Incidence of symptomatic Covid-19 infections in patients with mastocytosis and chronic myeloid leukemia: A comparison with the general Austrian population.

BACKGROUND: The SARS-COV-2 (Covid-19) pandemic has impacted the management of patients with hematologic disorders. In some entities, an increased risk for Covid-19 infections was reported, whereas others including chronic myeloid leukemia (CML) had a lower mortality. We have analyzed the prevalence of Covid-19 infections in patients with mastocytosis during the Covid-19 pandemic in comparison to data from CML patients and the general Austrian population. MATERIALS AND METHODS: The prevalence of infections and PCR-proven Covid-19 infections was analyzed in 92 patients with mastocytosis. As controls, we used 113 patients with CML and the expected prevalence of Covid-19 in the general Austrian population. RESULTS: In 25% of the patients with mastocytosis (23/92) signs and symptoms of infection, including fever (n = 11), dry cough (n = 10), sore throat (n = 12), pneumonia (n = 1), and dyspnea (n = 3) were recorded. Two (8.7%) of these symptomatic patients had a PCR-proven Covid-19 infection. Thus, the prevalence of Covid-19 infections in mastocytosis was 2.2%. The number of comorbidities, subtype of mastocytosis, regular exercise, smoking habits, age, or duration of disease at the time of interview did not differ significantly between patients with and without Covid-19 infections. In the CML cohort, 23.9% (27/113) of patients reported signs and symptoms of infection (fever, n = 8; dry cough, n = 17; sore throat, n = 11; dyspnea, n = 5). Six (22.2%) of the symptomatic patients had a PCR-proven Covid-19 infection. The prevalence of Covid-19 in all CML patients was 5.3%. The observed number of Covid-19 infections neither in mastocytosis nor in CML patients differed significantly from the expected number of Covid-19 infections in the Austrian population. CONCLUSIONS: Our data show no significant difference in the prevalence of Covid-19 infections among patients with mastocytosis, CML, and the general Austrian population and thus, in mastocytosis, the risk of a Covid-19 infection was not increased compared to the general population.

N-terminal pro-brain natriuretic peptide is a prognostic marker for response to intensive chemotherapy, early death, and overall survival in acute myeloid leukemia.

Patient-related factors are of prognostic importance in acute myeloid leukemia (AML). Likewise, cardiac disorders may limit the tolerance of intensive therapy. Little is known about the prognostic value of N-terminal pro-brain natriuretic peptide (NT-proBNP). We analyzed NT-proBNP levels at diagnosis in 312 AML patients (median age: 61 years; range 17-89 years) treated with 3 + 7-based induction-chemotherapy and consolidation with up to four cycles of intermediate or high-dose ARA-C. NT-proBNP levels were elevated in 199 patients (63.8%), normal (0-125 pg/ml) in 113 (36.2%), and highly elevated (>2000 pg/ml) in 20 patients (6.4%). Median NT-proBNP levels differed significantly among patients with complete remission (153.3 pg/ml), no remission (225.9 pg/ml), or early death (735.5 pg/ml) (p = .002). In multivariate analysis, NT-proBNP, age, and the 2009 European LeukemiaNet (ELN-2009) classification were independent predictors of outcome after induction chemotherapy. Overall survival (OS) differed significantly between patients with normal, moderately elevated, and highly elevated NT-proBNP (p < .001). These differences were observed in all patients and in patients <60 years but not in those ≥60 years. In multivariate analysis, NT-proBNP, age, and ELN-2009 remained independent prognostic variables for OS (p < .01). Together, NT-proBNP is an independent prognostic factor indicating the risk of induction failure, early death, and reduced OS in patients with AML.

Presence of viremia during febrile neutropenic episodes in patients undergoing chemotherapy for malignant neoplasms.

