Genetic heterogeneity of BCR/ABL+ adult B-cell precursor acute lymphoblastic leukemia: impact on the clinical, biological and immunophenotypical disease characteristics

Jak2/STAT6/c-Myc pathway is vital to the pathogenicity of Philadelphia-positive acute lymphoblastic leukemia caused by P190BCR-ABL

BACKGROUND

The Philadelphia chromosome encodes the BCR-ABL fusion protein, which has two primary subtypes, P210 and P190. P210 and P190 cause Philadelphia-positive chronic myeloid leukemia (Ph+ CML) and Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL), respectively. The Ph+ ALL is more malignant than Ph+ CML in disease phenotype and progression. This implies the key pathogenic molecules and regulatory mechanisms caused by BCR-ABL in two types of leukemia are different. It is reported that STAT6 was significantly activated only in P190 transformed cells. However, the potential role and the mechanism of STAT6 activation in Ph+ ALL and its activation mechanism by P190 are still unknown.

METHODS

The protein and mRNA levels of STAT6, c-Myc, and other molecules were measured by western blot and quantitative real-time PCR. The STAT6 inhibitor AS1517499 was used to specifically inhibit p-STAT6. The effect of p-STAT6 inhibition on Ph+ CML and Ph+ ALL cells was identified by CCK-8 and FCM assay. Dual luciferase reporter and ChIP assay were performed to confirm the direct binding between STAT6 and c-Myc. The impact of STAT6 inhibition on tumor progression was detected in Ph+ CML and Ph+ ALL mouse models.

RESULTS

Our results demonstrated that P210 induced CML-like disease, and P190 caused the more malignant ALL-like disease in mouse models. STAT6 was activated in P190 cell lines but not in P210 cell lines. Inhibition of STAT6 suppressed the malignancy of Ph+ ALL in vitro and in vivo, whereas it had little effect on Ph+ CML. We confirmed that p-STAT6 regulated the transcription of c-Myc, and STAT6 was phosphorylated by p-Jak2 in P190 cell lines, which accounted for the discrepant expression of p-STAT6 in P190 and P210 cell lines. STAT6 inhibition synergized with imatinib in Ph+ ALL cells.

CONCLUSIONS

Our study suggests that STAT6 activation plays an essential role in the development of Ph+ ALL and may be a potential therapeutic target in Ph+ ALL. Video abstract.

An easy-to-use nomogram predicting overall survival of adult acute lymphoblastic leukemia

Adult acute lymphoblastic leukemia (ALL) is heterogeneous both biologically and clinically. The outcomes of ALL have been improved with the application of children-like regimens and novel agents including immune therapy in young adults. The refractory to therapy and relapse of ALL have occurred in most adult cases. Factors affecting the prognosis of ALL include age and white blood cell (WBC) count at diagnosis. The clinical implications of genetic biomarkers, including chromosome translocation and gene mutation, have been explored in ALL. The interactions of these factors on the prediction of prognosis have not been evaluated in adult ALL. A prognostic model based on clinical and genetic abnormalities is necessary for clinical practice in the management of adult ALL. The newly diagnosed adult ALL patients were divided into the training and the validation cohort at 7:3 ratio. Factors associated with overall survival (OS) were assessed by univariate/multivariate Cox regression analyses and a signature score was assigned to each independent factor. A nomogram based on the signature score was developed and validated. The receiver operating characteristic (ROC) curve, calibration curve, and decision curve analysis (DCA) were used to assess the performance of the nomogram model. This study included a total of 229 newly diagnosed ALL patients. Five independent variables including age, WBC, bone marrow (BM) blasts, MLL rearrangement, and ICT gene mutations (carried any positive mutation of IKZF1, CREBBP and TP53) were identified as independent adverse factors for OS evaluated by the univariate, Kaplan-Meier survival and multivariate Cox regression analyses. A prognostic nomogram was built based on these factors. The areas under the ROC curve and calibration curve showed good accuracy between the predicted and observed values. The DCA curve showed that the performance of our model was superior to current risk factors. A nomogram was developed and validated based on the clinical and laboratory factors in newly diagnosed ALL patients. This model is effective to predict the overall survival of adult ALL. It is a simple and easy-to-use model that could efficiently predict the prognosis of adult ALL and is useful for decision making of treatment.

