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Clinical and Diagnostic Laboratory Immunology, April 2005, p. 477-483, Vol. 12, No. 4
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.4.477-483.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Simplified Fluorescent Multiplex PCR Method for Evaluation of the T-Cell Receptor Vß-Chain Repertoire

Sanjit Fernandes, Surendra Chavan, Vivek Chitnis, Nina Kohn, and Savita Pahwa^*

Immunology and Inflammation Center of Excellence, North Shore—Long Island Jewish Research Institute, North Shore University Hospital—NYU School of Medicine, Manhasset, NY 11030

Received 11 March 2004/ Returned for modification 20 July 2004/ Accepted 19 November 2004

Top Abstract Introduction Materials and Methods Results Discussion References

 
Rationale: evaluation of the T-cell receptor (TCR) Vß-chain repertoire by PCR-based CDR3 length analysis allows fine resolution of the usage of the TCR Vß repertoire and is a sensitive tool to monitor changes in the T-cell compartment. A multiplex PCR method employing 24 labeled upstream Vß primers instead of the conventionally labeled downstream Cß primer is described. Method: RNA was isolated from purified CD4 and CD8 T-cell subsets from umbilical cord blood and clinical samples using TRI reagent followed by reverse transcription using a Cß primer and an Omniscript RT kit. The 24 Vß primers were multiplexed based on compatibility and product sizes into seven reactions. cDNA was amplified using 24 Vß primers (labeled with tetrachloro-6-cardoxyfluorescein, 6-carboxyfluorescein, and hexachloro-6-carboxyfluorescein), an unlabeled Cß primer, and Taqgold polymerase. The fluorescent PCR products were resolved on an automated DNA sequencer and analyzed using the Genotyper 2.1 software. Results: Vß spectratypes of excellent resolution were obtained with RNA amounts of 250 ng using the labeled Vß primers. The resolution was superior to that obtained with the labeled Cß primer assay. Also the numbers of PCRs were reduced to 7 from the 12 required in the Cß labeling method, and the sample processing time was reduced by half. Conclusion: The method described for T-cell receptor Vß-chain repertoire analysis eliminates tedious dilutions and results in superior resolution with small amounts of RNA. The fast throughput makes this method suitable for automation and offers the feasibility to perform TCR Vß repertoire analyses in clinical trials.

Top Abstract Introduction Materials and Methods Results Discussion References

 
T cells recognize the antigen presented by antigen-presenting cells in the context of major histocompatibility complex class I (MHC I) and II molecules through the T-cell receptors (TCR) (4). The diversity in recognition of innumerable antigens is dependent on the diversity in TCR (3). TCR is a heterodimeric glycoprotein consisting of an alpha and beta chain (6). Each chain is the product of a complex gene recombination rearrangement process that takes place during the intrathymic differentiation (16). During recombination, TCR variable (V) diversity (D) and junctional (J) region segments are coupled to a constant (C) gene domain. The immense diversity created by these random recombination events and other processes, such as random nucleotide insertion, make the V-D-J region extremely variable in nature. The variable length of the CDR3 region is a function of the non-germ line-encoded event of nucleotide insertion by TdT and is the most hypervariable region of the ß-chain. It is this region that has been predicted to confer fine specificity of recognition to the TCR for the peptide-MHC complexes. Analysis of the CDR3 region of the TCR ß chain can thus provide insights into the heterogeneity of the T-cell compartment and of immune mechanisms operative in infectious and autoimmune diseases (18).

The TCR Vß repertoire can be analyzed by different methods (2), including anchor PCR (12), heteroduplex PCR analysis (20, 21), and flow cytometry (10). Anchor PCR analysis amplifies the entire gene segment of the known and unknown families of the TCR repertoire but fails to resolve fine specificity of the CDR3 segment or the Vß gene usage. In the heteroduplex assay, the amplified cDNA forms a duplex, and the output may compromise the fine specificity of each Vß family in comparison to that determined by the CDR3 length analysis. TCR repertoire analysis by flow cytometry utilizes monoclonal antibodies against the TCRß chains and has the advantage of coupling the identification of TCR Vß families with phenotypic characterization of T cells. However, the method is limited by availability of monoclonal antibodies and its inability to determine diversity and restrictions in TCR gene usage, as is feasible by PCR analysis.