The importance of viral infections as a leading cause of morbidity and mortality is well documented in severely immunosuppressed patients undergoing allogeneic stem cell transplantation. By contrast, viral infections generally receive less attention in patients with malignant disorders undergoing chemotherapy, where the onset of neutropenic fever is mostly associated with bacterial or fungal infections, and screening for viral infections is not routinely performed. To address the occurrence of invasive viral infections in a clinical setting commonly associated with less pronounced immunosuppression, we have prospectively screened 237 febrile neutropenic episodes in pediatric (n = 77) and adult (n = 69) patients undergoing intensive chemotherapy, primarily for treatment of acute leukemia. Serial peripheral blood specimens were tested by RQ-PCR assays for the presence and quantity of the clinically relevant viruses CMV, EBV, HHV6 and HAdV, commonly reactivated in highly immunocompromised patients. Viremia was documented in 36 (15%) episodes investigated, including the detection of HHV6 (n = 14), EBV (n = 15), CMV (n = 6), or HAdV (n = 1). While low or intermediate levels of viremia (<104 virus copies/mL) were commonly associated with bacterial or fungal co-infection, viremia at higher levels (>104 copies/mL) was documented in patients without evidence for other infections, raising the possibility that at least in some instances the onset of fever may have been attributable to the virus detected. The observations suggest that viral infections, potentially resulting from reactivation, might also play a clinically relevant role in patients receiving chemotherapy for treatment of malignant neoplasms, and routine screening for viremia in this clinical setting might be warranted.

The KIT and PDGFRA switch-control inhibitor DCC-2618 blocks growth and survival of multiple neoplastic cell types in advanced mastocytosis.

Systemic mastocytosis is a complex disease defined by abnormal growth and accumulation of neoplastic mast cells in various organs. Most patients exhibit a D816V-mutated variant of KIT, which confers resistance against imatinib. Clinical problems in systemic mastocytosis arise from mediator-related symptoms and/or organ destruction caused by malignant expansion of neoplastic mast cells and/or other myeloid cells in various organ systems. DCC-2618 is a spectrum-selective pan KIT and PDGFRA inhibitor which blocks KIT D816V and multiple other kinase targets relevant to systemic mastocytosis. We found that DCC-2618 inhibits the proliferation and survival of various human mast cell lines (HMC-1, ROSA, MCPV-1) as well as primary neoplastic mast cells obtained from patients with advanced systemic mastocytosis (IC50 <1 µM). Moreover, DCC-2618 decreased growth and survival of primary neoplastic eosinophils obtained from patients with systemic mastocytosis or eosinophilic leukemia, leukemic monocytes obtained from patients with chronic myelomonocytic leukemia with or without concomitant systemic mastocytosis, and blast cells obtained from patients with acute myeloid leukemia. Furthermore, DCC-2618 was found to suppress the proliferation of endothelial cells, suggesting additional drug effects on systemic mastocytosis-related angiogenesis. Finally, DCC-2618 was found to downregulate IgE-mediated histamine release from basophils and tryptase release from mast cells. Together, DCC-2618 inhibits growth, survival and activation of multiple cell types relevant to advanced systemic mastocytosis. Whether DCC-2618 is effective in vivo in patients with advanced systemic mastocytosis is currently under investigation in clinical trials.

Intensive consolidation with G-CSF support: Tolerability, safety, reduced hospitalization, and efficacy in acute myeloid leukemia patients ≥60 years.

The aim of this study was to evaluate the efficacy and feasibility of intensified consolidation therapy employing fludarabine and ARA-C in cycle 1 and intermediate-dose ARA-C (IDAC) in cycles 2 through 4, in elderly acute myeloid leukemia (AML) patients and to analyze the effects of pegfilgrastim on the duration of neutropenia, overall toxicity, and hospitalization-time during consolidation in these patients. Thirty nine elderly patients with de novo AML (median age 69.9 years) who achieved complete remission (CR) after induction-chemotherapy were analyzed. To examine the effect of pegfilgrastim on neutropenia and hospitalization, we compared cycles 2 and 4 where pegfilgrastim was given routinely from day 6 (IDAC-P) with cycle 3 where pegfilgrastim was only administered in case of severe infections and/or prolonged neutropenia. All four planned cycles were administered in 23/39 patients (59.0%); 5/39 patients (12.8%) received 3 cycles, 3/39 (7.7%) 2 cycles, and 8/39 (20.5%) one consolidation-cycle. The median duration of severe neutropenia was 7 days in cycle 2 (IDAC-P), 11.5 days in cycle 3 (IDAC), and 7.5 days in cycle 4 (IDAC-P) (P < .05). Median overall survival was 1.1 years and differed significantly between patients aged <75 and ≥75 years (P < .05). The probability to be alive after 5 years was 32%. Together, intensified consolidation can be administered in AML patients ≥60, and those who are <75 may benefit from this therapy. Routine administration of pegfilgrastim during consolidation shortens the time of neutropenia and hospitalization in these patients.