Philadelphia Chromosome-Positive Leukemia in the Lymphoid Lineage-Similarities and Differences with the Myeloid Lineage and Specific Vulnerabilities

Philadelphia chromosome (Ph) results from a translocation between the breakpoint cluster region (BCR) gene on chromosome 9 and ABL proto-oncogene 1 (ABL1) gene on chromosome 22. The fusion gene, BCR-ABL1, is a constitutively active tyrosine kinase which promotes development of leukemia. Depending on the breakpoint site within the BCR gene, different isoforms of BCR-ABL1 exist, with p210 and p190 being the most prevalent. P210 isoform is the hallmark of chronic myeloid leukemia (CML), while p190 isoform is expressed in majority of Ph-positive B cell acute lymphoblastic leukemia (Ph+ B-ALL) cases. The crucial component of treatment protocols of CML and Ph+ B-ALL patients are tyrosine kinase inhibitors (TKIs), drugs which target both BCR-ABL1 isoforms. While TKIs therapy is successful in great majority of CML patients, Ph+ B-ALL often relapses as a drug-resistant disease. Recently, the high-throughput genomic and proteomic analyses revealed significant differences between CML and Ph+ B-ALL. In this review we summarize recent discoveries related to differential signaling pathways mediated by different BCR-ABL1 isoforms, lineage-specific genetic lesions, and metabolic reprogramming. In particular, we emphasize the features distinguishing Ph+ B-ALL from CML and focus on potential therapeutic approaches exploiting those characteristics, which could improve the treatment of Ph+ B-ALL.

Dasatinib as an investigational drug for the treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia in adults

INTRODUCTION

Acute lymphoblastic leukemia (ALL) with BCR-ABL1 translocation is an aggressive malignancy that is usually treated with intensive chemotherapy with the possibility of allogeneic stem cell transplantation. The encoded fusion protein may be important for leukemogenesis; clinical studies show that dasatinib has an antileukemic effect in combination with steroids alone or intensive chemotherapy. Areas covered: Relevant publications were identified through literature searches (the used terms being acute lymphoblastic leukemia plus dasatinib) in the PubMed database. We searched for original articles and reviews describing the pharmacology and clinical use of dasatinib in ALL with BCR-ABL1. The mechanism of action, pharmacology and clinical study findings are examined. Expert opinion: Dasatinib is associated with a high complete remission rate in ALL when used alone and in combination with steroids or intensive chemotherapy. However, mutations at T315 and F317 are associated with dasatinib resistance. Overall toxicity has been acceptable in these studies and no unexpected toxicity was observed. It is not known whether the antileukemic effect of dasatinib differs between subsets of BCR-ABL1⁺ patients or is attributed to inhibition of the fusion protein alone, or a combined effect on several kinases, and whether dasatinib-containing combination treatment should be preferred in these patients instead of other emerging strategies, e.g. monoclonal antibodies.

Additional Cytogenetic Abnormalities with Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia on Allogeneic Stem Cell Transplantation in the Tyrosine Kinase Inhibitor Era

Cytogenetic abnormalities are well known and powerful independent prognostic factors for various hematologic disorders. Although the combination of chemotherapy with tyrosine kinase inhibitor (TKI) is now considered the standard of care in patients with Philadelphia chromosome-positive acute lymphoblastic leukemia, little is known about the impact of additional cytogenetic abnormalities (ACAs). Therefore, we retrospectively evaluated 1375 adult patients who underwent their first allogeneic hematopoietic stem cell transplantation in the TKI era. In this study, 224 patients had ACAs (16.3%). The ACAs that were seen in more than 20 cases (1.5%) were as follows: -7, der(22), der(9), +8, and +X. Overall survival at 4 years was 56.9% (95% confidence interval [CI], 49.4% to 63.7%) in the group with ACAs and 60.5% (95% CI, 57.3% to 63.5%) in the group without ACAs (P = .266). The cumulative incidence of relapse at 4 years was 28.9% (95% CI, 22.6% to 35.6%) in the group with ACAs and 21.9% (95% CI, 19.4% to 24.6%) in the group with Ph alone (P = .051). In multivariate analyses there were no statistically significant differences in the risk of overall mortality or risk of relapse between the groups with and without ACAs. In the subgroup analyses of specific ACAs, although the presence of +8 was associated with a higher relapse rate in univariate and multivariate analyses, no specific ACA was associated with poor overall survival. Further studies will be needed to verify the impact of specific ACAs on transplantation outcomes.

Prognostic significance of recurrent additional chromosomal abnormalities in adult patients with Philadelphia chromosome-positive acute lymphoblastic leukemia

In Philadelphia (Ph) chromosome-positive acute lymphoblastic leukemia (ALL), additional chromosomal abnormalities (ACAs) are frequently observed. We investigated the cytogenetic characteristics and prognostic significance of ACAs in Ph-positive ALL. We reviewed the clinical data and bone marrow cytogenetic findings of 122 adult Ph-positive ALL patients. The ACAs were examined for partial or whole chromosomal gains or losses, and structural aberrations. The overall survival (OS) and disease-free survival (DFS) of patients who received hematopoietic cell transplantation were compared between the isolated Ph group and ACA group. ACAs were present in 73.0% of all patients. The recurrent ACAs were extra Ph (24.7%), 9/9p loss (20.2%), and 7/7p loss (19.1%). Complex karyotype was found in 28.1% of patients in the ACA group. Younger patients (19-30 years) in the ACA group showed the highest frequency of extra Ph (54%) compared to other age groups. The OS in the ACA group was significantly shorter than in the isolated Ph group. The presence of an extra Ph chromosome or 9/9p loss was significantly associated with shorter OS and DFS, whereas 7/7p loss and complex karyotype were not associated with poorer prognosis. We suggest that subclassification of ACAs could be applied to prognostic investigation of Ph-positive ALL.

