Chronic Myelomonocytic Leukemia Samples Research Articles

Cellular Interactions within Clonal Dendritic Cell Aggregates Drive Immune Tolerance in Chronic Myelomonocytic Leukemia Bone Marrow Microenvironment

Introduction: Clonal dendritic cell (DC) aggregates in chronic myelomonocytic leukemia (CMML) are seen in approximately 20-30% patients at diagnosis. Previously, these were thought to be comprised of CD123+ plasmacytoid DCs but our data has suggested that these are heterogenous and comprise of myeloid DCs, monocytes, and myeloid-derived suppressor cells. Furthermore, these aggregates uniformly express immune checkpoints such as indoleamine 2,3-dioxygenase-1 (IDO), associate with an IDO-specific systemic impact (increased trytophan catabolism), and expanded regulatory T cell population in CMML, suggesting a role in inducing immune tolerance. DC aggregates are also associated with increased risk of acute myeloid leukemia (AML) transformation and resistance to hypomethylating agents, highlighting that they are important for disease progression in CMML (Mangaonkar A et al. Blood Adv 2020). We performed this study to decipher the architecture of a CMML DC aggregate to understand the complex inter-cellular interactions, and assess their impact on the adaptive immune system. Methods: In this study, we used archival fresh-frozen paraffin-embedded (FFPE) bone marrow biopsy specimens obtained from CMML patients, and isolated monocytes (CD14+ magnetic bead sorting) and lymphocytes (CD14-ve fraction) from untreated CMML and age-matched normal control (NC) peripheral blood mononuclear cells (PBMCs). DCs were cultured from monocytes using a commercial protocol. Spatial architecture of the CMML BM microenvironment was interrogated through multiplex imaging of FFPE samples by co-detection by indexing (CODEX) using 30 markers (CCR6, CD107a, CD11c, CD20, CD21, CD31, CD3e, CD4, CD44, CD45, CD45RO CD56, CD68, CD8, E-Cadherin, FoxP3, HLA-DR, CD14, CD16, CD11b, CD33, CD15, CD66b, CD123, CD303, CD34, CD163 and IDO). Single-cell transcriptomic signatures were analyzed using the 10X single cell Fixed RNA profiling platform, and validated using bulk RNA seq (Illumina stranded mRNA prep) from isolated and cultured cells. Impact of DCs on lymphocytes was assessed via autologous mixed DC-T culture experiments. Results: BM FFPE samples from 5 CMML cases (3 with DC aggregates) were included for multiplex imaging via CODEX. Results confirm the significant interactions of CD8+ and CD4+ T cells with CD123+/HLA-DR+ DCs within a CMML DC aggregate (Fig. 1A). Upon quantitative assessment of cell-cell interactions, IDO+/CD8+T ( P=0.006), IDO+/MDSC ( P=0.005), and IDO+/macrophage ( P=0.001) interactions were significantly increased in CMML samples with versus without DC aggregates . Specific findings were validated using single-stain immunohistochemistry and multiplex immunoflourescence staining. Next, in order to assess transcriptomic signatures within BM at the single-cell level, we chose two cases; CMML (BM aspirate blast% 1, WBC 49.6 x 10 9/L, ASXL1/GATA2/SETBP1/SRSF2 mutations) and AML transformed from CMML (BM aspirate blast% 81, WBC 152 x 10 9/L, NPM1/DNMT3A/TET2 mutations). Approximately, 10,000 cells were obtained and analyzed with cell type annotation through human PBMC reference (Azimuth). Results show an expanded regulatory T cell population in AML compared to CMML (UMAP plot, Fig. 1B), suggestive of immune tolerance. In order to validate findings and perform functional experiments, we used sorted monocytes and cutured DCs from CMML and NC. DC phenotype was confirmed both through visual inspection and flow cytometry, and clonality was confirmed through Sanger sequencing (for previously identified mutations). Differential gene expression analysis through bulk RNAseq showed significant differences between CMML and NC lymphocytes with immunoinhibitory receptor, LILRB2 (log2fold change=7.05, adjusted P=0.0002) being one of the top five significantly upregulated genes, further confirming immune tolerance. Finally, mixed autologous DC-lymphocyte reaction (1:4 ratio) experiments demonstrated that DCs induce T cell tolerance in CMML (expansion of exhausted PD1/TIM3/LAG3+ CD8 T cells) when compared to NC. Conclusion: Clonal dendritic cell aggregates within the CMML bone marrow microenviroment interact with T cells and induce immune tolerance. This represents a novel mechanism of disease progression in CMML with potential therapeutic targets (IDO, LILRB2, and/or CD123).

Phenotypic and Molecular Landscape of Bone Marrow CD8+ T Cells in Myeloid Neoplasms Predicts Response to Treatment with Hypomethylating Agents

Background and aims Myeloid malignancies encompass a diverse group of conditions, including myelodysplastic neoplasms (MDS) and chronic myelomonocytic leukemia (CMML). There is evidence suggesting the role of bone marrow (BM) environment and immune cells in the development and progression of MDS and CMML. Azacytidine (AZA) remains the backbone therapy for higher-risk MDS and non-proliferative CMML. To date, molecular predictors of response to AZA are not yet well-defined. Herein, we sought to investigate the immune landscape of BM samples from patients with lower-risk MDS (LR-MDS; i.e., IPSS-R <3.5), CMML, higher-risk MDS (HR-MDS; i.e., IPSS-R ≥3.5), and acute myeloid leukemia (AML). Methods Samples were collected before treatment initiation. Mass cytometry (CyTOF) was performed on isolated BM mononuclear cells from 48 patients, using the Maxpar® Direct™ Immune Profiling Assay. Flow cytometry was performed on a secondary cohort of 56 patients. scRNA-sequencing was performed on sorted BM CD8+ T cells from patients with HR-MDS (n=4) and AML (n=5), using a 10x Genomics pipeline. Mann-Whitney U test and the Kruskal-Wallis test were used as appropriate. Kaplan-Meier analysis was utilized for survival analysis, and the log-rank test was employed to assess the significance. The level of significance was established at P < 0.05. Results The immunophenotypic analysis using CyTOF demonstrated increased expression of CXCR3 on cytotoxic CD8+ T-cells in CMML and AML samples compared to samples from patients with MDS. Increased frequency of the CD57 +CXCR3 +CD8 + T-cell subset was further observed in patients with HR-MDS and AML that were non-responders to AZA, compared to responders, as observed by both CyTOF and flow cytometry. After determining the optimal cut-off for the frequency of CD8 +CD57 +CXCR3 + T cells at 29%, we observed that HR-MDS and AML patients (Figure 1A) with a frequency of CD57 +CXCR3 +CD8 + of <29% had better overall survival (OS).Multivariate analysisshowed that a frequency of CD57 +CXCR3 +CD8 + of >29% was independently associated with decreased survival in patients with TET2 mutations (HR=2.603; 1.275-5.317). scRNA-seq analysis of isolated BM CD8 + T cells was further performed to characterize the molecular signature that favors response to AZA, which resulted in the identification of several cell clusters based on gene expression. The cluster characterized by the expression of genes associated with cytotoxicity showed significant differences between responders and non-responders. Specifically, within the cytotoxic cluster, genes associated with IFN-related pathways were upregulated in cells from responders to AZA. In contrast, genes upregulated in non-responders displayed an enrichment for the TGF-β signaling pathway, which is known to be associated with the suppression of the killing capacity of T cells (Figure 1B). The aforementioned molecular signatures were further associated with a higher cytotoxic molecular signature in the cytotoxic cell cluster from the group of responders. Conclusion In this study, we focused on BM CD8 + T cells in samples from patients with myeloid neoplasias and performed deep phenotypic analysis using CyTOF coupled with scRNA, in order to characterize the BM immune environment. We demonstrate for the first time that BM CD8 + T cells show different phenotypic and transcriptomic characteristics in responders to AZA. Specifically, we show that the frequency of the effector CD57 +CXCR3 +CD8 + subset is decreased in responders before treatment initiation, and this is associated with better survival. Despite the decreased proportion of this cytotoxic cell population in responders, there are specific signatures associated with effector T cell functionality that can explain the improved outcomes in these patients. These findings underscore the significance of the crosstalk between leukemic and immune cells in the progression of the disease and the effect of treatment. Figure legend A. Increased (%) CD57 +CXCR3 + correlates significantly with worse survival of HR-MDS and AML patients. Kaplan Meier curves for Overall Survival in HR-MDS and AML patients respectively. B. Gene signature derived from the scRNAseq analysis. Interferon-stimulated gene (ISG) signature is increased in the cytotoxic cell cluster in responders and and TGF-β signature in non-responders.

