Dissection of subclonal evolution by temporal mutation profiling in chronic lymphocytic leukemia patients treated with ibrutinib.

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib is inducing durable responses in chronic lymphocytic leukemia (CLL) patients with refractory/relapsed disease or with TP53 defect, with BTK and phospholipase C gamma 2 (PLCG2) mutations representing the predominant mechanisms conferring secondary ibrutinib resistance. To understand the landscape of genomic changes and the dynamics of subclonal architecture associated with ibrutinib treatment, an ultra-deep next-generation sequencing analysis of 30 recurrently mutated genes was performed on sequential samples of 20 patients, collected before and during single-agent ibrutinib treatment. Mutations in the SF3B1, MGAand BIRC3 genes were enriched during ibrutinib treatment, while aberrations in the BTK, PLCG2, RIPK1, NFKBIE and XPO1 genes were exclusively detected in posttreatment samples. Besides the canonical mutations, four novel BTK mutations and three previously unreported PLCG2 variants were identified. BTK and PLCG2 mutations were backtracked in five patients using digital droplet PCR and were detectable on average 10.5 months before clinical relapse. With a median follow-up time of 36.5 months, 7/9 patients harboring BTK mutations showed disease progression based on clinical and/or laboratory features. In conclusion, subclonal heterogeneity, dynamic clonal selection and various patterns of clonal variegation were identified with novel resistance-associated BTK mutations in individual patients treated with ibrutinib.

NFKB1 -94ins/delATTG polymorphism is a novel prognostic marker in first line-treated multiple myeloma.

Nuclear factor kappa B (NFKB) plays an important role in multiple myeloma (MM), and bortezomib affects this pathway. We retrospectively analysed the effect of the NFKB1 -94ins/delATTG polymorphism on the survival of 295 MM patients treated at a single centre. The median progression-free survival (PFS) was 790 (659-921) d in patients with NFKB1 homozygous insertion genotype (I/I, n = 99) and 624 (515-733) d in deletion-carriers (I/D&D/D, n = 196, P = 0·013). In multivariate analysis, I/I carriers showed a favourable PFS compared to I/D&D/D with a hazard ratio of 0·622 (0·457-0·847), P = 0·003, in addition to international staging system (ISS) score, fluorescence in situ hybridization (FISH) risk score, age and bortezomib treatment. I/I patients benefited more from bortezomib treatment [PFS 902 (703-1101) and 580 (343-817), P = 0·008] than I/D&D/D patients [PFS 659 (487-831) and 488 (323-653), P = 0·531]; in addition the beneficial effect of low ISS score was not observed in the I/D&D/D group [PFS 639 (454-824) and 650 (458-842), P = 0·226], while it was clear in I/I patients [PFS 1140 (803-1477) and 580 (408-752), P < 0·001]. We conclude that homozygous carriers of the insertion allele of the NFKB1 -94ins/delATTG polymorphism have a better prognosis and probably benefit more from bortezomib treatment than MM patients carrying the deletion allele.

IGH::NSD2 Fusion Gene Transcript as Measurable Residual Disease Marker in Multiple Myeloma.

Multiple myeloma (MM) is the second most common hematological malignancy. Approximately 15% of MM patients are affected by the t(4;14) translocation resulting in the IGH::NSD2 fusion transcript. Breakage occurs in three major breakpoint regions within the NSD2 gene (MB4-1, MB4-2, and MB4-3), where MB4-1 leads to the production of full-length protein, while truncated proteins are expressed in the other two cases. Measurable residual disease (MRD) has been conclusively established as a crucial prognostic factor in MM. The IGH::NSD2 fusion transcript can serve as a sensitive MRD marker. Using bone marrow (BM) and peripheral blood (PB) samples from 111 patients, we developed a highly sensitive quantitative real-time PCR (qPCR) and digital PCR (dPCR) system capable of detecting fusion mRNAs with a sensitivity of up to 1:100,000. PB samples exhibited sensitivity three orders of magnitude lower compared to BM samples. Patients with an MB4-2 breakpoint demonstrated significantly reduced overall survival (p = 0.003). Our novel method offers a simple and sensitive means for detecting MRD in a substantial proportion of MM patients. Monitoring may be carried out even from PB samples. The literature lacks consensus regarding survival outcomes among patients with different NSD2 breakpoints. Our data align with previous findings indicating that patients with the MB4-2 breakpoint type tend to exhibit unfavorable overall survival.