The number of PCRs or probes needed to detect all Vß genes is a cumbersome feature of the assay, especially when multiple samples need to be analyzed. Several groups have applied the multiplex PCR method for the analysis of TCR genes (5, 7). Maslanka et al. (13) developed a system utilizing two specific T-cell receptor Vß-chain primers in each PCR for analysis of 23 T-cell receptor Vß-chain families coupled with spectratyping technology, and subsequently, a method (8, 14) that multiplexed two to three Vß primers with one primer specific for the TCR ß constant region was described. Another method (1) utilized a multiplex PCR system employing five PCRs combining 24 Vß primers. We have developed a multiplex PCR system that employs seven PCRs with four to six primers in each tube for the detection of the 24 Vß families. In this study we demonstrate the specificity and sensitivity of this multiplex system with a relatively low cell input and illustrate the resolution of the assay in patient samples.

Top Abstract Introduction Materials and Methods Results Discussion References

 
Reagents. Human anti-CD4/CD8 antibody-coated magnetic beads were purchased from Dynal Corp, Inc. (Great Neck, NY). Molecular biology grade chloroform, isopropanol, dimethyl formamide, and TRI reagent were obtained from Sigma-Aldrich (St. Louis, MO). Glycoblue and Superasin were purchased from Ambion, Inc. (Austin, TX). An Omniscript reverse transcription (RT) kit was purchased from QIAGEN (Valencia, CA). AmplTaq Gold polymerase, deoxynucleoside triphosphates (dNTPs), internal size standard 6-carboxytetramethylrhodamine, AmpliTaq polymerase, dNTP mix, and the fluorescent dyes 6-carboxyfluorescein (FAM), which is blue, tetrachloro-6-cardoxyfluorescein (TET), which is green, and hexachloro-6-carboxyfluorescein (HEX), which is yellow, were procured from PE Applied Biosystems (Foster City, CA).

Samples. Umbilical cord blood samples were obtained under the guidelines of IRB-approved protocols from the North Shore—Long Island Jewish Research Institute University Hospital in heparinized tubes within 4 h of delivery. Heparinized venous blood was also obtained from human immunodeficiency virus-positive (HIV⁺) patients engaged in clinical protocols under informed consent and from healthy volunteers. The cord blood mononuclear cells (CBMC) and peripheral blood mononuclear cell samples were isolated by standard Ficoll-Hypaque gradient centrifugation. CD4 and CD8 T cells were separated from cord blood mononuclear cells and peripheral blood mononuclear cells by positive selection using immunomagnetic beads coated with human anti-CD4 and anti-CD8 monoclonal antibodies (Dynal Corporation, Great Neck, NY), as previously described (2, 11, 19).

RNA extraction and cDNA synthesis. Total RNA was extracted from positively selected CD4 and CD8 T cells by a TRI reagent-chloroform extraction method (TRI reagent and molecular biology reagents, chloroform, isopropanol, and dimethyl formamide from Sigma, St. Louis, MO) according to the manufacturer's protocol. A total of 10 µl of 50 µg/ml of glycoblue (Ambion, Austin, TX) was added to each ml of aqueous phase, and the RNA was subsequently precipitated with an equal volume of isopropanol. The precipitated RNA was dissolved in 10 µl of DEPC-treated water containing 1U/µl of superasine (both from Ambion, Austin, TX). A total of 1 to 0.125 µg of RNA was reverse transcribed into cDNA by using an Omniscript RT kit according to the manufacturer's protocol using an unlabeled Cß-Reverse primer (Cß-R) in a 40-µl reaction mixture.

Multiplex PCR primer combination. Table 1 lists the TCR Vß and the Cß-R primers used in this study. Locations of primers are shown in Fig. 1. Our first objective was to multiplex the Vß families into as few sets as possible without primer incompatibility and amplicon size differing in at least more than 10 nucleotides. Primer compatibility was analyzed using the Oligos 1998 to 2001 V.8.72 primer design freeware software available on the Internet site http://www.biocenter.helsinki.fi/bi/bare-1_html/ (Institute of Biotechnology, University of Helsinki, Finland). Based on the amplicon size and primer compatibility, the Vß families were divided into three groups and labeled with fluorescent dyes FAM, TET, and HEX (Table 1).