Sting-Mediated Interferon Signaling Exerts Potent Antileukemic Effects in High-Risk Myeloid and Monocytic Malignancies

Clinical outcomes of patients (pts) with high-risk (HR) myeloid neoplasms remain dismal despite available therapies. Interferons (IFN) regulate hematopoietic stem-progenitor cell (HSPC) differentiation, proliferation and self-renewal capabilities and preferentially impair clonal HSPC fitness. To evaluate if myelodysplastic syndrome (MDS) and chronic myelomonocytic leukemia (CMML) HSPCs activate IFN responses we performed RNA sequencing in bone marrow (BM) CD34 + cells obtained from pts with MDS (n=58), CMML (n=27) and age-matched healthy donors (HDs, n=17). This analysis revealed significant deregulation of IFN pathway genes in HSPCs from pts with CMML and to a lesser extent in those of pts with MDS. Activation of the stimulator of interferon genes (STING) can inhibit stem-cell function and induce myeloid and monocytic cell death via IRF3-dependent and independent mechanisms. Therefore, we hypothesized that STING pathway activation might have therapeutic potential in high risk (HR) myeloid and monocytic (MyMo) neoplasms. In vitro treatment of monocytic MOLM13 and THP1 cell lines with the novel synthetic STING agonist dazostingag resulted in induction of IRF3 phosphorylation, caspase 3 cleavage and apoptosis. Dazostingag was also able to induce enhanced cell death in multiple myeloid cell line cultures. Given the ability of dazostingag to induce apoptosis of monocytic cell lines, we sought to evaluate the activity of monocyte-directed STING activation using TAK-500, an IgG1 anti-CCR2 antibody linked to dazostingag as a STING agonist payload. To do so, we first analyzed the expression of the monocyte-specific cysteine-cysteine chemokine receptor 2 (CCR2) in primary pts samples and cell lines. Both CCR2 RNA and protein expression levels were higher in CMML compared to HDs or MDS. In accordance with this finding, monocytic cell lines (MOLM13, THP1) had significantly higher CCR2 expression compared to non-monocytic cell lines (SKM1, HL60, U937, KG1). Treatment of MOLM13 and THP1 cell lines with TAK-500 induced strong IRF3 phosphorylation, caspase 3 cleavage and apoptosis. In vitro treatment of BM mononuclear cells (MNCs) from pts with MDS (n=10), CMML (n=11) or AML (n=8) in co-culture with mesenchymal stromal cells with TAK-500 (0.5 mM) or dazostingag (1 mM) resulted in increased cell death of MNCs from pts with CMML and AML. TAK-500 (0.5 mM) significantly depleted CCR2 + BM MNCs from all disease groups but did not affect CCR2 + cells from HDs. Next, to evaluate whether STING activation impairs repopulation potential of neoplastic HSPCs we performed colony-formation studies in CD34 + BM cells from pts with CMML (n=8), MDS (n=3) and AML (n=4). Treatment with TAK-500 (0.5mM) and dazostingag (1mM) resulted in significantly impaired myeloid colony-formation in all disease groups without significantly impairing erythroid colony-formation in MDS or CMML samples. Taken together, these data suggests that STING activation might induce aberrant myelomonocytic cell death and deplete aberrant HSPCs in HR-MyMo neoplasms. To evaluate the in vivo efficacy of TAK-500 and dazostingag, we established xenograft models by inoculating NOG-IL15 transgenic mice with MOLM13 cells. Treatment with TAK-500 and dazostingag resulted in reduction of tumor burden evaluated by bioluminescence with no observed toxicities. Administration of weekly doses of TAK-500 induced enhanced and sustained tumor burden suppression. To determine the in vivo effect of STING activation in an immune competent model of CMML, we then evaluated the effects of TAK-500 and dazostingag in Vav-KDM6B/Tet2 f/f/Vav-Cre mice, a previously reported (Wei et al Leukemia 2022) animal model with CMML phenotype. Treatment with TAK-500 led to enhanced apoptosis of Ccr2 + BM cells in these mice. Moreover, the number of colonies formed by lineage negative/Sca1 positive/cKit positive BM progenitor (LSK) cells isolated from TAK-500 treated mice was significantly lower than in vehicle treated control mice, suggesting a negative regulation of repopulating capacity of Tet2 deficient/ KDM6B overexpressing BM HSPCs by TAK-500. Evaluation of the efficacy of TAK-500 and dazostingag in patient-derived xenograft models of primary CMML samples is planned. Taken together, our data suggests that CCR2-directed STING activation might have therapeutic potential in HR-MyMo neoplasms by depleting CCR2 + cells and impairing clonal HSPC repopulation potential.

Chronic Myelomonocytic Leukemia Diagnosis By Flow Cytometry: An Italian Center Experience

Chronic myelomonocytic leukemia (CMML) is a myeloid neoplasm characterized by dysplasia, abnormal production of monocytes, and an increased risk of leukemic evolution. According to WHO, CMML patients show a persistent (≥3 months) absolute PB monocytosis (≥1×109/L) and relative monocytosis (≥10% of PB leukocytes), with the exclusion of Chronic Myeloid Leukemia (CML), Myeloproliferative Neoplasms, and a blast cell count <20% in PB and/or BM. In addition, morphological and/or histopathological evidence for diagnostic dysplasia ≥1 of the three major BM cell lineages must be present. If dysplasia is absent or not diagnostic (<10%), the presence of cytogenetic or molecular alterations or flow cytometry (FC) abnormalities may be utilized as co-criteria for the diagnosis of CMML. FC is helpful in confirming the monocyte and blast cell counts. In addition, FC is useful for confirming the presence of distinct monocyte populations. Based on the expression of CD14 and CD16, monocytes are classified into classical (MO1) (CD14+/CD16−), intermediate (MO2) (CD14+/CD16+) and non-classical (MO3) (CD14-/CD16+). FC analysis of PB monocytes was proposed as a quick and efficient tool for distinguishing CMML from reactive monocytosis by highlighting an increase in the MO1 fraction above 94% and a decrease in the percentage of MO3. Using FC, we evaluated 25 patients with a confirmed diagnosis of CMML in BM and PB samples, as well as 11 patients with other malignancies (MPN-monocytosis), and 28 patients with reactive monocytosis only in PB samples. Among these patients, 21/25 (84%) of CMML patients displayed MO1 ≥94%, while in patients with reactive monocytosis, MO1≥94% was observed in 11/28 (39%) and 2/11 (18%) in patients with MPN-monocytosis. Then we analyzed the MO3 fraction, which was <1.13% in 18/25 (72%) CMML patients, only one patient with MO1 lower than 94% resulted in an M3 fraction >1.13%. The evaluation of SLAN positivity in this fraction MO3 was always lower than 1.7%. The patient with MO1<94% and MO3 > 1.13% had an active ureteral carcinoma and, at NGS evaluation, had TET2, JAK2, and ZRSR2 mutations. In BM and PB samples from MPN patients, the MO3 fraction was in 2/11 <1.13%, the same patients with MO1> 94%, the diagnosis was a CML in one patient and a PMF triple negative in the other patient. PB samples from reactive monocytosis MO3 fraction were in 11/28 (39%) <1.13%, the same patients with MO1> 94%. The evaluation of SLAN positivity in this fraction MO3 in MPN and reactive monocytosis was always superior at 1.7% (range 4.9-60%). BM samples from CMML and MPN patients reflected the percentage of MO1 and MO3 of PB. Commonly PB and BM monocytes in CMML display aberrant expression of CD56. Furthermore, it was detectable a fraction of non-maturing neutrophils (CD66b+/CD11b-) in nearly half of CMML patients. In conclusion, our real-life experience of routinely FC study on PB and BM CMML samples is similar to the studies described in the literature. It confirms the comparable percentages of monocyte subpopulations in both samples, suggesting that PB samples can be used for diagnostic FC in these patients.

