Detection of Clonality in Lymphoproliferations Using PCR of the Antigen Receptor Genes: Does Size Matter?

• Published in: Blood Vol. 108; no. 11; p. 4622
• Main Authors: Rothberg, Paul G., Vargas, Roberto L., Felgar, Raymond E., Polochock, Susan L., Frazier, Sharon D.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 16-11-2006
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V108.11.4622.4622

A biopsy of a nasal mass was received from another institution for a hematopathology consultation. The specimen had morphologic and immunostaining features consistent with a B-cell lymphoma, histologically low-grade, and suggestive for an extranodal marginal cell lymphoma of mucosa associated lymphoid tissue (MALT) type. We used PCR of the IgH gene to evaluate clonality on DNA derived from this specimen. The primers were from the BIOMED-2 report (van Dongen et al. 2003, Leukemia 17:2257) and the amplicons were subjected to heteroduplex formation prior to PAGE. A homoduplex of approximately 140 bp was obtained reproducibly from the FR2 and JH primers, which is below the usually acceptable size limits of 250–295 bps. No homoduplex was obtained using FR3 and JH primers. We sequenced the FR2/JH amplicon using the PCR primers as sequencing primers. The amplicon was 137 bps, with 92 bps between the primers. After the upstream VH3 FR2 primer there were approximately 25 bps from the FR2 region of several members of the VH3 family, with VH3-49 (allele *03) being the best match. Adjacent to the downstream consensus JH primer there were approximately 30 bp from the J6 segment. Between the identifiable sequences there were 37 bp that we could not identify. Blast searches turned up several matches of 18 bp, but nothing that gave convincing evidence for its origin. We interpret these results as indicating a clonal IgH rearrangement followed by a deletion that removed most of the downstream portion of the V segment, including the FR3 region. It is likely that the 37 bp in between the identified IgH segments consists of randomly inserted nucleotides and IgH sequence that has been somatically mutated beyond recognition, although other interpretations are possible. However, the amplicon does appear to be derived from an IgH rearrangement, which is consistent with derivation from a monoclonal population of B-lymphocytes. This work illustrates that DNA fragments outside of the size range expected from PCR of the antigen receptor genes may still be consistent with a monoclonal result. Thus, this type of result should not be dismissed, but should be subjected to further analysis.