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From the Department of Pathology, Stanford University School of Medicine, Stanford, California
| Abstract |
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| Introduction |
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The diagnosis of MCL has important implications for prognosis and treatment because the clinical course is aggressive and MCL often responds poorly to conventional B-NHL therapies.2 The morphological appearance can vary broadly, and MCL may in some instances be difficult to distinguish from other lymphomas such as follicular lymphoma (FL), marginal zone lymphoma (MZL), and variant forms of CLL. Distinguishing MCL from CLL presents a common diagnostic dilemma because they can sometimes overlap both morphologically and immunophenotypically. The typical MCL immunophenotype is CD20 positive, CD5 positive, and CD23 negative, whereas CLL is usually positive for the latter.2 However, MCL shows an aberrant phenotype in approximately 7% of cases.7 While morphology and immunophenotyping are often sufficient, additional studies are sometimes necessary to make a definitive diagnosis.
The CCND1 protein (also known as BCL1 or PRAD1) can by detected by immunohistochemical (IHC) methods in approximately 70% of cases,8 although the staining and interpretation can be difficult, especially in bone marrow preparations.
By standard cytogenetic analysis, the t(11;14) is reported to be detectable in only 60 to 80% of cases for technical reasons.9 When routinely available for clinical use, it is virtually always detectable by fluorescence in situ hybridization (FISH).9 PCR for t(11;14) has complications because the breakpoints occur across 120 kb, although approximately 50% occur within a span called the major translocation cluster (MTC). Consequently, the PCR detection rate for t(11;14) is approximately 40 to 60%.2 Southern blot methods can detect 70 to 80% if multiple probes are used.9 However, this method requires large amounts of sample and is technically laborious and challenging in a clinical setting. Similarly, the labor-intensive and technically difficult Northern blot assays for CCND1 mRNA are not suitable for clinical use.
An approach used by others has been to assay for CCND1 mRNA by reverse transcription PCR (RT-PCR), since normal B cells express very low levels of CCND1.10 Again, there are caveats. Increased CCND1 levels have been reported in a minority of cases of other B-NHLs, CLLs, MMs, acute myeloid leukemias (AML), and hairy cell leukemias (HCL), sometimes in the absence of t(11;14).11, 12, 13 Furthermore, epithelial cells inherently express high levels of CCND1.14 Such cells may be found in significant numbers in extranodal sites being evaluated for NHL.
It is not surprising, therefore, that non-quantitative RT-PCR methods do not adequately distinguish MCL from other B-cell lymphoproliferations.15 Semi-quantitative methods and real-time quantitative methods have shown improvement in specificity. Bijwaard16 and Suzuki12 each describe a real-time quantitative method, with normalization of the results to a housekeeping gene. These appear to separate the MCLs in most cases, however neither evaluated any CLL cases. Nor do they resolve the issue of discerning MCL in a specimen containing an epithelial component, although Bijwaard16 does mention this caveat. Specht4 and Thomazy9 resolve the latter using microdissection of the specimen before RT-PCR.
We postulated that a simpler approach would be to quantitate the ratio of CCND1 to cyclin D3 (CCND3). There are previous reports by others that support this approach. Ott et al17 used immunohistochemistry to demonstrate that while CCND1 was overexpressed in MCL, it was accompanied by reduced or absent CCND3 expression. Suzuki et al18 demonstrated by Northern blotting that in lymphoid malignancies showing an overexpression of CCND1 or cyclin D2 (CCND2), the CCND3 expression was reduced. Furthermore, Uchimura et al19 used a semi-quantitative assay for cyclins D1, D2, and D3, where they showed that a strong CCND1 signal with a weaker CCND3 signal is highly specific for the t(11;14)malignancies. Therefore, we adapted Uchimuras19 assay as a real-time quantitative RT-PCR assay. We measured CCND1, CCND3, and a housekeeping gene (glyceraldehyde dehydrogenase phosphate or GADPH) on all specimens. The CCND1 and CCND3 are each normalized to GADPH, and the results are reported as a ratio of CCND1 to CCND3.
| Materials and Methods |
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The reverse transcription reaction contained the following in a 40 µl volume: 400 units MMLV enzyme, 10 mmol/L dithiothreitol (DTT), 1X MMLV buffer (all from Invitrogen), 80 units RNasin (Promega, Madison, WI), 0.5 µg random hexamers (Amersham Biosciences), 0.5 mmol/L dNTPs (Amersham Biosciences) and DNase-treated total RNA. The minimum absolute RNA quantity used for the reverse transcription was one microgram, and the maximum was 10 micrograms. The reaction incubated at 25°C for 10 minutes, 37°C for 2 hours, and 70°C for 15 minutes. Control and reference RNAs were reverse-transcribed alongside patient RNA for each run.