Single Cell Deconvolution of Myeloblasts Reveals Depletion of HSCs and Expansion of Inflammatory Granulocyte-Monocyte Progenitors (GMPs) Associated with Adverse Outcomes in Chronic Myelomonocytic Leukemia (CMML)

Single Cell Deconvolution of Myeloblasts Reveals Depletion of HSCs and Expansion of Inflammatory Granulocyte-Monocyte Progenitors (GMPs) Associated with Adverse Outcomes in Chronic Myelomonocytic Leukemia (CMML)

RNA Editing By APOBEC3A Confers Dynamic Mutational Load in Monocytic Leukemias

Background: Although genomic mutations play an important role in the initiation or progression of myeloid leukemias, the role of mutations at the transcript level is less well understood. Myeloid neoplasms have recurrent somatic mutations in genes for pre-mRNA splicing, cohesin complex, histone modification, and DNA methylation. However, the number of somatic mutations identified in myeloid neoplasms (average 9-13) is usually lower than that of solid tumors. Recent analyses of baseline transcriptome sequences in various cancers have revealed abundant adenosine to inosine (A>I) RNA editing events, mainly at intronic and untranslated regions of genes. The role of condition-specific RNA editing in cancer, especially of the cytosine to uracil (C>U) type, however, remains essentially unknown. We recently discovered antiviral restriction enzyme APOBEC3A (A3A) cytidine deaminase as a novel cellular site-specific C>U RNA editing enzyme in monocytes. RNA editing by A3A is dynamically induced by interferons and/or severe hypoxia in monocytes, resulting in stop codon gains or missense changes in transcripts of scores of genes. The effect of hypoxia in inducing RNA editing by A3A can be mimicked by inhibition of mitochondrial respiration. Whether A3A-mediated RNA editing occurs in monocytic leukemias, including acute monocytic leukemia (AMoL) and chronic myelomonocytic leukemia (CMML), is unknown. We hypothesize that dynamic C>U RNA editing by A3Acontributes to mutational load of leukemic cells under stressful conditions of hypoxia and interferon exposure. In this study, we examined transcript sequences of monocytic leukemias for evidence of inducible RNA editing. We also examined the role of mitochondrial respiratory inhibition, which induces RNA editing by A3A, in growth of leukemic progenitors of CMML.Methods: Monocytic leukemia samples are obtained from the RPCI Leukemia Bank. Standard diagnostic information included classification (WHO 2008 and FAB), fraction of monocytic component (mature monocytes, promonocytes or monoblasts by flow cytometry and/or aspirate differential count), cytogenetic analyses (conventional karyotype and targeted FISH), and survival data. Leukemic BM mononuclear cells (BM-MNC) prepared by the Ficoll gradient method are thawed and cultured in hypoxia (1% O2) with interferon type 1 (IFN-1). DNA and RNA are isolated. AMoL samples are subjected to nextgen high throughput exome and RNA sequencing. Once variants from DNA and RNA of corresponding samples are obtained, the set difference of variants is extracted to keep those detected on RNA samples. We also examined 3 CMML bone marrow samples for evidence of hypoxia-inducible RNA editing by analyzing selected RNA editing sites. Colony forming unit (CFU) assays are also performed in CMML samples.Results: We find that the A3A gene is robustly expressed inboth in AMoL and CMML. Hypoxia (with or without IFN-1) induced A3A-mediated RNA editing in AMoL and CMML samples. We previously showed that several RNA edited genes by A3A in normal monocytes function in recurrently altered pathways in myeloid leukemias. Sanger sequencing confirmed RNA editing of such genes in monocytic leukemia samples as well (Table 1), suggesting that epitranscriptomic sequence changes may contribute to molecular defects driving leukomogenesis. RNA seq analysis of AMoL samples (n=3) showed that dozens of genes acquire nonsense or missense mutations at the transcript level under the conditions of severe hypoxia and IFN-1. CFU assays of CMML samples showed that inhibition of mitochondrial respiration, which triggers A3A-mediated RNA editing, inhibits the growth of progenitor cells (Figure 1).Conclusions: We show that A3A-mediated RNA editing is active in monocytic leukemias and targets genes functioning in pathways recurrently altered in myeloid leukemias. RNA editing by A3A may contribute to growth arrest and survival of leukemic progenitors under certain stress conditions. To our knowledge, these results provide the first experimental evidence that conditional RNA editing by A3A confers substantial mutational load in myeloid leukemias. Such RNA editing events will dynamically increase the total mutational load in monocytic leukemias, and may create neo-antigens for immune therapy by checkpoint inhibition. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

LILRB4 expression in CMML and MDS based on response to hypomethylating agents.

e18550 Background: Leukocyte immunoglobulin-like receptor B4 (LILRB4) is expressed on M4 and M5 monocytic acute myeloid leukemia (AML) cells and leads to negative regulation of immune cell activation via T cell suppression. Its expression and role in chronic myelomonocytic leukemia (CMML) and myelodysplastic syndrome (MDS) are unknown. We investigated LILRB4 expression in patients with CMML and MDS and correlated it with response to hypomethylating agent (HMA) therapy. Methods: We evaluated bone marrow samples from 19 patients with CMML and 27 patients with MDS from 2008-2014. Transcriptomic and splicing analysis by RNA sequencing were performed on CD34-positive cells in CMML and MDS patient samples in addition to AML or MDS cell lines (n = 6). Gene set enrichment analysis was used to identify pathways associated with increased LILRB4 expression. Results: By the WHO 2016 classification for CMML, there were 8 CMML-0, 5 CMML-1, and 6 CMML-2 patients, and there were 2 low-risk, 8 intermediate-1-risk, 12 intermediate-2-risk, and 5 high-risk MDS patients by IPSS. A total of 12 CMML patients and 27 MDS patients received HMA, with 6 and 12 showing response, respectively. RNA expression of LILRB4 was increased in CMML patients when compared to MDS patients and healthy controls (q &lt; 0.1) with no difference in expression based on risk groups. Pathway analysis revealed upregulation of PD-1 signaling (p = 0.004), CTLA-4 signaling (p = 0.004), and inflammatory response (p = 0.004), and gene correlates revealed a positive association with CTLA-4 expression (p = 0.05). LILRB4 expression was slightly increased in CMML patients who responded to HMAs (q &gt; 0.1). In cell lines, LILRB4 was expressed in MOLM13 (AML M5), SKM1 (AML M5), and U937 (histiocytic lymphoma), with an increase in HMA-sensitive MOLM13 cells compared to HMA-resistant MOLM13 cells (q &lt; 0.01) and no difference based on HMAs seen in other cell lines. Conclusions: LILRB4 expression is increased in CMML, with further increase in those exhibiting response to HMA therapy. It is positively correlated with immune checkpoint signaling pathways, particularly CTLA-4 expression. This may set the basis for exploring the possibility of anti-LILRB4 and anti-CTLA-4 combinations.

