These two authors contributed equally to this work.
The BCL2L11 (BIM) deletion polymorphism is a possible criterion for discontinuation of imatinib in chronic myeloid leukaemia patients
Article first published online: 1 NOV 2012
© 2012 Blackwell Publishing Ltd
British Journal of Haematology
Volume 160, Issue 2, pages 269–271, January 2013
How to Cite
Katagiri, S., Umezu, T., Ohyashiki, J. H. and Ohyashiki, K. (2013), The BCL2L11 (BIM) deletion polymorphism is a possible criterion for discontinuation of imatinib in chronic myeloid leukaemia patients. British Journal of Haematology, 160: 269–271. doi: 10.1111/bjh.12111
- Issue published online: 10 JAN 2013
- Article first published online: 1 NOV 2012
- chronic myeloid leukaemia;
- discontinuation of imatinib;
- BCL2L11 deletion polymorphism;
- complete molecular remission
Treatment with tyrosine kinase inhibitors (TKIs) can be effective in the majority of patients with chronic myeloid leukaemia (CML) with the BCR-ABL1 fusiongene, and the standard of care using imatinib has been established (Baccarani et al, 2009). Although 20% of CML patients showed primary resistance to first-line imatinib therapy, some patients obtained an optimal response to imatinib and then could be induced to complete molecular response (CMR), as assessed by the currently available quantitative polymerase chain reaction (PCR) assay (Mahon et al, 2010; Takahashi et al, 2012). The reduction of the BCR-ABL1 transcript to the CMR level is now considered to be the ideal target point of TKI treatment (Cortes et al, 2004).
Recent studies highlighted that some patients with sustained CMR are able to maintain this molecular condition after the discontinuation of imatinib. In a nonrandomized prospective study, among sustained CMR patients who had stopped imatinib treatment for at least 2 years, 41% maintained CMR (Mahon et al, 2010). These studies demonstrated that some CML patients have long-lasting CMR after the discontinuation of imatinib, although CML cells detected by DNA PCR persisted even with CMR (Ross et al, 2010). We recently demonstrated an increasing number of natural killer (NK) cells in sustained CMR patients after the discontinuation of imatinib (Ohyashiki et al, 2012), suggesting that immunological surveillance could be important for maintaining CMR. However, we treated one CML patient in CMR showing an increasing percentage of NK cells, but the patient relapsed 3 months after discontinuation of imatinib. This experience caused us to consider what factors underlie the sustained CMR status.
Ng et al (2012) demonstrated that CML patients with a common intronic deletion polymorphism in the gene encoding BCL2-like 11 protein (BCL2L11, also called BIM), lacking the pro-apoptotic BCL2-homology domain 3 (BH3), show an inferior response to TKIs when compared to those without the polymorphism. It is well known that imatinib activates several pro-apoptotic BH3-only proteins by a post-transcriptional mechanism, and therefore BCL2L11 plays a major role in imatinib-induced apoptosis of the BCR-ABL1 CML cells (Kuroda et al, 2006). Thus, it remains unclear how the BCL2L11 deletion polymorphism affects imatinib therapy in patients who have achieved CMR.
The aim of this study was to identify CML patients in CMR who would be possible candidates for the safe discontinuation of imatinib.
We studied 50 CML patients referred to the Tokyo Medical University hospital who had achieved CMR. They consisted of five patients who maintained CMR for >12 months after the discontinuation of imatinib, eight patients who maintained CMR for <12 months after the discontinuation of imatinib, 20 patients who maintained CMR for 24 consecutive months while taking TKIs, and 17 patients treated with TKIs who showed fluctuating CMR over the course of the 24-month study. This study was approved by the institutional review board of Tokyo Medical University (no. 1655: approved on January 28, 2011).