Dipeptidylpeptidase IV (CD26) defines leukemic stem cells (LSC) in chronic myeloid leukemia.

Chronic myeloid leukemia (CML) is a stem cell (SC) neoplasm characterized by the BCR/ABL1 oncogene. Although mechanisms of BCR/ABL1-induced transformation are well-defined, little is known about effector-molecules contributing to malignant expansion and the extramedullary spread of leukemic SC (LSC) in CML. We have identified the cytokine-targeting surface enzyme dipeptidylpeptidase-IV (DPPIV/CD26) as a novel, specific and pathogenetically relevant biomarker of CD34(+)/CD38(─) CML LSC. In functional assays, CD26 was identified as target enzyme disrupting the SDF-1-CXCR4-axis by cleaving SDF-1, a chemotaxin recruiting CXCR4(+) SC. CD26 was not detected on normal SC or LSC in other hematopoietic malignancies. Correspondingly, CD26(+) LSC decreased to low or undetectable levels during successful treatment with imatinib. CD26(+) CML LSC engrafted NOD-SCID-IL-2Rγ(-/-) (NSG) mice with BCR/ABL1(+) cells, whereas CD26(─) SC from the same patients produced multilineage BCR/ABL1(-) engraftment. Finally, targeting of CD26 by gliptins suppressed the expansion of BCR/ABL1(+) cells. Together, CD26 is a new biomarker and target of CML LSC. CD26 expression may explain the abnormal extramedullary spread of CML LSC, and inhibition of CD26 may revert abnormal LSC function and support curative treatment approaches in this malignancy.

Karyotype plus NPM1 mutation status defines a group of elderly patients with AML (≥60 years) who benefit from intensive post-induction consolidation therapy.

Although it is generally appreciated that a subset of elderly patients with acute myeloid leukemia (AML) may benefit from intensive consolidation, little is known about variables predicting such benefit. We analyzed 192 consecutive patients with de novo AML aged ≥60 years who were treated with intensive chemotherapy. About 115 patients (60%) achieved complete hematologic remission (CR). Among several parameters, the karyotype was the only independent variable predicting CR (P < 0.05). About 92% (105/115) of the CR-patients received up to four consolidation cycles of intermediate dose ARA-C. Median continuous CR (CCR) and disease-free survival (DFS) were 1.3 and 1.1 years, respectively. CCR, DFS, and survival at 5 years were 23%, 18%, and 15%, respectively. Only karyotype and mutated NPM1 (NPM1mut) were independent predictors of survival. NPM1mut showed a particular prognostic impact in patients with normal (CN) or non-monosomal (Mkneg) karyotype by Haemato-Oncology Foundation for Adults in the Netherlands (HOVON)-criteria, or intermediate karyotype by Southwest Oncology Group (SWOG)-criteria. The median CCR was 0.94, 1.6, 0.9, and 0.5 years for core-binding-factor, CN/Mkneg-NPM1mut, CN/Mkneg-NPM1-wild-type AML, and AML with monosomal karyotype, respectively, and the 5-year survival was 25%, 39%, 2%, and 0%, respectively (P < 0.05). Similar results (0.9, 1.5, 0.9, and 0.5 years) were obtained using modified SWOG criteria and NPM1 mutation status (P < 0.05). In summary, elderly patients with CN/Mkneg-NPM1mut or CBF AML can achieve long term CCR when treated with intensive induction and consolidation therapy whereas most elderly patients with CN/Mkneg-NPM1wt or Mkpos AML may not benefit from intensive chemotherapy. For these patients either hematopoietic-stem-cell-transplantation or alternative treatments have to be considered. Am. J. Hematol. 91:1239-1245, 2016. © 2016 Wiley Periodicals, Inc.