Effective venetoclax-based treatment in relapsed/refractory multiple myeloma patients with translocation t(6;14).

Introduction: The selective Bcl-2 inhibitor venetoclax has shown promising therapeutic potential in multiple myeloma, particularly in cases associated with t(11;14) IGH::CCND1 translocation. However, the efficacy of venetoclax in myeloma patients with the t(6;14) IGH::CCND3 translocation remains less investigated. Methods: In this study, we conducted a retrospective analysis to investigate the efficacy of venetoclax-based therapy in relapsed/refractory myeloma patients with t(6;14) translocation. The treatment courses of three patients, that included previous therapies and responses to venetoclax, were assessed. Clinical data, laboratory results, and adverse events were analyzed to evaluate treatment outcomes. Results: Our findings demonstrated remarkable therapeutic responses in three consecutive patients with t(6;14) translocation-associated myeloma who received venetoclax-based therapy. Patient 1, a lenalidomide-bortezomib-daratumumab and alkylator treatment refractory patient, achieved sustained stringent complete remission (sCR) after combining carfilzomib-dexamethasone with venetoclax, which was his best response ever. Similarly, Patient 2, refractory to frontline bortezomib-thalidomide-dexamethasone therapy, attained CR following a transition to bortezomib-dexamethason-venetoclax treatment. Patient 3, who was immunomodulatory (IMID)-intolerant, showed a highly favorable response to venetoclax-dexamethasone therapy after his first relapse following autologous stem cell transplantation. No significant adverse effects were observed in any of the patients. Discussion: Our study provides compelling preliminary evidence for the efficacy of venetoclax in t(6;14) translocation-associated myeloma. The outcomes observed in our patients suggest that venetoclax-based therapy holds substantial promise as an effective treatment option for this specific genetic subgroup. Furthermore, the similarities in treatment response between t(11;14) and t(6;14) translocation subgroups highlight the importance of personalized approaches targeting specific genetic abnormalities to optimize therapeutic outcomes.

Additional chromosome abnormalities, BCR-ABL tyrosine kinase domain mutations and clinical outcome in Hungarian tyrosine kinase inhibitor-resistant chronic myelogenous leukemia patients.

BACKGROUND: Additional chromosome abnormalities (ACAs), mutations of the BCR-ABL tyrosine kinase domain (TKD) and BCR-ABL splice variants may cause resistance to first- and second-generation tyrosine kinase inhibitors (TKIs) in chronic myelogenous leukemia (CML) and Philadelphia-positive (Ph+) acute lymphoid leukemia (ALL). METHODS: Karyotyping and BCR-ABL TKD mutation screening were performed in 71 imatinib-resistant CML patients and 6 Ph+ ALL patients. A total of 56 out of these 77 patients received second-generation TKI. RESULTS: ACAs were present in 30 of 65 imatinib-resistant patients (46%). In 27 of 74 imatinib-resistant patients (36%), 15 different BCR-ABL TKD mutations were detected. Mutations were found in 25% of chronic-phase patients (12/47), 33% of accelerated-phase patients (5/15), 71% of blast crisis CML patients (5/7) and 100% of ALL patients. In nilotinib-resistant patients, Y253H, T315I and F359I/V mutations were detected; in dasatinib-resistant patients, L248M, E279K and T315I mutations were detected. T315I was found more frequently in patients on dasatinib than on imatinib therapy. The presence of ACAs predicted shorter survival during first- and second-generation TKI therapy, while TKD mutations only influenced survival during second-generation TKI therapy. CONCLUSION: For patients with TKI resistance, mutation and ACA screening may play a role in identifying patients with poorer prognosis.

