Presented in abstract form at the 50th Annual Meeting of the American Society of Hematology, San Francisco, California, December 6-9, 2008.
N.V. designed the study, wrote the article, and analyzed the data; J.C. designed the study, reviewed the article, analyzed the data, and treated the patients; R.C. treated the patients and reviewed the article; H.M.K. treated the patients and reviewed the article; D.J. performed research and reviewed the article; G.R. performed research and reviewed the article; S.G. treated the patients and reviewed the article; G.B. treated the patients and reviewed the article; and M.D.L. treated the patients and reviewed the article.
Resistance to tyrosine kinase inhibitor (TKIs) therapy is associated with the development of kinase domain mutations. Although many imatinib-resistant mutations respond well to second-generation TKIs, the threonine-to-isoleucine mutation at codon 315 of the breakpoint cluster region/v-abl Abelson murine leukemia viral oncogene protein fusion Bcr-Abl (T315I) is insensitive to all currently available TKIs. The outcome in such patients after stem cell transplantation (SCT) is unknown.
Eight patients with TKI-resistant CML who had T315I mutations underwent 9 transplantations. At the time of SCT, 2 patients were in chronic phase, 3 patients were in accelerated phase; and 3 patients were in second chronic phase.
The best responses after SCT were a complete molecular response (CMR) in 3 patients, a complete cytogenetic response (CCyR) in 4 patients, and a complete hematologic response (CHR) in 1 patient, and 1 patient had no response. The best outcome was for patients who underwent transplantation in chronic phase, and both of those patients remained alive and in complete molecular remission 14 months and 42 months after SCT. After a median follow-up of 13 months from SCT, 5 patients remained alive, including 3 patients in CMR, 1 patient in CCyR, and 1 patient in CHR.
The treatment of chronic myeloid leukemia (CML) is based on tyrosine kinase inhibitors (TKI). Approximately 50% of patients with CML who develop resistance to imatinib therapy have mutations in the v-abl Abelson murine leukemia viral oncogene (ABL) kinase domain. Second-generation TKIs are active in vitro and are clinically effective against most breakpoint cluster region-ABL (BCR-ABL) mutants, with the exception of a threonine-to-isoleucine mutation at codon 315 of the Bcr-Abl protein fusion (T315I).
T315I represents a substitution of the amino acid isoleucine for threonine in the Bcr-Abl kinase domain and is insensitive to all currently available TKIs (imatinib, dasatinib, nilotinib) in vitro and clinically.1-3 T315I, also known as the gatekeeper of the kinase domain, reportedly represents 4% to 20% of all mutations associated with TKI resistance.4, 5 The outcome of patients with T315I depends on the disease stage at the time it is discovered.6, 7 Although the outcome of patients with the T315I mutation may not be immediately fatal, particularly among those in chronic phase (CP), currently, there are no established treatment options for these patients.
Stem cell transplantation (SCT) frequently is recommended as the treatment of choice for patients with T315I. However, to our knowledge, there are no available data on the outcome of patients with T315I who underwent SCT. In this report, we present the outcome of patients who had CML with the T315I mutation and underwent SCT.