Indoleamine 2,3-Dioxygenase-1 Expressing Dendritic Cell Populations Are Associated with Tumor-Induced Immune Tolerance & Aggressive Disease Biology in Chronic Myelomonocytic Leukemia

Introduction:Chronic myelomonocytic leukemia (CMML) is a chronic myeloid malignancy associated with monocytosis, autoimmunity (~30%) & an inherent risk for leukemic transformation. Bone marrow (BM) dendritic cell (DC) populations occur in ~30% of patients, with a poorly defined biological & prognostic role. The malignant immune microenvironment is regulated by indoleamine 2,3-dioxygenase-1 (IDO-1) expressing DCs, which modulate regulatory T (Treg) cells & block their conversion into proinflammatory T helper (Th17)-like cells. IDO-1 is a known immune checkpoint & functions by catabolizing tryptophan, an amino acid essential for T cell function. We hypothesized that distinct IDO-1 expressing DC populations in CMML modulate Tregs & contribute towards immune tolerance & aggressive disease biology.Methods:Primary diagnostic CMML peripheral blood mononuclear cells (PBMC) & BM biopsy specimens were obtained after Mayo Clinic IRB approval. A DC population was defined on H&E stained biopsy sections as focal collections (>10) of cells with characteristic elongated nuclei & cytoplasmic extensions. Transcriptomic & protein expression studies assessing IDO-1 expression were done by previously described methods. In addition, IHC expression of PD-1, PD-L1 & CTLA-4 was also done. IDO-1 promoter methylation studies with DIP-seq were performed. The impact on immune tolerance was assessed using mass cytometry (CyTOF).Results:Cohort: Twenty eight patients with CMML were included in the study, median age 70 (range: 51-80) years; 71% males. Eleven (39%) patients had coexisting autoimmune conditions. Of these, 8 (73%) had detectable DC populations either at diagnosis, or during the course of their disease. At a median follow-up of 46 (95% CI 27, 84) months, there were 14 (50%) deaths & 9 (32%) leukemic transformations.IHC results: Nine (32%) patients were identified to have a DC population at CMML diagnosis. CD123 & TCL1 staining was performed in 5 (56%) patients, with 3 being positive for both, & 2 positive for CD123 only (additional IHC studies ongoing). IDO1 expression by IHC was documented in all 9 (100%) cases (Fig 1A & 1B), while rare populations of PD-1, PD-L1 & CTLA-4 lymphocytes were also seen in all cases. Due to the low DC burdens (median cellularity ≤ 5%) & uniform staining intensity, IHC-based grading was not done. Samples at serial time-points, post-HMA therapy & at the time of blast transformation, were available in 5 & 3 patients respectively. Among the patients who did not have DC populations at diagnosis, 5 (42%) developed them post-HMA therapy, while 3 (50%) developed them at the time of LT. The development of DC populations was associated with loss of response to HMA (50%) & disease progression (50%).Transcriptomic analysis: RNA expression data was available on 7 (25%) patients, of whom only 1 (14%) had DC populations at diagnosis. The IDO-1 RPKM value in the former was higher than the mean pooled value in the latter group (330 versus 74, p=0.05).Methylation studies: DIP-seq was performed on 12 (43%) cases from the primary IHC cohort. Qualitative analysis of IDO-1 promoter hypomethylation was conducted & confirmed in all 9 (100%) cases with 5-mC & 5-hmC marks compared to input as displayed in figure 1C.Immune profiling: CyTOF was performed on 4 CMML samples (3 with IDO-1 expressing DC populations at diagnosis) from the primary IHC cohort & compared to a normal PBMC control. Results confirmed an increase in DC populations (fig 1D& 1E), & reduced % of Th17-like T cells in CMML samples compared to control (1.1 versus 5.07, p=0.05, fig 1F).Clinical correlates & survival analysis: With the exception that CMML patients with DC populations had a higher frequency of NRAS (P=0.007) mutations, the two groups were comparable for cytogenetic & molecular abnormalities. The median OS for the cohort was 45 (95% CI 29, 84) months. CMML patients with IDO-1 expressing DC populations at diagnosis had a shorter median OS, in comparison to those without (median OS 30 vs 45, p=0.03, Kaplan-Meier analysis in fig 1G).Conclusions:In conclusion, we demonstrate that DC populations are seen in ~30% of patients with CMML with a uniform expression of IDO-1 & limited expression of PD-1, PD-L1 & CTLA-4. CMML patients with BM DC populations have a higher frequency of NRAS mutations & DC IDO-1 expression is associated with tumor induced immune tolerance. Additional IHC, genomic & preclinical studies with IDO-1 inhibitors are ongoing. [Display omitted] DisclosuresAl-Kali:Novartis: Research Funding.

Evaluation of Combination Tagraxofusp (SL-401) and Hypomethylating Agent (HMA) Therapy for the Treatment of Chronic Myelomonocytic Leukemia (CMML)

Background: Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder that is characterized by cytopenias, organomegaly, constitutional symptoms, autoimmune phenomena, and ultimately progression to acute myeloid leukemia (AML). The only known cure for CMML remains allogeneic stem cell transplant. Aside from stem cell transplant, currently utilized therapeutic modalities include hydroxyurea, erythropoietin stimulating agents (ESAs) and hypomethylating agents (HMAs). Azacitidine (AZA) and Decitabine (DAC) have been utilized to treat CMML patients, particularly those with cytopenias, with variable efficacy such that complete response only occurs in a minority of patients. Recent work has identified CD123 (interleukin-3 receptor-α; IL-3R-α) as a potential therapeutic target in myeloid malignancies. CD123 is expressed in a variety of myeloid malignancies, including AML, myelodysplastic syndrome (MDS) and CMML. Further, plasmacytoid dendritic cell infiltrates (pDC) which are known to infiltrate the bone marrow in CMML, express CD123. Tagraxofusp (Elzonris™, SL-401) is a targeted therapy directed to CD123, comprised of recombinant IL-3 fused to a truncated diphtheria toxin payload. Clinical studies of tagraxofusp are being carried out in a variety of hematologic malignancies, including blastic plasmacytoid dendritic cell neoplasm (BPDCN), myelofibrosis (MF), and CMML. Data from an ongoing Phase I/II trial of tagraxofusp in relapsed/refractory CMML (n=16 patients) demonstrated spleen size reductions in 100% (8/8) patients with baseline splenomegaly and 2 bone marrow complete responses (BMCRs). Thus, tagraxofusp appears to have single agent clinical activity in CMML. Given this activity, and the known activity of HMAs in CMML, we sought to determine if combination HMA and tagraxofusp may provide added therapeutic utility over HMA therapy alone.Methods: To address this question, we performed preclinical studies using human leukemia cell lines as well as mononuclear cells from primary patient CMML samples. In order to determine active concentrations of both AZA and tagraxofusp in vitro, cell viability assays were performed. K562 cells, which have been previously demonstrated to express CD123, were first studied for sensitivity to AZA and tagraxofusp. The IC50 of AZA was 772uM and 4.8nM for tagraxofusp (Figure 1A). We next performed viability assays using fresh mononuclear cells from CMML patients. The IC50 of single agent AZA was 1442uM, whereas the IC50 of combination AZA and tagraxofusp (at a concentration of 4.8nM) was 725uM. As well, adding tagraxofusp at a concentration of 4.8nM to 1uM AZA in this assay induced a significant reduction in cell viability (Figure 1B; p<0.05). In colony assays, combination AZA and tagraxofusp significantly reduced colony formation when compared to single agent AZA alone (Figure 1 C-E, p<0.05). This effect was observed in samples with a relatively high sensitivity to AZA (Figure 1D) as well as in less sensitive samples (Figure 1E). Addition of AZA to increasing concentrations of tagraxofusp demonstrated a similar significant reduction in colony formation (Figure 1 F, p<0.05). Importantly, a combination effect was observed across samples of different genotypes including patient samples with high risk genotypes, including NRAS/ASXL1/TET2 (Figure 1E) and mutations in SRSF2/TET2/STAG2 (Figure 1C).Conclusions: Current therapeutic options for CMML are limited and CMML remains a significant unmet medical need. Although HMA therapy has demonstrated efficacy in CMML, the effects are often limited in extent and duration. Our preclinical data, including in primary CMML samples, demonstrates a potential therapeutic role for the combination of an HMA and tagraxofusp in CMML. Further in vitro data from primary patient samples, including impact of single and dual agent therapy on immunophenoytpe and clonal architecture, as well as in vivo efficacy data, will be presented. [Display omitted] DisclosuresChen:Stemline Therapeutics: Employment, Equity Ownership. Brooks:Stemline Therapeutics: Employment, Equity Ownership. Rampal:Constellation: Research Funding; Celgene: Honoraria; Jazz: Consultancy, Honoraria; Incyte: Honoraria, Research Funding; Stemline: Research Funding.