Two myeloproliferative diseases in one patient - co-occurence of clones / Két myeloproliferativ betegség egy betegben - klónok együttélése és vetélkedése

Classical myeloproliferative diseases can be divided into Philadelphia chromosome-positive chronic myeloid leukemia and Philadelphia chromosome-negative myeloproliferative neoplasm. The driver mutations of the latter occur in the Janus kinase 2 or calreticulin genes. The coincidence of Philadelphia chromosome-negative and -positive myeloproliferative neoplasms in the same patient is exceptionally rare in the literature. During the long-term follow-up of our 120 patients with chronic myeloid leukemia, we investigated the clinical data of patients in whom Philadelphia chromosome-negative myeloproliferative disease was also confirmed. Philadelphia chromosome was detected by classical cytogenetic methods and/or fluorescence in situ hybridization. The amount of BCR-ABLI fusion RNA was monitored by quantitative real-time polymerase chain reaction. Mutations in the Janus kinase 2 and calreticulin genes were detected by quantitative allele-specific polymerase chain reaction and fragment analysis. The dynamics of disease development were inferred from the change in the amount of mutant clones over time and from the clinical data. We identified four cases carrying both Philadelphia chromosome and Janus kinase 2/calreticulin gene mutation. In some cases, competition between the clones, in other cases their co-occurrence in a common clone was observed. Isolated thrombocytosis at the time of diagnosis or persisting thrombocytosis during targeted therapy with good molecular response may call attention to the possibility of the co-occurrence of the two diseases. Co-occurrence of Philadelphia chromosome-positive and -negative myeloproliferative neoplasms is more frequent than the literature suggests. If the disease has an unusual appearance, the association of the two myeloproliferative dieseases may be suspected.

[Calreticulin: Pathophysiology of an unusual gain-of-function and its clinical consequences]. / Kalretikulin: egy különleges funkciónyerés patofiziológiája és klinikai következményei.

One characteristic type of the common somatic mutations causing myeloproliferative neoplasias is the frameshift mutation of the calreticulin gene that leads to proteins of abnormal structure. The pathologic protein induces novel cell biological processes that are fundamental to the onset and maintenance of myeloproliferative diseases. In this review, an insight is provided into these processes, aiding better understanding of the underlining pathobiological processes and eventually to more effective therapy in the future.

Targeted Venetoclax Therapy in t(11;14) Multiple Myeloma: Real World Data From Seven Hungarian Centers.

Despite the introduction of novel agents, multiple myeloma remains incurable for most patients, necessitating further therapeutic options. Venetoclax, a selective BCL-2 inhibitor, had shown promising results in patients with translocation t(11;14), but questions remain open about its optimal use. We have contacted all Hungarian haematology centers for their experience treating t(11;14) myeloma patients with venetoclax. 58 patients were reported. 37 received venetoclax in the relapsed/refractory setting with few or no other therapeutic options available. 21 patients started venetoclax as salvage after failing to achieve satisfactory response to first line therapy. In the relapsed/refractory setting objective response rate (ORR) was 94%, median progression-free survival (PFS) 10.0 months and median overall survival (OS) 14.6 months. In reinduction patients, ORR was 100%, median PFS and OS were not reached. Importantly, we found no adverse effect of high risk features such as deletion 17p or renal failure, in fact renal failure ameliorated in 42% of the cases, including three patients who became dialysis independent. Our study also reports the highest number of plasma cell leukemia cases successfully treated with venetoclax published in literature, with refractory plasma cell leukemia patients achieving a median PFS of 10.0 and a median OS of 12.2 months.

The prognostic impact of germline 46/1 haplotype of Janus kinase 2 in cytogenetically normal acute myeloid leukemia.