CD34(+)/CD38(-) stem cells in chronic myeloid leukemia express Siglec-3 (CD33) and are responsive to the CD33-targeting drug gemtuzumab/ozogamicin.

BACKGROUND: CD33 is a well-known stem cell target in acute myeloid leukemia. So far, however, little is known about expression of CD33 on leukemic stem cells in chronic leukemias. DESIGN AND METHODS: We analyzed expression of CD33 in leukemic progenitors in chronic myeloid leukemia by multi-color flow cytometry and quantitative polymerase chain reaction. In addition, the effects of a CD33-targeting drug, gemtuzumab/ozogamicin, were examined. RESULTS: As assessed by flow cytometry, stem cell-enriched CD34(+)/CD38(-)/CD123(+) leukemic cells expressed significantly higher levels of CD33 compared to normal CD34(+)/CD38(-) stem cells. Moreover, highly enriched leukemic CD34(+)/CD38(-) cells (>98% purity) displayed higher levels of CD33 mRNA. In chronic phase patients, CD33 was found to be expressed invariably on most or all stem cells, whereas in accelerated or blast phase of the disease, the levels of CD33 on stem cells varied from donor to donor. The MDR1 antigen, supposedly involved in resistance against ozogamicin, was not detectable on leukemic CD34(+)/CD38(-) cells. Correspondingly, gemtuzumab/ozogamicin produced growth inhibition in leukemic progenitor cells in all patients tested. The effects of gemtuzumab/ozogamicin were dose-dependent, occurred at low concentrations, and were accompanied by apoptosis in suspension culture. Moreover, the drug was found to inhibit growth of leukemic cells in a colony assay and long-term culture-initiating cell assay. Finally, gemtuzumab/ozogamicin was found to synergize with nilotinib and bosutinib in inducing growth inhibition in leukemic cells. CONCLUSIONS: CD33 is expressed abundantly on immature CD34(+)/CD38(-) stem cells and may serve as a stem cell target in chronic myeloid leukemia.

Identification of CD203c as a New Basophil-Specific Flow-Marker in Ph+ Chronic Myeloid Leukemia.

Basophilia is a crucial prognostic variable in Ph-chromosome-positive chronic myeloid leukemia (CML). The ectoenzyme CD203c is an activation-linked surface antigen that is expressed specifically on basophil-committed progenitor cells and mature basophils. We examined the expression of CD203c on progenitors and/or basophils in 21 healthy donors and 44 patients with CML. As expected, the numbers of CD203c+ blood leukocytes were significantly higher in CML patients compared to controls (percentage of CD203c+ cells among viable cells in CML at diagnosis: 4.19 ± 3.68% vs. controls: 0.53 ± 0.23%, p < 0.05). Moreover, CML basophils expressed higher levels of CD203c compared to normal basophils (median staining-index in CML at diagnosis: 29.41 ± 19.14 versus controls: 20.44 ± 13.45). We also found that the numbers and percentage of circulating CD203c+ cells at diagnosis correlate with the disease-related risk-profile. Incubation of CML basophils with an anti-IgE-antibody resulted in further upregulation of CD203c. After successful treatment with imatinib and/or other BCR::ABL1 inhibitors leading to major or complete molecular responses, the numbers of CD203c+ basophils decreased substantially in our CML patients compared to pre-treatment values. Together, CD203c is overexpressed on CML basophils, is further upregulated by IgE receptor cross-linking, and may serve as a biomarker to quantify basophilia in patients with CML at diagnosis and during therapy.

Extensive pleural and pericardial effusion in chronic myeloid leukemia during treatment with dasatinib at 100 mg or 50 mg daily.

