Acute Myeloid Leukemia Bone Marrow Research Articles

Dysregulated Activating and Inhibitory Receptors on Natural Killer Cells Predicts Immune Escape and Poor Outcomes in Acute Myeloid Leukemia

Background: Although improvements have been made in understanding the pathophysiology of Acute Myeloid Leukemia (AML), heading to development of emerging therapies targeting leukemic stem cells, relapse is still a major problem leading to poor long-term survival and low cure rates. Of particular interest, Natural Killer (NK) cells are regulated by opposing signals from receptors that activate and inhibit effector function and are known to mediate anti-leukemic immunosurveillance in AML, but the mechanisms underlying the control of hematopoietic neoplasms by NK cells remains unclear and not yet explored as therapeutical options. Aims: We hypothesized that functionally impaired NK cells due to imbalanced expression of inhibitory and activating receptors can predict poor outcomes in AML. Methods: NK cell phenotypes based on the expression of DNAM-1 and NKG2D (activating) and NKG2A and KIR2DL1 (inhibitory) receptors on CD56+, CD56bright CD16- and CD56dim CD16+ NK subsets were profiled by multiparametric flow cytometry in 100 de novo AML bone marrow (BM) samples (Table 1), followed up from February 2016 to June 2022 and 17 healthy bone marrows (HBM). Correlations between NK phenotype with ELN2017 risk stratification, complete remission (CR), relapse (R), measurable residual disease (MRD), overall survival (OS) and relapse-free survival (RFS) were verified. Six BM from AML patients in remission after induction chemotherapy (AML-CR) were used to evaluate NK cell frequency and receptors recovery. Co-culture of AML-exposed CD56+ NK cells and K562 cell line was used to assay for killing (1:1, 5:1, 10:1 E:T ratios) and degranulation (CD107a). Mann Whitney, Kruskal-Wallis and mixed effects tests were performed to determine associations, and Log Rank test and Kaplan Meir curves were used for survival analysis. Results: The frequency of all NK cell subsets were decreased in AML (P < .01). AML CD56+ NK cells showed decreased expression of NKG2D (P < .01), a trending to decreased DNAM-1 and increased NKG2A (P = .04) and KIR2DL1 (P < .01), while recovering to near healthy values in AML-CR. Expression of both NKG2D and DNAM-1 activating receptors was decreased (P < .01), while inhibitory NKG2A (P = .02) and KIR2DL1 (P < .01) were considerably increased in CD56dim NK, which is known to carry out the most cytotoxic activity. The expression of both activating receptors by CD56dim subset was found to be decreased in ELN2017 adverse versus low/intermediate risk (NKG2D, P = .05; DNAM-1, P < .01), in relapse (P < .01), and with similar trends in MRD+ patients after remission induction. The opposite was observed for inhibitory receptors, found to be increased in adverse risk (P < .01), relapse (NKG2A, P < .01; KIRDL1, P < .05) and MRD+ (NKG2A, P = .03) patients. Degranulation (P < .01) and specific target cell death (5:1, P = .01; 10:1, P = .002) were significantly decreased in AML. Patients with lower frequency of CD56dim NK expressing low NKG2D and DNAM-1 showed less degranulation and specific target cell death (P = .03), whereas patients with higher inhibitory receptors demonstrated lower degranulation (NKG2A, P=0.06) and cytotoxicity (KIR2DL1, P=.005). Of note, RFS was decreased in patients with lower frequency of CD56+ NK cells (P = .02) and both OS and RFS were decreased in patients with lower frequency of CD56dim NK cells (OS, P = .04; RFS, P = .03) and in patients with lower expression of NKG2D (OS, P = .03; RFS, P = .008) and DNAM-1 (OS, P = .02; RFS, P = .11) activating receptors, strongly suggesting an imbalance between activation and inhibition of NK cell activity. Conclusion: Our data indicate that CD56dim NK show an exhaustion immunophenotype with high expression of KIR2DL1 and NKG2A inhibitory receptors and low expression of NKG2D and DNAM-1 activating receptors and that this imbalance leads to impaired cytotoxicity, compromised anti-leukemic activity and can be predictive of poor outcomes in AML, such as response to treatment, relapse and MRD positivity. Additionally, this NK phenotype at diagnosis could be considered an adverse risk prognostic factor associated with lower survival rates. Closing these gaps in the knowledge of NK-mediated immune evasion in leukemia is of significant interest for targeting the leukemic microenvironment by NK cell-mediated immunotherapy. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Full Spectrum 40-Parameter Single-Tube Flow Cytometry Analysis for Longitudinal Immunophenotyping and Tracing of Clonal Heterogeneity in AML

