RESUMO
Rejection of solid organ transplant and graft versus host disease (GvHD) continue to be challenging in post transplantation management. The introduction of calcineurin inhibitors dramatically improved recipients' short-term prognosis. However, long-term clinical outlook remains poor, moreover, the lifelong dependency on these toxic drugs leads to chronic deterioration of graft function, in particular the renal function, infections and de-novo malignancies. These observations led investigators to identify alternative therapeutic options to promote long-term graft survival, which could be used concomitantly, but preferably, replace pharmacologic immunosuppression as standard of care. Adoptive T cell (ATC) therapy has evolved as one of the most promising approaches in regenerative medicine in the recent years. A range of cell types with disparate immunoregulatory and regenerative properties are actively being investigated as potential therapeutic agents for specific transplant rejection, autoimmunity or injury-related indications. A significant body of data from preclinical models pointed to efficacy of cellular therapies. Significantly, early clinical trial observations have confirmed safety and tolerability, and yielded promising data in support of efficacy of the cellular therapeutics. The first class of these therapeutic agents commonly referred to as advanced therapy medicinal products have been approved and are now available for clinical use. Specifically, clinical trials have supported the utility of CD4+CD25+FOXP3+ regulatory T cells (Tregs) to minimize unwanted or overshooting immune responses and reduce the level of pharmacological immunosuppression in transplant recipients. Tregs are recognized as the principal orchestrators of maintaining peripheral tolerance, thereby blocking excessive immune responses and prevent autoimmunity. Here, we summarize rationale for the adoptive Treg therapy, challenges in manufacturing and clinical experiences with this novel living drug and outline future perspectives of its use in transplantation.
RESUMO
Cancer development is an evolutionary genomic process with parallels to Darwinian selection. It requires acquisition of multiple somatic mutations that collectively cause a malignant phenotype and continuous clonal evolution is often linked to tumor progression. Here, we show the clonal evolution structure in 15 myelofibrosis (MF) patients while receiving treatment with JAK inhibitors (mean follow-up 3.9 years). Whole-exome sequencing at multiple time points reveal acquisition of somatic mutations and copy number aberrations over time. While JAK inhibition therapy does not seem to create a clear evolutionary bottleneck, we observe a more complex clonal architecture over time, and appearance of unrelated clones. Disease progression associates with increased genetic heterogeneity and gain of RAS/RTK pathway mutations. Clonal diversity results in clone-specific expansion within different myeloid cell lineages. Single-cell genotyping of circulating CD34 + progenitor cells allows the reconstruction of MF phylogeny demonstrating loss of heterozygosity and parallel evolution as recurrent events.
Assuntos
Evolução Clonal , Mielofibrose Primária/genética , Idoso , Exoma , Feminino , Seguimentos , Heterogeneidade Genética , Humanos , Masculino , Pessoa de Meia-Idade , Mutação , Proteína Oncogênica p21(ras)/genética , Estudos Prospectivos , Análise de Célula Única , Células-Tronco/citologiaAssuntos
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Proteínas de Fusão bcr-abl/genética , Transplante de Células-Tronco Hematopoéticas , Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , RNA Mensageiro/genética , Proteínas de Ligação a RNA/genética , Idoso , Dasatinibe/uso terapêutico , Progressão da Doença , Feminino , Proteínas de Fusão bcr-abl/metabolismo , Expressão Gênica , Humanos , Mesilato de Imatinib/uso terapêutico , Interferons/uso terapêutico , Leucemia Mielogênica Crônica BCR-ABL Positiva/diagnóstico , Leucemia Mielogênica Crônica BCR-ABL Positiva/mortalidade , Leucemia Mielogênica Crônica BCR-ABL Positiva/terapia , Estudos Longitudinais , Masculino , Pessoa de Meia-Idade , Mutação , Pirimidinas/uso terapêutico , RNA Mensageiro/metabolismo , Proteínas de Ligação a RNA/metabolismo , Estudos Retrospectivos , Análise de SobrevidaRESUMO
Inherited gene variants play an important role in malignant diseases. The transcriptional repressor growth factor independence 1 (GFI1) regulates hematopoietic stem cell (HSC) self-renewal and differentiation. A single-nucleotide polymorphism of GFI1 (rs34631763) generates a protein with an asparagine (N) instead of a serine (S) at position 36 (GFI1(36N)) and has a prevalence of 3%-5% among Caucasians. Because GFI1 regulates myeloid development, we examined the role of GFI1(36N) on the course of MDS disease. To this end, we determined allele frequencies of GFI1(36N) in four independent MDS cohorts from the Netherlands and Belgium, Germany, the ICGC consortium, and the United States. The GFI1(36N) allele frequency in the 723 MDS patients genotyped ranged between 9% and 12%. GFI1(36N) was an independent adverse prognostic factor for overall survival, acute myeloid leukemia-free survival, and event-free survival in a univariate analysis. After adjustment for age, bone marrow blast percentage, IPSS score, mutational status, and cytogenetic findings, GFI1(36N) remained an independent adverse prognostic marker. GFI1(36S) homozygous patients exhibited a sustained response to treatment with hypomethylating agents, whereas GFI1(36N) patients had a poor sustained response to this therapy. Because allele status of GFI1(36N) is readily determined using basic molecular techniques, we propose inclusion of GFI1(36N) status in future prospective studies for MDS patients to better predict prognosis and guide therapeutic decisions.