Dasatinib is considered an effective drug in imatinib-resistant chronic myeloid leukemia. Although reported to be well-tolerated, severe events such as pleural or pericardial effusion have been reported at 140 mg daily. We examined our chronic myeloid leukemia patients treated with dasatinib at 100 mg or 50 mg daily and identified 4 of 13 patients who developed marked effusion formation. In 2 patients, grade III/IV pleural and/or pericardial effusions were recorded. All 4 patients had received previous anti-leukemia therapy but none had pre-existing cardiac or pulmonary diseases. In 3 patients, dasatinib had to be discontinued despite treatment with diuretics and glucocorticosteroids. In conclusion, dasatinib-treated chronic myeloid leukemia patients are at risk for the development of pleural and pericardial effusions even when the drug is administered at 100 mg or 50 mg daily. Therefore, all patients should be examined for pre-existing comorbidity and risk factors before starting dasatinib and all should have repeated chest X-rays during long-term dasatinib therapy.

Progressive peripheral arterial occlusive disease and other vascular events during nilotinib therapy in CML.

The second generation BCR/ABL kinase inhibitor nilotinib is increasingly used for the treatment of imatinib-resistant chronic myeloid leukemia (CML). So far, nilotinib is considered a well-tolerated drug with little if any side effects, although an increase in the fasting glucose level has been reported. We examined a series of 24 consecutive CML patients treated with nilotinib in our center for the development of non-hematologic adverse events. Three of these 24 CML patients developed a rapidly progressive peripheral arterial occlusive disease (PAOD) during treatment with nilotinib. In all three cases, PAOD required repeated angioplasty and/or multiple surgeries within a few months. No PAOD was known before nilotinib-therapy in these patients, although all three had received imatinib. In two patients, pre-existing risk factors predisposing for PAOD were known, and one of them had developed diabetes mellitus during nilotinib. In the other 21 patients treated with nilotinib in our center, one less severe PAOD, one myocardial infarction, one spinal infarction, one subdural hematoma, and one sudden death of unknown etiology were recorded. In summary, treatment with nilotinib may be associated with an increased risk of vascular adverse events, including PAOD development. In a subgroup of patients, these events are severe or even life-threatening. Although the exact mechanisms remain unknown, we recommend screening for pre-existing PAOD and for vascular risk factors such as diabetes mellitus in all patients before starting nilotinib and in the follow up during nilotinib-therapy.

Impact of HFE gene variants on iron overload, overall survival and leukemia-free survival in myelodysplastic syndromes.

Although iron overload is a clinical challenge, little is known about the clinical impact of HFE-variants in myelodysplastic syndromes (MDS) to date. We analyzed the HFE status in 167 MDS patients and 494 healthy controls. One or more of the 3 HFE-variants (H63D, C282Y, S65C) were found in 65/167 (38.9%) MDS patients and in 164/494 (33.2%) controls. At diagnosis, the median serum ferritin levels were higher in MDS patients with HFE-variants (409 µg/L; range: 23-7415) compared to those without HFE-variants (346.5 µg/L; range: 10-5450) (P=0.62). Moreover, 'HFE-mutated' patients had a slightly faster increase in serum ferritin in follow up examinations. The percentage of patients with HFE-variants was higher in refractory anemia (RA) (22/53=41.5%) or RA with ring sideroblasts (RARS) (17/39=43.6%) compared to RA with excess of blasts (RAEB) (16/46=34.8%) or RAEB in transformation (RAEB-T) (5/17=29.4%). Differences were also detectable when comparing low- and high-risk MDS variants defined by the World Health Organization classification. There was no significant correlation between HFE-variants and MDS-related somatic mutations. Progression-free survival was substantially longer in patients with HFE-variants compared to those without HFE-variants H63D and C282Y (P=0.089). Together, the HFE-variants H63D and C282Y are frequently detected in Austrian MDS patients. These patients have substantially higher ferritin levels at diagnosis, accumulate iron slightly faster and have a better progression-free survival than non-mutated patients.

Delineation of target expression profiles in CD34+/CD38- and CD34+/CD38+ stem and progenitor cells in AML and CML.