Acute Myeloid Leukemia (AML) remains notoriously difficult to treat. AMLs manifest themselves within individual patients with remarkable heterogeneity. Heterogeneity can be observed within the tumor itself, whereby multiple genetically distinct subclones can co-exist. We have shown that such differences in genetics translate into differences at the cell biological level as well (epigenome, transcriptome, proteome, metabolome and drug sensitivities) (de Boer et al. 2018) (Erdem et al. 2022). More recently, we began to dissect the heterogeneity within the tumor immune microenvironment. For instance, we identified a subgroup of AML patients that harbor a large population of tumor supportive M2 polarized macrophages in the bone marrow and these patients have the poorest prognosis. Reversely, patients with large populations of tumor suppressive M1 polarized macrophages display a much better prognosis. We also uncovered that patients with high levels of CD4+ T cells display a relatively favorable outcome. Little is known about clonal dynamics and microenvironmental changes over time or as a consequence of treatment. With the rise of new mutation-specific treatments targeting specific genetic subclones, it is important to examine the clonal composition of residual cells, especially at Measurable Residual Disease (MRD) timepoints. This can pose challenges as patients in morphologic complete remission have relatively low blast counts and limited material is available. Full spectrum flow cytometry is a novel technique that allows the use of 40 fluorescent markers in a single panel, enabling extensive immunophenotyping requiring relatively low cell numbers. We set up two antibody panels, one for immunophenotyping based on the OMIP-069 panel (39 colors) (Park et al. 2020) and one for the detection of subclones and macrophages (37 colors). We ran both panels on AML bone marrow samples at diagnosis (n=20), after initial induction therapy (n=4) and on normal bone marrow (NBM) (n=5). Full spectrum flow cytometry showed similar results to conventional flow cytometry, although with a higher resolution. With both panels combined we could identify and quantify 105 distinct cell types. UMAP landscapes were created as a template by merging AML samples and NBM samples, on top of which activation markers and aberrant AML-specific plasma membrane (PM) protein expression profiles could be projected. Additionally, density plots of individual patient samples were generated to compare longitudinal alterations in clonal dynamics and the tumor immune microenvironment before and after treatment. Additional univariate and multivariate survival analyses were performed to link observed changes to disease progression. At diagnosis, considerable heterogeneity amongst individual patients was observed, as expected. Patients either had a tumor supportive M2 macrophage phenotype or a tumor suppressive M1 macrophage phenotype. The lymphoid compartment was overall strongly reduced in AML compared to NBM, but was highly heterogeneous between individual patients whereby the strongest heterogeneity was noted in CD4+ and TCR gamma delta (TCRγδ) T cell subsets. Low levels of either CD4+ T cells and TCRγδ showed trends towards poorer prognosis. After induction therapy, the immune landscapes recovered and started to resemble those of NBM, most notably for T cell subsets but less so for B cells that took longer to recover. AMLs with an M2 phenotype at diagnosis shifted towards an M1 phenotype and non-classical monocytes shifted to more classical monocytes. In general, AML-specific PM markers were lost upon treatment reaching complete remission, although in some cases markers remained detectable within CD45+ blast populations. One patient containing NPMcyt (VAF=0.4) and FLT3-ITD (VAF=0.04) mutations was treated with gilteritinib in addition to cytarabine, reached morphologic complete remission whereby the FLT3-ITD mutation was lost, and the immune landscape restored. However, NPM1 droplet PCR analyses revealed the presence of residual mutant cells, which corresponded with residual cell numbers expressing aberrant CKIT/IL1RAP expression. Whether these cells will give rise to relapsed disease is currently under close investigation. We conclude that full spectrum flow cytometry is a powerful approach that allows extensive longitudinal immunophenotyping and subclone detection requiring low cell numbers. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Single-Cell Profiling of Acute Myeloid Leukemia Identified ARMH1, a Novel Protein Associated with Proliferation, Migration, and Drug Resistance

