We read with great interest the report of Delfau-Larue et al1 on the ongoing discussion about the significance of dominant T-cell clones as a hallmark of T-cell malignancy. The authors showed the occurrence of dominant T-cell clones in the peripheral blood of patients with cutaneous T-cell lymphoma (CTCL) (30%), non-CTCL-related skin diseases (41%), and other benign infiltrates (34%). From these findings, they conclude that demonstration of T-cell clonality in the peripheral blood is not of undetermined significance, but of no significance at all. Based on our own results, we wish to point out the view shared by many investigators using polymerase chain reaction (PCR) for clonality studies: that, with some technical precautions taken, T-cell receptor gene rearrangement analysis is reliable and specific and may considerably add to the diagnosis of malignant lymphoproliferative disorders, even in peripheral blood.
We are well aware that expansion of T-cell clones is a prerequisite for antigen-specific T-cell responses and that T-cell clones may be present under many reactive conditions. Therefore, it is not surprising that different PCR-based methods are able to amplify dominant T-cell clones with varying frequency depending on their sensitivity. We have shown that overinterpretation of these dominant PCR products with respect to the diagnosis of malignancy can be avoided by repeated independent PCR determinations of the same samples and application of high resolution separation techniques such as GeneScan analysis and/or sequencing.2 Under reactive conditions dominant PCR products vary, whereas under malignant conditions dominant PCR products are exactly reproducible. Our investigation of 21 clear-cut benign skin infiltrates (psoriasis and contact dermatitis) revealed dominant T-cell clones in only 3 cases. Repeated PCR and GeneScan analyses of these 3 samples demonstrated that the dominant amplificates were of different size, indicating the presence of several different predominant T-cell clones in these lesions. Therefore, we decided to consider cases that do not show identical dominant PCR products in repeated PCR analyses of the same sample as pseudo monoclonal.
Here, we show that this holds also true for peripheral blood samples of patients with cutaneous T-cell lymphoma (CTCL), parapsoriasis, and pseudo T-cell lymphoma (Table1). Similar to the results of Delfau-Larue et al, 19 of 30 cases (63%) of parapsoriasis and pseudo T-cell lymphoma showed a dominant T-cell clone in the peripheral blood at prima vista analysis. But repeated analysis of these samples revealed PCR products of different size, that is, pseudo monoclonality, in all but 1 of the samples, so that the truely monoclonal cases in these nonmalignant conditions amounted to just 3.3%. In stage IV CTCL patients, the opposite picture appeared: the prima vista dominant PCR products seen in 9 of 11 patients (81.8%) were confirmed by repeated analysis of the same sample. In addition, identical amplificates were generated from lesional skin and peripheral blood samples in these 9 patients, further confirming T-cell clonality in different lymphocyte recirculation compartments as expected from T-cell malignancies. In contrast, true T-cell clonality is a very rare finding under nonmalignant conditions; in such cases, the term “T-cell clonality of undetermined significance” should be reserved, in analogy to the term “monoclonal gammopathy of undetermined significance.” In the study by Delfau-Larue et al, only 6% of 211 patients with non-CTCL lesions showed the same clonal T-cell population (of undetermined significance) after denaturing gradient gel electrophoresis (DGGE) analysis in skin and peripheral blood; the identity of the comigrating bands, however, should be confirmed by an independent assay with higher resolution such as GeneScan analysis or sequencing.3Patients with clinically clear-cut nonmalignant conditions and confirmed T-cell clonality should be carefully documented and followed to further determine the natural course of T-cell clonality of undetermined significance.
T-cell clonality in the peripheral blood of 49 patients with cutaneous T-cell lymphoma, parapsoriasis, and pseudo T-cell lymphoma
| Diagnosis . | No. of patients . | Dominant clone . | Oligo/polyclonality . | Pseudo monoclonality . | Monoclonality . | Identical clone in skin and PB . |
|---|---|---|---|---|---|---|
| CTCL | ||||||
| Stages Ia-III* | 8 | 1 | 7 | 0 | 1 | 1 |
| Stage IV† | 11 | 9 | 2 | 0 | 9 | 9 |
| Parapsoriasis‡ | 15 | 11 | 4 | 10 | 1 | ND |
| Pseudo T-cell lymphoma1-153 | 15 | 8 | 7 | 8 | 0 | 0 |
| Diagnosis . | No. of patients . | Dominant clone . | Oligo/polyclonality . | Pseudo monoclonality . | Monoclonality . | Identical clone in skin and PB . |
|---|---|---|---|---|---|---|
| CTCL | ||||||
| Stages Ia-III* | 8 | 1 | 7 | 0 | 1 | 1 |
| Stage IV† | 11 | 9 | 2 | 0 | 9 | 9 |
| Parapsoriasis‡ | 15 | 11 | 4 | 10 | 1 | ND |
| Pseudo T-cell lymphoma1-153 | 15 | 8 | 7 | 8 | 0 | 0 |
Analysis is TCRγ-PCR and GeneScan analysis. ND, not determined.
CTCL confined to the skin.
CTCL with lymph node involvement.
Small plaque parapsoriasis, n = 5; large plaque parapsoriasis, n = 7; lichenoid parapsoriasis, n = 3.
Lymphocytic infiltration of the skin.
In summary, we wish to suggest that “dominant T-cell clone”1 is a rather technical term of still unknown clinical relevance which should be interpreted carefully. The term “clonality”1 should only be used when pseudo monoclonality has been excluded by repeated independent PCR determinations. Under these considerations, the analysis of peripheral blood samples of patients suffering from cutaneous T-cell lymphoproliferative diseases is of high diagnostic value.
Peripheral blood T-cell clonality of no cutaneous T-cell lymphoma diagnostic value
I thank Dr Dippel and his colleagues for their comments on our report concerning the diagnostic value of peripheral blood (PB) T-cell clonality in clinical suspicion of CTCL. We have argued that demonstration of T-cell clonality in PB is of unknown significance (not “of no significance”) and, more precisely, that it has no CTCL diagnostic value as long as the same clone has not been identified in the skin (in contrast to Gene Scan analysis, DGGE migration of PCR products depends on CDR3 sequences and not only on CDR3 size). By contrast, identification of the same clone in skin and blood is of high diagnostic value.
As Dippel et al remind us, PB T-cell clonal expansions occur in multiple clinical settings.1-1 For example, peripheral blood expansion of CD8+ clones have been described in healthy individuals, as well as in patients with rheumatoid arthritis, and have been shown to be remarkably stable over time (up to 4 years).1-2 They increased with age in both the CD45RA+ (naive or long-life memory cells) and CD45RO+ (memory) compartments.1-3 Accordingly, it has been our experience that, using PCRγ-DGGE, we detect a T-cell clone, dominant over polyclonal background, in the blood of 30% to 40% of studied patients, whether with cutaneous malignancy or benign disease. Moreover, dominant T-cell clones are increasingly detected with age, and once detected in a given patient, the T-cell clone remained detectable on all 2001 serial samples with a follow-up as long as 6 years (unpublished data, 2001).
Finally, although Dippel et al's concept of “pseudoclonality” seems to us of no physiologic relevance, we agree with them that the study of peripheral blood samples in patients with a suspicion of CTCL is helpful for the diagnosis as long as the same T-cell clone is detectable in both skin and blood samples.
References
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