinated mice. (C) Offset histograms showing CD62L expression by gag-specific CD8 T cells in G0 (green), in G1 (blue), and in S-G2/M (red) from LNs (top) and spleen&#160;(bottom) of vaccinated mice. The y-axes indicate normalized number of events. The figure shows 1 representative example out of 5 independent experiments with a total of 15 mice. <a href="https://www.jove.com/files/ftp_upload/61867/61867fig4v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplementary Material: Flow cytometer settings.&#160;<a href="https://www.jove.com/files/ftp_upload/61867/JoVE-DiRosa-FlowCytometer-Configuration_.xlsx" target="_blank">Please click here to download this file.</a>

Watch this Scientific Journal Video about A DNA/Ki67-Based Flow Cytometry Assay for Cell Cycle Analysis of Antigen-Specific CD8 T Cells in Vaccinated Mice at JoVE.com

A DNA/Ki67-Based Flow Cytometry Assay for Cell Cycle Analysis of Antigen-Specific CD8 T Cells in Vaccinated Mice

Clonal expansion is a key feature of antigen-specific T cell response. However, the cell cycle of antigen-responding T cells has been poorly investigated, partly because of technical limitations. We describe a flow cytometric method to analyze clonally expanding antigen-specific CD8 T cells in spleen and lymph nodes of vaccinated mice.

The cell cycle of antigen-specific T cells in vivo has been examined by using a few methods, all of which possess some limitations. Bromodeoxyuridine ...

a-dnaki67-based-flow-cytometry-assay-for-cell-cycle-analysis-antigen

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JoVE Journal

Immunology and Infection

6.9K Views.  National Research Council of Italy (CNR). Clonal expansion is a key feature of antigen-specific T cell response. However, the cell cycle of antigen-responding T cells has been poorly investigated, partly because of technical limitations. We describe a flow cytometric method to analyze clonally expanding antigen-specific CD8 T cells in spleen and lymph nodes of vaccinated mice.

Video: A DNA/Ki67-Based Flow Cytometry Assay for Cell Cycle Analysis of Antigen-Specific CD8 T Cells in Vaccinated Mice

Flow Cytometry Analysis of Immune Cells Within Murine Aortas

Atherosclerosis is a chronic inflammatory process of medium and large size vessels that is characterized by the formation of plaques consisting of foam cells, immune cells, vascular endothelial and smooth muscle cells, platelets, extracellular matrix, and a lipid-rich core with extensive necrosis and fibrosis of surrounding tissues.1 The innate and adaptive arms of the immune response are involved in the initiation, development and persistence of atherosclerosis.2, 3 There is a significant body of evidence that different subsets of the immune cells, such as macrophages, dendritic cells, T and B lymphocytes, are present within the aortas of healthy and atherosclerosis-prone mice4. Additionally, immune cells are found in the surrounding aortic adventitia which suggests an important role of this tissue in atherogenesis.2
For some time, the quantitative detection of different types of immune cells, their activation status, and the cellular composition within the aortic wall was limited by RT-PCR and immunohistochemical methods for the study of atherosclerosis. Few attempts were made to perform flow cytometry using human aortas, and a number of problems, such as a high autofluorescence, have been reported5,6. Human atherosclerotic plaques were digested with collagenase 1, and free cells were collected and stained for CD14+/CD11c+ to highlight macrophage-derived foam cells. In this study, a "mock" channel was used to avoid false-positive staining.6 Necrotic materials accumulating during the digestion process give rise in a large amount of debris that generates a high autofluorescence in aortic samples. To resolve this problem, a panel of negative and positive controls has been proposed, but only double staining could be applied in these samples. We have developed a new flow cytometry-based method7 to analyze the immune cell composition and characterize the activation, proliferation, differentiation of immune cells in healthy and atherosclerosis-prone aorta. This method allows the investigation of the immune cell composition of the aortic wall and opens possibilities to use a broad spectrum of immunological methods for investigations of immune aspects of this disease.

This paper presents a flow cytometry-based method to investigate the immune composition of aortas. The paper also illustrates an additional technique that allows examining surrounding adventitia and vessel wall separately. This method opens possibilities to perform phenotypical analyses of aortic leukocytes and apply several immunological assays for atherosclerosis studies.

Atherosclerosis is a chronic inflammatory process of medium and large size vessels that is characterized by the formation of plaques consisting of foam ...