BACKGROUND: Prognostic risk stratification according to acquired or inherited genetic alterations has received increasing attention in acute myeloid leukemia in recent years. A germline Janus kinase 2 haplotype designated as the 46/1 haplotype has been reported to be associated with an inherited predisposition to myeloproliferative neoplasms, and also to acute myeloid leukemia with normal karyotype. The aim of this study was to assess the prognostic impact of the 46/1 haplotype on disease characteristics and treatment outcome in acute myeloid leukemia. DESIGN AND METHODS: Janus kinase 2 rs12343867 single nucleotide polymorphism tagging the 46/1 haplotype was genotyped by LightCycler technology applying melting curve analysis with the hybridization probe detection format in 176 patients with acute myeloid leukemia under 60 years diagnosed consecutively and treated with curative intent. RESULTS: The morphological subtype of acute myeloid leukemia with maturation was less frequent among 46/1 carriers than among non-carriers (5.6% versus 17.2%, P = 0.018, cytogenetically normal subgroup: 4.3% versus 20.6%, P = 0.031), while the morphological distribution shifted towards the myelomonocytoid form in 46/1 haplotype carriers (28.1% versus 14.9%, P = 0.044, cytogenetically normal subgroup: 34.0% versus 11.8%, P = 0.035). In cytogenetically normal cases of acute myeloid leukemia, the 46/1 carriers had a considerably lower remission rate (78.7% versus 94.1%, P = 0.064) and more deaths in remission or in aplasia caused by infections (46.8% versus 23.5%, P = 0.038), resulting in the 46/1 carriers having shorter disease-free survival and overall survival compared to the 46/1 non-carriers. In multivariate analysis, the 46/1 haplotype was an independent adverse prognostic factor for disease-free survival (P = 0.024) and overall survival (P = 0.024) in patients with a normal karyotype. Janus kinase 2 46/1 haplotype had no impact on prognosis in the subgroup with abnormal karyotype. CONCLUSIONS: Janus kinase 2 46/1 haplotype influences morphological distribution, increasing the predisposition towards an acute myelomonocytoid form. It may be a novel, independent unfavorable risk factor in acute myeloid leukemia with a normal karyotype.

Nucleophosmin1 and isocitrate dehydrogenase 1 and 2 as measurable residual disease markers in acute myeloid leukemia.

Monitoring measurable residual disease (MRD) in acute myeloid leukemia (AML) plays an important role in predicting relapse and outcome. The applicability of the leukemia-initiating nucleophosmin1 (NPM1) gene mutations in MRD detection is well-established, while that of isocitrate dehydrogenase1/2 (IDH1/2) mutations are matter of debate. The aim of this study was to investigate the stability of NPM1 and IDH1/2 mutations at diagnosis and relapse retrospectively in 916 adult AML patients. The prognostic value of MRD was evaluated by droplet digital PCR on the DNA level in a selected subgroup of patients in remission. NPM1 re-emerged at relapse in 91% (72/79), while IDH1/2 in 87% (20/23) of mutation-positive cases at diagnosis. NPM1 mutation did not develop at relapse, on the contrary novel IDH1/2 mutations occurred in 3% (3/93) of previously mutation-negative cases. NPM1 MRD-positivity after induction (n = 116) proved to be an independent, adverse risk factor (MRDpos 24-month OS: 39.3±6.2% versus MRDneg: 58.5±7.5%, p = 0.029; HR: 2.16; 95%CI: 1.25-3.74, p = 0.006). In the favorable subgroup of mutated NPM1 without fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) or with low allelic ratio, NPM1 MRD provides a valuable prognostic biomarker (NPM1 MRDpos versus MRDneg 24-month OS: 42.9±6.7% versus 66.7±8.6%; p = 0.01). IDH1/2 MRD-positivity after induction (n = 62) was also associated with poor survival (MRDpos 24-month OS: 41.3±9.2% versus MRDneg: 62.5±9.0%, p = 0.003; HR 2.81 95%CI 1.09-7.23, p = 0.032). While NPM1 variant allele frequency decreased below 2.5% in remission in all patients, IDH1/2 mutations (typically IDH2 R140Q) persisted in 24% of cases. Our results support that NPM1 MRD even at DNA level is a reliable prognostic factor, while IDH1/2 mutations may represent pre-leukemic, founder or subclonal drivers.