In an attempt to identify novel markers and immunological targets in leukemic stem cells (LSCs) in acute myeloid leukemia (AML) and chronic myeloid leukemia (CML), we screened bone marrow (BM) samples from patients with AML (n = 274) or CML (n = 97) and controls (n = 288) for expression of cell membrane antigens on CD34+/CD38- and CD34+/CD38+ cells by multicolor flow cytometry. In addition, we established messenger RNA expression profiles in purified sorted CD34+/CD38- and CD34+/CD38+ cells using gene array and quantitative polymerase chain reaction. Aberrantly expressed markers were identified in all cohorts. In CML, CD34+/CD38- LSCs exhibited an almost invariable aberration profile, defined as CD25+/CD26+/CD56+/CD93+/IL-1RAP+. By contrast, in patients with AML, CD34+/CD38- cells variably expressed "aberrant" membrane antigens, including CD25 (48%), CD96 (40%), CD371 (CLL-1; 68%), and IL-1RAP (65%). With the exception of a subgroup of FLT3 internal tandem duplication-mutated patients, AML LSCs did not exhibit CD26. All other surface markers and target antigens detected on AML and/or CML LSCs, including CD33, CD44, CD47, CD52, CD105, CD114, CD117, CD133, CD135, CD184, and roundabout-4, were also found on normal BM stem cells. However, several of these surface targets, including CD25, CD33, and CD123, were expressed at higher levels on CD34+/CD38- LSCs compared with normal BM stem cells. Moreover, antibody-mediated immunological targeting through CD33 or CD52 resulted in LSC depletion in vitro and a substantially reduced LSC engraftment in NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice. Together, we have established surface marker and target expression profiles of AML LSCs and CML LSCs, which should facilitate LSC enrichment, diagnostic LSC phenotyping, and development of LSC-eradicating immunotherapies.

CDK4/CDK6 inhibition as a novel strategy to suppress the growth and survival of BCR-ABL1T315I+ clones in TKI-resistant CML.

PURPOSE: Ponatinib is the only approved tyrosine kinase inhibitor (TKI) suppressing BCR-ABL1T315I-mutated cells in chronic myeloid leukemia (CML). However, due to side effects and resistance, BCR-ABL1T315I-mutated CML remains a clinical challenge. Hydroxyurea (HU) has been used for cytoreduction in CML for decades. We found that HU suppresses or even eliminates BCR-ABL1T315I+ sub-clones in heavily pretreated CML patients. Based on this observation, we investigated the effects of HU on TKI-resistant CML cells in vitro. METHODS: Viability, apoptosis and proliferation of drug-exposed primary CML cells and BCR-ABL1+ cell lines were examined by flow cytometry and 3H-thymidine-uptake. Expression of drug targets was analyzed by qPCR and Western blotting. FINDINGS: HU was more effective in inhibiting the proliferation of leukemic cells harboring BCR-ABL1T315I or T315I-including compound-mutations compared to cells expressing wildtype BCR-ABL1. Moreover, HU synergized with ponatinib and ABL001 in inducing growth inhibition in CML cells. Furthermore, HU blocked cell cycle progression in leukemic cells, which was accompanied by decreased expression of CDK4 and CDK6. Palbociclib, a more specific CDK4/CDK6-inhibitor, was also found to suppress proliferation in primary CML cells and to synergize with ponatinib in producing growth inhibition in BCR-ABL1T315I+ cells, suggesting that suppression of CDK4/CDK6 may be a promising concept to overcome BCR-ABL1T315I-associated TKI resistance. INTERPRETATION: HU and the CDK4/CDK6-blocker palbociclib inhibit growth of CML clones expressing BCR-ABL1T315I or complex T315I-including compound-mutations. Clinical studies are required to confirm single drug effects and the efficacy of `ponatinib+HU´ and ´ponatinib+palbociclib´ combinations in advanced CML. FUNDING: This project was supported by the Austrian Science Funds (FWF) projects F4701-B20, F4704-B20 and P30625.

Phenotyping and Target Expression Profiling of CD34+/CD38- and CD34+/CD38+ Stem- and Progenitor cells in Acute Lymphoblastic Leukemia.