Assuntos
Alelos , Proteínas de Ligação a DNA/genética , Síndromes Mielodisplásicas/genética , Síndromes Mielodisplásicas/mortalidade , Polimorfismo de Nucleotídeo Único , Fatores de Transcrição/genética , Adulto , Idoso , Substituição de Aminoácidos , Biomarcadores , Medula Óssea/patologia , Estudos de Coortes , Análise Citogenética , Feminino , Frequência do Gene , Genótipo , Humanos , Masculino , Pessoa de Meia-Idade , Síndromes Mielodisplásicas/diagnóstico , Síndromes Mielodisplásicas/tratamento farmacológico , Pancitopenia , Fenótipo , Prognóstico , Análise de SobrevidaRESUMO
A better understanding of events triggering chronic myeloid leukemia progression is critical for optimized clinical management of chronic myeloid leukemia (CML). We sought to validate that increased expression of Musashi 2 (MSI2), a post-transcription regulator, is associated with progression and prognosis. Screening of 152 patients with CML showed that MSI2 was significantly decreased among patients with CML in chronic phase (CP) at diagnosis (p < 0.0001), but found no significant difference between the normal control group and treated patients with CML in CP. Moreover MSI2 was significantly increased (p < 0.0001) in patients with advance disease (AD) CML. Furthermore, our human hematopoietic cell line data imply that MSI2 and BCR-ABL1 mRNA expression are correlated. However, these data cast a doubt on earlier reports that MSI2 effects HES1 expression via NUMB-NOTCH signaling.
Assuntos
Regulação Leucêmica da Expressão Gênica , Células-Tronco Hematopoéticas/metabolismo , Leucemia Mieloide de Fase Crônica/metabolismo , Leucemia Mieloide de Fase Crônica/patologia , Proteínas de Ligação a RNA/metabolismo , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Criança , Progressão da Doença , Feminino , Seguimentos , Proteínas de Fusão bcr-abl/genética , Células-Tronco Hematopoéticas/patologia , Humanos , Técnicas Imunoenzimáticas , Leucemia Mieloide de Fase Crônica/genética , Leucemia Mieloide de Fase Crônica/mortalidade , Masculino , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Prognóstico , RNA Mensageiro/genética , Proteínas de Ligação a RNA/genética , Reação em Cadeia da Polimerase em Tempo Real , Estudos Retrospectivos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de Sinais , Taxa de Sobrevida , Regulação para Cima , Adulto JovemRESUMO
Janus kinases are critical components of signaling pathways that regulate hematopoiesis. Mutations of the non-receptor tyrosine kinase JAK2 are found in many BCR-ABL-negative myeloproliferative neoplasms. Preclinical results support that JAK2 inhibitors could show efficacy in treating chronic myeloproliferative neoplasms. JAK2 has also been postulated to play a role in BCR-ABL signal transduction. Therefore, inhibitors of JAK2 kinases are turning into therapeutic strategies for treatment of chronic myelogenous leukemia (CML). In this study, the effects of two novel JAK2 inhibitors, NVP-BSK805 and NVP-BVB808, have been investigated in cell lines expressing either BCR-ABL or mutant JAK2. Possible synergies between NVP-BSK805/NVP-BVB808 and the kinase inhibitors imatinib and nilotinib were assessed. Proliferation and apoptosis tests with both substances showed response in the following cell lines: CHRF-288-11, SET-2 and UKE-1. All BCR-ABL-positive cell lines showed some reduction in proliferation, but with half-maximal growth-inhibitory values >1 µM. Combination of the JAK2 inhibitors with imatinib and nilotinib showed no significant additive or synergistic effects, although all BCR-ABL-positive cell lines responded well to both CML therapeutic agents. Interestingly, it seemed that the combination of imatinib with NVP-BSK805 had a protective effect on the cells. Combination treatment with nilotinib did not show this effect.