All five patients who maintained CMR for >12 months after stopping imatinib showed only the 4226-bp band, whereas three of the eight patients who had discontinued imatinib for <12 months had the BCL2L11 deletion polymorphism (Fig 1, Table 1). Notably, the three patients with the BCL2L11 deletion polymorphism (unique patient number [UPN] 22, UPN 47, and UPN 49) relapsed at 3–4 months after the discontinuation of imatinib, whereas the remaining five patients in this group maintained CMR (median follow-up period after stopping imatinib was 7 months) (Table 1). In the three relapsed patients with the BCL2L11 deletion polymorphism, BCR-ABL1 transcript had completely disappeared for >24 months before the discontinuation of imatinib. Among the 20 patients showing sustained CMR for >24 months while still taking TKIs, one patient (UPN 67) had the BCL2L11 deletion polymorphism. In the group of 17 patients with fluctuating CMR under TKI therapy, one patient (UPN 29, taking nilotinib) had the BCL2L11 deletion polymorphism.
|BCL2L11 deletion status||Clinical status|
|Patient groups||Cases examined (n)||Cases without BCL2L11 deletion polymorphism (n)||Cases with BCL2L11 deletion polymorphism (n)||Molecular relapse within 6 months||Sustained CMR without imatinib|
|Maintained CMR after discontinuation of imatinib for >12 months||5||5||0||0||5 (1)|
|Maintained CMR after discontinuation of imatinib for <12 months||8||5||3||3||5 (1)|
|Sustained CMR for >24 months under TKIs therapy||20||19||1||NA||NA|
|Fluctuating CMR for >24 months under TKIs therapy||17||16||1||NA||NA|
|Total number of patients||50||45||5||3|
Three patients with the BCL2L11 deletion polymorphism who discontinued imatinib relapsed within 3–4 months, suggesting that the BCL2L11 deletion polymorphism is strongly linked to molecular relapse after discontinuation of imatinib. In the current study, we identified five CML patients with the BCL2L11 deletion polymorphism, and the incidence was 10·0% (5/50) in this population. We could not estimate the incidence of the deletion polymorphism in an eastern Asian CML population, because CML cells with the deletion may be more resistant to TKI therapy (Ng et al, 2012). It is possible that CML patients who do not achieve a major molecular response or CMR may show a much higher incidence of the BCL2L11 deletion polymorphism. Ng et al (2012) reported a higher incidence of the BCL2L11 deletion polymorphism in an eastern Asian population compared with that of Caucasians. However, molecular relapse after the discontinuation of imatinib is evident even in Caucasian CML patients, and the resistance rate to first-line imatinib does not seem to be high in the Japanese CML population, indicating that some factors other than the BCL2L11 deletion polymorphism are responsible for the resistance to TKI therapy in CML patients. Our findings suggest that CML patients with the BCL2L11 deletion polymorphism can achieve CMR under TKI treatment (including imatinib), but they may not be able to discontinue TKI therapy. In other words, CML patients with the BCL2L11 deletion polymorphism may be TKI-dependent, even though they achieve long-lasting CMR. Although this study did not reveal a difference in the incidence of BCL2L11 deletion polymorphism between the sustained and fluctuating CMR groups under TKI therapy (1/20 vs. 1/17), a large-scale study of CML populations of various ethnicities may reveal the exact effect of the deletion on achieving sustained CMR under TKI therapy.
One possible factor underlying the maintenance of CMR after the discontinuation of imatinib is immunological surveillance, including cytotoxic T cells and/or NK cells. Although it remains unclear whether the BCL2L11 deletion is the only risk factor for relapse after stopping imatinib, BCL2L11 status might serve as an additive marker when deciding whether to discontinue TKI treatment in sustained CMR patients. Moreover, the role of immunological surveillance in CML patients, especially those with the BCL2L11 deletion polymorphism, should be further researched.
Conflict of interest
The authors declare no conflict of interest.
This study was supported by the Private University Strategic Research Based Support Project: Epigenetic Research Project Aimed at General Cancer Cure Using Epigenetic Targets from MEXT (Ministry of Education, Culture, Sports, Science and Technology), Tokyo, Japan. Thanks are due to Drs. T Tauchi, Y Kimura, A Gotoh, K Ando, S Okabe, Y Tanaka, and T Kitahara, Tokyo Medical University, for their participation in this study.
SK and KO wrote the manuscript; TU performed the experiments; JHO analyzed the data and designed the study; KO supervised the study.
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