[Clinical analysis of adult Philadelphia chromosome-positive acute lymphoblastic leukemia with p16 gene deletion]

Objective: To investigate the clinical implications of p16 gene deletion in adult Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL) . Methods: Retrospective analysis of clinical, immunophenotypic, cytogenetics, molecular characteristics and prognosis of 80 newly diagnosed Ph(+) ALL patients with p16 deletion. Results: Of 80 adult Ph(+) ALL, the prevalence of p16 gene deletion was 31.3%. p16 gene deletion carriers frequently accompanied with high WBC counts (WBC≥30×10(9)/L) and CD20 expression. The incidence of complex chromosome abnormality in p16 gene deletion group was higher than that in non-deletion group, with alternations in chromosome 7, 8, 19 and der (22) more frequently observed. There was no difference occurred between patients with or without p16 gene deletion in complete remission (CR) rate following induction chemotherapy combined with tyrosine kinase inhibitors (TKIs) . However, after three cycles of chemotherapy, the MMR and CMR rate in the p16 gene deletion group was lower than patients with wild-type p16 gene (P=0.034, P=0.036) . The p16 gene deletion patients showed no significant differences in MMR, CMR and relapse rate between Imatinib or Dasatinib plus chemotherapy (P>0.05) . Deletion of p16 gene was significantly associated with poor outcomes including worse overall survival (OS) (37.1% vs 54.1%, P=0.037) , lower disease free-survival (DFS) (12.4% vs 45.9%, P=0.026) , and increased cumulative incidence of relapse (P=0.033) . Among the 25 patients with p16 deletion, 14 underwent allo-HSCT and the median survival was 21 months, better than that of patients received chemotherapy alone (12 months) (P=0.030) . Conclusion: This study indicated that deletion of p16 was associated with poor prognosis in adult Ph(+) ALL, and the utility of second-generation TKI (Dasatinib) does not necessarily have an edge on efficacy over Imatinib, but allo-HSCT has the potential of elongating life expectancy. It is an important significance to define the status of p16 in Ph(+) ALL for predicting prognosis and guiding therapy decision-making.

Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia Is Separated into Two Subgroups Associated with Survival by BCR-ABL Fluorescence in situ Hybridization of Segmented Cell Nuclei: Report from a Single Institution

Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) may include the lymphoid blast crisis of chronic myeloid leukemia (CML-BC). We applied fluorescence in situ hybridization (FISH) of the BCR-ABL fusion gene to peripheral blood and/or bone marrow smears to determine whether the fusion was restricted to mononuclear cell nuclei or if segmented cell nuclei representing mature neutrophils also carried the fusion (Seg-FISH). Among 20 patients with Ph+ ALL without a prior diagnosis of CML, 9 were Seg-FISH+ and 11 were Seg-FISH-. Seg-FISH+ cases were characterized by a higher rate of p210-type BCR-ABL transcripts, higher white cell and blast counts, and a higher rate of myeloid and T-lymphoid antigen expression than Seg-FISH- cases, in addition to 'major route' cytogenetic abnormalities associated with CML-BC. Eighteen patients were treated with tyrosine kinase inhibitors (TKIs) either alone or in combination with multiagent chemotherapy, and 7 underwent allogeneic hematopoietic stem cell transplantation. Progression-free and overall survivals were greater in the Seg-FISH+ group than in the Seg-FISH- group. These results suggest that the Seg-FISH+ group represents lymphoid CML-BC that occurs de novo, while the Seg-FISH- represents Ph+ ALL in the strict sense, and the two groups are associated with survival when treated with TKIs or TKI-combined therapy.

Primary testicular Ph-positive B lymphoblastic lymphoma: an unusual presentation and review

Primary testicular B-lymphoblastic lymphoma is a rare entity. Primary testicular Ph-positive B lymphoblastic lymphoma was not reported before. We reported a 27-year-old man with primary testicular Ph-positive B lymphoblastic lymphoma, for which fluorescent in-situ hybridization (FISH) for the Philadelphia chromosome was not performed at the initial hospitalization. The patient showed manifestation of Ph-positive acute lymphoblastic leukemia at relapse. In this report, we reviewed the current literature about primary testicular B-lymphoblastic lymphoma, Ph-positive lymphoma and Ph-positive clone evolution. This report has 3 meanings. First: This is first report on primary testicular Ph-positive B lymphoblastic lymphoma. Second: This shows the importance of cytogenics for lymphoma treatment. Third: This implies Philadelphia-positive subclone evolution.