Assuntos
Proteínas de Fusão bcr-abl/genética , Janus Quinase 2/antagonistas & inibidores , Janus Quinase 2/genética , Mutação , Inibidores de Proteínas Quinases/farmacologia , Quinoxalinas/farmacologia , Apoptose/efeitos dos fármacos , Benzamidas/administração & dosagem , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Proteínas de Fusão bcr-abl/metabolismo , Humanos , Mesilato de Imatinib , Células K562 , Leucemia Mielogênica Crônica BCR-ABL Positiva/tratamento farmacológico , Leucemia Mielogênica Crônica BCR-ABL Positiva/enzimologia , Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , Transtornos Mieloproliferativos/tratamento farmacológico , Transtornos Mieloproliferativos/enzimologia , Transtornos Mieloproliferativos/genética , Fosforilação/efeitos dos fármacos , Piperazinas/administração & dosagem , Inibidores de Proteínas Quinases/administração & dosagem , Pirimidinas/administração & dosagem , Quinoxalinas/administração & dosagem , Fator de Transcrição STAT5/metabolismo , Proteínas Supressoras de Tumor/metabolismoRESUMO
Assessing the clinical significance of JAK2 V617F mutant allele burden is complicated by a myriad of techniques reported to detect and quantify the mutation. As a consequence, the level of sensitivity and how the data is reported vary. Harmonization of well-defined molecular studies would permit evaluation of the clinical significance of measuring allele burden and rapid determination of the efficacy of novel agents for the treatment of chronic myeloproliferative neoplasia via multicenter clinical trials, at the subclinical level. Here we report a comparison between the widely available TaqMan quantitative real time polymerase chain reaction (Q-PCR) and competitive PCR (C-PCR) assays. We found that the tumor load was invariably greater when measured by C-PCR compared to that recorded by Q-PCR. Furthermore, none of the samples converted from undetectable to detectable when the enriched granulocyte (GR) fraction was tested. While a difference in the V617F allele levels was detected between GR fraction and whole blood, this was not statistically significant.
Assuntos
Alelos , Janus Quinase 2/genética , Mutação , Transtornos Mieloproliferativos/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Granulócitos/metabolismo , Heterozigoto , Homozigoto , Humanos , Leucócitos Mononucleares/metabolismo , Masculino , Pessoa de Meia-Idade , Transtornos Mieloproliferativos/diagnóstico , Reação em Cadeia da Polimerase , Reação em Cadeia da Polimerase em Tempo Real , Adulto JovemRESUMO
PURPOSE: Imatinib induces a durable response in most patients with Philadelphia chromosome-positive chronic myeloid leukemia, but it is currently unclear whether imatinib reduces the leukemic stem cell (LSC) burden, which may be an important step toward enabling safe discontinuation of therapy. In this article, we use mathematical models of BCR-ABL levels to make inferences on the dynamics of LSCs. EXPERIMENTAL DESIGN: Patients with at least 1 BCR-ABL transcript measurement on imatinib were included (N = 477). Maximum likelihood methods were used to test 3 potential hypotheses of the dynamics of BCR-ABL transcripts on imatinib therapy: (i) monoexponential, in which there is little, if any, decline in BCR-ABL transcripts; (ii) biexponential, in which patients have a rapid initial decrease in BCR-ABL transcripts followed by a more gradual response; and (iii) triexponential, in which patients first exhibit a biphasic decline but then have a third phase when BCR-ABL transcripts increase rapidly. RESULTS: We found that most patients treated with imatinib exhibit a biphasic decrease in BCR-ABL transcript levels, with a rapid decrease during the first few months of treatment, followed by a more gradual decrease that often continues over many years. CONCLUSIONS: We show that the only hypothesis consistent with current data on progenitor cell turnover and with the long-term, gradual decrease in the BCR-ABL levels seen in most patients is that these patients exhibit a continual, gradual reduction of the LSCs. This observation may explain the ability to discontinue imatinib therapy without relapse in some cases.