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TABLE 1. Primers used for TCR Vß analysis using labeled Vß primersa

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FIG. 1. TCR Vß repertoire in cord blood CD4 T cells, amplified by two different approaches. A, with labeled Vß forward primer and unlabeled Cß reverse primer; B, with unlabeled Vß forward primer and labeled Cß reverse primer. The resolution of TCR Vß families Vß 14, 15, 21, and Vß 24 is superior with labeled Vß primers.

Multiplex PCR by labeled Vß primer. In this new method, seven set multiplex PCRs were carried out on a PTC-225 Peltier thermal cycler (MJ Research, San Francisco, CA). Primer sequences and how they were mixed are shown in Table 1. The primer set mixtures in tubes A to F were as follows: A (Vß 1, 2, 5.1, 5.2); B (Vß 6, 7, 8, 9, 16); C (Vß 12, 13.1, 13.2); D (Vß 11, 20, 15); E (Vß 3, 21, 17, 24); F (Vß 14, 18, 23); G (Vß 4, 22). Each multiplex reaction contained 1 µl cDNA, 1 µl each of TCR Vß primer set specific for 3 to 5 different Vß families, and 2 µM Cß-R, 1 mM dNTPs, 2 mM MgCl₂, and 1U of AmpliTaq Gold DNA polymerase in a final reaction mixture of 12.5 µl. For the Vß primers 2, 7, 13.1, and 17, it was determined that the labeled primers had to be mixed with unlabeled primers at a ratio of 3:1 in order to prevent disproportionately high signal intensity. The PCR conditions were 94°C for 12 min for enzyme activation, followed by 35 cycles of 94°C for 20 s, 58°C for 20 s, and 72°C for 30 s, and finally one cycle of 72°C for 10 min. The titration of MgCl₂ and of each TCR Vß primer concentration was performed to optimize each multiplex reaction, to provide uniform amounts of amplified products.

Multiplex PCR by labeled Cß primer. In this previously described conventional method (2, 11, 19), 12 reaction tubes were used with two to three primers in each tube. Multiplex PCRs were carried out as before on a PTC-225 Peltier thermal cycler.

Analysis by spectratyping. The amplified PCR products were diluted 10 times with molecular biology grade water. The 2 µl of the diluted product was mixed with 12 µl of dimethyl formamide containing 0.5 µl of Tamara 350 as internal size standard. The mixture was denatured at 95°C for 5 min and immediately cooled in an ice water bath for 5 min and resolved and size fractionated on an ABI 310 genetic analyzer (PE Biosystems, Foster City, CA). Raw data were further analyzed using a Genotyper 2.1 apparatus (PE Biosystems, Foster City, CA).

Top Abstract Introduction Materials and Methods Results Discussion References

 
The spectratype of cord blood T cells determined by multiplex PCR exhibits a Gaussian pattern. The spectratype of TCR Vß repertoire in cord blood CD4 T cells was performed using labeled Vß forward primers and unlabeled Cß reverse primer (Fig. 1A) and with unlabeled Vß forward primers and labeled Cß reverse primer, as illustrated in Fig. 1B. All the 24 known functional TCR Vß families could be amplified successfully from CD4 and CD8 T cells. Each Vß family is represented by a set of peaks, with each peak representing a set of T-cell clones bearing the same CDR3 length with different nucleotide sequences corresponding to different amino acid compositions. Within a TCR Vß family, the difference between each successive peak is three nucleotides, i.e., one amino acid. An unperturbed polyclonal repertoire for any Vß family is represented by a set of peaks distributed in a Gaussian pattern, with the highest-intensity CDR3 segment lying in the center. Deviation from this Gaussian pattern or reduction in the number of peaks is termed as perturbation and results either from overrepresentation, underrepresentation, or the absence of one or more CDR3 segments. Umbilical cord blood T cells have a relatively unperturbed repertoire and were used to create a standard profile against which the test sample is evaluated. Each cord blood Vß profile was measured as a frequency histogram and translated into a relative frequency probability distribution, with a total area equal to 1, as previously described (7). By averaging the frequency distributions obtained in 10 cord blood samples, a control composite profile was generated for each Vß family (Fig. 2). Deviation from the control profile for each Vß family in a test sample could theoretically range from 0 (complete overlap) to 100% (complete nonoverlap) perturbation. In order to assess the variation between the cord bloods themselves, percent perturbation was determined for each Vß family in individual cord blood T cells against the composite profile.