MATERIALS AND METHODS
The records from all patients with CML who received treatment with TKIs at The University of Texas M. D. Anderson Cancer Center were reviewed to identify those who had developed the T315I mutation and subsequently underwent SCT. Patients were classified in CP, accelerated phase (AP), or blast phase (BP) according to standard criteria.8 BP was categorized as lymphoid or myeloid by immunohistochemistry and flow cytometry. Criteria for response and treatment failure were defined according to recommendations of the European LeukemiaNet.8
Reverse transcripase-quantitative polymerase chain reaction (PCR) analysis was used to follow Bcr-Abl transcripts from total RNA isolated from peripheral blood in a single tube assay detecting the b2a2, b3a2, and e1a2 forms and normalized to total abl transcripts as described previously.9 Mutational analysis was performed using nested PCR-based Sanger sequencing of the entire BCR-ABL kinase domain (codons 221-500) with a sensitivity of 10% to 20% mutation-bearing BCR-ABL transcripts. Quantification of the T315I mutation was performed by pyrosequencing with a similar nested PCR approach (HSQ96 Pyrosequencer; Biotage, Uppsala, Sweden) with a sensitivity of 1% to 5% mutation-bearing BCR-ABL transcripts.5
Engraftment was defined as the first of 3 consecutive days with an absolute neutrophil count >0.5 × 109/L. Chimerism studies were evaluated on Day 30, Day 100, and every 3 months thereafter. Mixed chimerism was defined as the presence of any detectable (≥1%) recipient DNA. Infection prophylaxis during the peritransplantation period was given to all patients. After recovery of the neutrophil count to >1.0 × 109/L, patients were eligible to receive prophylaxis against Pneumocystis carinii infection using trimethoprim-sulfamethoxazole given orally twice weekly or pentamidine given intravenously every 3 weeks. Toxicity was established according to National Cancer Institute Common Terminology Criteria. Graft-versus-host disease (GVHD) was graded according to established criteria.10 Failure was defined as death from any cause, recurrence of T315I, loss of molecular response, loss of cytogenetic response, or loss of hematologic response. All patients were treated in institutional review board-approved protocols and/or registered in an institutional review board-approved retrospective chart review protocol.
Between September 2004 and January 2008, 8 patients with T315I mutation underwent 9 SCTs (7 from matched unrelated donor [MUD] and 2 from cord blood). The median age at the time of SCT was 46 years (range, 26-64 years). All patients had received imatinib (4 as initial therapy and 4 after interferon failure) and had become resistant. After imatinib failure, 5 patients received dasatinib, and 1 patient received nilotinib. All but 1 patient failed to respond to a second-generation TKI after T315I had been detected (Table 1). One patient in AP (Patient 7) had no T315I when nilotinib was started but developed the mutation 2 months after the start of therapy. At the time, she had achieved a complete cytogenetic response (CCyR) that was sustained for 18 months. She eventually lost her CCyR but maintained a partial cytogenetic response (PCyR) for 8 months and had a PCyR (10% Philadelphia chromosome-positive metaphases) when she underwent SCT.
Table 1. Patient and Transplantation Characteristics
Age at SCT, y
Stage at Start of Imatinib
Months on Imatinib
Failing TKI at Detection of T315I
Stage at Detection of T315I
Second TKI After Detection of T315I
Other Additional Treatment Before SCT
T315I to SCT, mo
Dx to SCT, mo
Stage at SCT
Response at SCT
UPIN indicates unique patient identifier; SCT, stem cell transplantation; TKI, tyrosine kinase inhibitor; T315I, threonine-to-isoleucine mutation at codon 315 of the breakpoint cluster region (Bcr)/v-abl Abelson murine leukemia viral oncogene (Abl) protein fusion Bcr-Abl; Dx, diagnosis; CP, chronic phase; IM, imatinib; AP, accelerated phase; DAS, dasatinib; MK, MK-0457, a novel kinase inhibitor; Flu, fludarabine; Ara-C, cytosine arabinoside; Bu, busulfan; CB, cord blood; BP, blast phase; HCVAD, hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone; MMR, major molecular response; PCyR, partial cytogenetic response; MUD, matched, unrelated donor; Hy, hydroxyurea; IA, idarubicin plus cytarabine; mCyR, minor cytogenetic response; NA, not applicable; CMR, complete molecular response; LyBP, lymphoid blast phase; NIL, nilotinib; IL-2, interleukin-2.
This patient underwent SCT at another institution.
Patient 5 underwent a second transplantation after a recurrence developed; thus, 5A represents the first transplantation, and 5B represents the second transplantation for this patient.
The median time from CML diagnosis to SCT was 57 months (range, 9-160 months), and the median time from fist detection of T315I to SCT was 7 months (range, 2-29 months). At the time of SCT, 2 patients in CP (Patients 3 and 7) had a PCyR; 3 patients in AP, all without a complete hematologic response (CHR); and there were 3 patients in second or greater CP from lymphoid BP, including 1 patient who underwent 2 transplantations (both times in second CP), of whom 1 patient who had a minor cytogenetic response (Patient 5a; first MUD), 2 patients who had a major molecular response (Patients 2 and 6), and 1 patient had a complete molecular response (CMR) (Patient 5b; second MUD for extramedullary recurrence) (Table 1).