Despite advancements in treatments, half of pediatric acute myeloid leukemia (AML) patients relapse (Chen, J. & Glasser, C.L., 2020), making it pertinent to identify novel biomarkers that can be used for better stratification of patients post end of induction (EOI) therapy as well as to develop targeted therapies that could lead to higher clinical remission (CR) rates. Single-cell RNA sequencing (scRNAseq) analysis has revolutionized cancer research by identifying novel cell types, genes, and pathways. Our group used scRNAseq analysis of pediatric AML bone marrow (BM) samples collected at diagnosis (Dx) and EOI to identify the upregulation of multiple genes including a novel gene, Armadillo like helical domain containing 1 (ARMH1)/C1orf228, in cancerous blast cells (Thomas, B.E. et al., 2020). ARMH1 has not been previously associated with AML. Also, ARMH1 expression was observed to be significantly higher at Dx in samples from patients with relapse compared to samples from patients with CR (P<2.2e-16). Independent validation for ARMH1 blast-association using single cell and bulk transcriptome profiling revealed that ARMH1 expression was significantly higher in scRNAseq data of AML Dx blast cells compared to EOI non-blast cells (fold change, FC=1.8, P<2.2e-31) as well as in bulk RNAseq data of Dx samples with high blast% (>90%) compared to EOI samples (FC=1.8, P=.003) (Ulukaya, G. et al., 2021). Further analysis on other leukemias like T cell-acute lymphocytic leukemia (T-ALL) and mixed phenotypic acute leukemia (MPAL) also revealed higher expression of ARMH1 in the blast cells as compared to non-blast cells. Survival analysis on bulk RNAseq data using the survival genie platform (Dwivedi, B. et al., 2022) revealed that higher expression of ARMH1 was significantly associated with poor overall survival (OS) in both AML (P=.003) (Ulukaya, G. et al., 2021) and T-ALL (P=.014) datasets. Comparative gene expression analysis using the the Pediatric Single Cell Cancer Atlas - PedSCAtlas - tool (Mumme, H.L. et al., 2021), revealed negligible expression of ARMH1 in normal lymphoid, myeloid, and erythroid cell lineages, further confirming the leukemic blasts-specific over-expression of ARMH1. ARMH1 encodes a cytosolic protein of yet unknown function. The malignant blast specificity of ARMH1 suggested a role in leukemic cells' survival/maintenance. To ascertain its functional involvement in cancer cells, ARMH1 was silenced using siRNAs in both normal and AML cell lines. Through in vitro assays, we demonstrate that ARMH1 silencing significantly reduced leukemic cells' capacity to proliferate (P=.0041) and migrate (P=.0001). We also observed slightly increased sensitivity to chemotherapy drug, Cytarabine in the ARMH1 silenced cancer cells compared to control cancer cells in which the gene is fully functional. However, suppression of ARMH1 expression had no effect on cell growth in the normal HEK293t cell line (P=0.913). On the other hand, overexpression of ARMH1 via transient transfection of ARMH1 gene into the AML cell line, made the cells more resistant to Cytarabine and significantly increased both migration (P=.041) and cell proliferation (P=.032). In conclusion, we demonstrate for the first time that ARMH1, a still poorly understood protein, contributes to the increased proliferation and migration of malignant AML cells. With specific overexpression in blast cells of several pediatric leukemias and the newly discovered roles in proliferation, migration, and chemotherapy resistance, ARMH1 may be a good candidate for targeted treatment of pediatric leukemias.

Preclinical Characterization of NGM936, a Novel Bispecific T Cell Engager Targeting ILT3 for the Treatment of Acute Myeloid Leukemia with Monocytic Differentiation

Acute myeloid leukemia (AML) with monocytic differentiation [M4 and M5 AML per the French-American-British (FAB) classification] accounts for 25-30% of all AML cases and has a particularly poor prognosis, with a <15% five-year overall survival rate and an increased risk of bone marrow and extramedullary relapse after stem cell transplant compared with other AML subtypes. The use of T cell engagers in AML has been limited by the lack of suitable target antigens with high specificity for AML cells and minimal expression on healthy bone marrow progenitors. Immunoglobulin-like transcript 3 (ILT3, also known as LILRB4) is a highly specific marker of AML with monocytic differentiation and is not expressed on non-monocytic blood cells or hematopoietic progenitor cells. This highly restricted expression profile makes ILT3 a promising target for monocytic AML, with the potential to enable effective elimination of AML cells with less toxicity than current therapies. Here, we report the pre-clinical characterization of NGM936, an ILT3-based T cell engager for the treatment of monocytic AML and other ILT3+ hematologic malignancies. NGM936 is a monovalent scFv-Fab bispecific on an effectorless human IgG1 backbone (LALA) with a knob-in-hole Fc design for heterodimeric assembly. NGM936 demonstrates sub-nM affinity towards ILT3 of human origin (KD = 0.2 nM at 25°C by surface plasmon resonance) and is not cross-reactive towards other LILRA/B family members. A panel of more than 30 ILT3 x CD3 engagers in various formats was generated and screened in assays to measure both T cell-dependent cytotoxicity and cytokine release. NGM936 was identified for its ability to potently induce T cell-dependent cytotoxicity (TDCC) against ILT3+ AML cells while inducing minimal cytokine release. In both whole blood cytokine release assays and in TDCC assays in which cytokine secretion was measured after target engagement, induction of TNF-α, IL-6, IFN-γ, and IL-2 by NGM936 was considerably lower than that induced by a vibecotamab biosimilar (CD123 x CD3). NGM936 induced potent cytotoxicity when both expanded and naïve T cells were used as effectors. Importantly, NGM936 efficiently ablated tumor cells with a range of ILT3 expression, from ~1500 copies/cell to ~40,000 copies/cell. In addition, NGM936 failed to induce T cell-dependent cytotoxicity against CD34+ hematopoietic stem cells or non-monocytic immune cells, consistent with the lack of ILT3 expression on these cell types. In ex vivo cultures of primary M5 AML bone marrow, NGM936 induced a dose-dependent depletion of AML cells and a concordant increase in T cell proliferation and activation. Finally, NGM936 induced a dose-dependent depletion of circulating tumor cells in a xenograft model in which irradiated, immunodeficient NSG mice were engrafted with human PBMCs and human ILT3+ AML cells. NGM936 thus represents a promising new treatment strategy for monocytic AML, with the potential to eliminate monocytic leukemia cells while minimizing the myelotoxicity associated with ablation of healthy bone marrow.

