No evidence of IGH‐MALT1 translocation in the Ma‐1 cell line

We read with great interest the article from Kuo et al. entitled ‘‘Establishment of a novel MALT lymphoma cell line, Ma-1, from a patient with t(14;18)(q32;q21) positive Helicobacter pylori-independent gastric MALT lymphoma’’ (Kuo et al., 2011). The authors kindly agreed to send us an aliquot, which we have further characterized by G-banding, comparative genomic hybridization (CGH), fluorescence in situ hybridization (FISH), and multicolor FISH (M-FISH). We could widely confirm the published karotype, but found additionally a fra(2) and a marker chromosome der(8) (confirmed by M-FISH). Concerning the t(14;18) IGH-MALT1 (IGH green, Malt1 red), the authors report the following signal constellations: (1) 1F1r1g: 1F on Chr.18, 1r on Chr.18, 1g on Chr.14; (2) 1F1r2g: 1F on Chr.18, 1r on Chr.18, 2g on Chr.14. The latter is the signal constellation we also found in nearly 100% of the metaphases considered (n 1⁄4 30). We did not observe the signal constellation 1F1r1g at all. Additionally, we performed FISH with a MALT1 break-apart probe (Vysis/Abbott, Des Plaines, IL). In line with the findings by Kuo et al. (2011), there was no split detected. Concerning the t(14;18) IGH-BCL2, Kuo et al. (2011) describe the following signal constellations: (1) 1F1r1g: 1F on Chr.14, 1r on Chr.18, 1g on Chr.14; (2) 1F1r1g: 1F on Chr.14, 1r on Chr.18, 1g on Chr.18; (3) 1F1r2g: 1F on Chr.14, 1r on Chr.18, 1g on Chr.14, 1g on Chr.18. We observed constellation (1) in only one single metaphase and constellation (3) in 28% of all metaphases considered (n 1⁄4 40). We did not observe constellation (2) at all. In 63% of all metaphases we had the following constellation: 2F 1r 1g: 1F on Chr.14, 1F on Chr.18, 1g on Chr.14, 1r on Chr.18, which represents the typical signal constellation expected when the balanced translocation between IGH and BCL2 is present. Nevertheless, in about a third of these metaphases (7/25), the red signal contributing to the fusion signal on Chr.18 was remarkably weaker in intensity pointing to a putative partial deletion of the BCL2 locus. Results from FISH with IGH and BCL2 break-apart probes were positive for splits in these two loci, confirming the presence of an IGH-BCL2-translocation in 100% of the investigated metaphases. Taken together, we doubt the presence of a classical IGH-MALT1 translocation in the Ma-1 cell line due to the following reasons: (1) no split within MALT1 present; (2) all signals for MALT1 are located on Chr.18. Hence, since the major breakpoint region of MALT1 is located at the 50NCR (Murga Penas et al., 2010; SanchezIzquierdo et al., 2003; Streubel et al., 2003), there should be one signal for the MALT1 locus be observable at Chr.14 if the IGH-MALT1 translocation was present; (3) only 1 fusion signal for the IGH/MALT1 probe present. A balanced translocation such as the IGH-MALT1 translocation should result in two fusion signals (one located on Chr.14, the other one on Chr.18) plus one red signal (MALT1, Chr.18) and one green signal (IGH, Chr.14), at least when detected with a dual color fusion translocation probe (we used the respective probe from Vysis/Abbott). We noticed that Kuo et al. (2011) have used a mixture of BAC clones covering the IGH locus; nevertheless, the FISH should give the same result, regardless of the probe set used. The single fusion signal observed with the IGH/MALT1 probe is always located on Chr.18 and is—in our opinion—an artifact from the IGH-BCL2 translocation. Possibly, there is a small deletion between BCL2 and MALT1, lying anyway very close together, leading to this artificial fusion signal. We observed a weaker red signal in a subset of metaphases screened with the IGH-BCL2 translocation probe, supporting this hypothesis. We conclude that the cell line Ma-1 harbors the IGHBCL2 translocation, which is a typical hallmark of follicular lymphoma. It would be of particular interest to clarify whether the primary tumour and/or its metastases/recurrences in neck, nasopharynx, and bone marrow carry this translocation as well. Opinions regarding the presence of an IGH-BCL2 translocation in mucosa-associated lymphoid tissue (MALT) lymphoma are controversial, so Ma-1 is to be considered a lymphoma cell line not harboring the common genetic changes observed in MALT lymphoma. This all the more important, since the MALT concept including transformation in a blastic marginal zone B-cell lymphoma is expanding and in vitro work will have to focus on mechanisms involved including the use of cell lines stemming from this particular type of lymphoma (Barth et al., 2007; Flossbach et al., 2011, 2013).