Gene Expression Profiling Identifies Distinct Signatures for Dysplastic and Proliferative Chronic Myelomonocytic Leukemia

Background: The 2016 revision to the World Health Organization classification of myeloid neoplasms has recommended distinction between "proliferative" (WBC ≥ 13 x 10(9)/L) and "dysplastic" (WBC < 13 X 10(9)/L) subtypes of chronic myelomonocytic leukemia (CMML). In addition, CMML is characterized by a spectrum of cytogenetic and molecular abnormalities (Patnaik Leukemia 2014). In the current study, we looked for correlations between gene expression profiles (GEP) and morphologic or molecular categories of previously untreated patients with CMML.Methods: 35 patients with CMML were included in the study. Targeted capture assays were carried out on BM DNA specimens obtained at diagnosis for 28 myeloid-relevant genes (Patnaik Blood C. J.). RNA sequencing (Stranded Total RNA- Illumina, San Diego, CA), was performed on 9 normal BM controls, and 35 CMML samples (25 peripheral blood (PB) and 10 BM). The RNA-Seq data was analyzed using MAPRSeq v.2.0. Normalization and differential expression analysis was performed using edgeR 2.6.2. We selected genes that were differentially expressed with a False Discovery Rate (FDR) <0.1 and a fold change bigger than 2. Pathway enrichment analysis was performed using Ingenuity Pathway Analysis (IPA).Results: Among the 35 study patients, 75% were males and median age was 71 years (range, 55-87). 21 (60%), 9 (25%) and 5 (15%) patients were classified as CMML-0, 1 and 2, respectively. 16 (45%) had a dysplastic while 19 (55%) had a proliferative phenotype. At a median follow-up of 16 months, 5 (14%) deaths and 4 (14%) leukemic transformations were documented. Mutational frequencies included; TET2 45%, ASXL1 45%, SRSF2 40%, NRAS 14%, SETBP1 13%, CBL 10%, JAK2 7%, RUNX1 6%, DNMT3A 6%, U2AF1 6%, SF3B1 5%, ZRSR2 4%, Tp53 4%, and IDH2 4%. Abnormal cytogenetics (n=9, 35%) included; -Y 8%, trisomy 8 6%, monosomy 7 3%, del(13q) 3% and monosomal karyotype 3%.i) Differential GEP in PB samples:25 PB CMML samples were analyzed. Unsupervised GEP demonstrated two unique clusters (figure one); cluster one was enriched with dysplastic CMML (90%) and cluster two with proliferative CMML (64%). Consistent with the difference in the distribution of morphologic categories, in comparison to cluster one, patients in cluster two had a higher white blood count (p=0.003), higher monocyte count (p=0.02) and higher risk prognostication by the Mayo Model (p=0.016); there was no significant difference between the two clusters in terms of age and gender distribution, hemoglobin level, neutrophil and platelet counts, PB or BM blast content, cytogenetic risk stratification, ASXL1, TET2, RAS, CBL and SETBP1 mutational status. Genes significantly upregulated (FDR<1e-5 and fold change ≥ 16x); in cluster two (proliferative CMML) in comparison to cluster one included; PRG2, CTSG, BEX1, CD34, CRISP2, while those significantly down-regulated included (FDR<1e-15 and fold change ≥ 5x); IL2RB, PRF1, GNLY, PDGFRB. IPA analysis identified the following pathways preferentially expressed in cluster two (proliferative CMML) 1) mitotic roles of polo-like kinase (KIF23, WEE-1, PLK1, PLK4), 2) Cell cycle: G2/M checkpoint regulation (CDC25C, WEE-1, AURKA, CDK1), 3) Cell cycle: chromosomal replication (CDC45, RPA3, MCM2, CDC7), and 4) BRCA1 in DNA damage response (BARD1, RBBP8, PLK1, RAD51). Whereas in the cluster one (dysplastic CMML), preferentially expressed pathways included; 1) T-cell receptor signalling (CD247 PRKCQ, CD4, PLCG1, CD28) and 2) STAT3 signalling (SOCS3, MAP3K9).ii) Differential GEP in BM samples:10 BM CMML samples were analyzed along with 10 normal controls. Samples and controls clustered separately and within the CMML samples two clusters were identified (figure two). These clusters had equal representations of dysplastic (n=5) and proliferative (n=5) CMML sub-types. Additional samples are being processed.Conclusions: Differential gene expression profiling in patients with CMML identifies two unique clusters, clinically demarcated, at least in PB samples, by "proliferative" and "dysplastic" CMML subtypes. The proliferative cluster is enriched in genes involved in cell cycle regulation and DNA damage response; whereas the dysplastic cluster is enriched in T-cell receptor and STAT3 signalling. The prognostic and therapeutic impact of these gene clusters remains to be assessed in a larger group of informative patients. [Display omitted] [Display omitted] DisclosuresAl-Kali:Novartis: Research Funding; Celgene: Research Funding.

Targeting Cell-Bound MUC1 on Myelomonocytic and Monocytic Leukemias and Leukemic Stem Cells: Therapeutic Implications

Monocytic neoplasms comprise a heterogeneous group of hematologic malignancies including chronic myelomonocytic leukemia (CMML), juvenile myelomonocytic leukemia (JMML), acute myelomonocytic and monocytic leukemia (AML-M4 and AML-M5), and monocytic sarcoma. Monocytic or granulomonocytic hyperplasia is a finding frequently-if not invariably-shared by these different entities, as is a poor therapeutic outcome in the absence of hematopoietic stem cell transplantation. Cell surface molecules aberrantly expressed or overexpressed by leukemic cells represent potential disease-specific therapeutic targets. MUC1, a polymorphic type I high molecular weight glycoprotein represents such a molecule. MUC1 consists of an extracellular domain containing 20 to 125 tandem repeats of a 20 amino acid-long sequence, followed by a transmembrane domain and a short cytoplasmic tail leading to intracellular signaling. Cleavage of MUC1 yields two unequal chains: a large extracellular alpha subunit containing the tandem repeat array bound in a strong non-covalent interaction to a smaller beta subunit containing the transmembrane and cytoplasmic domains. Essentially all anti-MUC1 antibodies reported to date target the highly immunogenic tandem repeat of the MUC1 alpha chain. Because the alpha chain binds the cell-bound domains of MUC1 only intermittently in an 'on-and-off' manner, agents directed against the alpha chain will not effectively target MUC1+ cells. In contrast, the MUC1 SEA domain represents a stable structure fixed to the cell surface at all times. We therefore generated mAbs that specifically recognize the cell-bound MUC1 SEA domain. One of them, a partially humanized murine mAb termed DMB-5F3 was used to examine the expression of MUC1 on AML cells by flow cytometry. A series of twenty-two AML samples (blood-derived n=12; bone marrow-derived n=10; AML0=2, AML1=2, AML2=10, AML4=1, AML5=5, AML6=2) collected either at the time of diagnosis or at relapse were analysed for MUC1 expression by flow cytometry. A murine mammary tumor cell line stably transfected with human MUC1 DNA served as control. Blasts cells from 5 AML samples highly expressed MUC1, and significantly, all were of monocytic or myelomonocytic lineage (AML4=1, AML5=4). Leukemic stem cells (CD34pos or CD34neg linneg) from the MUC1+ AMLs were examined and likewise found to express MUC1. In addition, AML cell lines MV411, MOLM14, and SHI-1 derived from monocytic leukemic lineage clearly expressed cell surface MUC1, while non- monocytic leukemic cell lines U937, K562, and HL60 had little or no expression. Normal monocytes and monocytes derived from patients with activated monocytosis were also found to express MUC1. Based on these findings we examined MUC1 expression in a series of myelomonocytic leukemia (CMML and JMML). In fifteen CMML samples examined (type 1 n=11, type 2 n=4) (blood n=7, BM n=7) 92%-100% (median 99.7%) of CD14+CD56+ CMML cells bound mAb DMB-5F3 to cell-surface MUC1. CD14+CD16+CD56+ blast cells from 2 pts with JMML were also found to express MUC1 (between 64% and 71 % positive). Based on these findings we conclude that expression of MUC1 is restricted to monocytic and myelomonocytic leukemias and that MUC1 represents an effective target for leukemic immunotherapy. Significantly, anti-MUC1 mAb also targets monocytic leukemic stem cells, reinforcing its therapeutic potential. The fact that the anti-MUC1 antibody DMB-5F3 can enter cells and thereby ferry Ab-bound toxin opens the way for us to demonstrate leukemic cell killing with anti-MUC1 mAb-immunotoxin conjugates. DisclosuresMoreau:Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen-Cilag: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees.