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FIG. 2. Frequency distribution histograms of TCR Vß families derived from normal umbilical cord blood T cells. The frequency probability distributions (y axis) of different CDR3 lengths (x axis) of individual TCR Vß families from 10 cord blood samples were averaged to generate a control composite profile for each Vß family, as described in the text.

Comparison of TCR Vß repertoire obtained using labeled Cß versus labeled Vß primers. Both methods provide good resolution of the different TCR transcripts. However, the multiplex PCR method performed by the labeled Vß forward primer method resulted in better resolution and higher signal intensities compared to that performed using labeled Cß reverse primers. The comparative analysis performed in 10 different CD4 and CD8 T cells isolated from 10 different cord blood revealed that the resolution of TCR Vß families Vß 14, 15, 21, and 24 improved significantly by using labeled Vß primers (Figs. 1A and 1B). The summary value of mean perturbations for all Vß families in cord blood was determined to be 8.83% with a standard deviation of 2.43 and an upper limit of 12.83% in the labeled Vß primer-7 tube method. For the 12 tube labeled Cß reverse primer method, the mean perturbation was 13.42% with a standard deviation of 1.48 and an upper limit of 15.86%. Importantly, the time and the reagents required for multiplex PCR performed by labeled Vß primers to amplify TCR Vß families is approximately half of that required for the multiplex PCR performed with the labeled Cß reverse primer.

RNA titration to determine the sensitivity of multiplex PCR using labeled Vß primers. The RNA input required to obtain optimal resolution of the TCR Vß repertoire was determined using different concentrations of RNA ranging from 125 ng to 1,000 ng by double dilution in a 40-µl RT reaction. The average yield of RNA was approximately 1.0 µg per million cells. All TCR Vß families were amplified at 1,000 ng to 250 ng of starting RNA. As shown in Fig. 3, the TCR Vß resolution was compromised at 125 ng RNA, resulting in a perturbed spectratype pattern, compared to that obtained with RNA input of 250 ng.

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FIG. 3. RNA titration to determine the optimal input in the multiplex PCR using labeled Vß primers: amplification of the TCR Vß families at 250 ng RNA input is superior to that observed at an RNA input of 125 ng.

Analysis of TCR Vß repertoire in clinical samples. A "control" TCR Vß profile was developed using CD4 and CD8 T cells from normal umbilical cord blood samples to represent an unperturbed or naïve T-cell repertoire as described above. For each study subject, percent perturbations within each Vß family were computed after summing the absolute differences between each peak of the control profile and that of the study subject's profile. A single dominant peak constituting >50% of the total area of the other CDR3 segments in that particular Vß family was designated as dominant, which was previously shown to be clonal in nature by sequence analysis (14). The 7-tube method using the labeled Vß primers has recently been used for assessing perturbations in clinical samples from HIV-infected and uninfected adolescents (15). The percent perturbations in CD4 T cells were comparable to uninfected controls, but the incidence of clonal dominance was greater in patients CD4 T cells. In CD8 T cells, perturbations and clonal dominance in the infected patients was significantly greater than that of uninfected volunteers. Figure 4 is an example, showing the TCR Vß profiles of a subject with HIV infection. It can be noted that CD4 T cells showed perturbations in six TCR Vß families (mean perturbation, 15%), but almost all CD8 TCR Vß families were perturbed (mean perturbation, 29.5%) and five of them had a dominant profile.

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FIG. 4. Example of the TCR Vß repertoire in an HIV-infected patient using labeled Vß primers. The asterisks represent perturbations, and the arrows depict TCR Vß families exhibiting clonal dominance.

Top Abstract Introduction Materials and Methods Results Discussion References

 
The multiplex PCR using the labeled Vß forward primers described here was developed to facilitate the rapid qualitative analysis of the TCR Vß gene expression and to characterize alterations in the T-cell receptor repertoire. The method is very sensitive, is highly reproducible, and yields an improved resolution of the TCR Vß families in comparison to previously described methods. Additional advantages of this newly developed method are the feasibility of using small patient samples and the speed with which it can be performed relative to the old method.