Killer Artificial Antigen Presenting Cells (KaAPC) for Efficient In Vitro Depletion of Human Antigen-specific T Cells

Current treatment of T cell mediated autoimmune diseases relies mostly on strategies of global immunosuppression, which, in the long term, is accompanied by adverse side effects such as a reduced ability to control infections or malignancies. Therefore, new approaches need to be developed that target only the disease mediating cells and leave the remaining immune system intact. Over the past decade a variety of cell based immunotherapy strategies to modulate T cell mediated immune responses have been developed. Most of these approaches rely on tolerance-inducing antigen presenting cells (APC). However, in addition to being technically difficult and cumbersome, such cell-based approaches are highly sensitive to cytotoxic T cell responses, which limits their therapeutic capacity. Here we present a protocol for the generation of non-cellular killer artificial antigen presenting cells (KaAPC), which allows for the depletion of pathologic T cells while leaving the remaining immune system untouched and functional. KaAPC is an alternative solution to cellular immunotherapy which has potential for treating autoimmune diseases and allograft rejections by regulating undesirable T cell responses in an antigen specific fashion.

Killer Artificial Antigen Presenting Cells KaAPC for Efficient In Vitro Depletion of Human Antigen-specific T Cells

Guidelines are presented for the generation of killer artificial antigen presenting cells, KaAPC, an efficient tool for in vitro depletion of human antigen-specific T cells and an alternative solution to cellular immunotherapy for the treatment of T cell-mediated autoimmune diseases in an antigen-specific fashion without compromising the remaining immune system.

Current treatment of T cell mediated autoimmune diseases relies mostly on strategies of global immunosuppression, which, in the long term, is accompanied ...

Whole-animal Imaging and Flow Cytometric Techniques for Analysis of Antigen-specific CD8+ T Cell Responses after Nanoparticle Vaccination

Traditional vaccine adjuvants, such as alum, elicit suboptimal CD8+ T cell responses. To address this major challenge in vaccine development, various nanoparticle systems have been engineered to mimic features of pathogens to improve antigen delivery to draining lymph nodes and increase antigen uptake by antigen-presenting cells, leading to new vaccine formulations optimized for induction of antigen-specific CD8+ T cell responses. In this article, we describe the synthesis of a &#8220;pathogen-mimicking&#8221; nanoparticle system, termed interbilayer-crosslinked multilamellar vesicles (ICMVs) that can serve as an effective vaccine carrier for co-delivery of subunit antigens and immunostimulatory agents and elicitation of potent cytotoxic CD8+ T lymphocyte (CTL) responses. We describe methods for characterizing hydrodynamic size and surface charge of vaccine nanoparticles with dynamic light scattering and zeta potential analyzer and present a confocal microscopy-based procedure to analyze nanoparticle-mediated antigen delivery to draining lymph nodes. Furthermore, we show a new bioluminescence whole-animal imaging technique utilizing adoptive transfer of luciferase-expressing, antigen-specific CD8+ T cells into recipient mice, followed by nanoparticle vaccination, which permits non-invasive interrogation of expansion and trafficking patterns of CTLs in real time. We also describe tetramer staining and flow cytometric analysis of peripheral blood mononuclear cells for longitudinal quantification of endogenous T cell responses in mice vaccinated with nanoparticles.

We describe whole-animal imaging and flow cytometry-based techniques for monitoring expansion of antigen-specific CD8+ T cells in response to immunization with nanoparticles in a murine model of vaccination.

Traditional vaccine adjuvants, such as alum, elicit suboptimal CD8+ T cell responses. To address this major challenge in vaccine development, various ...

Development of Stem Cell-derived Antigen-specific Regulatory T Cells Against Autoimmunity

Autoimmune diseases arise due to the loss of immunological self-tolerance. Regulatory T cells (Tregs) are important mediators of immunologic self-tolerance. Tregs represent about 5 - 10% of the mature CD4+ T cell subpopulation in mice and humans, with about 1 - 2% of those Tregs circulating in the peripheral blood. Induced pluripotent stem cells (iPSCs) can be differentiated into functional Tregs, which have a potential to be used for cell-based therapies of autoimmune diseases. Here, we present a method to develop antigen (Ag)-specific Tregs from iPSCs (i.e., iPSC-Tregs). The method is based on incorporating the transcription factor FoxP3 and an Ag-specific T cell receptor (TCR) into iPSCs and then differentiating on OP9 stromal cells expressing Notch ligands delta-like (DL) 1 and DL4. Following in vitro differentiation, the iPSC-Tregs express CD4, CD8, CD3, CD25, FoxP3, and Ag-specific TCR and are able to respond to Ag stimulation. This method has been successfully applied to cell-based therapy of autoimmune arthritis in a murine model. Adoptive transfer of these Ag-specific iPSC-Tregs into Ag-induced arthritis (AIA)-bearing mice has the ability to reduce joint inflammation and swelling and to prevent bone loss.

We present here a method to develop functional antigen (Ag)-specific regulatory T cells (Tregs) from induced pluripotent stem cells (iPSCs) for immunotherapy of autoimmune arthritis in a murine model.

Autoimmune diseases arise due to the loss of immunological self-tolerance. Regulatory T cells (Tregs) are important mediators of immunologic ...