The Use of RNA Sequencing to Identify Disease-Specific Gene Expression Signatures and Critical Regulatory Networks Across Hematologic Malignancies

IntroductionTranscriptome analysis by next-generation sequencing (RNA-seq) allows investigation of hematologic malignancies at unsurpassed resolution and provides promising insights into their molecular etiology. Dissecting the underlying biology depends on specific molecular signatures deregulated in the disease subtypes. In addition, gene expression profiles may potentially be used to identify driver genetic alterations and stratify patients based on molecular subtype. In this study, we generated gene expression profiles from RNA-seq data derived from patients with hematologic disease, including acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL), chronic myelomonocytic leukemia (CMML), myelodysplastic syndrome (MDS), chronic myeloid leukemia (CML) and multiple myeloma (MM). Using these data, we aimed to identify disease-specific differentially expressed genes and gain better understanding of the biological functions of these genes for the development of biomarkers and therapeutic strategies in these malignancies.MethodsMononuclear cells (MNCs) were isolated from bone marrow or peripheral blood by Ficoll separation from AML (n=24), ALL (n=5), CMML (n=10), MDS (n=4), CML (n=2) and MM (n=7) patients. For MM, CD138+ cells were enriched from MNCs by immunomagnetic bead selection. Total RNA from isolated cells was depleted of ribosomal RNA and reverse transcribed for cDNA. RNA-seq libraries were prepared and sequenced on the Illumina HiSeq instrument. Reads were filtered and aligned to the hg19 human reference genome using TopHat. Second step normalization was carried out to compare gene expression values (FPKM) across samples using a normalization factor derived from 18 reference genes. A log normalized relative expression value for each gene was calculated compared to the median value across all samples. Average linkage based hierarchical clustering was performed and then visualized with TreeView. Network and pathway analyses were performed with IPA (www.ingenuity.com) and Cytoscape¨.ResultsUnsupervised hierarchical clustering of all samples resulted in grouping based on clinical phenotypes with a unique gene signature characteristic for each group (Figure). Analyses of different hematologic malignancies ensured credibility of the classification and highlighted differences in underlying cell signaling networks of each disease. Group I consisted of the multiple myeloma samples, where we identified 25 frequently upregulated genes. Network analyses revealed expression of the upregulated molecules is controlled by two major transcription factors, IRF4 and JUN, which represent the major hubs of the gene signature network. Group II consisted of samples with the BCR-ABL1 fusion and BCR-ABL-like ALLs. Enriched genes in this subgroup included regulators of B-cell development and maturation, plus genes involved in antigen presentation including TCL1A, CD19, CD79, HLA-DQA1, HLA-DQB1 and HLA-DRB1. Group III represented myelodysplastic and myeloproliferative neoplasms and included the MDS and CMML samples. A set of 14 genes differentially enriched in this group formed a unique pro-inflammatory signature. This included TNF-α and IL1B, which act as major regulators of smoldering inflammation driving NF-κB activity and orchestrating downstream activation of signature genes. While MM is known to have activated NF-κB signaling, the gene expression signatures of the MM and MDS/MPN groups were distinct from each other, and included activation of separate sets of cytokines and chemokines. AML samples exhibited heterogeneity in gene expression and formed two groups (IVA, IVB). A HOX gene family expression signature was observed in the FLT3-ITD positive AML samples.SummaryOur results show that RNA-seq can be used to identify dominant gene expression patterns characterizing different hematologic disease samples, including those sharing a common genetic base (e.g. BCR-ABL, FLT3-ITD) or clinical phenotype (e.g. MDS/MPN, MM). Based on our results, IRF4 may be an attractive therapeutic target for MM. CMML is difficult to diagnose, however, it can be defined by a set of differentially expressed genes that could potentially be used as diagnostic markers. We also show a pivotal role for NF-κB and TNF-α signaling in the pathogenesis of MDS/MPN suggesting that drugs targeting these factors may be useful for the treatment of these diseases. [Display omitted] DisclosuresPorkka:BMS: Honoraria; BMS: Research Funding; Novartis: Honoraria; Novartis: Research Funding; Pfizer: Research Funding. Kallioniemi:Medisapiens: Consultancy, Membership on an entity’s Board of Directors or advisory committees. Heckman:Celgene: Research Funding.

Evidence of ETNK1 Somatic Variants in Atypical Chronic Myeloid Leukemia

Atypical Chronic Myeloid Leukemia (aCML) is a clonal disorder belonging to the Myeloproliferative/Myelodysplastic (MPN/MDS) group. The molecular lesions responsible for the onset of aCML remained unknown until 2013 when recurrent somatic mutations of SETBP1 were identified. However, the frequency of SETBP1 mutations in aCML does not exceed 25-30%, which suggests that other lesions may play a role in the remaining cases.To gain further insight into the somatic variants responsible for the onset of aCML, we generated whole-exome and transcriptome sequencing data on 15 matched case/control aCML samples. A total of 151 non-synonymous and 42 synonymous single-nucleotide somatic variants were identified. Of these, 140 were transitions and 53 transversions. Of the non-synonymous mutations, 141 were missense and 10 nonsense mutations. In 2/15 (13.3%) samples we identified the presence of missense, single-nucleotide somatic variants occurring in the ETNK1 gene affecting two contiguous residues: H243Y and N244S. Sanger sequencing confirmed the presence and the somatic nature of the variants. Targeted resequencing of 383 clonal hematological disorders showed evidence of mutated ETNK1 in 7/70 aCML (10.0%, 95% C.I. 4.6-19.5%) and in 2/77 chronic myelomonocytic leukemia samples (CMML; 2.6%, 95% C.I. 0.2-9.5%) %), while no ETNK1 mutations were identified in the remaining hematological disorders. All the variants were heterozygous and clustered in the same, highly conserved region within the kinase domain (1/9 H243Y and 8/9 N244S).Somatic, heterozygous ETNK1 variants have been also recently reported in 10% of Systemic Mastocytosis (SM) cases and in 22% of SM with associated hypereosinophilia (Lasho T et al., Abstract 4062, EHA2014); strikingly, there is a large overlap between the variants that we identified in aCML and CMML and those described for SM (3 N244S and 2 G245A), which suggests that the common hotspot region may play a critical and yet unknown functional role.The hitherto described data suggest that ETNK1 variants are restricted to a limited subset of hematological disorders. This is further supported by the lack of somatic ETNK1 mutations in 60 paired whole-genome and over 600 exomes, comprising 276 paired tumor/germline primary samples and 344 cancer cell lines (http://cancer.sanger.ac.uk/cancergenome/projects/cell_lines/).In 2/6 ETNK1 mutated aCML cases (33%, 95% C.I. 9%-70%), we detected the presence of a coexisting somatic SETBP1 variant. The fraction of SETBP1 mutations identified in this group is perfectly in line with the overall frequency of SETBP1 mutations in aCML, suggesting that mutations occurring in ETNK1 and SETBP1 are not mutually exclusive. To discriminate if ETNK1 and SETBP1 mutations occur in different or in the same clone, we performed colony assay experiments, revealing the coexistence of the two somatic mutations within the same clone.Liquid Chromatography – Mass Spectrometry experiments revealed that in ETNK1 mutated cells the intracellular levels of phosphoethanolamine are over 5-fold lower than in the wild-type counterpart (p < 0.05), suggesting that ETNK1 mutations may impair the physiological catalytic activity of the kinase.Taken globally these data identify ETNK1 somatic mutations as a new oncogenic lesion in aCML and CMML, two overlapping MDS/MPN neoplasms. They also show that ETNK1 variants apparently cause a loss-of-function effect, leading to a decrease in the intracellular levels of phosphoethanolamine. DisclosuresCampbell:14M Genomics Limited: Consultancy, Equity Ownership.