Leukemic stem cells (LSCs) are an emerging target of curative anti-leukemia therapy. In acute lymphoblastic leukemia (ALL), LSCs frequently express CD34 and often lack CD38. However, little is known about markers and targets expressed in ALL LSCs. We have examined marker- and target expression profiles in CD34+/CD38- LSCs in patients with Ph+ ALL (n = 22) and Ph- ALL (n = 27) by multi-color flow cytometry and qPCR. ALL LSCs expressed CD19 (B4), CD44 (Pgp-1), CD123 (IL-3RA), and CD184 (CXCR4) in all patients tested. Moreover, in various subgroups of patients, LSCs also displayed CD20 (MS4A1) (10/41 = 24%), CD22 (12/20 = 60%), CD33 (Siglec-3) (20/48 = 42%), CD52 (CAMPATH-1) (17/40 = 43%), IL-1RAP (13/29 = 45%), and/or CD135 (FLT3) (4/20 = 20%). CD25 (IL-2RA) and CD26 (DPPIV) were expressed on LSCs in Ph+ ALL exhibiting BCR/ABL1p210, whereas in Ph+ ALL with BCR/ABL1p190, LSCs variably expressed CD25 but did not express CD26. In Ph- ALL, CD34+/CD38- LSCs expressed IL-1RAP in 6/18 patients (33%), but did not express CD25 or CD26. Normal stem cells stained negative for CD25, CD26 and IL-1RAP, and expressed only low amounts of CD52. In xenotransplantation experiments, CD34+/CD38- and CD34+/CD38+ cells engrafted NSG mice after 12-20 weeks, and targeting with antibodies against CD33 and CD52 resulted in reduced engraftment. Together, LSCs in Ph+ and Ph- ALL display unique marker- and target expression profiles. In Ph+ ALL with BCR/ABL1p210, the LSC-phenotype closely resembles the marker-profile of CD34+/CD38- LSCs in chronic myeloid leukemia, confirming the close biologic relationship of these neoplasms. Targeting of LSCs with specific antibodies or related immunotherapies may facilitate LSC eradication in ALL.

TKI rotation-induced persistent deep molecular response in multi-resistant blast crisis of Ph+ CML.

In chronic myeloid leukemia (CML) resistance against one or more BCR-ABL1 tyrosine kinase inhibitors (TKI) remains a clinical challenge. Preclinical data suggest that TKI combinations may overcome resistance. We report on a heavily pre-treated 78 year-old female patient with CML who developed multi-resistant blast crisis with bone marrow fibrosis and a Ph- clone. Treatment with ponatinib resulted in blast cell clearance, decrease in fibrosis, and disappearance of BCR-ABL1, but also in severe thrombocytopenia with bleedings requiring platelet transfusions. We therefore switched from ponatinib to bosutinib. During bosutinib, platelet counts recovered. However, after 6 months, BCR-ABL1 mRNA levels increased to > 1%. Therefore, we ´switched back´ to ponatinib, and this was again followed by disappearance of BCR-ABL1 and a decrease in platelets. During the next 2 years, we applied ponatinib and bosutinib in continuous rotation-cycles and added hydroxyurea in order to suppress all sub-clones and to balance between efficacy and potential side effects following the principle of personalized medicine. With this approach the patient remained in complete molecular response and reached normal blood counts and a normal quality of life without vascular or other side effects. In conclusion, TKI rotation is a novel potent approach to suppress multiple resistant sub-clones and to balance between clinical efficacy and side effects in patients with advanced CML. Clinical trials are now warranted to show that TKI-rotation is in general safe and effective in these patients.

Maintenance therapy with histamine plus IL-2 induces a striking expansion of two CD56bright NK cell subpopulations in patients with acute myeloid leukemia and supports their activation.