Identification of a novel susceptibility locus at 16q23.1 associated with childhood acute lymphoblastic leukemia in Han Chinese

Recently, genome-wide association studies (GWAS) have identified several susceptibility loci for childhood acute lymphoblastic leukemia (ALL) in populations of European descent; only a few loci could be confirmed in Asian populations because of those populations' genetic heterogeneity. To identify genetic factors associated with childhood ALL risk in the Chinese population, we performed a three-stage GWAS of 1184 childhood ALL cases and 3219 non-ALL controls. The combined analysis identified a new locus (rs1121404 in WWOX) at 16q23.1 associated with childhood ALL susceptibility (odds ratio (OR) = 1.38, P = 5.29 × 10^-10), especially in the subtype of B-ALL (OR = 1.39, P = 2.47 × 10^-9). The functional studies subsequently revealed that the expression of WWOX in ALL bone marrow was significantly lower than that in normal bone marrow. The G allele of rs1121404 displayed significantly decreased levels of mRNA expression of WWOX These results suggest that WWOX plays an important role in the development of childhood ALL and provide new insights into the etiology of childhood ALL.

Correlation between deletion of the CDKN2 gene and tyrosine kinase inhibitor resistance in adult Philadelphia chromosome-positive acute lymphoblastic leukemia

BACKGROUND

Frequency relapses are common in Philadelphia chromosome-positive (Ph-positive) acute lymphoblastic leukemia (ALL) following tyrosine kinase inhibitors (TKIs). CDKN2A/B is believed to contribute to this chemotherapy resistance.

METHODS

To further investigate the association between CDKN2 status and TKI resistance, the prevalence of CDKN2 deletions and its correlation with a variety of clinical features was assessed in 135 Ph-positive ALL patients using interphase fluorescence in situ hybridization (I-FISH).

RESULTS

Results showed that no difference occurred between patients with CDKN2 deletion (44/135) and wild-type patients in sex, age, and complete remission (CR) rate following induction chemotherapy combined with tyrosine kinase inhibitors (TKIs). However, CDKN2 deletion carriers demonstrated higher white blood cell (WBC) count, enhanced rates of hepatosplenomegaly (P = 0.006), and upregulation of CD20 expression (P = 0.001). Moreover, deletions of CDKN2 resulted in lower rates of complete molecular response (undetectable BCR/ABL), increased cumulative incidence of relapse, short overall survival (OS), and disease-free survival (DFS) time (P < 0.05) even though these patients received chemotherapy plus TKIs followed by allogenic hematopoietic stem cell transplantation (Allo-HSCT). In the case of 44 patients who presented with CDKN2 deletion, 18 patients were treated with dasatinib treatment, and another 26 patients were treated with imatinib therapy, and our study found that there were no differences associated with OS (P = 0.508) and DFS (P = 0.555) between the two groups.

CONCLUSIONS

CDKN2 deletion is frequently acquired during Ph-positive ALL progression and serves as a poor prognostic marker of long-term outcome in Ph-positive ALL patients with CDKN2 deletion even after the second-generation tyrosine kinase inhibitor treatment.

Therapy-related B-lymphoblastic leukemia associated with Philadelphia chromosome and MLL rearrangement: Single institution experience and the review of the literature

Therapy related acute lymphoblastic leukemia (t-ALL) of B cell origin is rare and constitutes approximately 2% of all ALL. Previously compiled data on the complete cytogenetic analysis of 48 t-B-ALL cases suggested that MLL rearrangement at 11q23 gene locus is the most common abnormality. Philadelphia chromosome (Ph) and a normal karyotype were reported as the second and third most common karyotypes, respectively. We investigated cytogenetic karyotypes of six t-B-ALL cases with a pre-B cell immunophenotype. Ph + t-B-ALL was noted in four of six patients previously treated with radiation and/or chemotherapy. In addition, one case demonstrated MLL rearrangement at 11q23 locus while one case demonstrated normal cytogenetic karyotype. Five of the six t-B-ALL patients had persistent leukemia following initiation of chemotherapy for secondary leukemia with survival ranging from 10 to 21 months. To our knowledge, only fourteen patients with Ph + t-B-ALL have been described in the literature. In the current study, three of four cases with Ph + t-B-ALL were associated with treated breast carcinoma while one patient was treated for Hodgkin lymphoma. All four patients had undergone radiation therapy. The results may indicate a plausible association between Ph+t-B-ALL and prior radiation exposure.

An adult B-cell precursor acute lymphoblastic leukemia with multiple secondary cytogenetic aberrations

BACKGROUND

We report a clinically diagnosed acute lymphoblastic leukemia (ALL) with yet unreported secondary chromosomal aberrations.

RESULTS

A complete cytogenetic and molecular cytogenetic analysis, using GTG banding, fluorescence in situ hybridization (FISH) and array-proven multicolor banding (aMCB), for a female patient with clinically diagnosed ALL and immunophenotypically confirmed pre-B ALL (FAB classifications), revealed the presence of a complex structural rearrangement, der (2) (20qter- > 20q13.33::2q21- > 2p14::2q21 > 2qter) along with t (9;22) (q34;q11), t (12;14) (q12;p12) and a monosomy of chromosome 7.