MP0533: A Multispecific Darpin CD3 Engager Targeting CD33, CD123, and CD70 for the Treatment of AML and MDS Designed to Selectively Target Leukemic Stem Cells

Introduction: Acute myeloid leukemia (AML) is driven by leukemia stem cells (LSCs) that resist conventional chemotherapy and are the major cause of relapse. Newer therapies, including chimeric antigen receptor (CAR) T cells and T cell engagers (TCE) that target specific tumor associated antigens (TAAs) overexpressed on stem cells and leukemic blasts, are promising options for AML. We postulated that a TCE able to simultaneously target multiple TAAs could allow highly efficient and specific T cell-mediated killing of AML LSCs and circulating blast cells while minimally affecting healthy cells. Moreover, the simultaneous targeting of different TAAs has the potential to address tumor heterogeneity, allowing targeting of AML cells with different co-expression patterns and/or expression levels of each TAA. Methods: Our DARPin (Designed Ankyrin Repeat Protein) libraries contain trillions of molecules allowing the generation of highly diverse binders against target proteins that can be easily combined into multi-specific DARPins to elicit desired biological effects. We leveraged this proprietary platform to screen multi-specific CD3 engaging DARPin molecules, including serum albumin binding DARPins for systemic half-life extension, to generate MP0533, the first half-life extended avidity-engineered CD3 engaging DARPin capable of targeting CD33, CD123, and CD70 simultaneously. Efficacy and safety of MP0533 was extensively tested in vitro and ex vivo, with cell lines and primary cells in both allogenic and autologous settings, and in vivo in different cell line-derived xenograft mouse models. Results: We demonstrated the avidity effect of the multi-targeting MP0533 in co-culture assays with genetically engineered Molm-13 cells and allogenic T cells, where MP0533 induced up to 10-fold higher T cell mediated killing of cells expressing any combination of at least 2 of the 3 targeted TAAs vs. cells expressing a single TAA. Overall, an EC50 potency ranging from 5 to 25 pM was measured on multiple cell lines showing different levels of expression and co-expression of all TAAs (Molm-13, THP-1, RPMI8226). Efficacy was additionally assessed on primary unsorted AML bone marrow samples: MP0533 demonstrated the ability to induce autologous T cell activation and killing of AML cells in samples from newly diagnosed and previously treated patients with different TAA expression/co-expression levels and E:T ratios ranging from 10:1 to 1:28. MP0533-induced killing of LSC and selectivity over healthy hematopoietic stem cells (HSCs) was analyzed in clonogenic assays in co-cultures of sorted CD34+ cells with allogenic T cells. After 4 days initial killing assay, and 2 weeks colony culture in semi-solid media, MP0533 was able to show depletion of LSC at doses where HSC where only minimally affected. While T-cell activation, proliferation, and cytotoxicity were not affected, the multi-specific TCE format of MP0533 resulted in a significant decrease in cytokine release in both tumor cell killing assays and whole blood test systems when compared to other mono-targeting TCEs, indicating potential for improved safety. Moreover, the avidity approach and the safer profile on single-TAA expressing cells was confirmed by the absence of toxicity measured on CD123-expressing endothelial cells, indicating a low risk of capillary leak syndrome induced by MP0533. Also, potential T cell fratricide induced by CD70 expression on activated T cells was not observed. Finally, efficacy and safety profiles were also confirmed in in vivo xenograft models in human PBMC- or CD34-reconstituted mice. In such models MP0533 induced T cell infiltration in s.c. implanted tumors, leading to anti-tumor activity. Importantly, activation of T cells and release of cytokines were only localized in the tumors, indicating absence of potential systemic on-target off-tumor toxicities induced by MP0533. Conclusion: We generated a multi-specific avidity-driven CD3 engaging DARPin molecule with tailored affinities towards different TAAs showing high efficacy and with the potential for better LSC selectivity and lower cytokine release compared with mono-specific TCE approaches. Further, our approach to achieve systemic half-life extension could ensure a more convenient Q1W IV therapy. A Phase I clinical trial to evaluate safety and dose of MP0533 in humans is imminent.

Orthogonal Proteogenomic Approaches Identify the Druggable PA2G4-MYC Axis in 3q26 AML