Chronic Myelomonocytic Leukemia Monocytes Uniformly Display a Population of Monocytes With CD11c Underexpression

To examine the utility of CD11c expression on monocytes in normal controls and patients with chronic myelomonocytic leukemia (CMML) (n = 23) with flow cytometric immunophenotyping. Twenty-three CMML samples and 10 control bone marrows submitted for lymphoma staging without evidence of disease were examined. Monocytes in CMML samples ranged from 4% to 35%. Expression of at least one aberrant monocytic marker was found on the monocytes in 18 (82%) of 22 evaluable cases. The most common aberrancy was underexpression of CD11c (n = 15), while none of the bone marrow controls showed underexpression of CD11c. A distinct heterogeneous population of monocytic cells with underexpression of CD11c was identified in all these cases. CD11c underexpression was independent of other aberrancies, including HLA-DR underexpression (n = 14), aberrant CD56 expression (n = 11), and underexpression of CD33, CD38, and CD14 (n = 6, 5, and 5, respectively), supporting the utility of CD11c expression status on monocytes in establishing a CMML diagnosis.

GM-CSF–dependent pSTAT5 sensitivity is a feature with therapeutic potential in chronic myelomonocytic leukemia

AbstractGranulocyte-macrophage–colony-stimulating factor (GM-CSF) hypersensitivity is a hallmark of juvenile myelomonocytic leukemia (JMML) but has not been systematically shown in the related human disease chronic myelomonocytic leukemia (CMML). We find that primary CMML samples demonstrate GM-CSF–dependent hypersensitivity by hematopoietic colony formation assays and phospho-STAT5 (pSTAT5) flow cytometry compared with healthy donors. Among CMML patients, the pSTAT5 hypersensitive response positively correlated with high-risk disease, peripheral leukocytes, monocytes, and signaling-associated mutations. When compared with IL-3 and G-CSF, GM-CSF hypersensitivity was cytokine specific and thus a possible target for intervention in CMML. To explore this possibility, we treated primary CMML cells with KB003, a novel monoclonal anti–GM-CSF antibody, and JAK2 inhibitors. We found that an elevated proportion of immature GM-CSF receptor-α(R) subunit-expressing cells were present in the bone marrow myeloid compartment of CMML. In survival assays, we found that myeloid and monocytic progenitors were sensitive to GM-CSF signal inhibition. Our data indicate that a committed myeloid precursor expressing CD38 may represent the progenitor population with enhanced GM-CSF dependence in CMML, consistent with results in JMML. These preclinical data indicate that GM-CSF signaling inhibitors merit further investigation in CMML and that GM-CSFR expression on myeloid progenitors may be a biomarker for this therapy.

Preclinical Characterization of KB003, a Novel Humaneered™ Monoclonal Anti-GM-CSF Antibody, Demonstrates That the GM-CSF Signaling Axis Is a Therapeutic Target in Chronic Myelomonocytic Leukemia (CMML)

AbstractAbstract 3793 Introduction:Chronic Myelomonocytic Leukemia (CMML) is a genetically diverse hematologic malignancy characterized by cytopenias with or without leukocytosis, marrow dysplasia, monocytosis, splenomegaly, and a propensity to transform to Acute Myeloid Leukemia (AML). It is among the most aggressive chronic myeloid malignancies with a three year overall survival approximating twenty percent. The current treatment armamentarium is generally ineffective and mostly derived from studies that focused on Myelodysplastic Syndromes (MDS). As has been well defined in Juvenile Myelomonocytic Leukemia (JMML), we previously reported that primary CMML bone marrow mononuclear cells exhibit GM-CSF-dependent pSTAT5 hypersensitivity. To determine whether this signaling pathway is a viable therapeutic target, we present the preclinical characterization of KB003 activity on primary CMML bone marrow mononuclear cells. Methods:KB003 was engineered and provided by KaloBios Pharmaceuticals. The ability of KB003 to neutralize GM-CSF was tested in two ways using doses that ranged from .01 to 10,000 ng/ml of KB003. First, 10 ng/ml of GM-CSF was used to induce IL-8 production by the U937 cell line as measured by ELISA. Second, the GM-CSF-dependent cell line, MO7e, was cultured in the absence and in the presence of 0.1, 1, and 10 ng/ml of GM-CSF with or without KB003. Apoptosis and viability was assessed by annexin and 4′,6-diamidino-2-phenylindole (DAPI) staining by flow cytometry. To determine anti-GM-CSF sensitivity in CMML, primary cryoperserved bone marrow samples from 10 patients were reconstituted in prewarmed StemSpan H3000 with 10% FBS and microcultured in a 96 well plate with increasing doses of GM-CSF and KB003. After a 48-hour incubation period, cells were stained with myeloid-specific antibodies (CD34, CD38, CD14, CD33) and measured by multi-color flow cytometry. DAPI was used to measure cell viability. MethoCult hematopoietic progenitor assays were used to quantify the expansion and differentiation of CMML mononuclear cells in the presence of GM-CSF and escalating concentrations of KB003 in those samples with sufficient cell number for analysis (n=7). Results:KB003 effectively neutralized GM-CSF-induced IL-8 secretion in U937 cells with an IC50 of 48.2 ng/ml, as shown in Figure 1a. A dose of 0.1, 1, and 10 ng/ml of GM-CSF was used to protect MO7e cells from apoptosis and a survival benefit was achieved at each dose tested (Fig 1b). In this assay, KB003 neutralized 0.1 ng/ml of GM-CSF, but was unable to neutralize GM-CSF at higher doses (10 ng/ml). Using CMML samples, doses ranging from 10 to 100 μg/ml of KB003 were tested in apoptosis and in colony formation assays. Using the gating strategy shown in Figure 2a, the percentage of mature (CD33+/CD14+) and immature (CD33+/CD14-) myeloid subpopulations within the viable gate after KB003 treatment was decreased (Figure 2b). As expected, KB003 had no effect on CD3+ T-cells in the mixed culture populations. In addition to myeloid subpopulations identified by CD14, the CD33+/CD38+ cells were also more sensitive than CD33+/CD38- or CD38+/CD34+ inhibition by KB003 (Figure 2c, p<0.05). As shown in Figure 2d, hematopoetic colony formation assays confirmed the viability results. Using a one way ANOVA, there was a dose dependent decrease in the number of hematopoietic colonies, coupled with less organized and more diffuse appearance of colonies after KB003 treatment (Figure 2d). Conclusion:GM-CSF neutralization using KB003 suppresses CMML progenitor survival in vitro. These preclinical data suggest that KB003 and other GM-CSF signaling axis inhibitors merit further investigation in CMML. A more committed myeloid precursor expressing CD38 may represent the progenitor population with enhanced GM-CSF dependence in CMML. This is consistent with the results showing CD38 to be a marker of GM-CSF-dependent pSTAT5 sensitivity in JMML and may prove to be predictive biomarker for anti-GM-CSF therapy in CMML. [Display omitted] [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Human Monocytes and Monocyte-Like Cells Are Highly Sensitive to Plitidepsin-Induced Cell Death In In Vitro Assays