Conditioning regimens were myeloablative in 2 patients, 4 patients received reduced-intensity conditioning, and 1 patient underwent first transplantation with an ablative regimen followed by a second transplantation with a reduced-intensity regimen. Regimen details were unknown for 1 patient (SCT was performed elsewhere) (Table 2). The stem cell source was bone marrow in 4 patients, peripheral blood in 1 patient, cord blood in 2 patients, and unknown in 2 patients. Unrelated donors were used in all transplantations. GVHD prophylaxis was tacrolimus-based in 6 transplantations and unknown in 3 transplantations. The median time to engraftment was 12 days (range, 10-14 days). The best responses after SCT were CMR in 3 patients (2 in CP, 1 in second CP), CCyR in 4 patients (2 in AP, 2 in second CP), and CHR in 1 patient (in AP). One patient did not achieve any response (second CP). The median time from SCT to last follow-up was 13 months (range, 5-42 months). (Table 2)
Five patients remained alive a median of 20 months after SCT (range, 10-42 months). Two patients who underwent transplantation in CP remained alive 14 months and 42 months after SCT, both in CMR. One patient in BP (Patient 5) has a CMR that has been sustained for 10 months after a second SCT (this patient developed a recurrence 5 months after the first SCT). One patient who underwent transplantation in AP (Patient 1) has a sustained CCyR 26 months after SCT with persistent T315I (representing 94% of transcripts). And another patient who underwent transplantation in AP (Patient 8) had a CHR and persistent T315I 39 months after the SCT and currently is receiving treatment with omacetaxine (homoharringtonine).
None of the 2 patients in CP has failed; both patients are alive and in CMR 14 months and 42 months after SCT. The median failure-free survival after SCT was 6 months for patients who underwent transplantation in AP and 4 months for patients who underwent transplantation in BP (Fig. 1, top). T315I recurrence was the reason for failure in 3 patients. However, only 1 of the patients (Patient 6) who underwent transplantation in second CP had disease progression to AP and died. Two patients (Patients 1 and 8) are alive and have maintained their responses (CCyR and CHR) 41 months and 45 months after the detection of T315I.
Only 1 patient was weaned off immunosuppressors after loosing chimerism (Patient 8). Two patients had grade 3 acute GVHD, and all responded to therapy. The median overall survival after SCT has not been reached. Three patients died, all with recurrent disease, including 1 patient in AP (Patient 4) who died 10 months after SCT and 2 patients in second CP (Patients 2 and 6) who died 8 months and 5 months after SCT, respectively. No transplantation-related deaths were reported (Fig. 1, bottom).
Despite the excellent results achieved with imatinib as initial therapy for patients with CML and with second-generation TKIs after imatinib failure, some patients do not achieve an optimal response, and others eventually lose their response. The most common mechanism of resistance identified in patients after failure to therapy with TKI is the development of ABL kinase domain mutations. There are over 90 different mutants reported in the literature, and most of these are inhibited both in vitro and in vivo by currently available TKIs.4 The 1 exception is T315I, which is insensitive both in vitro and in vivo to the available inhibitors. The reported incidence of T315I after imatinib failure ranges from 4% to 20%, and it has been suggested that the incidence may increase after second-generation TKI therapy, with reported incidences up to 30%.5, 11-13 T315I also seems to be observed more frequently with disease transformation.13, 14 Recent reports from studies with nilotinib and dasatinib have demonstrated the anticipated clinical inefficacy of these agents in patients who develop this mutation.15, 16 There is variability in the reported long-term outcome of patients with T315I. It is clear that the expected survival depends greatly on the disease stage at the time T315I is identified. In 1 series, Nicolini et al reported a median survival of 42.5 months from start of imatinib for patients in CP, and a recent multicenter series reported a median survival of 22 months for such patients.7, 17 In contrast, the median survival was not reached in the series reported by Jabbour et al, who reported a 2-year survival rate of 87%, similar to that of other patients who had similar criteria for imatinib failure, regardless of mutations status.6 Still, patients with T315I are considered to have a poor long-term outcome in view of the lack of available effective treatment options.