Despite next-generation technologies improved our understanding of the complexity of high-risk acute myeloid leukemia (AML), effective targeted therapies are delayed due to the prevalence of major oncogenic disease drivers such as RAS, RUNX1, TP53. In some cases, the integration of orthogonal omics led to the identification or repurposing of drugs for "undruggable" transcription factors (TFs), prospecting a benefit for patients with the most aggressive leukemia subtypes. Here, we sought to discover how to target the Ecotropic Viral Integration Site-1 gene (EVI1/MECOM), the most lethal oncogenic TF in AML carrying chromosome 3q26 abnormalities. To this end, we intersected phenotypic, gene expression-based and proteomic high-throughput approaches for small molecule and target identification. We screened a collection of 5294 compounds enriched for Food and Drug Administration (FDA) approved or bioactive drugs at 1 µM and identified those that caused more than 95% reduction of cell viability compared to vehicle control in MOLM1 and UCSD/AML1 cell lines carrying 3q26 rearrangments (EVI1high). We then selected a set of sentinel genes that defined an EVI1 "on" and "off" transcriptional signature based on the TF1 EVI1high cell line treated with an EVI1-directed siRNA or control, and used the Connectivity Map to identify inducers of an EVI1 "off" state. Histone deacetylase inhibitors (HDACi) scored as the top class of compounds able to repress leukemia proliferation by suppressing the EVI1 signature. We focused on the compounds with pan (AR-42, belinostat) or selective (entinostat) HDAC inhibitory properties. These molecules induced apoptosis and decreased the levels of EVI1 in AML cell lines and in primary EVI1high blast cells. Interestingly, the expression of EVI1 sensitizes cells to HDAC inhibition both in an inducible EVI1 cell model and in EVI1high compared to EVI1low AML cell lines. Primary EVI1high blasts were also more sensitive to HDAC inhibition compared to those from other AML subtypes, while equally resistant to chemotherapy agents. We translated these results in a "N-of-1" clinical trial proposing entinostat in association with azacytidine to patients with relapse/refractory 3q26 AML based on a compassionate use program for this regimen. Pharmacodynamic modulation of EVI1 was assessed at 6 hours (T6) after entinostat administration in patients and in matched patient-derived AML xenografts (PDLX). EVI1 expression markedly decreased in circulating blasts collected at T6 compared to T0 (before treatment), and EVI1 depletion paralleled clinical and hematologic improvements at follow-up evaluations. This effect was not observed in patients treated with cytarabine. Longitudinal single-cell RNA sequencing (scRNASeq) of bone marrow AML cells collected before and after patients' treatment cycle revealed an inhibitory effect on Myc target genes in the leukemic clone. This effect was also observed in cell lines treated with AR-42, belinostat and entinostat suggesting that different HDACi regulates the Evi1-Myc axis in 3q26 AML. Not surprisingly, HDACi mediated or genetic silencing of EVI1 led to a decrement of MYC in EVI1high AML models. To dissect the EVI1 co-transcriptional complex and explain for the modulation of Myc signaling in EVI1high AML, we performed rapid immunoprecipitation mass spectrometry of endogenous proteins (RIME). Sixty-nine proteins co-immunoprecipitated with endogenous EVI1 both in cell lines and in 3q26 PDLX models. Eleven of these EVI1 interactors were targets of Myc signaling, including PA2G4, a RNA-binding protein that was markedly modulated by HDACi. Importantly, PA2G4 silencing or inhibition (WS6) depletes MYC at transcriptional and protein levels recapitulating the phenotypic effect seen with HDACi in EVI1high cell models. Consequently, WS6 treatment reduced the growth of AML cells in PDLX models in vivo by suppressing an EV1-MYC signature at single-cell leukemia level without inducing widespread toxicities. In contrast, PA2G4 overexpression rescued EVIhigh AML cell lines from the effects induced by HDACi inhibition. These data support the evidence that PA2G4 is a mediator of Evi1-Myc axis in AML. In conclusion, our work positions PA2G4 at the crosstalk of the Evi1-Myc leukemogenic signal for developing new therapeutics and, at this interesting time, urges upfront HDACi-based combination therapies in patients with 3q26 AML.

METTL3 mediates chemoresistance by enhancing AML homing and engraftment via ITGA4

Chemoresistant leukemia relapse is one of the most common causes of death for acute myeloid leukemia (AML) patients and the homing/engraftment in bone marrow (BM) are crucial steps for AML cells to acquire chemoresistance by interacting with stromal cell components. No crosstalk between m6A modification and homing/engraftment has been reported. Here, we performed comprehensive high-throughput analyses, including RNA sequencing of CR (complete remission) and relapsed AML patients, and reverse-phase protein arrays of chemoresistant cells to identify METTL3 as a key player regulating AML chemoresistance. Then, METTL3-mediated m6A modification was proved to induce the chemoresistance in vitro and in vivo. Furthermore, AML homing/engraftment was discovered being enhanced by upregulated-METTL3 in chemoresistant cells. And the homing/engraftment and drug-resistance associated phenotypes of chemoresistant cells could be reversed by a METTL3 inhibitor. Mechanistically, METTL3 extended the half-life of ITGA4 mRNA by m6A methylation, and then, increased expression of ITGA4 protein to enhance homing/engraftment of AML cells. The results provide insights into the function of m6A modification on the interaction between AML cells and BM niches and clarify the relationship between METTL3 and AML homing/engraftment, suggesting a therapeutic strategy for the treatment of refractory/relapsed AML with METTL3 inhibitors.

Comparative analysis of extracellular vesicle isolation methods from human AML bone marrow cells and AML cell lines.