[Importance of next generation sequencing in precision oncology approach of acute myeloid leukemia]. / Az új generációs szekvenálás jelentõsége az akut mieloid leukémia precíziós onkológiai megközelítésében.

In contrast to solid tumours, the genetic background of acute myeloid leukemia (AML) is characterized by a relatively low number of alterations per sample (average 3-5 mutations similarly to paediatric malignancies). Although the mutational background is rather heterogeneous, the detection of genetic alterations has diagnostic, prognostic and therapeutic relevance. We investigated cytogenetic and most commonly occurring molecular genetic alterations, and their co-occurrence in 830 AML patients diagnosed and treated in our institute between 2001 and 2019. Results from the recently introduced next generation sequencing for seven AML patients are also presented. Both methods (previously performed standard PCR-based tests and NGS) achieved the same results for commonly occurring mutations, but NGS technique was capable to identify further, rarely occurring mutations which bear diagnostic and prognostic importance according to the recent European LeukemiaNet recommendations. The introduction of NGS techniques to routine laboratory diagnostic applications is a required step following international expertise.

The adverse effect of FOPNL genomic variant is reversed by bortezomib-based treatment protocols in multiple myeloma.

Fibroblast growth factor receptor 1 oncogene partner N-terminal like gene (FOPNL) rs72773978 polymorphism was identified as an adverse prognostic factor in multiple myeloma (MM). We aimed to investigate the associations of rs72773978 with clinical characteristics and treatment outcome in 373 Hungarian MM patients. In our cohort, FOPNL polymorphism showed differential prognostic effect that depended on the treatment applied. Among patients treated with non-proteasome inhibitor (PI)-based therapy, carriership of the minor allele was significantly associated with adverse overall survival (p=.022). In contrast, the adverse effect was overcome by the application of PI-containing treatment (p=.048). Multivariate analyses revealed the independent adverse effect of rs72773978 on survival in the non-PI-treated group (p=.045), but not in PI treatment (OS: p=.093). We confirmed the adverse prognostic effect of rs72773978 associated with non-PI-based treatment regimens. Our results point to the importance of genotypic prognostic information associated with complex clinical background MM.

Lipoprotein Lipase as a Prognostic Marker in Chronic Lymphocytic Leukemia.

The marked clinical heterogeneity of CLL makes early prognosis assessment important. Lipoprotein lipase (LPL) has been shown to confer adverse prognosis in CLL, recent data indicating it might also contribute to CLL cell survival and metabolism. We determined LPL mRNA expression in unselected peripheral blood of 84 CLL patients by RT PCR. Results were correlated with other prognostic markers and outcome. 30/84 (40 %) of cases were LPL positive based on the cutoff established by ROC analysis. In LPL positive patients significantly shorter median survival (136 vs 258 months, p < 0.0001) and time to first treatment intervals (36 vs 144 months, p < 0.002) were documented. LPL values correlated with male gender, higher stages, more treatment requirement, CD38 positivity and unmutated IgVH genes. Among cases with 13q deletion, LPL positivity identified a subcohort with poor outcome (median survival 108 months vs NR, p < 0.0001). In multivariate analysis, cytogenetic aberrations and LPL had significant impact on survival. Our results confirm that LPL is a strong predictor of outcome in CLL, able to improve prognostic accuracy in good risk cytogenetic subgroups. The relationship between its prognostic and functional role in CLL needs to be explored further.

