Funding was provided by the National Institutes of Health Grants R00-HL116234, U19 AI117941, and R56 HL126544; the National Science Foundation Grant DMS-1516675; the National Research Foundation of Korea (NRF-2011-0030049, NRF-2014M3C9A3064552); and the KRIBB initiative program.

1. Generating Upstream (left)- and Downstream (right)-junction Sequence Libraries
<ol>
	<li>DNA linker preparation:
	<ol>
		<li>Prepare a 10 &#181;L linker DNA solution by adding 2 &#181;L of 100 &#181;M LINKER_A oligos (final: 20 &#181;M), 2 &#181;L of 100 &#181;M LINKER_B oligos (final: 20 &#181;M), 2 &#181;L of 5 M NaCl (final: 1M), and 4 &#181;L of nuclease-free water in a PCR tube. See Table 1 for the linker sequences.</li>
		<li>Incubate the linker DNA solution at 95 &#176;C for ...

<ol>
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V., Verovskaya, E., Zwart, E., Broekhuis, M., de Haan, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Counting+stem+cells:+methodological+constraints.">Counting stem cells: methodological constraints.</a> Nat Meth. 9 (6), 567-574 (2012).</li><li>Schr&#246;der, 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=HIV-1+integration+in+the+human+genome+favors+active+genes+and+local+hotspots.">HIV-1 integration in the human genome favors active genes and local hotspots.</a> Cell. 110 (4), 521-529 (2002).</li><li>Silver, J., Keerikatte, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+use+of+polymerase+chain+reaction+to+amplify+cellular+DNA+adjacent+to+an+integrated+provirus.">Novel use of polymerase chain reaction to amplify cellular DNA adjacent to an integrated provirus.</a> J. 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Ther. 24 (1), 38-47 (2013).</li><li>Aker, M., Tubb, J., Miller, D. G., Stamatoyannopoulos, G., Emery, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integration+Bias+of+Gammaretrovirus+Vectors+following+Transduction+and+Growth+of+Primary+Mouse+Hematopoietic+Progenitor+Cells+with+and+without+Selection.">Integration Bias of Gammaretrovirus Vectors following Transduction and Growth of Primary Mouse Hematopoietic Progenitor Cells with and without Selection.</a> Mol. Ther. 14 (2), 226-235 (2006).</li><li>Gabriel, R., Kutschera, I., Bartholomae, C. C., von Kalle, C., Schmidt, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Linear+Amplification+Mediated+PCR;+Localization+of+Genetic+Elements+and+Characterization+of+Unknown+Flanking+DNA.">Linear Amplification Mediated PCR; Localization of Genetic Elements and Characterization of Unknown Flanking DNA.</a> J Vis Exp. (88), e51543 (2014).</li><li>Kim, 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=High-throughput,+sensitive+quantification+of+repopulating+hematopoietic+stem+cell+clones.">High-throughput, sensitive quantification of repopulating hematopoietic stem cell clones.</a> J. 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The authors have nothing to disclose.

The bidirectional assay enables the simultaneous analysis of both the upstream (left) and downstream (right) vector-host DNA junction sequences and is useful in a number of gene therapy, stem cell, and cancer research applications. The use of GTAC-motif enzymes (RsaI and CviQI) and the bidirectional PCR approach significantly improves the chances of detecting an integrome (or a clonal population) when compared to previous TCGA-motif enzyme (Taq&#945;I)-based assays2,<sup class=...