Assuntos
Proteínas de Fusão bcr-abl/genética , Leucemia Mielogênica Crônica BCR-ABL Positiva/tratamento farmacológico , Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , Células-Tronco Neoplásicas/efeitos dos fármacos , Piperazinas/farmacologia , Pirimidinas/farmacologia , Antineoplásicos/farmacologia , Benzamidas , Proteínas de Fusão bcr-abl/biossíntese , Hematopoese/efeitos dos fármacos , Humanos , Mesilato de Imatinib , Leucemia Mielogênica Crônica BCR-ABL Positiva/metabolismo , Leucemia Mielogênica Crônica BCR-ABL Positiva/patologia , Células-Tronco Neoplásicas/metabolismo , Células-Tronco Neoplásicas/patologia , Inibidores de Proteínas Quinases/farmacologia , Proteínas Tirosina Quinases/antagonistas & inibidores , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , Reação em Cadeia da Polimerase em Tempo RealAssuntos
Mobilização de Células-Tronco Hematopoéticas/métodos , Leucemia Mielogênica Crônica BCR-ABL Positiva/terapia , Piperazinas/uso terapêutico , Pirimidinas/uso terapêutico , Adulto , Idoso , Antineoplásicos/uso terapêutico , Benzamidas , Intervalo Livre de Doença , Feminino , Seguimentos , Mobilização de Células-Tronco Hematopoéticas/efeitos adversos , Humanos , Mesilato de Imatinib , Leucemia Mielogênica Crônica BCR-ABL Positiva/mortalidade , Masculino , Pessoa de Meia-Idade , Piperazinas/efeitos adversos , Pirimidinas/efeitos adversos , Análise de Sobrevida , Fatores de Tempo , Adulto JovemRESUMO
This study examines the prognostic significance of early molecular response using an expanded dataset in chronic myeloid leukemia patients enrolled in the International Randomized Study of Interferon and STI571 (IRIS). Serial molecular studies demonstrate decreases in BCR-ABL transcripts over time. Analyses of event-free survival (EFS) and time to progression to accelerated phase/blast crisis (AP/BC) at 7 years were based on molecular responses using the international scale (IS) at 6-, 12-, and 18-month landmarks. Patients with BCR-ABL transcripts > 10% at 6 months and > 1% at 12 months had inferior EFS and higher rate of progression to AP/BC compared with all other molecular response groups. Conversely, patients who achieved major molecular response [MMR: BCR-ABL (IS) ≤ 0.1%] by 18 months enjoyed remarkably durable responses, with no progression to AP/BC and 95% EFS at 7 years. The probability of loss of complete cytogenetic response by 7 years was only 3% for patients in MMR at 18 months versus 26% for patients with complete cytogenetic response but not MMR (P < .001). This study shows a strong association between the degree to which BCR-ABL transcript numbers are reduced by therapy and long-term clinical outcome, supporting the use of time-dependent molecular measures to determine optimal response to therapy. This study is registered at www.clinicaltrials.gov as NCT00006343.