Histamine dihydrochloride (HDC) plus IL-2 has been proposed as a novel maintenance-immunotherapy in acute myeloid leukemia (AML). We analyzed the immunophenotype and function of natural killer (NK) cells in blood of AML patients treated after chemotherapy with HDC plus IL-2. The treatment caused a striking expansion of CD56brightCD16neg and CD56brightCD16low NK cell subpopulations. A reduced NK cell fraction recovered and high proportions of cells expressed the activating receptors NKG2D, NKp30, and NKp46. Concomitantly, KIR-expressing NK cells were reduced and NK cells with inhibitory NKG2A/CD94 receptors increased beyond normal levels. In addition, the immunotherapy-induced NK cells exhibited high capacity to produce IFN-γ and to degranulate. Furthermore, we provide evidence from subsequent in vitro studies that this is caused in part by direct effects of IL-2 on the CD56bright cells. IL-2 specifically induced proliferation of both CD56bright subpopulations, but not of CD56dim cells. It further preserved the expression of activating receptors and the capacity to produce IFN-γ and to degranulate. These data suggest that therapy with HDC plus IL-2 supports the reconstitution of a deficient NK cell fraction through the specific amplification of CD56bright NK cells giving rise to a functional NK cell compartment with high potential to combat leukemic disease.

Identification of CD25 as STAT5-Dependent Growth Regulator of Leukemic Stem Cells in Ph+ CML.

PURPOSE: In chronic myelogenous leukemia (CML), leukemic stem cells (LSC) represent a critical target of therapy. However, little is known about markers and targets expressed by LSCs. The aim of this project was to identify novel relevant markers of CML LSCs. EXPERIMENTAL DESIGN: CML LSCs were examined by flow cytometry, qPCR, and various bioassays. In addition, we examined the multipotent CD25(+)CML cell line KU812. RESULTS: In contrast to normal hematopoietic stem cells, CD34(+)/CD38(-)CML LSCs expressed the IL-2 receptor alpha chain, IL-2RA (CD25). STAT5 was found to induce expression of CD25 in Lin(-)/Sca-1(+)/Kit(+)stem cells in C57Bl/6 mice. Correspondingly, shRNA-induced STAT5 depletion resulted in decreased CD25 expression in KU812 cells. Moreover, the BCR/ABL1 inhibitors nilotinib and ponatinib were found to decrease STAT5 activity and CD25 expression in KU812 cells and primary CML LSCs. A CD25-targeting shRNA was found to augment proliferation of KU812 cellsin vitroand their engraftmentin vivoin NOD/SCID-IL-2Rγ(-/-)mice. In drug-screening experiments, the PI3K/mTOR blocker BEZ235 promoted the expression of STAT5 and CD25 in CML cells. Finally, we found that BEZ235 produces synergistic antineoplastic effects on CML cells when applied in combination with nilotinib or ponatinib. CONCLUSIONS: CD25 is a novel STAT5-dependent marker of CML LSCs and may be useful for LSC detection and LSC isolation in clinical practice and basic science. Moreover, CD25 serves as a growth regulator of CML LSCs, which may have biologic and clinical implications and may pave the way for the development of new more effective LSC-eradicating treatment strategies in CML.

Serum-tryptase at diagnosis: a novel biomarker improving prognostication in Ph(+) CML.

Basophilia is an established prognostic variable in Ph-chromosome+ chronic myeloid leukemia (CML). However, in CML, basophils are often immature and thus escape microscopic quantification. We have previously shown that tryptase is produced and secreted by immature CML basophils. In the current study, serum samples of 79 CML patients (chronic phase=CP, n=69; accelerated/blast phase=AP/BP, n=10) treated with BCR/ABL inhibitors, were analyzed for their tryptase content. Serum-tryptase levels at diagnosis were found to correlate with basophil counts and were higher in AP/BP patients (median tryptase: 29.9 ng/mL) compared to patients with CP (11.7 ng/mL; p<0.05). In 20/69 patients with CP, progression occurred. The progression-rate was higher in patients with tryptase >15 ng/mL (31%) compared to those with normal tryptase levels (9%, p<0.05). To validate tryptase as new prognostic variable, we replaced basophils by tryptase levels in the EUTOS score. This modified EUTOS-T score was found to predict progression-free and event-free survival significantly better, with p values of 0.000064 and 0.00369, respectively, compared to the original EUTOS score (progression-free survival: p=0.019; event-free survival: p=0.156). In conclusion, our data show that the serum-tryptase level at diagnosis is a powerful prognostic biomarker in CML. Inclusion of tryptase in prognostic CML scores may improve their predictive value.