Retroviruses insert their genomic DNA into the host genome at various sites. This unique property, which may contribute to the development of cancers and other forms of viral pathogenesis, has the ironic benefit of making these viruses highly amenable to cellular engineering for gene therapy and basic biology research. The viral Integration Site (IS) &#8211; the location on the host genome where a foreign DNA (virus) is integrated &#8211; has important implications for the fate of both the integrated viruses and the host cells. IS assays have been used in various biological and clinical research settings to study retroviral integration site selection and pathogenesis, cancer development, stem cell biology, and developmental biology1,2,3,4. Low detection sensitivity, poor data reproducibility, and frequent cross-contamination are among the key factors limiting the applications of IS assays to current and planned studies.
Many IS analysis technologies have been developed. Restriction enzyme-based integration site assays, including Linker-Mediated (LM) Polymerase Chain Reaction (PCR)5, inverse PCR6, and Linear-Amplification-Mediated (LAM) PCR7, are the most widely used. The use of site-specific restriction enzymes, however, generates a bias during the retrieval of the IS, allowing only a subset of integromes (a foreign DNA integrated into the host genome) in the vicinity of the restriction site to be recovered4. Assay technologies that more comprehensively assess vector IS have also been introduced in recent years. These assays employ various strategies, including Mu transposon-mediated PCR8, nonrestrictive (nr)-LAM PCR9, type-II restriction enzyme-mediated digestion10, mechanical shearing11, and random hexamer-based PCR (Re-free PCR)12, to fragment genomic DNAs and amplify IS. Current technologies have varying levels of detection sensitivity, genome coverage, target specificity, high-throughput capacity, complexity of assay procedures, and biases in detecting the relative frequencies of target sites. Given the varying qualities of the existing assays and the variety of purposes for which they can be used, the optimal assay approach should be carefully selected.
This work provides detailed experimental procedures and a computational data analysis workflow for a bidirectional assay that significantly improves detection rates and sequence quantification accuracy by simultaneously analyzing the IS upstream and downstream of the integrated target DNA (see Figure 1 for a schematic view of the assay procedures). This approach also provides the means to characterize the retroviral integration process (for example, the fidelity of target site duplication and variations in the genomic sequences of upstream and downstream insertions). Other bidirectional methods have been used primarily for cloning and sequencing both ends of the target DNA11,13,14. This assay is extensively optimized for the high-throughput and reproducible quantification of vector-marked clones, using the well-established LM-PCR method and computational analysis mapping, and for quantifying both upstream and downstream junctions. Bidirectional analysis with the Taq&#945;I enzyme has proven useful for high-throughput clonal quantification in stem cell gene therapy preclinical studies2,15. This paper describes a modified method using a more frequent cutter (RsaI/CviQI - motif: GTAC) that doubles the chances of detecting integromes compared to a Taq&#945;I-based assay. Detailed experimental and data analysis procedures that use GTAC motif enzymes for lentiviral (NL4.3 and its derivatives) and gamma-retroviral (pMX vectors) vector IS analysis are described. The oligonucleotides used in the assay are listed in Table 1. An in-house programming script for IS sequence analysis is provided in the supplemental document.