Assuntos
Antineoplásicos/uso terapêutico , Leucemia Mielogênica Crônica BCR-ABL Positiva/tratamento farmacológico , Piperazinas/uso terapêutico , Pirimidinas/uso terapêutico , Adolescente , Adulto , Idoso , Benzamidas , Intervalo Livre de Doença , Feminino , Genes abl , Humanos , Mesilato de Imatinib , Interferons/uso terapêutico , Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , Masculino , Pessoa de Meia-Idade , Prognóstico , Indução de Remissão , Fatores de Tempo , Resultado do Tratamento , Adulto JovemRESUMO
Resistance to therapeutic agents is a major factor in the failure of cancer treatments. In leukemia, the resistant cells remaining in the bone marrow and/or peripheral blood constitute minimal residual disease and are detectable by highly sensitive assays when the patient appears to be in complete remission. Early detection of the expansion of residual cells permits clinical intervention with the aim of reversing the proliferation of resistant leukemic cells. Therefore, accurate and precise measurement of minimal residual disease can greatly enhance optimization of oncology patients' clinical management. This notion is supported by a large body of data among chronic myeloid leukemia patients, but minimal residual disease detection and monitoring is increasingly applied to other types of leukemia, and is starting to be a factor in decision-making for some therapeutic trials in childhood acute lymphoblastic leukemia. Here, from the solid ground of minimal residual disease detection in chronic myeloid leukemia, the current state of the art and development of molecular techniques in other leukemias and the growing field of multiparameter flow cytometry are reviewed in two separate parts reporting on the respective advances, advantages and pitfalls of these emerging methods.
Assuntos
Leucemia/diagnóstico , Neoplasia Residual/diagnóstico , Citometria de Fluxo/métodos , Citometria de Fluxo/normas , Humanos , Imunofenotipagem , Leucemia/genética , Leucemia/imunologia , Neoplasia Residual/imunologia , Padrões de Referência , Reprodutibilidade dos Testes , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Reação em Cadeia da Polimerase Via Transcriptase Reversa/normas , Sensibilidade e EspecificidadeRESUMO
The majority of patients with chronic myeloid leukemia in chronic phase gain substantial benefit from imatinib but some fail to respond or lose their initial response. In 2006, the European LeukemiaNet published recommendations designed to help identify patients responding poorly to imatinib. Patients were evaluated at 3, 6, 12, and 18 months and some were classified as "failure" or "suboptimal responders." We analyzed outcomes for 224 patients with chronic myeloid leukemia in chronic phase treated in a single institution to validate these recommendations. Patients were followed for a median of 46.1 months. At each time point, patients classified as "failure" showed significantly worse survival, progression-free survival, and cytogenetic response than other patients; for example, based on the assessment at 12 months, the 5-year survival was 87.1% versus 95.1% (P = .02), progression-free survival 76.% versus 90% (P = .002), and complete cytogenetic response rate 26.7% versus 94.1% (P < .001). Similarly, the criteria for "suboptimal response" at 6 and 12 months identified patients destined to fare badly, although criteria at 18 months were less useful. The predictive value of some other individual criteria varied. In general, the LeukemiaNet criteria have useful predictive value, but a case could now be made for combining the categories "failure" and "suboptimal response."
Assuntos
Bases de Dados Factuais , Diretrizes para o Planejamento em Saúde , Leucemia Mielogênica Crônica BCR-ABL Positiva/diagnóstico , Leucemia Mielogênica Crônica BCR-ABL Positiva/tratamento farmacológico , Piperazinas/uso terapêutico , Pirimidinas/uso terapêutico , Adolescente , Adulto , Idoso , Algoritmos , Antineoplásicos/uso terapêutico , Benzamidas , Resistencia a Medicamentos Antineoplásicos , Europa (Continente) , Feminino , Humanos , Mesilato de Imatinib , Leucemia Mielogênica Crônica BCR-ABL Positiva/mortalidade , Leucemia Mielogênica Crônica BCR-ABL Positiva/patologia , Masculino , Pessoa de Meia-Idade , Prognóstico , Análise de Sobrevida , Falha de Tratamento , Resultado do Tratamento , Adulto JovemRESUMO
PURPOSE: Kinase domain (KD) mutations in the BCR-ABL gene are associated with resistance to imatinib in chronic myeloid leukemia (CML) but their incidence and prognostic significance in chronic phase (CP) patients without resistance are unclear. PATIENTS AND METHODS: We analyzed outcome for 319 patients with CML-CP who were treated with imatinib; 171 were in early CP (ECP) and 148 were in late CP (LCP). Patients were screened routinely for mutations using direct sequencing regardless of response status. The 5-year cumulative incidence of mutations was 6.6% for ECP and 17% for LCP patients. RESULTS: Of the 319 patients, 214 (67%) achieved complete cytogenetic responses (CCyR). The identification of a mutation without other evidence of imatinib resistance was highly predictive for loss of CCyR (RR, 3.8; P = .005) and for progression to advanced phase (RR, 2.3; P = .01), though the intervals from first identification to loss of CCyR and disease progression were relatively long (median, 21 and 16 months, respectively). Mutations in the P-loop (excluding residue 244) were associated with a higher risk of progression than mutations elsewhere. CONCLUSION: We conclude that routine mutation screening of patients who appear to be responding to imatinib may identify those at high risk of disease progression.
