Leukemia and Lymphoma, 2003 Vol. 44 (2), pp. 375–376
Letter to the Editor
B3/A3 Rearrangement in a Patient with Chronic Myeloid Leukemia ˜ Oa,b,*, MELISSA ARE´VALOa and PAOLA E. LEONEa,b CE´SAR PAZ-Y-MIN a Laboratorio de Gene´tica Molecular y Citogene´tica Humana, Departamento de Ciencias Biolo´gicas, Pontificia Universidad Catolica del Ecuador, Apartado 17-1-2184, Quito, Ecuador; bUnidad de Gene´tica, Facultad de Medicina, Pontificia Universidad Catolica del Ecuador, Apartado 17-1-2184, Quito, Ecuador
The role of BCR/ABL isoforms and their relationships to leukemia phenotype are discussed continuously because of the variety of information reported. Here we describe a man with CML an atypical b3/a3 rearrangement, who had a good response to INFa treatment. This may be due to a deletion of the ABL exon 2 sequences, which are an essential part of the ABL SH3 domain inducing STAT5 expression, which is indeed crucial for the BCR/ABL leukemogenesis; because of its role in anti-apoptotic activity and cell cycle progress. Keywords: BCR/ABL; B3/A3; CML; INFa
INTRODUCTION The actual case describes a Phþ chronic myeloid leukaemia (CML) patient with an unusual b3/a3 BCR/ABL junction. Apparently, it seems that the clinical outcome shows haematological remission and a mosaicism cytogenetically. The BCR/ABL junction is the most common rearrangement in adult Ph þ CML (90 – 95%); in Ecuadorian population the BCR/ABL rearrangement frequencies are as follows: b2/a2 (94.6%); b3/a2 (5.4%), in CML and e1/a3 (100%) in ALL [1]. The diagnosis was made in July 16th 2001, in a Caucasoid, Italian, Phþ , patient at the age of 69 residing in Ecuador. The haematological findings showed 17 g/l haemoglobin, 58% hematocrit, 2,86,000/l platelets, WBC count of 29,900: 81.1% neutrophils, 10.4% lymphocytes, 7.03% monocytes, 0.902% basophils, 0.504% eosinophils. The therapy used after diagnosis was INFa (9 million ml/week/cc) during seven months, which apparently had a good outcome, since it revealed a Phþ mosaic cytogenetically with a WBC count of 18,400: 66% neutrophils, 17.5% lymphocytes, 14% monocytes, 1.6% basophils, 0.5% eosinophils and without splenomegaly. In order to determine the BCR/ABL junction, RNA was extracted from bone marrow using RNAesy mini kit (QIAGEN, MD, USA); followed by RT-PCR (M-MLV and random primers) using primers previously described [1].
The cytogenetic study was carried out with RPMI-1640 medium (enriched with: L -glutamine, calf serum and antibiotic-antimicotic) cultured for 24 and 48 h. The patient, who now seems to have shown a good response, initially showed an unexpected product of 243 pb corresponding to a b3/a3 fragment (Fig. 1, lane 6) and 46,XY(40%)/46,XY,Ph þ (60%) karyotype. The b2a2 is the most common BCR/ABL rearrangement in CML, however, transcripts lacking Abl exon a2 are very rare. Until now, only 10 cases (including CML, ALL and others) [2] have been reported. This is the fourth report of a patient with the b3/a3 rearrangement and the 11th lacking Abl exon a2; additionally, the age of onset is not in agreement with the other three cases reported which are 3, 23 and 39 years old [2], respectively. Proceeding studies have also reported in e1/a3 patient with a less aggressive type of leukaemia (WBC count of 19.2 £ 109/l) [3]. Our report suggests that the same response may be occurring in this b3a3 patient, who also seems to have shown a good response to INFa therapy. The relationship between a specific molecular defect and a distinct clinic-haematological manifestation of the disease still remains unclear [4]. Nevertheless, Abl exon 2, which is missing in the b3/a3 rearrangement, codes for a part of the SH3 region of ABL protein [3] and such a deletion is expected to increase the transforming ability of ABL [5]. Despite this, recent studies have shown that SH3 does not
*Corresponding author. Tel.: þ 593-2-2565627. Ext. 1193. Fax: þ 593-2-2565627. Ext. 1193. E-mail:
[email protected] ISSN 1042-8194 print/ISSN 1029-2403 online q 2003 Taylor & Francis Ltd DOI: 10.1080/1042819021000029678
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junction could be related to a delayed onset and increased survival, as in a study carried out on a murine model. This hypothesis is in agreement with a prior case report in a patient lacking Abl exon a2 who displayed a good prognosis and response to INFa treatment, which is known to induce clinical remission in 15% of patients treated [6]. References
FIGURE 1 Rearrangement of BCR/ABL oncogen. Lanes 1 and 2 show b2/a2 rearrangement, lane 3 mosaic b2/a3– b2/a2, lanes 4 and 5 b2/a3, lane 6 b3a3. MW-2123 bp DNA ladder (Promega, WI, USA).
appear to influence the intracellular signalling that regulates the proliferation and survival of Phþ cells. SH3 induces STAT5 expression, which is crucial for the BCR/ABL leukemogenesis due to its role in anti-apoptotic activity and cell cycle progress. The b3/a3
[1] Paz-y-Min˜o, C., Burgos, R., Morillo, S.A., Santos, J.C., Fiallo, B.F. and Leone, P.E. (2002) “BCR–ABL rearrangement frequencies in chronic myeloid leukemia and acute lymphoblastic leukemia in Ecuador”, Cancer Genet. Cytogenet. 123, 65 –67. [2] Amabile, M., Martelli, G., Terragna, C., Motejusco, V., Tabilio, A. and Tura, S. (1999) “An atypical (b3/a3) junction of the bcr/abl gene lacking abl exon a2 in a patient with chronic myeloid leukemia”, Haematologica 84, 575 –576. [3] Roman, J., Jimenez, A., Barrios, M., Castillejo, J.A., Maldonado, J. and Torres (2001) “E1A3 as a unique, naturally occurring BCR-ABL transcript in an indolent case of chronic myeloid leukemia”, Br. J. Haematol. 114, 635–637. [4] Giovanni, E., Luppi, M., Morasca, R. and Torrelli, G. (1997) “Relationship between BCR/ABL fusion proteins and leukemia phenotype”, Blood 89, 3889. [5] Melo, J.V., “BCR-ABL variants”, Baillie´re’s Clin. Haematol. 10, 203–222. [6] Brizard, F., Chomel, J.C., Veinstein, A., Rivel, J., Giraud, C., Kitzis, A., Guihot, F. and Brizard, A. (1999) “Does BCR –ABL genomic rearrangement persist in CML patients in complete remission after interferon a therapy?”, Leukemia 12, 1076–1080.