CONCLUSIONS

Molecular cytogenetic studies are suited best for identification and characterization of chromosomal rearrangements in acute leukemia. Single case reports as well as large scale studies are necessary to provide further insights in karyotypic changes taking place in human malignancies.

Current concepts in pediatric Philadelphia chromosome-positive acute lymphoblastic leukemia

The t(9;22)(q34;q11) or Philadelphia chromosome creates a BCR-ABL1 fusion gene encoding for a chimeric BCR-ABL1 protein. It is present in 3-4% of pediatric acute lymphoblastic leukemia (Ph(+) ALL), and about 25% of adult ALL cases. Prior to the advent of tyrosine kinase inhibitors (TKI), Ph(+) ALL was associated with a very poor prognosis despite the use of intensive chemotherapy and frequently hematopoietic stem-cell transplantation (HSCT) in first remission. The development of TKIs revolutionized the therapy of Ph(+) ALL. Addition of the first generation ABL1 class TKI imatinib to intensive chemotherapy dramatically increased the survival for children with Ph(+) ALL and established that many patients can be cured without HSCT. In parallel, the mechanistic understanding of Ph(+) ALL expanded exponentially through careful mapping of pathways downstream of BCR-ABL1, the discovery of mutations in master regulators of B-cell development such as IKZF1 (Ikaros), PAX5, and early B-cell factor (EBF), the recognition of the complex clonal architecture of Ph(+) ALL, and the delineation of genomic, epigenetic, and signaling abnormalities contributing to relapse and resistance. Still, many important basic and clinical questions remain unanswered. Current clinical trials are testing second generation TKIs in patients with newly diagnosed Ph(+) ALL. Neither the optimal duration of therapy nor the optimal chemotherapy backbone are currently defined. The role of HSCT in first remission and post-transplant TKI therapy also require further study. In addition, it will be crucial to continue to dig deeper into understanding Ph(+) ALL at a mechanistic level, and translate findings into complementary targeted approaches. Expanding targeted therapies hold great promise to decrease toxicity and improve survival in this high-risk disease, which provides a paradigm for how targeted therapies can be incorporated into treatment of other high-risk leukemias.

Individualized leukemia cell-population profiles in common B-cell acute lymphoblastic leukemia patients

Immunophenotype is critical for diagnosing common B-cell acute lymphoblastic leukemia (common ALL) and detecting minimal residual disease. We developed a protocol to explore the immunophenotypic profiles of common ALL based on the expression levels of the antigens associated with B lymphoid development, including IL-7Rα (CD127), cytoplasmic CD79a (cCD79a), CD19, VpreB (CD179a), and sIgm, which are successive and essential for progression of B cells along their developmental pathway. Analysis of the immunophenotypes of 48 common ALL cases showed that the immunophenotypic patterns were highly heterogeneous, with the leukemic cell population differing from case to case. Through the comprehensive analysis of immunophenotypic patterns, the profiles of patient-specific composite leukemia cell populations could provide detailed information helpful for the diagnosis, therapeutic monitoring, and individualized therapies for common ALL.

Aberrations of chromosomes 9 and 22 in acute lymphoblastic leukemia cases detected by ES-fluorescence in situ hybridization

A reciprocal translocation between chromosomes 9 and 22 creates oncogenic BCR/ABL fusion in the breakpoint region of the derivative chromosome 22. The aim of this study was to evaluate the importance of atypical fluorescence in situ hybridization (FISH) signal patterns in pediatric and adult acute lymphoblastic leukemia (ALL) cases. We evaluated t(9;22) translocation in 208 cases with ALL (294 tests), including 139 childhood and 69 adult cases by FISH technique using BCR/ABL extra signal (ES) probe. FISH signal patterns observed in pediatric ALL cases were as follows; Major-BCR/ABL (M-BCR/ABL) (1.4%), minor-BCR/ABL (m-BCR/ABL) (3.6%), trisomy 9 (4.3%), trisomy 22 (4.3%), trisomy or tetrasomy of both chromosomes 9 and 22 (2.9%), monosomy 9 (1.4%), monosomy 22 (0.7%), ABL gene amplification (1.4%), derivative chromosome 9 deletion (1.4%), and extra copies of the Philadelphia chromosome (1.4%). FISH signal patterns observed in adult ALL cases were as follows; M-BCR/ABL (5.8%), m-BCR/ABL (11.6%), two different cell clones with major and minor BCR/ABL signal pattern (2.9%), extra copies of Philadelphia chromosome (4.3%), derivative chromosome 9 deletion (1.4%), trisomy 9 (2.9%), tetraploidy (1.4%), monosomy 9 (1.4%), trisomy 22 (1.4%), and coexistence of both trisomy 22 and monosomy 9 (1.4%). Trisomy 9, trisomy 22, and polyploidy of chromosomes 9 and 22 were specific atypical FISH signal patterns for childhood B cell acute lymphoblastic leukemia (B-ALL) patients. However, monosomy 9 and ABL gene amplification were highly specific for childhood T cell acute lymphoblastic leukemia (T-ALL) patients. Our report presents the correlation between atypical FISH signal patterns and clinical findings of a large group of ALL cases.