Assuntos
Genes abl/genética , Leucemia Mielogênica Crônica BCR-ABL Positiva/tratamento farmacológico , Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , Fosfotransferases/genética , Estrutura Terciária de Proteína/genética , Adolescente , Adulto , Idoso , Antineoplásicos/uso terapêutico , Benzamidas , Doença Crônica , Progressão da Doença , Feminino , Humanos , Mesilato de Imatinib , Masculino , Pessoa de Meia-Idade , Mutação , Piperazinas/uso terapêutico , Pirimidinas/uso terapêuticoRESUMO
PURPOSE: Imatinib is remarkably effective in treating newly diagnosed patients with chronic myeloid leukemia (CML) in chronic phase (CP). To date, most of the available data come from a single multicenter study in which some of the patients were censored for diverse reasons. Here, we report our experience in treating patients at a single institution in a setting where all events were recorded. PATIENTS AND METHODS: A total of 204 consecutive adult patients with newly diagnosed CML in CP received imatinib from June 2000 until August 2006. Response (hematologic, cytogenetic, and molecular), progression-free survival (PFS) and survival were evaluated. RESULTS: At 5 years, cumulative incidences of complete cytogenetic response (CCyR) and major molecular response (MMR) were 82.7% and 50.1%, respectively. Estimated overall survival and PFS were 83.2% and 82.7%, respectively. By 5 years, 25% of patients had discontinued imatinib treatment because of an unsatisfactory response and/or toxicity. The 5-year probability of remaining in major cytogenetic response while still receiving imatinib was 62.7%. Patients achieving a CCyR at 1 year had a better PFS and overall survival than those failing to reach CCyR, but achieving a MMR conferred no further advantage. The identification of a kinase domain mutation was the only factor predicting for loss of CCyR. CONCLUSION: Imatinib is highly effective in most patients with CML-CP; patients who respond are likely to live substantially longer than those treated with earlier therapies. Achieving CCyR correlated with PFS and overall survival, but achieving MMR had no further predictive value. However, approximately one third of patients still need better therapy.
Assuntos
Antineoplásicos/administração & dosagem , Células da Medula Óssea/patologia , Leucemia Mielogênica Crônica BCR-ABL Positiva/diagnóstico , Leucemia Mielogênica Crônica BCR-ABL Positiva/tratamento farmacológico , Piperazinas/administração & dosagem , Pirimidinas/administração & dosagem , Adolescente , Adulto , Idoso , Análise de Variância , Benzamidas , Estudos de Coortes , Intervalos de Confiança , Intervalo Livre de Doença , Relação Dose-Resposta a Droga , Esquema de Medicação , Diagnóstico Precoce , Feminino , Seguimentos , Humanos , Mesilato de Imatinib , Leucemia Mielogênica Crônica BCR-ABL Positiva/mortalidade , Masculino , Pessoa de Meia-Idade , Modelos de Riscos Proporcionais , Estudos Retrospectivos , Medição de Risco , Índice de Gravidade de Doença , Estatísticas não Paramétricas , Taxa de Sobrevida , Resultado do TratamentoRESUMO
We sought kinase domain (KD) mutations at the start of treatment with dasatinib in 46 chronic myeloid leukemia (CML) patients resistant to or intolerant of imatinib. We identified BCR-ABL mutant subclones in 12 (26%) cases and used pyrosequencing to estimate subsequent changes in their relative size after starting dasatinib. Four patients lost their mutations, which remained undetectable, 3 patients retained the original mutation or lost it only transiently, 3 lost their original mutations but acquired a new mutation (F317L), and 2 developed another mutation (T315I) in addition to the original mutation within the same subclone. This study shows that expansion of a mutant Ph-positive clone that responds initially to a second generation tyrosine kinase inhibitor may be due either to late acquisition of a second mutation in the originally mutated clone, such as the T315I, or to acquisition of a completely new mutant clone, such as F317L.