Several agents are being investigated that have promising in vitro clinical activity against T315I; and, for some of those agents, early clinical results suggest that some patients may respond.18-23 With omacetaxine, early reports suggest a CHR rate of 85% and a cytogenetic response rate of 28%.23 The novel kinase inhibitor MK-0457 induced anecdotal responses, but its development was halted for safety reasons.24 Some responses have been reported in early results of trials with the Aurora kinase inhibitors XL-228 (cytogenetic responses in 3 of 9 patients with T315I who were treated)22 and PHA-739358 (cytogenetic responses in 2 of 6 patients with T315I).25 AP24534 and DCC2036 are promising agents with strong preclinical activity in vitro, and phase 1 studies have been initiated.20, 26 Still, it is widely perceived that SCT would be the preferred therapy for patients who would be eligible for this treatment option. In fact, despite the availability of the investigational options mentioned above, at our institution, SCT is offered to all patients who develop T315I, although transplantation may or may not happen immediately, depending on availability of donors, patient's preference, and other factors. To our knowledge, despite the limited numbers presented in this report, this represents the first series of patients with the T315I mutation who underwent SCT.
The role of SCT has evolved over the last few years as the treatment of CML has improved with the emergence of TKIs. Today, few patients are considered for SCT as initial therapy in CP, although SCT remains an important consideration after imatinib failure. It has been demonstrated that prior therapy with imatinib not only does not adversely affect the outcome of patients who undergo allogeneic SCT, but it actually may improve survival after transplantation for those who undergo transplantation in first CP.27 Similarly, it has been reported that previous exposure to a second-generation TKI did not increase transplantation-related toxicity or the risk thereof.28
Although the published experience is limited, it has been demonstrated that SCT is effective in the setting of ABL kinase domain mutations. In a series of 10 patients with various mutations (2 patients with T315I, who were included in the current report; 5 patients with P-loop mutationsl and 3 patients with other mutations), 7 patients achieved a CMR, and 2 patients achieved a major molecular response (1 patient did not respond to the transplantation).29 Seven patients were alive at the time of the report, including 6 patients in CMR at a median follow-up of 19 months. That the presence of TKI mutations would have little if any impact on the outcome of transplantation may not be unexpected, because neither the agents used for conditioning nor the immune mechanisms involved in graft-versus-leukemia effect are specific to the sequence of Bcr-Abl; therefore, they would not be affected by the configuration changes that result from mutations in the way these may affect the binding or effect of TKI. However, different mutants may affect the transformation potency of BCR-ABL. It has been reported, for example, that the tyrosine-to-phenylalanine mutation at codon 253 (Y253F) and the glutamic acid-to-lysine mutation at codon 255 (E255K) have increased transformation potency.30 T315I has significantly inferior kinase activity, whereas its transformation potency, although variable in different assays, is grossly equivalent to that of unmutated Bcr-Abl.30
The results presented here suggest that SCT indeed represents an effective treatment strategy for patients with this condition. Although many patients developed recurrent disease, both patients who were treated in CP and 1 additional patient who was treated in second CP have sustained complete molecular responses that have lasted for 14 months, 42 months, and 10 months, respectively. The finding that the patients who underwent transplantation in earlier stages had more durable responses is a known phenomenon and emphasizes the need to consider this treatment option as soon as this mutation is identified. In more advanced stages, despite frequent recurrences, some patients may have transient responses, and recurrences may be only molecular, which means that SCT still is an important option to consider. It might be possible to integrate new drugs as they are developed into the SCT strategy, either as part of the conditioning or after transplantation to minimize the risk of recurrence. It is noteworthy that, in this report, all patients had unrelated donor or underwent cord blood transplantation. It would be expected that results from sibling donors would be at least equivalent if not better. A patient with this condition who has a matched sibling should be considered for SCT.
In conclusion, SCT may induce long-term remissions in patients with CML who have developed the T315I mutation after therapy with TKI. The outcome depends greatly on the disease stage at the time of transplantation. Thus, patients with CML (ideally in CP) who develop T315I should be considered for SCT as soon as this abnormality is discovered if they are eligible for this procedure.
CONFLICT OF INTEREST DISCLOSURES
J.C. and H.M.K. receive research support from Novartis and Bristol-Myers Squibb.