Pathobiology of acute lymphoblastic leukemia

In the present review, the authors described the pathobiological features of B- and T-ALL, which appear to be quite heterogeneous with regard to molecular pathogenesis. The last edition of the World Health Organization Classification considered this aspect by defining many entities based on genetic findings. This approach is not only important for prognostic stratification, but also in the near future will surely represent the basis for the definition of patient-specific therapeutic approaches. A striking example is Ph+ acute lymphoblastic leukemia (ALL), which until the advent of tyrosine kinase inhibitors (TKI) has been regarded as the most aggressive ALL. The use of imatinib, dasatinib, and possibly more recent inhibitors has dramatically changed the clinical scenario, offering new opportunities to patients, especially the elderly. Similarly, the use of FLT3 inhibitors in mixed lineage leukemia-positive cases, gamma-secretase inhibitors in T-ALL, novel TKI, and monoclonal antibodies may represent a successful approach in the future.

Prognostic significance of immunophenotypic and karyotypic features of Philadelphia positive B-lymphoblastic leukemia in the era of tyrosine kinase inhibitors

BACKGROUND

Philadelphia chromosome (Ph)-positive B-lymphoblastic leukemia exhibits immunophenotypic, karyotypic, and molecular genetic heterogeneity. The prognostic significance of these parameters was assessed in the context of intensive tyrosine kinase inhibitor (TKI)-based chemotherapy.

METHODS

The authors studied 65 adult patients with Ph-positive acute lymphoblastic leukemia (ALL) who received treatment with TKI-based therapy, correlated their clinicopathologic heterogeneity with patient outcome, and compared the findings with those from 60 adult patients with diploid B-cell ALL who received similar chemotherapy without a TKI.

RESULTS

Ph-positive ALL was associated with older age (P = .01), the common-B immunophenotype characterized by a greater frequency of CD13 (alanine aminopeptidase) coexpression (P = .004), CD66c (carcinoembryonic antigen-related cell adhesion molecule 3) expression (P = .007), and CD25 (interleukin-2 receptor alpha chain) expression (P < .001) and with a lower frequency of CD15 (3-fucosyl-N-acetyl-lactosamine) expression (P < .001). Conventional karyotypic analyses indicated that the Ph chromosome was the sole abnormality in 19 patients (30%), was present with other aberrancies in 43 patients (65%), and was absent (detectable only by fluorescence in situ hybridization [FISH] or quantitative reverse transcriptase-polymerase chain reaction [RT-PCR] analysis) in 3 patients (5%). The presence of the breakpoint cluster region-v-Abelson murine leukemia viral oncogene homolog fusion gene (BCR-ABL) was confirmed in all patients by FISH or RT-PCR (the 190-kDa protein [p190] construct was present in 49 patients [77%], and the p210 fusion transcript construct was present in 15 patients [23%]). The presence of a supernumerary Ph chromosome was correlated with a higher incidence of CD20 (B-lymphocyte antigen, nonglycosylated phosphoprotein) expression (P < .001), whereas the p210 construct was correlated with aberrant CD25 expression (P = .05). Outcomes were not influenced by the degree of karyotypic complexity (including the presence or absence of a supernumerary Ph chromosome), CD20 expression, or myeloid antigen expression (CD13, CD33 [myeloid lineage transmembrane receptor], CD66c). CD25 expression was associated with inferior survival in univariate analysis (P = .051) but not in multivariate analysis (P = .092).

CONCLUSIONS

In the context of intensive, TKI-based chemotherapy, the immunophenotypic, karyotypic, and molecular heterogeneity of Ph-positive ALL no longer influences outcome.

Surrogate marker profiles for genetic lesions in acute leukemias

The basic hypothesis of surrogate marker profiles is that individual genetic lesions result in characteristic distortions of the cellular phenotype with some predictable consistency that can be exploited by sophisticated immunophenotyping. While cytogenetic and molecular aberrancies currently are accepted prognostic predictors in acute leukemias, single antigen expression and even antigenic profiles rarely impact on prognosis. However, increasingly, phenotypes are delineated which can serve as surrogates for underlying genetic aberrations of clinical importance. This development is of particular significance as antileukemic therapy becomes available that targets any component of the disturbed molecular pathways associated with these genetic lesions. This chapter will focus on established surrogate marker profiles, such as those for PML/RARα, AML1/ETO, FLT3-gene mutated acute lymphocytic leukemia (ALL), and BCR/ABL(POS) ALL. As the list of therapeutic targets grows, the role of surrogate antigen profiles will grow, as they can predict for the efficacy of targeted approaches in lieu of expensive, time-consuming and not always accessible genetic analyses.

