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Background Since the FDA approval of clofarabine for the treatment of relapsed or refractory acute lymphoblastic leukemia (ALL) at childhood, several studies have been launched which put clofarabine under scrutiny in combination with other cytostatic drugs as second or third line therapy. As a novel treatment-strategy we introduced the combination of clofarabine with pegylated asparaginase (PEG-ASP) in a randomized fashion in comparison to the standard consolidation course with high dose cytarabine (Hidac) combined with PEG-ASP into the frontline management of ALL within the CoALL 08-09 protocol. The primary objective of the study was to compare the MRD based assessment of the cytotoxic efficacy of the randomized courses in pediatric ALL. Patients and methods CoALL 08-09 was an open, interventional, multi-center, prospective, and randomized clinical trial for patients with newly diagnosed ALL. In March 2010 the trial had been opened for enrollment of patients under 18 years with confirmed diagnosis of acute B- or T-cell precursor leukemia. After a stratified phase I/II, in which patients with high-risk features and high post-induction MRD received the combination of clofarabine and PEG-ASP, the randomized trial started in November 2013. All patients with a measurable MRD at the end of induction (EOI), as measured by RQ-PCR according to EURO-MRD guidelines, were eligible for randomization to receive either the combination of clofarabine 5 x 40 mg/m2 or high dose cytarabine (HIDAC) 4 x 3g/m2 bothin combination with PEG-ASP 2.500 IU/m2 at the beginning of the consolidation phase. Until December 2019 303 study patients were randomized allocating 151 patients towards the clofarabine and 152 patients to the HIDAC arm. Patient characteristics and MRD burden prior to this treatment element were highly comparable. Results The reduction of minimal residual disease was significantly more profound after clofarabine compared to cytarabine (p(Cochran-Armitage)=.01 for BCP-ALL with 93 vs 79 patients reaching MRD negativity (Table 1). MRD status of BCP-ALL after the first randomized consolidation block (day 50) was of prognostic relevance with a statistically significant impact on EFS and relapse rate (Fig. 2a). However, no difference in outcome regarding the event-free and overall survival between the randomized arms was observed (5-year EFS: Clofarabine 85.7, SE=4.1 vs Hidac 84.8, SE=4.7 (p=.96) and OS: 95.7, SE=1.9 vs 92.2, SE=3.2(p=.59) Fig. 2b). This finding was recapitulated independent of gender, age, WBC count at diagnosis, ETV6-RUNX 1 translocation, immunophenotype or overall risk strata). Results for T-ALL patients are in the same range but because of small numbers not statistically significant. No differences in the incidence of severe or persistent toxicity btween randomized treatment elements as well as in the subsequent treatment realization were registered. Conclusion Clofarabine combined with PEG-asparaginase is highly effective and well tolerated in the frontline treatment of ALL. Although the prognostic impact of MRD is still discernible in early consolidation, the greater cytotoxic efficacy of clofarabine reflected by a more frequent eradication of MRD, did not translate into an apparent improvement of outcome likely due to a lack of power in the comparative analysis of randomized patients. Disclosures No relevant conflicts of interest to declare.

Accumulation of CD3(+) T-cell receptor (TCR)αβ(+)CD4(-)CD8(-) double-negative T cells (DNT) is a hallmark of autoimmune lymphoproliferative syndrome (ALPS). DNT origin and differentiation pathways remain controversial. Here we show that human ALPS DNT have features of terminally differentiated effector memory T cells reexpressing CD45RA(+) (TEMRA), but are CD27(+)CD28(+)KLRG1(-) and do not express the transcription factor T-bet. This unique phenotype was also detected among CD4(+) or CD8(+) ALPS TEMRA cells. T-cell receptor β deep sequencing revealed a significant fraction of shared CDR3 sequences between ALPS DNT and both CD4(+) and CD8(+)TEMRA cells. Moreover, in ALPS patients with a germ line FAS mutation and somatic loss of heterozygosity, in whom biallelic mutant cells can be tracked by absent Fas expression, Fas-negative T cells accumulated not only among DNT, but also among CD4(+) and CD8(+)TEMRA cells. These data indicate that in human Fas deficiency DNT cannot only derive from CD8(+), but also from CD4(+) T cells. Furthermore, defective Fas signaling leads to aberrant transcriptional programs and differentiation of subsets of CD4(+) and CD8(+) T cells. Accumulation of these cells before their double-negative state appears to be an important early event in the pathogenesis of lymphoproliferation in ALPS patients.