Cellular crosstalk between hematopoietic stem/progenitor cells and the bone marrow (BM) niche is vital for the development and maintenance of myeloid malignancies. These compartments can communicate via bidirectional transfer of extracellular vesicles (EVs). EV trafficking in acute myeloid leukemia (AML) plays a crucial role in shaping the BM microenvironment into a leukemia-permissive niche. Although several EV isolation methods have been developed, it remains a major challenge to define the most accurate and reliable procedure. Here, we tested the efficacy and functional assay compatibility of four different EV isolation methods in leukemia-derived EVs: (1) membrane affinity-based: exoEasy Kit alone and (2) in combination with Amicon filtration; (3) precipitation: ExoQuick-TC; and (4) ultracentrifugation (UC). Western blot analysis of EV fractions showed the highest enrichment of EV marker expression (e.g., CD63, HSP70, and TSG101) by precipitation with removal of overabundant soluble proteins [e.g., bovine serum albumin (BSA)], which were not discarded using UC. Besides the presence of damaged EVs after UC, intact EVs were successfully isolated with all methods as evidenced by highly maintained spherical- and cup-shaped vesicles in transmission electron microscopy. Nanoparticle tracking analysis of EV particle size and concentration revealed significant differences in EV isolation efficacy, with exoEasy Kit providing the highest EV yield recovery. Of note, functional assays with exoEasy Kit-isolated EVs showed significant toxicity towards treated target cells [e.g., mesenchymal stromal cells (MSCs)], which was abrogated when combining exoEasy Kit with Amicon filtration. Additionally, MSC treated with green fluorescent protein (GFP)-tagged exoEasy Kit-isolated EVs did not show any EV uptake, while EV isolation by precipitation demonstrated efficient EV internalization. Taken together, the choice of EV isolation procedure significantly impacts the yield and potential functionality of leukemia-derived EVs. The cheapest method (UC) resulted in contaminated and destructed EV fractions, while the isolation method with the highest EV yield (exoEasy Kit) appeared to be incompatible with functional assays. We identified two methods (precipitation-based ExoQuick-TC and membrane affinity-based exoEasy Kit combined with Amicon filtration) yielding pure and intact EVs, also suitable for application in functional assays. This study highlights the importance of selecting the right EV isolation method depending on the desired experimental design.

IMBALANCED ACTIVATING AND INHIBITORY RECEPTORS ON CD56DIM NATURAL KILLER CELLS PREDICTS POOR OUTCOMES IN ACUTE MYELOID LEUKEMIA

Even with advances in understanding the physiopathology of Acute Myeloid Leukemia (AML), most patients still relapse leading to poor long-term prognosis and cure rates. Natural Killer (NK) cells are regulated by opposing signals from receptors that activate and inhibit effector function and are known to mediate anti-leukemic immunosurveillance in AML, but the mechanisms by which they control hematopoietic neoplasms remain unclear. We hypothesize that functionally impaired NK cells can predict poor outcomes in AML. We analyzed the expression of DNAM-1 and NKG2D (activating) and NKG2A and KIR2DL1 (inhibitory) receptors on CD56 + , CD56 bright CD16 - and CD56 dim CD16 + NK subsets, by flow cytometry, in 100 de novo AML bone marrow (BM), followed up from 02/2016 to 06/2022, 17 healthy BM (HBM) and 6 BM from remission after induction chemotherapy (AML-CR). Correlations with ELN2017 risk, complete remission (CR), relapse (R), measurable residual disease (MRD), overall survival (OS), and relapse-free survival (RFS) were verified. Co-culture of AML-exposed NK cells and K562 cell line was used to assay for killing and degranulation. Proteomics and genomics were accessed by CITE-seq single-cell sequencing. All NK cell subsets were decreased in AML (p < .01). AML CD56+ NK cells showed decreased NKG2D (p <.01) and increased NKG2A (p = .04) and KIR2DL1 (p < .01), recovering to near healthy values in AML-CR. NKG2D and DNAM-1 activating receptors were decreased (p < .01), while inhibitory NKG2A (p = .02) and KIR2DL1 (p < .01) were increased in CD56 dim NK (Most cytotoxic subset). Both activating receptors within CD56 dim NK were decreased in ELN2017 adverse risk (NKG2D, p =.05; DNAM-1, p < .01), in relapse (p < .01), and in MRD+ patients after remission induction. Inhibitory receptors were increased in adverse risk (p < .01), relapse (NKG2A, p < .01; KIRDL1, p < .05), and MRD+ (NKG2A, p = .03) patients. Degranulation (p < .01) and target cell death (5:1, p = .01; 10:1, p = .002) were decreased in AML. Patients with lower frequency of CD56 dim NK expressing low NKG2D and DNAM-1 showed less degranulation and target cell death (p = .03), whereas in those with higher inhibitory receptors lower degranulation (NKG2A, p = .06) and cytotoxicity (KIR2DL1, p = .005) was found. Both OS and RFS were decreased in patients with lower CD56 dim NK (OS, p = .04; RFS, p = .03) and patients with lower expression of NKG2D (OS, p = .03; RFS, p = .008) and DNAM-1 (OS, p = .02; RFS, p = .11). Our single cell preliminary analysis showed that NK cells from AML display a distinct pro-inflammatory gene signature compared to HBM, which is strongly correlated to its impaired function. Our data points that CD56 dim NK shows an exhaustion phenotype with high expression of inhibitory and low expression of activating receptors. This imbalance leads to impaired cytotoxicity, compromised anti-leukemic activity, and can predict worst response to treatment, relapse, and MRD positivity, and so, can be considered an adverse risk prognostic factor associated with lower survival rates. On top of that, identifying a pro-inflammatory gene signature on AML NK cells can lead to the identification of pathways that prevent their activation and functionality, making it possible to intervene and prevent the onset of the disease. Closing these gaps in the knowledge of NK-mediated immune evasion in leukemia is of significant interest for targeting the leukemic microenvironment by NK cell-mediated immunotherapy.