In Situ MHC-tetramer Staining and Quantitative Analysis to Determine the Location, Abundance, and Phenotype of Antigen-specific CD8 T Cells in Tissues

T cells are critical to many immunological processes, including detecting and eliminating virus-infected cells, preventing autoimmunity, assisting in B-cell and plasma-cell production of antibodies, and detecting and eliminating cancer cells. The development of MHC-tetramer staining of antigen-specific T cells analyzed by flow cytometry has revolutionized our ability to study and understand the immunobiology of T cells. While extremely useful for determining the quantity and phenotype of antigen-specific T cells, flow cytometry cannot determine the spatial localization of antigen-specific T cells to other cells and structures in tissues, and current disaggregation techniques to extract the T cells needed for flow cytometry have limited effectiveness in non-lymphoid tissues. In situ MHC-tetramer staining (IST) is a technique to visualize T cells that are specific for antigens of interest in tissues. In combination with immunohistochemistry (IHC), IST can determine the abundance, location, and phenotype of antigen-specific CD8 and CD4 T cells in tissues. Here, we describe a protocol to stain and enumerate antigen-specific CD8 T cells, with specific phenotypes located within specific tissue compartments. These procedures are the same that we used in our recent publication by Li et al., entitled &#34;Simian Immunodeficiency Virus-Producing Cells in Follicles Are Partially Suppressed by CD8+ Cells In Vivo.&#34; The methods described are broadly applicable because they can be used to localize, phenotype, and quantify essentially any antigen-specific CD8 T cell for which MHC tetramers are available, in any tissue.

In Situ MHC-tetramer Staining and Quantitative Analysis to Determine the Location, Abundance, and Phenotype of Antigen-specific CD8 T Cells in Tissues

Here, we describe a method that combines in situ MHC-tetramer staining with immunohistochemistry to determine localization, phenotype, and quantity of antigen-specific T cells in tissues. This protocol is used to determine the spatial and phenotypic characteristics of antigen-specific CD8 T cells relative to other cell type and structures in tissues.

T cells are critical to many immunological processes, including detecting and eliminating virus-infected cells, preventing autoimmunity, assisting in ...

In Vivo Assay for Detection of Antigen-specific T-cell Cytolytic Function Using a Vaccination Model

Current methodologies for antigen-specific killing are limited to in vitro use or utilized in infectious disease models. However, there is not a protocol specifically intended to measure antigen-specific killing without an infection. This protocol is designed and describes methods to overcome these limitations by allowing for the detection of antigen-specific killing of a target cell by CD8+ T cells in vivo. This is accomplished by merging a vaccination model with a traditional CFSE-labeled target killing assay. This combination allows the researcher to assess the antigen-specific CTL potential directly and quickly as the assay is not dependent upon tumor growth or infection. In addition, the readout is based on flow cytometry and so should be readily accessible to most researchers. The major limitation of the study is identifying the timeline in vivo that is appropriate to the hypothesis being tested. Variations in antigen strength and mutations in the T cells that may result in differential cytolytic function need to be carefully assessed to determine the optimal time for cell harvest and assessment. The appropriate concentration of peptide for vaccination has been optimized for hgp10025-33 and OVA257-264, but further validation would be needed for other peptides that may be more appropriate to a given study. Overall, this protocol allows a quick assessment of killing function in vivo and can be adapted to any given antigen.

In Vivo Assay for Detection of Antigen-specific T-cell Cytolytic Function Using a Vaccination Model

The goal of this protocol is to allow for detection of in vivo antigen-specific killing of a target cell in a murine model.

Current methodologies for antigen-specific killing are limited to in vitro use or utilized in infectious disease models. However, there is not a protocol ...

Preparation of Whole Bone Marrow for Mass Cytometry Analysis of Neutrophil-lineage Cells

In this article, we present a protocol that is optimized to preserve neutrophil-lineage cells in fresh BM for whole BM CyTOF analysis. We utilized a myeloid-biased 39-antibody CyTOF panel to evaluate the hematopoietic system with a focus on the neutrophil-lineage cells by using this protocol. The CyTOF result was analyzed with an open-resource dimensional reduction algorithm, viSNE, and the data was presented to demonstrate the outcome of this protocol. We have discovered new neutrophil-lineage cell populations based on this protocol. This protocol of fresh whole BM preparation may be used for 1), CyTOF analysis to discover unidentified cell populations from whole BM, 2), investigating whole BM defects for patients with blood disorders such as leukemia, 3), assisting optimization of fluorescence-activated flow cytometry protocols that utilize fresh whole BM.

Here, we present a protocol to process fresh bone marrow (BM) isolated from mouse or human for high-dimensional mass cytometry (Cytometry by Time-Of-Flight, CyTOF) analysis of neutrophil-lineage cells.