AbstractAbstract 4942Plitidepsin (Aplidin®) is a marine-derived cyclic depsipeptide with strong cytotoxic effects against a variety of cancer cell types. It is currently in Phase II/III clinical trials for solid and hematologic malignancies. We evaluated the cytotoxic effects of Plitidepsin on lymphoid and monocyte cells from healthy donors and analysed the mechanisms involved. We found that monocyte cells showed a markedly higher sensitivity to Plitidepsin compared to lymphoid subsets as determined by incorporation of 7-AAD and flow cytometry analysis. Plitidepsin induced a dose- and time-dependent cell death on freshly isolated monocytes (7-AAD+ cells at 24 h: control: 3±1% versus Plitidepsin 10 nM: 47±5%, mean±SEM, n=6) and on macrophages (5±2 vs 49±3, n=5) and dendritic cells (4±1 vs 21±4, n=5) differentiated in vitro. By contrast, resting or mitogen-activated lymphocytes were not affected by Plitidepsin at 10 nM. The mechanisms of induced cell death in monocytes involved the early exposure of phosphatidylserine to the outer leaflet of plasma membrane, activation of caspase-3 and subsequent PARP fragmentation, indicative of death via apoptosis. Incubation of monocytes with Plitidepsin (10 or 100 nM) for 30 minuntes induced ROS production. On the other hand, the cytotoxic effect of Plitidepsin was significantly diminished when monocytes were pre-incubated with the antioxidant reagent Ebselen, which acts as an scavenger of peroxynitrite. We also determined Plitidepsin activity on malignant cells from chronic myelomonocytic leukemia (CMML) and chronic lymphocytic leukemia (CLL) patients. Monocyte-like cells obtained from 3 CMML samples resulted sensitive to Plitidepsin, though to a different extent (viable CD14+ cells at 24 h: control 100%, incubated with Plitidepsin 10 nM: sample 1: 79%, sample 2: 82%, sample 3: 29%). Finally we evaluated the effects of Plitidepsin on nurse-like cells (NLC) from CLL patients. These cells represent a subset differentiated from monocytes that favours leukemic cell progression through pro-survival signals. NLC were very sensitive to Plitidepsin and, more importantly, their death indirectly decreased neoplasic clone viability (7-AAD+ leukemic B cells co-cultured with control NLC: 36±10 versus 7-AAD+ leukemic B cells co-cultured with NLC exposed to Plitidepsin 100 nM for 24 h: 47±6, n=5, p<0.05). Myeloid cells are present in tumor microenvironment and actively affect the malignant cells, both directly and indirectly via the suppression of host immunity. Given their relevance in supporting tumor growth, the sensitivity of monocyte-like cells to Plitidepsin may contribute to its antitumoral effects. Disclosures:Galmarini: PharmaMar: Employment, Equity Ownership. Giordano: PharmaMar: Research Funding.

Genetic characterization of TET1, TET2, and TET3 alterations in myeloid malignancies

AbstractDisease alleles that activate signal transduction are common in myeloid malignancies; however, there are additional unidentified mutations that contribute to myeloid transformation. Based on the recent identification of TET2 mutations, we evaluated the mutational status of TET1, TET2, and TET3 in myeloproliferative neoplasms (MPNs), chronic myelomonocytic leukemia (CMML), and acute myeloid leukemia (AML). Sequencing of TET2 in 408 paired tumor/normal samples distinguished between 68 somatic mutations and 6 novel single nucleotide polymorphisms and identified TET2 mutations in MPN (27 of 354, 7.6%), CMML (29 of 69, 42%), AML (11 of 91, 12%), and M7 AML (1 of 28, 3.6%) samples. We did not identify somatic TET1 or TET3 mutations or TET2 promoter hypermethylation in MPNs. TET2 mutations did not cluster in genetically defined MPN, CMML, or AML subsets but were associated with decreased overall survival in AML (P = .029). These data indicate that TET2 mutations are observed in different myeloid malignancies and may be important in AML prognosis.

MicroRNA Expression Profiles in Chronic Myelomonocytic Leukemia

Chronic myelomonocytic leukemia (CMML) is a hematopoietic malignancy with hybrid myeloproliferative and myelodysplastic features. The diagnostic criteria for CMML are evolving with the progress of our knowledge on various genetic lesions involved in the pathogenesis of myeloid neoplasms. This shift, including molecular genetic lesions in the diagnosis process, is highlighted in updated 2008 WHO classification system, which excludes myeloproliferative neoplasms with PDGFRB rearrangement, monocytosis and eosinophilia from CMML category. Despite these recent advancements, CMML remains a heterogeneous group of diseases with variable patient outcomes and no well-defined targeted therapy. To further investigate the biological diversity of this disorder, we studied microRNA (miRNA) expression profiles, their relation to the diagnostic and clinical parameters in CMML, and compared these profiles to global miRNA expression in normal reference bone marrow samples. MicroRNAs are a class of non-coding RNA molecules that alter gene expression by targeting and blocking mRNA. The role of miRNAs in carcinogenesis is related to their targeting of messenger RNAs encoding for oncogenes and tumor suppressor genes. Bone marrow samples from 22 patients with CMML were included in the study. Median age of the patients was 71 years with a range from 39 to 92 years. There were 15 males and 7 females. Seventeen patients presented with CMML-1 (blasts less than 5% in peripheral blood and less than 10% of bone marrow differential count). The remaining patients showed CMML-2. Nine patients had WBC below 13×109/L defining a myelodysplastic type of CMML. Cytogenetic results were available in 20 patients. Fourteen patients demonstrated a normal karyotype. Normal pooled bone marrow samples were used as a reference. The total RNA was isolated using RecoverAll RNA extraction kit. Micoroarray studies were performed using Agilent human miRNA microarrays (version 1.0) containing probes for 470 human and 64 human viral miRNAs cataloged in the Sanger database v9.1. The results were analyzed using BRB array tool and Genesis software. Unsupervised hierarchical clustering discovered two different groups of CMML samples with patterns of miRNA expression distinct from normal bone marrows (oneway ANOVA). Twenty seven miRNAs were differentially expressed in normal bone marrow reference samples vs. CMML-1 and -2. There was an overlap in miRNA profiles between groups of CMML based on blast percentage (CMML-1 vs. CMML-2), WBC count (<13×109/L vs. ≥13×109/L) and presence or absence of cytogenetic abnormalities. However, using PAM algorithm the following miRNAs showed predictive power: hsa-miR-519b (in CMML-1 vs. 2); hsa-miR-15b and hsa-miR-432* (in groups of samples separated by a cut-off WBC of 13×109/L) and hsa-miR-223 (comparing CMML with and without cytogenetic abnormalities). In summary, significantly different miRNA profiles were seen in CMML as compared to normal reference bone marrow. Two distinct subgroups of CMML were defined by the miRNA expression profiles. Select miRNAs were differentially expressed in known biological and clinical subgroups of CMML. Further correlation of clinical and outcome data with subgroups of CMML defined by miRNA expression profiles will be presented.

Bcl11a Causes p21Cip1 Down-Regulation and Transplantable Leukemia in Nf1-Deficient Mice.

Inactivation of the tumor suppressor gene, NF1, is associated with chronic and acute forms of myeloid diseases including juvenile myelomonocytic leukemia. Nf1-deficiency mouse models have shown some phenotypes reminiscent of those of the human disease. However, Nf1mutation in itself does not lead to leukemia. We reported the identification of 37 common proviral insertion sites, loci containing candidate genes whose mutation could cooperate with inactivation of Nf1 to result in BXH-2 AML. Among these candidate genes, Bcl11a, was able to cause leukemia/lymphoma in bone marrow transduction and transplantation assay using Nf1-deficient cells. In this report, we have found that transplantation of these leukemia cells induced secondary leukemia in syngeneic recipient mice. In patients, we previously reported that BCL11A was expressed in juvenile myelomonocytic leukemia and chronic myelomonocytic leukemia samples. Interestingly, high expression levels of BCL11A are also observed in two specific subsets of samples from a large cohort of patients with acute myelogenous leukemia. Moreover, these subsets of patients tended to have a worse outcome. Regarding the biochemical mechanisms underlying the oncogenicity of Bcl11a, we have recently found that p21Cip1 induction by doxorubicin is severely impaired in Bcl11a-expressing cells, while other cell-cycle regulatory proteins are not affected. Examination of BCL11A's role in leukemia patients using both over-expression and shRNA knocking-down approaches is underway.