<table border="0" cellpadding="0" cellspacing="0" width="1004">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">Thermostable DNA polymerase</td>
			<td style="width:208px;">Agilent</td>
			<td style="width:119px;">600424</td>
			<td style="width:347px;">PicoMaxx Polymerase</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Thermostable DNA polymerase buffer</td>
			<td style="width:208px;">Agilent</td>
			<td>600424</td>
			<td style="width:347px;">PicoMaxx Polymerase buffer</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;">Deoxynucleotide (dNTP) solution mix</td>
			<td style="width:208px;">New England Biolabs</td>
			<td>N0447L</td>
			<td>dNTP solution mix (10mM each)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PCR tubes</td>
			<td style="width:208px;">VWR International</td>
			<td style="width:119px;">53509-304</td>
			<td style="width:347px;">PCR Strip Tubes With Individual Attached Caps</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">2ml microcentrifuge tube</td>
			<td style="width:208px;">Molecular Bioproducts</td>
			<td style="width:119px;">3453</td>
			<td>microcentrifuge tubes</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">PCR purification kit</td>
			<td style="width:208px;">Qiagen</td>
			<td>28106</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">RsaI&#160;</td>
			<td style="width:208px;">New England Biolabs</td>
			<td>R0167L</td>
			<td>restriction enzyme</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">CviQI</td>
			<td style="width:208px;">New England Biolabs</td>
			<td>R0639L</td>
			<td>restriction enzyme</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">Buffer A</td>
			<td style="width:208px;">New England Biolabs</td>
			<td>B7204S</td>
			<td>NEB CutSmart buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">DNA Polymerase I large (klenow) fragment&#160;</td>
			<td style="width:208px;">New England Biolabs</td>
			<td>M0210L</td>
			<td>Blunting</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">streptavidin beads solution</td>
			<td>Invitrogen&#160;</td>
			<td>60101</td>
			<td>Dynabeads kilobaseBINDER kit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">Binding Solution</td>
			<td>Invitrogen&#160;</td>
			<td>60101</td>
			<td>Dynabeads kilobaseBINDER kit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">Washing Solution</td>
			<td>Invitrogen&#160;</td>
			<td>60101</td>
			<td>Dynabeads kilobaseBINDER kit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">magnetic stand</td>
			<td style="width:208px;">ThermoFisher</td>
			<td>12321D</td>
			<td>DynaMag&#8482;-2 Magnet</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">T4 DNA ligase</td>
			<td style="width:208px;">New England Biolabs</td>
			<td>M0202L</td>
			<td>T4 DNA ligase</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">10X T4 DNA ligase buffer</td>
			<td style="width:208px;">New England Biolabs</td>
			<td>B0202S</td>
			<td>T4 DNA ligase reaction buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">5X T4 DNA ligase buffer</td>
			<td style="width:208px;">Invitrogen&#160;</td>
			<td>46300-018</td>
			<td>T4 DNA ligase buffer with polyethylene glycol-8000</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">UV-Vis spectrophotometer</td>
			<td style="width:208px;">Fisher Scientific</td>
			<td>S06497</td>
			<td style="width:347px;">Nanodrop 2000</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">pvuII</td>
			<td style="width:208px;">new England Biolabs</td>
			<td>R0151L</td>
			<td>restriction enzyme</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">sfoI</td>
			<td style="width:208px;">new England Biolabs</td>
			<td>R0606L</td>
			<td>restriction enzyme</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Buffer B</td>
			<td style="width:208px;">new England Biolabs</td>
			<td>B7203S</td>
			<td>NEB buffer 3.1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">Nuclease free water</td>
			<td style="width:208px;">Integrated DNA Technologies</td>
			<td>11-05-01-14</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">Capillary electrophoresis</td>
			<td style="width:208px;">Qiagen</td>
			<td>9001941</td>
			<td style="width:347px;">QIAxcel capillary electrophoresis</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">Veriti 96-well Fast Thermal Cycler</td>
			<td style="width:208px;">Thermo Fisher Scientific</td>
			<td>4375305</td>
			<td>PCR Instrument</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">Rotating wheel (or Roller)</td>
			<td style="width:208px;">Eppendorf</td>
			<td>M10534004</td>
			<td>Cell Culture Roller Drums</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">DNA size marker</td>
			<td style="width:208px;">Qiagen</td>
			<td>929559</td>
			<td>QX size marker (100-2,500 bp)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">DNA size marker</td>
			<td style="width:208px;">Qiagen</td>
			<td>929554</td>
			<td>QX size marker (50-1,500 bp)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">DNA alignment markers</td>
			<td style="width:208px;">Qiagen</td>
			<td>929524</td>
			<td>QX DNA Alignment Marker</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:331px;">genomc DNA</td>
			<td style="width:208px;">Not Available</td>
			<td style="width:119px;">Not Available</td>
			<td>Sample genomc DNA from in vivo or in vitro experiments</td>
		</tr>
	</tbody>
</table>

bidirectional retroviral integration site pcr methodology and quantitative data analysis workflow

Integration Site (IS) assays are a critical component of the study of retroviral integration sites and their biological significance. In recent retroviral gene therapy studies, IS assays, in combination with next-generation sequencing, have been used as a cell-tracking tool to characterize clonal stem cell populations sharing the same IS. For the accurate comparison of repopulating stem cell clones within and across different samples, the detection sensitivity, data reproducibility, and high-throughput capacity of the assay are among the most important assay qualities. This work provides a detailed protocol and data analysis workflow for bidirectional IS analysis. The bidirectional assay can simultaneously sequence both upstream and downstream vector-host junctions. Compared to conventional unidirectional IS sequencing approaches, the bidirectional approach significantly improves IS detection rates and the characterization of integration events at both ends of the target DNA. The data analysis pipeline described here accurately identifies and enumerates identical IS sequences through multiple steps of comparison that map IS sequences onto the reference genome and determine sequencing errors. Using an optimized assay procedure, we have recently published the detailed repopulation patterns of thousands of Hematopoietic Stem Cell (HSC) clones following transplant in rhesus macaques, demonstrating for the first time the precise time point of HSC repopulation and the functional heterogeneity of HSCs in the primate system. The following protocol describes the step-by-step experimental procedure and data analysis workflow that accurately identifies and quantifies identical IS sequences.

The bidirectional IS assay generated different sizes of PCR amplicons for both the upstream (left) and downstream (right) vector host junctions (Figure 2). The size of a PCR amplicon is dependent on the location of the nearest GTAC motif upstream and downstream from an integrome. The assay also produced internal DNA PCR amplicons: retroviral sequences near the polypurine tract and the primer binding site were concomitantly amplified during left- and right-jun...