The quantitative real-time PCR was performed in the ABI 7700 with cycling as follows: an initial cycle for 10 minutes at 95°C, followed by 45 bi-phasic cycles of 15 seconds at 95°C and 1 minute at 60°C.
Each 96-well plate was divided into thirds, one for each target (CCND1, CCND3, and GADPH). Each third (32 wells) included the following: positive control, negative control, reference (or calibrator), no template control (water in lieu of cDNA template) and patient samples (all run in duplicate) as well as also no-RT controls for each patient sample run singly. The no-RT control is DNase-treated sample RNA that has not undergone the reverse transcription step. There was sufficient space for eight patient samples on each plate.
The CCND1 and CCND3 primers are as per Uchimura,19
and the probes for each were designed using Primer Express software (Applied Biosystems, Foster City, CA). The GADPH primers and probe were adapted from sequences used in the TaqMan GADPH Control Reagents Kit (Applied Biosystems), however we used FAM as the reporting fluorophore, rather than VIC. Primers and probes were manufactured by Operon Technologies (Alameda, CA). Note that the CCND1 and CCND3 reactions use the same forward primer (for homologous CCND regions), while the reverse primer and the probe is specific for either the D1 or D3 types. Each probe includes FAM (6-carboxy-fluorescein. emission 518 nm) at the 5'-end as the reporter and TAMRA (6-carboxy-tetramethyl-rhodamine, emission 582 nm) at the 3'-end as the quencher. Primer and probe sequences are listed in Table 2
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The reaction mixture for CCND3 contains the following in a final volume of 25 µl: 2.5U TaqGold, 1X TaqGold Buffer II, and 11 mmol/L MgCl2 (all from Applied Biosystems), 200 µmol/L dNTPs (Amersham Biosciences), 10 pmoles each of CCND-F primer, CCND3-R primer, and CCND3 probe, and 3 µl of cDNA.
The reaction mixture for GADPH contains the following in a final volume of 25 µl: 2.5U TaqGold, 1X TaqGold Buffer II, and 11 mmol/L MgCl2 (all from Applied Biosystems), 250 µmol/L dNTPs (Amersham Biosciences), 50 pmoles each of GADPH-F primer and GADPH-R primer, 40 pmoles of GADPH probe, and 3 µl of cDNA.
Data Analysis
Results were calculated by the "Comparative Ct Method of Quantitation" (
DCt) as per Applied Biosystems 7700 Sequence Detection System User Bulletin No. 2 (ABI Document No. 4303859, can be downloaded from the web as a pdf from: www.wzw.tum.de/gene-quantification/pe-rel-quan.pdf). In this method no standard curve is used, instead all results are calculated relative to a reference standard, called a "calibrator." Each of the three targets is analyzed separately, then CCND1 and CCND3 are each normalized to GADPH. The normalization is necessary to account for variabilities in RNA quantity and quality, and variabilities in reverse transcription efficiency among samples. In this study we required that the GADPH Ct be less than 30 to be considered an interpretable specimen. In our experience using GADPH in real time assays, higher Cts for the GADPH indicate insufficient template quantity, quality, and/or the presence of inhibitors. Only one sample (GADPH Ct of 36) was excluded because it failed to meet this criterion.
The 
Ct is then calculated separately for CCND1 and CCND3 for each sample, using the cell line Meg01 as the calibrator. Meg01 (American Type Culture Collection, Manassas, VA) was chosen as the reference calibrator material because it appears to express approximately equivalent amounts of CCND1 and CCND319
and, as a cell line, it is potentially a consistent and renewable source of calibrator template. We monitored the stability of the Meg01 cell line throughout this study, as described in the Results section below.
The 
Ct for CCND1 and the 
Ct for CCND3 are then reported as a simple ratio (
Ct CCND1 value divided by the 
Ct CCND3 value). The relative PCR amplification efficiencies for GADPH, CCND1, and CCND3 were empirically evaluated, also as per User Bulletin No. 2 and were determined to meet the manufacturers criteria for equivalency.