Homozygous deletion of CDKN2A (p16, p14) and CDKN2B (p15) genes is a poor prognostic factor in adult but not in childhood B-lineage acute lymphoblastic leukemia: a comparative deletion and hypermethylation study

The biological behavior of childhood B-lineage acute lymphoblastic leukemia (B-ALL) is different from that of adults. We performed a comprehensive analysis of the deletion and the methylation profile of CDKN2A (hereafter identified separately as p16 and p14, for the different proteins encoded) and CDKN2B (hereafter p15) in 91 newly diagnosed B-ALL patients (61 children, 30 adults). The prognostic significance of the profiles of these genes and the association between alterations in these genes and known cytogenetic prognostic factors (BCR/ABL; ETV6/RUNX1, formerly TEL/AML1; MLL rearrangement; and ploidy changes of chromosomes) were also assessed. The prevalence of homozygous deletion, hemizygous deletion, and no deletion of the 9p21 region was 11.5%, 16.4%, and 72.1%, respectively, in children and 30.0%, 20.0%, and 50.0%, respectively, in adults; the higher incidence of homozygous deletion in adults was significant (P=0.029). Homozygous deletion was associated with poor overall survival in adults (P=0.019), but not in children. The incidence of promoter methylation of p16, p14, and p15 was 34.4%, 14.8%, and 34.4%, respectively, in children and 26.7%, 10.0%, and 40.0%, respectively, in adults, with no significant difference between the two groups. No significant association was observed between deletion and methylation or with known cytogenetic prognostic factors. The difference in incidence, distribution, and prognostic effect of homozygous deletion in children and adults may explain the prognostic disparity.

Long-term culture of primary human lymphoblastic leukemia cells in the absence of serum or hematopoietic growth factors

OBJECTIVE

B-lineage acute lymphoblastic leukemia (ALL) and chronic myeloid leukemia in lymphatic blastic phase in adults have poor prognoses despite intensive chemotherapy. Novel targeted treatment modalities emerge, but their evaluation requires relevant in vitro models of lymphoblastic leukemia. Presently available cell lines do not fully represent this heterogeneous disease. Available in vitro culturing protocols do not support long-term proliferation of primary cells. We therefore aimed to develop a culture system that allows long-term proliferation of primary human B-lineage lymphoblastic leukemia.

MATERIALS AND METHODS

Primary lymphoblastic leukemia cells were cultured in a defined serum-free medium, in the absence or presence of human hematopoietic growth factors or serum.

RESULTS

In the defined serum-free medium, cells from 12 of 34 cases immediately proliferated in vitro. In the absence of hematopoietic growth factors and serum these cases proliferated for more than 1 year without signs of exhaustion. The culturing system supported different subtypes of lymphoblastic leukemia. Two chronic myeloid leukemia in lymphatic blastic phase, four bcr/abl-positive ALL, one etv6/abl-positive ALL, 2 e2a-pbx1-positive ALL, and one t(9;11)-positive ALL could be long-term expanded, as well as two ALL that displayed nontypical cytogenetics. Not all bcr/abl- or e2a-pbx1-positive ALL proliferated in vitro, demonstrating heterogeneity within these subtypes. The proliferating bcr/abl- and etv6/abl-positive cells displayed sensitivity to imatinib, demonstrating that their proliferation depended on the activity of these oncoproteins.

CONCLUSION

The serum-free culturing system may be a valuable instrument in the study of ALL cell biology, as well as in the evaluation of novel targeted therapeutics.

High-risk acute lymphoblastic leukemia cells with bcr-abl and INK4A/ARF mutations retain susceptibility to alloreactive T cells

INK4A/ARF mutations are acquired in bcr/abl(+) lymphoid blast phase chronic myelogenous leukemia (CML) and bcr/abl(+) acute lymphoblastic leukemia (ALL). Donor lymphocyte infusion and graft-versus-leukemia (GVL) are generally ineffective in such ALLs, whereas GVL is highly active against bcr/abl(+) CML, which does not have a lesion in the INK4A/ARF locus. The mechanisms for the ineffectiveness of GVL are not fully known, and it is possible that intrinsic resistance of acute lymphoid leukemias to immune effectors associated with allogeneic GVL may contribute to ineffectiveness. This work tested the hypothesis that INK4A/ARF mutations that are associated with transformation of bcr/abl(+) CML to an ALL phenotype, and that are associated with increased resistance to apoptosis render ALL cells insensitive to allogeneic immune responses to minor histocompatibility antigens (mHA). Murine acute pre-B ALLs were induced by transfer of the human p210 bcr/abl gene into bone marrow of INK4A/ARF null mice. These ALL lines were then studied in a murine model of MHC-matched, mHA-mismatched allogeneic BMT. In vivo growth of these ALLs was inhibited in allogeneic transplants characterized by active allogeneic immune responses compared to their behavior in syngeneic transplants. In vitro ALLs with INK4A/ARF, p210 bcr/abl, or p190 bcr/abl mutations remained sensitive to anti-mHA cytolytic T cells. In addition, the ALLs were capable of inducing primary immune responses to mHAs in vivo. Thus, ALLs with INK4A/ARF or bcr/abl mutations are not intrinsically resistant to allogeneic T cell responses, suggesting that active immunotherapies against mHA have the potential to control such acute lymphoblastic leukemias.