Identification of Survival-Related Genes in Acute Myeloid Leukemia (AML) Based on Cytogenetically Normal AML Samples Using Weighted Gene Coexpression Network Analysis.

The prognosis of acute myeloid leukemia (AML) remains a challenge. In this study, we applied the weighted gene coexpression network analysis (WGCNA) to find survival-specific genes in AML based on 42 adult CN-AML samples from The Cancer Genome Atlas (TCGA) database. Eighteen hub genes (ABCA13, ANXA3, ARG1, BTNL8, C11orf42, CEACAM1, CEACAM3, CHI3L1, CRISP2, CYP4F3, GPR84, HP, LTF, MMP8, OLR1, PADI2, RGL4, and RILPL1) were found to be related to AML patient survival time. We then compared the hub gene expression levels between AML peripheral blood (PB) samples (n = 162) and control healthy whole blood samples (n = 337). Seventeen of the hub genes showed lower expression levels in AML PB samples. The gene expression analysis was also done among AML BM (bone marrow) samples of different stages: diagnosis (n = 142), posttreatment (n = 42), and recurrent (n = 12) stages. The results showed a significant increase of ANXA3, CEACM1, RGL4, RILPL1, and HP in posttreatment samples compared to diagnosis and/or recurrent samples. Transcription factor (TF) prediction of the hub genes suggested LTF as the top hit, overlapping 10 hub genes, while LTF itself is just one of the hub genes. Also, 3671 correlation links were shown between 128 mRNAs and 209 lncRNAs found in survival time-related modules. Generally, we identified candidate mRNA biomarkers based on CN-AML data which can be extensively used in AML prognosis. In addition, we mapped their potential regulatory mechanisms with correlated lncRNAs, providing new insights into potential targets for therapies in AML.

Circ_0035381 Regulates Acute Myeloid Leukemia Development by Modulating YWHAZ Expression via Adsorbing miR-582-3p.

Acute myeloid leukemia (AML) is a common hematopoietic disorder. Many circular RNAs (circRNAs) are abnormally expressed in AML, including hsa_circ_0035381 (circ_0035381). Nevertheless, the function and mechanism of circ_0035381 in AML remain mostly unclear. Expression of circ_0035381 was determined by qRT-PCR. The impacts of circ_0035381 on AML cell proliferation, apoptosis, and mitochondrial damage were validated via performing loss-of-function experiments. Targeting relationship was predicted by bioinformatics analysis and verified via dual-luciferase reporter and RNA immunoprecipitation assays. Circ_0035381 was upregulated in AML bone marrow samples and cells. Circ_0035381 downregulation decreased AML cell growth in nude mice and restrained AML cell proliferation and contributed to AML apoptosis and mitochondrial damage in vitro. Circ_0035381 acted as a miR-582-3p sponge, and miR-582-3p downregulation mitigated the impacts of circ_0035381 interference on AML cell proliferation, apoptosis, and mitochondrial damage. MiR-582-3p targeted Tyrosine3-monooxygenase/tryptophan5-monooxygenase activation protein zeta (YWHAZ), and it restrained AML cell proliferation and facilitated AML cell apoptosis and mitochondrial damage by decreasing YWHAZ expression. Notably, circ_0035381 regulated YWHAZ expression via miR-582-3p. Circ_0035381 knockdown repressed cell proliferation and promoted cell apoptosis and mitochondrial damage via regulating the miR-582-3p/YWHAZ axis in AML.

HERVs characterize normal and leukemia stem cells and represent a source of shared epitopes for cancer immunotherapy.

Human endogenous retroviruses (HERVs) represent 8% of the human genome. The expression of HERVs and their immune impact have not been extensively studied in Acute Myeloid Leukemia (AML). In this study, we used a reference of 14 968 HERV functional units to provide a thorough analysis of HERV expression in normal and AML bone marrow cells. We show that the HERV retrotranscriptome accurately characterizes normal and leukemic cell subpopulations, including leukemia stem cells, in line with different epigenetic profiles. We then show that HERV expression delineates AML subtypes with different prognoses. We finally propose a method to select and prioritize CD8+ T cell epitopes derived from AML‐specific HERVs and we show that lymphocytes infiltrating patient bone marrow at diagnosis contain naturally occurring CD8+ T cells against these HERV epitopes. We also provide in vitro data supporting the functionality of HERV‐specific CD8+ T‐cells against AML cells. These results show that HERVs represent an important source of genetic information that can help enhancing disease stratification or biomarker identification and an important reservoir of alternative tumor‐specific T cell epitopes relevant for cancer immunotherapy.