Sensitivity
To assess the sensitivity of the assay, we performed the quantitative RT-PCR described above on a series of cell line dilutions. Cell suspensions of a t(11;14)-positive myeloma cell line (TIB-196, American Type Culture Collection, Manassas, VA) and a t(11;14)-negative cell line (OCI-Ly8, Stanford, CA) were prepared such that each contained 5 x 105 cells per microliter. The undiluted TIB-196 cell line was designated as 100%. The subsequent dilutions were named 50%, 25%, 10%, 5%, 1%, 0.5%, and 0.25%, which represented the percentage of TIB-196 cells in each, using the negative OCI-Ly8 cells as the diluent. After the cells were properly diluted, RNA was extracted as described above. The RNA was then Dnase treated, and reverse transcription and quantitative real-time PCR were performed as described above.
| Results |
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Assays of cell-line dilutions showed a sensitivity of 10%, the lowest dilution of MCL cells in non-MCL lymphocytes that gave a D1/D3 ratio of greater than 2.0. In other words, a tumor infiltrate comprising at least 10% of the cells analyzed is required to detect an abnormal result.
The Meg01 cell line showed stable relative expression of CCND1 and CCND3 over the three passages required to complete this study (a total of 24 test plates). For all test plates, the Meg01 mean
Ct D1-D3 was 8.70, with a coefficient of variance of 10.0%. This was evenly spread throughout the runs, with no shifts when changing lots of Meg01.
| Discussion |
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The single aberrantly low D1/D3 result in MCL was an axillary lymph node. Rosenwald et al22
reported gene expression microarray data that showed nine cases of MCL without increased CCND1 expression, and some of these showed increased CCND2 or CCND3 expression. Indeed, the 
Ct value for CCND3 in this case is 113.4, while the other MCL cases are very low in comparison, ranging from 0.51 to 9.09.
An important issue in CCND1 assay development is specificity. Of particular concern to us was the ability of the D1/D3 ratio method to distinguish MCL from CLL. At our institution, it is common to make a diagnosis of CLL from peripheral blood and/or bone marrow, and in some cases it is difficult to definitively rule out MCL. We performed the D1/D3 assay on 10 cases of CLL and this method was 100% specific at ruling out a diagnosis of MCL, with no false positives among the CLL cases.
Another concern was whether or not contaminating epithelial cells might falsely elevate the D1/D3 ratio. Epithelia are known to express high levels of CCND114 and extra-nodal presentations are not uncommon in MCL.2 Indeed, in CCND1 expression studies that included extra-nodal specimens, elevated CCND1 were sometimes seen in non-MCL NHL cases. These reports warn of potential false positive results in CCND1 expression levels in such cases.17
CCND3 levels in epithelia have not been reported to our knowledge. However, CCND3 is nearly ubiquitously expressed, along with either CCND1 or CCND2 in a given tissue type.19, 23
Therefore, we postulated that perhaps the ratio of CCND1/CCND3 might more reliably diagnose a MCL in tissues containing epithelia. To investigate this, we tested 7 non-malignant tissues containing a significant epithelial component that would be potential extranodal sites for MCL. The sites were thymus (2), lung (1), intestine (1), stomach (1), submaxillary tissue (1), and parotid (1). These tissues showed a broad range of epithelial tissue, ranging from
10% in the thymus specimens to >90% in the submaxillary specimen. Interestingly, an evaluation of the parotid specimen by CCND1 alone, without including CCND3, would give an apparent (false) positive result. This specimen contained 50% epithelial tissue. However, all of the epithelial specimens, including the parotid, were negative by CCND1/CCND3 ratio.
Table 5
shows the results for these specimens. All specimens yielded negative CCND1/CCND3 ratios (less than 2.0). Therefore, it appears that by this methodology, the presence of epithelial cells will not lead to false positive diagnoses of MCL in extra-nodal presentations.
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We did not perform testing on paraffin-embedded tissue in this study, because the described primer set yields amplicons of approximately 250 bp. In our experience, this amplicon size is larger than can routinely be obtained by isolating RNA from paraffin-embedded specimens. However, our approach of measuring a CCND1/CCND3 ratio could be tested by designing a primer set that yields smaller amplicons.
In conclusion, we describe a real-time quantitative PCR for cyclin D1 expression, reported as a ratio to cyclin D3. Our CCND1/CCND3 method reliably distinguishes MCL from other malignant and non-malignant samples. The CCND1/CCND3 ratio improves the specificity over an evaluation of CCND1 expression alone in the cases tested here. We conclude that the CCND1/CCND3 ratio offers a sensitive and specific test to aid in the diagnosis of MCL.
| Footnotes |
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Supported by National Institutes of Health grants 2PO1CA49605 and 2PO1CA34233.
Accepted for publication December 19, 2003.
| References |
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