Cytokine-dependent imatinib resistance in mouse BCR-ABL+, Arf-null lymphoblastic leukemia

Retroviral transduction of the BCR-ABL kinase into primary mouse bone marrow cells lacking the Arf tumor suppressor rapidly generates polyclonal populations of continuously self-renewing pre-B cells, virtually all of which have leukemic potential. Intravenous infusion of 20 such cells into healthy syngeneic mice induces rapidly fatal, transplantable lymphoblastic leukemias that resist imatinib therapy. Introduction of BCR-ABL into Arf-null severe combined immunodeficient (SCID) bone marrow progenitors lacking the cytokine receptor common gamma-chain yields leukemogenic pre-B cells that exhibit greater sensitivity to imatinib in vivo. Hence, salutary cytokines in the hematopoietic microenvironment can facilitate leukemic proliferation and confer resistance to targeted therapy.

Arf gene loss enhances oncogenicity and limits imatinib response in mouse models of Bcr-Abl-induced acute lymphoblastic leukemia

Mouse bone marrow cells transduced with retroviral vectors encoding either of two oncogenic Bcr-Abl isoforms (p210(Bcr-Abl) and p185(Bcr-Abl)) induce B cell lympholeukemias when transplanted into lethally irradiated mice. If the activity of the Arf tumor suppressor is compromised, these donor cells initiate a much more highly aggressive and rapidly fatal disease. When mouse bone marrow cells expressing Bcr-Abl are placed in short-term cultures selectively designed to support the outgrowth of pre-B cells, only those lacking one or two Arf alleles can initiate lympholeukemias when inoculated into immunocompetent, syngeneic recipient mice. Although the ABL kinase inhibitor imatinib mesylate (Gleevec) provides highly effective treatment for BCR-ABL-positive chronic myelogenous leukemia, it has proven far less efficacious in the treatment of BCR-ABL-positive acute lymphoblastic leukemias (ALLs), many of which sustain deletions of the INK4A-ARF (CDKN2A) tumor suppressor locus. Mice receiving Arf-/- or Arf+/- p210(Bcr-Abl)-positive pre-B cells do not achieve remission when maintained on high doses of oral imatinib therapy and rapidly succumb to lympholeukemia. Although cells expressing the Bcr-Abl kinase can proliferate in the absence of IL-7, they remain responsive to this cytokine, which can reduce their sensitivity to imatinib. Treatment of Arf-/-, p210(Bcr-Abl)-positive pre-B cells with imatinib together with an inhibitor of JAK kinases abrogates this resistance, suggesting that this combination may prove beneficial in the treatment of BCR-ABL-positive acute lymphoblastic leukemia.

Outcome of treatment in adults with Philadelphia chromosome-positive and/or BCR-ABL--positive acute lymphoblastic leukemia-retrospective analysis of Polish Adult Leukemia Group (PALG)

Patients with Philadelphia chromosome-positive (Ph+) and/or BCR-ABL+ acute lymphoblastic leukemia (ALL) have extremely poor prognoses. Most of these patients have additional, heterogenous karyotype abnormalities, the majority of which have uncertain clinical significance. In this study we analyzed the clinical characteristics, karyotype abnormalities, and outcome of 77 patients with Ph+ and/or BCR-ABL+ ALL registered in Poland in 1997-2004. In 31/55 patients with known karyotype, the sole t(9;22)(q34;q11) abnormality had been diagnosed; in one patient, variant translocation t(4;9;22)(q21q31.1;q34;q11), and additional abnormalities in 23 (42%) patients, had been diagnosed. The characteristics of the patients with Ph chromosome and additional abnormalities were not significantly different when compared with the entire analyzed group. Out of 77 patients, 54 (70%) achieved first complete remission (CR1) after one or more induction cycles. The overall survival (OS) probability of 2 years was 63, 43, and 17% for patients treated with allogeneic stem cell transplantation (alloSCT), autologous SCT, and chemotherapy, respectively (log rank p=0.002). Median OS from the time of alloSCT was significantly longer for patients transplanted in CR1 compared with alloSCT in CR >1 (p=0.032). There were no significant differences in CR rate, disease-free survival (DFS), and OS for patients with t(9;22) and additional abnormalities compared with the whole group. Only WBC >20 G/l at diagnosis adversely influenced OS probability (log rank p=0.0017). In conclusion, our data confirm poor outcome of Ph+ and/or BCR-ABL+ ALL. Only patients who received alloSCT in CR1 had longer DFS and OS. We have shown that additional karyotype abnormalities did not influence the clinical characteristics of the patients; however, their influence on treatment results needs to be further assessed.