Watch this Scientific Journal Video about Bidirectional Retroviral Integration Site PCR Methodology and Quantitative Data Analysis Workflow at JoVE.com

Bidirectional Retroviral Integration Site PCR Methodology and Quantitative Data Analysis Workflow

This manuscript describes the experimental procedure and software analysis for a bidirectional integration site assay that can simultaneously analyze upstream and downstream vector-host junction DNA. Bidirectional PCR products can be used for any downstream sequencing platform. The resulting data are useful for a high-throughput, quantitative comparison of integrated DNA targets.

Integration Site (IS) assays are a critical component of the study of retroviral integration sites and their biological significance. In recent retroviral ...

The overall goal of this procedure is to identify retroviral vector integration sites in the host genome and quantify the relative frequencies of clonal cell populations each sharing the same integration site. This method can help answer key questions in retroviral gene therapy, such as which part of the host genome vector has integrated, how a genetically engineered cell will repopulate after the transplant, and how they are functionally different. The main advantage of this technique is that retro-integration site sequences can be analyzed with higher accuracy and sensitivity by sequencing both upstream and downstream vector host DNA junctions simultaneously.Though this method can provide insight into the safety of vectors and gene engineered cell in gene therapy studies, it can also be applied to other basic biology studies to investigate individual cell behavior in vivo. The first step in this procedure is to determine the DNA concentration and the ratio of absorbance at 260 and 280 nanometers of the genomic DNA to be analyzed. After this, dilute one to two micrograms of the sample genomic DNA to a final volume of 170 microliters of genomic DNA solution using nuclease free water.Prepare a 200 microliter PCR reaction by mixing the following in a microcentrifuge tube. 2.5 microliters each of HIV-1 specific biotin primers, or a total of 10 microliters for four lentivirus-specific primers, 20 microliters of 10X thermostable DNA polymerase buffer, four microliters of 10 millimolar dNTPs, three microliters of thermostable DNA polymerase, and 163 microliters of genomic DNA. Divide the solution equally into four PCR tubes and carry out a single extension cycle under the following condition.94 degrees Celsius for 5 minutes, 56 degrees Celsius for 3 minutes, 72 degrees Celsius for 5 minutes, and 4 degrees C for storage. Pool all four PCR reactions into a two milliliter microcentrifuge tube. Follow the manufacturer's procedure of a PCR purification kit, and elute with 50 microliters of elution buffer.Prepare for a 100 microliter digestion by adding the following to a microcentrifuge tube. 50 microliters of DNA, 10 microliters of 10X buffer A, two microliters of RSAI enzyme, and 38 microliters of nuclease-free water. Incubate at 37 degrees Celsius in a thermal cycler for one hour.Next, add one microliter of CviQI enzyme to the reaction and incubate at 25 degrees Celsius for 30 minutes. When the RSAI and CviQI digestion is complete, proceed immediately with blunt ending. Prepare a 4.5 microliter mixture containing 2.5 microliters of DNA polymerase I, Large Fragment, and 2 microliters of 10 millimolar dNTPs.Transfer 1 microliter of the mixture to the DNA sample. The total volume will be 102 microliters. Mix well by vortexing and incubate at 25 degrees Celsius for one hour.Immediately proceed with streptavidin bead binding when the incubation is complete. Prepare the streptavidin beads by briefly vortexing the bead solution and transferring 50 microliters to a new two milliliter microcentrifuge tube. Remove the supernatant using a magnetic stand and wash the beans with 200 microliters of binding solution.Resuspend the beads in 100 microliters of binding solution and place the tube away from the magnetic stand. Transfer 100 microliters of the sample DNA to the 100 microliters of resuspended bead solution and mix carefully by pipetting to avoid any foaming of the solution. Incubate the tube at room temperature for 3 hours on a rotating wheel.Use the magnetic stand to capture the beads and discard the supernatant. Wash the beads twice in 400 microliters of washing solution and twice in 400 microliters of 1X T4 DNA ligase buffer. Resuspend the beads in 200 microliters of 1X T4 DNA ligase buffer and place it away from the magnetic stand.Linker ligation should be performed immediately after the streptavidin bead binding. Prepare a 400 microliter ligation reaction solution by mixing the following in a two milliliter microcentrifuge tube. 0.5 microliters of the DNA linker, 10 microliters of 10X T4 DNA ligase buffer, 20 microliters of 5X T4 DNA ligase buffer, 5 microliters of T4 DNA ligase, 164.5 microliters of nuclease free water, and 200 microliters of the resuspended beads.Place the reaction tube on a rotating wheel at room temperature for 3 hours. Wash the beads twice with the washing solution, and twice with 1X thermostable DNA polymerase buffer. Resuspend the beads in 50 microliters of 1X thermostable DNA polymerase PCR buffer, and place it away from the magnetic stand.To begin this procedure prepare a 200 microliter PCR reaction by adding the following to the resuspended beads. 