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

We thank Flossbach et al. for their comments on our article, 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). In their correspondence, Flossbach et al. have performed cytogenetic investigations (G-banding, CGH, FISH, and M-FISH) on the MALT-lymphoma cell line, MA-1, developed by Kuo et al. (2011). The authors demonstrated largely the same karyotypic findings as published by Kuo et al. (2011). However, the authors found the presence of an IGH-BCL2 translocation and the absence of a classical IGH-MALT1 translocation in MA-1, and suggested that MA-1 may not be a typical cell line for MALT lymphoma. Although t(14;18)(q32;q21)/IGHBCL2 is considered a hallmark for follicular lymphoma, this translocation has also been described in some cases of MALT lymphoma of the salivary glands, liver, stomach, and skin (Libra et al., 2004; Nakamura et al., 2007; Palmedo et al., 2007). Indeed, the possibility of follicular lymphoma in the present case was excluded by extensive histological and immunohistochemical studies: (1) the histological pattern of the lymphoma cells from the neck lymph node (small lymphoid cells mainly distributed in marginal zone) and Waldeyer’s ring (centrocyte-like cells and prominent lymphoepithelial lesions) was identical to the lymphoma originally found in the stomach; (2) lack of the follicular-cell lymphoma-specific germinal cell markers CD10 or BCL6 in all clinical samples and MA-1 cells. Although the authors disagree with our findings that t(14;18)(q32;q21)/IGH-MALT1 and t(14;18)(q32;q21)/IGHBCL2 coexist in MA-1 cells (Kuo et al., 2011), karyotypic analysis of the MA-1 cell line via G-banding and SKY showed multiple structural abnormalities with at least 13 alterations identified. Thus, the better description of the karyotype of translocation of MA-1 is ‘‘der(14)t(14;18) (q32;q21).’’ The nomenclature should be interpreted as major finding of the fusion being located on chromosome 14, not on the balanced translocation as mentioned by the authors. Although the term ‘‘t(14;18)’’ was sometimes used in the text by Kuo et al. (2011), it only reflected the existence of a translocated chromosome, a nomenclature commonly accepted in the literature to describe lymphoma. In addition, as described by Streubel et al. (2003) there are not only balanced t(14;18)(q32;q21) translocations observed but also unbalanced translocations with IGH-MALT1. This is in line with our findings. The statement by Flossbach et al. that ‘‘The single fusion signal observed with the IGH-MALT1 probe is an artifact from the IGH-BCL2 translocation’’ is questionable since we did not map the three genes IGH, BCL2, and MALT1 together at one time, so it was not possible to cause ‘‘artifact’’ as assumed. In the article by Kuo et al. (2011), Figure 5D, we clearly showed that the unbalanced translocation der(14)t(14;18) but not the reciprocal t(14;18) translocation was present in MA-1. In addition, by using respective probes from Vysis/Abbott, we have confirmed our previous findings that t(14;18)/IGH-MALT1 (IGH green, MALT red) was present in the paraffin section of the MA-1 cell line and in the MA-1 cell line (Fig. 1). A recent study has shown coexistence of t(14;18)(q32;q21)/IGH-MALT1 and t(14;18)(q32;q21)/IGH-BCL2 in six out of 30 primary cutaneous marginal zone B-cell lymphoma lesions (Palmedo et al., 2007). These findings indicate that MALT lymphoma can exhibit both t(14;18)(q32;q21)/IGH-BCL2 and t(14;18)(q32;q21)/IGH-MALT1. It cannot be overemphasized the risk of natural selection of cell clones of cell lines by repeated culture. As we mentioned in our article, at least three subclones were observed in the MA-1 cell line. It is possibility that the cells may generate new clones from time to time. In addition, MA-1, a low-grade lymphoma cell line, proliferates slowly and may be particularly vulnerable to the selection stress. It is preferable if the authors repeat the STR genotyping experiment on the MA1 to confirm the original characteristics of this cell line.