Familial hemophagocytic lymphohistiocytosis (FHL) is a genetically determined hyperinflammatory syndrome caused by uncontrolled immune response mediated by T-lymphocytes, natural killer (NK) cells, and macrophages. STXBP2 mutations have recently been associated with FHL5. To better characterize the genetic and clinical spectrum of FHL5, we analyzed a cohort of 185 patients with suspected FHL for mutations in STXBP2. We detected biallelic mutations in 37 patients from 28 families of various ethnic origins. Missense mutations and mutations affecting 1 of the exon 15 splice sites were the predominant changes detectable in this cohort. Patients with exon 15 splice-site mutations (n = 13) developed clinical manifestations significantly later than patients with other mutations (median age, 4.1 year vs 2 months) and showed less severe impairment of degranulation and cytotoxic function of NK cells and CTLs. Patients with FHL5 showed several atypical features, including sensorineural hearing deficit, abnormal bleeding, and, most frequently, severe diarrhea that was only present in early-onset disease. In conclusion, we report the largest cohort of patients with FHL5 so far, describe an extended disease spectrum, and demonstrate for the first time a clear genotype-phenotype correlation.

Butyrate induces cytodifferentiation in many tumor cells of different origin, suggesting that an as yet unidentified common mechanism inherent to malignant cells is the target of butyrate action. This study determined the role of different mitogen-activated protein (MAP) kinase signal transduction pathways in butyrate-induced erythroid differentiation of K562 human leukemia cells. Using a panel of anti-ERK, JNK, and p38 phosphospecific antibodies, the study showed that phosphorylation of ERK and JNK is decreased following treatment of cells with butyrate, whereas phosphorylation of p38 is increased. In contrast, a K562 subline defective in butyrate-mediated induction of erythroid differentiation did not reveal these changes in phosphorylation patterns. Inhibition of ERK activity by UO126 induces erythroid differentiation and acts synergistically with butyrate on hemoglobin synthesis and inhibition of cell proliferation, whereas inhibition of p38 activity by SB203580 completely abolished induction of hemoglobin expression by butyrate. Taken together, our data suggest a model in which butyrate induces erythroid differentiation of K562 cells by inhibition of ERK and activation of p38 signal transduction pathways.

Acute myeloid leukemia (AML) is a heterogenous disease according to morphology, immunophenotype, and genetics. The retained capacity of differentiation is the basis for the phenotypic classification of the bulk population of leukemic blasts and the identification of distinct subpopulations. Within the hierarchy of hematopoietic development and differentiation it is still unknown at which stage the malignant transformation occurs. It was our aim to analyze the potential involvement of cells with the immunophenotype of pluripotent stem cells in the leukemic process by the use of cytogenetic and cell sorting techniques. Cytogenetic analyses of bone marrow aspirates were performed in 13 patients with AML (11 de novo and 2 secondary) and showed karyotype abnormalities in 10 cases [2q+, +4, 6p, t(6:9), 7, +8 in 1 patient each and inv(16) in 4 patients each]. Aliquots of the samples were fractionated by fluorescence-activated cell sorting of CD34+ cells. Two subpopulations, CD34+/CD38-(early hematopoietic stem cells) and CD34+/CD38+ (more mature progenitor cells), were screened for karyotype aberations as a marker for leukemic cells. Clonal abnormalities and evaluable metaphases were found in 8 highly purified CD34+/CD38-populations and in 9 of the CD34+/CD38-specimens, respectively. In the majority of cases (CD34+/CD38-, 6 of 8 informative samples; CD34+/CD38+, 5 of 9 informative samples), the highly purified CD34+ specimens also contained cytogenetically normal cells. Secondary, progression-associated chromosomal changes (+8, 12) were identified in the CD34+/CD38-cells of 2 patients. We conclude that clonal karyotypic abnormalities are frequently found in the stem cell-like (CD34+/CD38-) and more mature (CD34+/CD38+) populations of patients with AML, irrespective of the phenotype of the bulk population of leukemic blasts and of the primary or secondary character of the leukemia. Our data suggest that, in AML, malignant transformation as well as disease progression may occur at the level of CD34+/CD38-cells with multilineage potential.

Pharmacologic stimulation of fetal hemoglobin (HbF) expression may be a promising approach for the treatment of β-thalassemia. In this study, we have investigated the HbF-inducing activity and molecular mechanisms of specific histone deacetylase (HDAC) inhibitors in human K562 erythroleukemia cells. Apicidin was the most potent agent compared with other HDAC inhibitors (trichostatin A, MS-275, HC-toxin, suberoylanilide hydroxamic acid [SAHA]) and previously tested compounds (butyrate, phenylbutyrate, isobutyramide, hydroxyurea, 5-aza-cytidine), leading to a 10-fold stimulation of HbF expression at nanomolar to micromolar concentrations. Hyperacetylation of histones correlated with the ability of HDAC inhibitors to stimulate HbF synthesis. Furthermore, analysis of different mitogen-activated protein (MAP) kinase signaling pathways revealed that p38 signaling was activated following apicidin treatment of cells and that inhibition of this pathway abolished the HbF-inducing effect of apicidin. Additionally, activation of the Aγ-globin promoter by apicidin could be inhibited by p38 inhibitor SB203580. In summary, the novel HDAC inhibitor apicidin was found to be a potent inducer of HbF synthesis in K562 cells. The present data outline the role of histone hyperacetylation and p38 MAP kinase signaling as molecular targets for pharmacologic stimulation of HbF production in erythroid cells.