10 microliters of one 1L-primer, 10 microliters of 1R-primer, 20 microliters of primer Link1, 10 microliters of 10X thermostable DNA polymerase buffer, four microliters of 10 milimolar dNTPs, eight microliters of thermostable DNA polymerase, and 88 microliters of nuclease-free water. Aliquot the reaction mixture into four PCR tubes and carry out PCR with the following condition.94 degrees Celsius for 2 minutes, 25 cycles of 94 degrees Celsius for 20 seconds, 56 degrees Celsius for 25 seconds, and 72 degrees Celsius for two minutes, and a final extension at 72 degrees Celsius for 5 minutes. Pool all four PCR reactions into a 2 ml microcentrifuge tube. Follow the procedure of the PCR purification kit and elute with 50 microliters of elution buffer.Determine the DNA concentration and the ratio of absorbance at 260 and 280 nanometers using a UV visible spectrophotometer. The DNA can now be stored at minus 20 degrees Celsius until ready for the next step. Since the procedures for the left junction and right junction specific amplifications are identical except for the primers used in the PCR, only the left junction amplification will be demonstrated.Prepare a 50 microliter PCR reaction by mixing the following in a PCR tube. Five microliters of DNA, five microliters of 10 micromolar 2L-primer, five microliters of 10 micromolar primer Link2, 5 microliters of 10X thermostable DNA polymerase buffer, one microliter of 10 milimolar dNTPs, two microliters of thermostable DNA polymerase, and 27 microliters of nuclease-free water. Carry out PCR with the following condition.94 degrees Celsius for 3 minutes, 8 to 15 cycles of 94 degrees Celsius for 20 seconds, 56 degrees Celsius for 25 seconds, and 72 degrees Celsius for two minutes, and a final extension at 72 degrees Celsius for 5 minutes. Use the PCR purification kit to purify the DNA and elute with 50 microliters of elution buffer. Determine the DNA concentration and ratio of absorbance at 260 and 280 nanometers.The last step in generating left and right junction sequence libraries is to analyze the PCR Amplicon length variations by performing capillary electrophoresis. This representative result shows varying lengths of PCR Amplicons in lentiviral vector integrations sites for both the upstream and downstream vector host junctions. The DNA size marker is in the M lane.After sequencing the PCR Amplicons, computational integration site sequence analysis is performed using an in-house programming script. The bi-directional integration site assay generates different sizes of PCR Amplicons for both the upstream and downstream vector host junctions visualized by capillary electrophoresis. A comparison of percent integration in genes Alu and L1 repeats of lentiviral vectors in humanized mouse repopulating cells within silico generated random integration events revealed that integration sites are significantly enriched in genes.The relative detection frequencies of vector integromes were calculated using only the sequence counts of integration site junctions generating smaller than 500bp PCR Amplicons. Approximately 77%of the vectors could be quantitatively analyzed by the bi-directional approach. In the strategy for clonal quantification we presume that each individual clone shares the same vector integrome.The relative frequencies of the left and right junctions are combined to represent the relative quantities of the clonal populations, or QVI. This color scheme shows the relative frequencies of 44 QVI clones in humanized mouse repopulating cells. Based on in silico 10, 000 random integration analysis, a 1.25 fold overestimation of clonal frequencies is expected when using GTAC motif enzymes, and a 2.56 overestimation is expected when using a TCGA motif enzyme.Once mastered, this technique can be divided in parts and completed in two days, if performed properly. While attempting this procedure it is important to remember that PCR steps are extremely sensitive, and precautions should be take to avoid any contamination. This technique has paved the way to examining the safety of therapeutic retroviral vectors, and to explore long-term repopulation patterns of hemotopoietic stem cell clones following transplant in rhesus macaques.

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JoVE Journal

Genetics

10.6K vues.  University of California at Los Angeles (UCLA). The overall goal of this procedure is to identify retroviral vector integration sites in the host genome and quantify the relative frequencies of clonal cell populations each sharing the same integration site. This method can help answer key questions in retroviral gene therapy, such as which part of the host genome vector has integrated, how a genetically engineered cell will repopulate after the transplant, and how they are functionally different. The main advantage of this technique is tha...