Hepatosplenic gammadelta T-cell lymphoma with ring chromosome 7, an isochromosome 7q equivalent clonal chromosomal aberration.

Hepatosplenic T-cell lymphoma is a rare, clinically aggressive lymphoma. Most cases represent a neoplasm of mature non-activated gammadelta T cells. Isochromosome 7q i(7)(q10) is thought to be the primary cytogenetic abnormality of this disease. In this paper, we describe a hepatosplenic gammadelta T-cell lymphoma case, with clonal ring chromosome 7 exemplifying an isochromosome 7q equivalent clonal aberration. A 62-year-old female patient presented with thrombocytopenia, isolated hepatosplenomegaly, and extremely high levels of LDH. Bone marrow work-up demonstrated a sinusoidal cytotoxic T-cell infiltrate with blastic features, while molecular studies verified monoclonal rearrangement for both TCR gamma and TCR delta genes. Cytogenetics revealed clonal abnormalities including ring chromosome 7, trisomy 8, and der(19), while FISH analysis detected 7q amplification with partial deletion of 7p in ring chromosome 7. To the best of our knowledge, this is the first reported T-cell lymphoma case with ring chromosome 7.

Medium-sized FLT3 internal tandem duplications confer worse prognosis than short and long duplications in a non-elderly acute myeloid leukemia cohort.

Internal tandem duplications (ITDs) of the fms-like tyrosine kinase 3 (FLT3) gene occur in about 25% of patients with adult acute myeloid leukemia (AML). The aim of our study was to investigate the frequency of FLT3-ITD mutations followed by a detailed analysis of the mutational load and size of ITD insertions in a cohort consisting of 324 patients younger than 60 years old and treated with curative intention. FLT3-ITD alone did not influence overall survival (OS) or disease-free survival (DFS). We observed worse OS and DFS for patients with high mutational load indicative for loss of the FLT3 wild type allele (p = 0.010, p = 0.038, respectively). In multivariate analyses, patients with FLT3-ITD(48-60bp) showed worse OS and DFS compared to other groups (FLT3-ITD(neg), FLT3-ITD (< 48b), FLT3-ITD (> 60bp); p = 0.014, p = 0.019, respectively). Our novel observation suggested that not only high FLT3-ITD load, but also medium-sized ITD insertions (48-60 bp) represented an adverse prognostic subgroup of patients with AML.

Type and location of isocitrate dehydrogenase mutations influence clinical characteristics and disease outcome of acute myeloid leukemia.

Mutations of isocitrate dehydrogenase 1 and 2 (IDH1/2) are genetic alterations in acute myeloid leukemia (AML). The aim of our study was to investigate the frequency and prognostic effect of IDH1/2 mutations together followed by an individual analysis of each substitution in a Hungarian cohort consisting of 376 patients with AML. IDH1(mut) and IDH2(mut) were mutually exclusive, detected in 8.5% and 7.5% of cases, respectively. IDH1/2(mut) was associated with: older age (p = 0.001), higher average platelet count (p = 0.001), intermediate karyotype (p < 0.0001), NPM1(mut) (p = 0.022) and lower mRNA expression level of ABCG2 gene (p = 0.006). Overall survival (OS), remission and relapse rates were not different in IDH1(mut) or IDH2(mut) vs. IDH(neg). IDH1(mut) and IDH2(mut) were associated differently with NPM1(mut); co-occurrence was observed in 14.3% of IDH1 R132C vs. 70% of R132H carriers (p = 0.02) and in 47.4% of IDH2 R140Q vs. 0% of R172K carriers (p = 0.02). IDH1 R132H negatively influenced OS compared to IDH(neg) (p = 0.02) or R132C (p = 0.019). Particular amino acid changes affecting the same IDH1 codon influence the clinical characteristics and treatment outcome in AML.

Chronic lymphoid leukemia cells are highly sensitive to the combination of prednisolone and daunorubicin, but much less to doxorubicin or epirubicin.