A major requirement of TCR Vß repertoire studies is that of good quality cDNA which is reverse transcribed from RNA that is isolated from highly purified populations of CD4 and CD8 T cells and their subsets. The amount of RNA in the reaction is thus an important factor for maintaining specificity, especially when analyzing T-cell receptor repertoire from various sources. Addition of an excessive amount of RNA can reduce the resolution of specific signals or generate spurious products. Excessive template is a potential cause for mispriming in allele-specific PCR (8). In developing this assay, the least amount of RNA that would yield optimal results was determined by titration of different concentrations of RNA (0.125 µg to 1.0 µg) for the RT into cDNA. RNA concentration of 0.25 µg was found to be sufficient for qualitative analysis of the 24 Vß families. This feature makes the test feasible in situations where the clinical samples are limited, as in blood samples from infants and young children.

Since each primer has different requirements for Mg⁺⁺ and dNTPs and different affinities for the cognate target sequences, the optimal concentrations and number of reaction cycles required for proper amplification will differ. Optimizing these factors individually for each multiplex set or for each primer is not realistic in a system designed to handle a large number of samples. Titration of MgCl₂ (1.5 to 2 mM) revealed that 1.5 mM was best suited for the amplification in the multiplex PCR. Multiplex PCR can result in competition between different primers for templates, and thus, determination of intraprimer compatibility is necessary for achieving the best amplification efficiency of given primer pairs. Analysis of the TCR Vß repertoire using 100% labeled Vß primers revealed that some of the primers (Vß 2, 7, 13.1, and 17) were amplified at a significantly higher level compared to the others. The high intensities of these primers led them to bleed into the neighboring channels of the detector. This problem persisted even if the individual concentrations of the Vß primers were lowered, but it was overcome by adding corresponding unlabeled Vß primers, which competed with the labeled primers and resulted in lowering the signal intensity.

For comparison between the assays using labeled Vß primers and the labeled Cß-R, we analyzed 10 cord blood samples by both methods. Cord blood provides an ideal source of an unperturbed TCR repertoire, because perturbation is a consequence of peripheral events (9). Moreover, it is fully diversified, as the genetic mechanisms for T-cell repertoire diversification are developed in the fetus by 24 weeks of gestation (17). The overall resolution of all the 24 Vß families was found to be superior with the use of labeled Vß primers in comparison to labeled Cß-R. This change in the method to using labeled Vß primers also decreased the assay steps and reduced the assay time almost by half.

As shown in the example of the TCR Vß repertoire of one patient, this method of analysis provides excellent resolution of TCR Vß repertoire in clinical samples. It readily lends itself for studies requiring analysis of perturbations in sequential samples from the same patient, or between different patients, because the cord blood provides an unbiased standard that allows objective comparison of samples. Thus, the degree of perturbation in relation to the cord blood composite can be evaluated for each sample, allowing for objective analysis of clonal dominance and the change over time in each CDR3 length. This analysis can be performed in major subsets of T cells (e.g., in CD4 and CD8 T cells) as well as in functional subsets of CD4 and CD8 T cells, e.g., in naïve, memory, and effector cells.

In conclusion, this method provides a tool for quantitative and qualitative assessment of the TCR Vß repertoire and can be used for few or many samples. The standardization procedure using the cord blood composite profile makes the results easier to interpret and to compare within and between subjects in longitudinal studies, making it feasible for analysis of TCR Vß repertoire in clinical trials.

 
* Corresponding author. Mailing address: University of Miami School of Medicine 712, Batchelor Children's Research Institute, University of Miami School of Medicine, 1580 N.W. 10th Avenue, Miami, FL 33136. Phone: (305) 243-7732. Fax: (305) 243-7211. E-mail: spahwa{at}med.miami.edu.

Top Abstract Introduction Materials and Methods Results Discussion References

 

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Clinical and Diagnostic Laboratory Immunology, April 2005, p. 477-483, Vol. 12, No. 4
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.4.477-483.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Fernandes, S. Articles by Pahwa, S. Search for Related Content PubMed PubMed Citation Articles by Fernandes, S. Articles by Pahwa, S.