In this article, we present a protocol that is optimized to preserve neutrophil-lineage cells in fresh BM for whole BM CyTOF analysis. We utilized a ...

Isolation of Mouse Kidney-Resident CD8+ T cells for Flow Cytometry Analysis

Tissue-resident memory T cell (TRM) is a rapidly expanding field of immunology research. Isolating T cells from various non-lymphoid tissues is one of the key steps to investigate TRMs. There are slight variations in lymphocyte isolation protocols for different organs. Kidney is an essential non-lymphoid organ with numerous immune cell infiltration especially after pathogen exposure or autoimmune activation. In recent years, multiple labs including our own have started characterizing kidney resident CD8+ T cells in various physiological and pathological settings in both mouse and human. Due to the abundance of T lymphocytes, kidney represents an attractive model organ to study TRMs in non-mucosal or non-barrier tissues. Here, we will describe a protocol commonly used in TRM-focused labs to isolate CD8+ T cells from mouse kidneys following systemic viral infection. Briefly, using an acute lymphocytic choriomeningitis virus (LCMV) infection model in C57BL/6 mice, we demonstrate intravascular CD8+ T cell labeling, enzymatic digestion, and density gradient centrifugation to isolate and enrich lymphocytes from mouse kidneys to make samples ready for the subsequent flow cytometry analysis.

Isolation of Mouse Kidney-Resident CD8+ T cells for Flow Cytometry Analysis

Following viral infection, kidney harbors a relatively large number of CD8+ T cells and offers an opportunity to study non-mucosal TRM cells. Here, we describe a protocol to isolate mouse kidney lymphocytes for flow cytometry analysis.

Tissue-resident memory T cell (TRM) is a rapidly expanding field of immunology research. Isolating T cells from various non-lymphoid tissues is one of the ...

Flow Cytometry-Based Quantification and Analysis of Myocardial B-Cells

A growing body of evidence shows that B-lymphocytes play an important role in the context of myocardial physiology and myocardial adaptation to injury. However, the literature reports contrasting data on the prevalence of myocardial B-cells. B-cells have been reported to be both among the most prevalent immune cells in the rodent heart or to be present, but at a markedly lower prevalence than myeloid cells, or to be quite rare. Similarly, several groups have described that the number of myocardial B-cells increases after acute ischemic myocardial injury, but one group reported no changes in the number of B-cells of the injured myocardium. Implementation of a shared, reproducible method to assess the prevalence of myocardial B-cells is critical to harmonize observations from different research groups and thus promote the advancement of the study of B-cell myocardial interactions. Based on our experience, the seemingly contrasting observations reported in the literature likely stem from the fact that murine myocardial B-cells are mostly intravascular and connected to the microvascular endothelium. Therefore, the number of B-cells recovered from a murine heart is exquisitely sensitive to the perfusion conditions used to clean the organ and to the method of digestion used. Here we report an optimized protocol that accounts for these two critical variables in a specific way. This protocol empowers reproducible, flow cytometry-based analysis of the number of murine myocardial B-cells and allows researchers to distinguish extravascular vs. intravascular myocardial B-cells.

Here we report a protocol for the quantification and differentiation of myocardial B-lymphocytes based on their location in the intravascular or endothelial space using flow cytometry.

A growing body of evidence shows that B-lymphocytes play an important role in the context of myocardial physiology and myocardial adaptation to injury. ...

Analysis of T-cell Receptor-Induced Calcium Influx in Primary Murine T-cells by Full Spectrum Flow Cytometry

Calcium influx in response to T-cell receptor stimulation is a common measure of T-cell signaling. Several calcium indicator dyes have been developed to assess calcium signaling by band-pass flow cytometry. This protocol is designed to measure calcium responses in primary murine T-cells using full spectrum flow cytometry. Total splenocytes are labeled with the ratiometric calcium indicator dye Indo-1, along with a panel of fluorochrome-conjugated antibodies to cell surface molecules. Leveraging the capabilities of full spectrum flow cytometry provides a platform for utilizing a wide array of cell surface stains in combination with Indo-1. Cells are then analyzed in real-time at 37 &#176;C before and after the addition of an anti-CD3 antibody to stimulate the T-cell receptor. After unmixing the spectral signals, the ratio of calcium-bound to calcium-free Indo-1 is calculated and can be visualized over time for each gated population of splenocytes. This technique can allow for the simultaneous analysis of calcium responses in multiple cell populations.

Calcium influx, a measure of T-cell signaling, is an effective way to analyze responses to T-cell receptor stimulation. This protocol for multiplexing Indo-1 with panels of antibodies directed at cell surface molecules takes advantage of the highly flexible capabilities of full spectrum flow cytometry.

Calcium influx in response to T-cell receptor stimulation is a common measure of T-cell signaling. Several calcium indicator dyes have been developed to ...