OBJECTIVE: To generate a comprehensive map of the drug sensitivity of chronic lymphoid leukemia cells (CLL) using a newly developed in vitro drug-sensitivity assay based on automated evaluation of cell viability on single-cell level. MATERIALS AND METHODS: Primary CLL cells from 77 patients were tested using automated digital fluorescence microscopy. The effect of 27 frequently used chemotherapeutic agents was measured in short-term fluorescence survival assay. To avoid typical in vitro artifacts such as growth factor depletion and oxidative damage, the cell were cultured in a novel, total human blood lysate-based medium (OmniSanguine) in order to preserve the composition of growth factor flora and redox conditions of the in vivo environment. RESULTS: CLL cells from different patients showed considerable heterogeneity in their drug-sensitivity patterns. This pattern was stable even after in vitro activation of cell proliferation. Half of the samples were sensitive to fludarabine and chlorambucil. Daunorubicin was the most potent drug. It was effective in 75 of 77 cases. In addition, daunorubicin and prednisolone showed a strong synergistic effect. CONCLUSIONS: We suggest that the combination of low-dose daunorubicin and prednisolone might be an additional treatment option for therapy-resistant cases of CLL.

First and second line imatinib treatment in chronic myelogenous leukemia patients expressing rare e1a2 or e19a2 BCR-ABL transcripts.

During the formation of the Philadelphia (Ph) chromosome, in the majority of chronic myelogenous leukemia (CML) patients, the chromosome 22 breakpoint is located in the major breakpoint cluster region of the BCR gene (M-bcr). Minor and micro breakpoint cluster regions (m-bcr with e1a2 transcript and micro-bcr with e19a2 transcript) are rarely affected and have been suggested to be associated with peculiar CML phenotypes. Despite the different clinical characteristics, it is currently not established, whether different therapeutic options are preferably recommended for the treatment of e1a2 or e19a2 CML. Here we report two patients with e1a2 and one patient with e19a2 translocations, treated with different approaches including imatinib. First and second line imatinib treatments induced haematologic response in all of the three patients, and major cytogenetic response in one patient with e1a2, as well as in the patient with e19a2 CML. However, relapse occurred in the patient with e19a2 CML, possibly caused by the presence of additional chromosomal abnormalities such as an extra Ph chromosome, and loss of chromosome Y. Stem cell transplantation (SCT) therapy caused complete haematologic response with molecular remission; however, the patient died of infectious complication. We conclude that in patients with rare BCR-ABL variants, the effectiveness of imatininb treatment may be influenced by the CML stage besides the actual molecular type of the rare transcript. However, this conclusion cannot be generalized to larger patient groups with rare BCR-ABL variants for which further studies may be needed.

In vitro expansion of long-term repopulating hematopoietic stem cells in the presence of immobilized Jagged-1 and early acting cytokines.

There is an increasing body of evidence that suggests that genes involved in cell fate decisions and pattern formation during development also play a key role in the continuous cell fate decisions made by adult tissue stem cells. Here we show that prolonged in vitro culture (14 days) of murine bone marrow lineage negative cells in medium supplemented with three early acting cytokines (stem cell factor, Flk-2/Flt-3 ligand, thrombopoietin) and with immobilized Notch ligand, Jagged-1, resulted in robust expansion of serially transplantable hematopoietic stem cells with long-term repopulating ability. We found that the absolute number of marrow cells was increased approximately 8 to 14-fold in all cultures containing recombinant growth factors. However, the frequency of high quality stem cells was markedly reduced at the same time, except in cultures containing growth factors and Jagged-1-coated Sepharose-4B beads. The absolute number of hematopoietic cells with long-term repopulating ability was increased approximately 10 to 20-fold in the presence of multivalent Notch ligand. These results support a role for combinatorial effects by Notch and cytokine-induced signaling pathways in regulating hematopoietic stem cell fate and to a potential role for Notch ligand in increasing cell numbers in clinical stem cell transplantation.