Expression of CD123 Related Long Non-coding RNA in Acute Myeloid Leukemia Bone Marrow Mononuclear Cells and Its Clinical Significance.

Acute myelogenous leukemia (AML) is a very common hematopoietic malignancy. Hematopoietic stem cell transplantation can improve the therapeutic effect of AML, but the 5-year survival rate is very low. CD123 imbalance, abnormal gene expression, and epigenetics play an important role in the pathogenesis of AML. This research was to explore the differential expression of CD123-related long non-coding RNA (lncRNA) in AML bone marrow mononuclear cells and provide a theoretical basis for targeted therapy of AML. High-throughput sequencing was performed to screen differentially expressed lncRNA in bone marrow mononuclear immunophenotypes of CD123+ and CD123- from patients with primary AML, and real-time quantitative PCR was adopted for screening and validation. There were 933 differentially expressed lncRNAs in the CD123+ group and the CD123- group, 407 lncRNAs were up-regulated and 463 lncRNAs were down-regulated in the CD123+ group. 14 lncRNAs with more than 2 times of difference were screened for identification, and it was found that compared with CD123- group, there was no substantial difference in the expression of JHDM1D-AS1, LINC01355, CASC15, FAM13A-AS1, HSPC324, LOC339803, LINC00877, and MAG12-AS3 in CD123+ group (P>0.05). The expressions of LOC101929698, BaALC-AS2, BOLA3-AS1, and FBX19-AS1 were considerably up-regulated (P<0.05), while the expressions of LOC100132249 and LINC02085 were considerably down-regulated (P<0.05). In summary, differentially expressed lncRNAs in bone marrow samples of CD123+ and CD123- group of newly diagnosed AML patients may be involved in the process of AML and seriously affect the prognosis of patients.

P389: BISPECIFIC ANTIBODIES ACTIVATE AUTOLOGOUS LEUKEMIA-REACTIVE T CELLS IN ACUTE MYELOID LEUKEMIA

Background: Acute myeloid leukemia (AML) is a highly immunosuppressive disease with a high risk of relapse. This makes the finding of effective immunotherapy-based treatments important, but also difficult. T cell-engaging bispecific antibodies (TCEs) are designed to bind to both T cells and target cells, activate the T cells and thus induce an immune response against the leukemia cells without employing the MHC-T cell receptor (TCR) interaction. Several therapies of this kind are under development for treatment of AML. Surprisingly, both in vitro and in vivo, a subset of these TCE immunocoached T cells (ICTs) can subsequently target autologous AML cells and mediate efficient TCR-MHC-dependent AML cell killing in the absence of the TCE. This points to that a) a portion of the T cells present in an AML are leukemia-reactive but have been immunosuppressed - a suppression that can be reversed by the addition of a TCE, b) that this anti-AML T cell reactivation may play an important part of the mechanism of action of AML-targeted TCEs and c) that by understanding this reactivation mechanism, we will be able to design improved AML immunotherapies in the future. Aims: To understand the mechanisms by which a TCE induces reactivation of leukemia-reactive T cells (LRTs) in AML. Methods: T cells in biobanked AML patient bone marrow samples were activated with either an anti-CD3 x anti-CD123 TCE or a conventional anti-CD3 antibody for 5 days before isolating the ICTs. ICT assay: ICTs were washed to remove the TCE, and isolated ICTs were co-cultured with additional autologous bone marrow cells at different E:T ratios. Killing efficiency and T cell expansion were determined over several days using flow cytometry. Trogocytosis assay: ICTs were co-cultured with stained additional autologous AML cells for 1 h and T cell populations of interest were isolated using FACS. T cell repertoires were analyzed by targeted RNAseq of the TCR. Results: ICTs generated with a TCE kill autologous AML cells efficiently without further addition of the TCE. Adding additional TCE at this stage also does not increase the AML killing efficiency of the ICTs. ICTs generated with an activating anti-CD3 antibody show a similar AML killing efficiency and a similar trogocytotic behavior as TCE ICTs. Most of the TCR clones present in the AML bone marrow pre-stimulation were also represented among the ICTs and trogocytotic ICTs (ICTs that are directly targeting the AML cells after either TCE or anti-CD3 stimulation; Figure 1), suggesting that the bulk of T cells in an AML bone marrow represent heterogeneous immunosuppressed LRTs which can be equally well reactivated by a TCE or an anti-CD3 antibody. Trogocytotic ICTs generated from both types of T cell activation have a similar TCR distribution. ICTs derived from the bone marrow target autologous AML cells more efficiently than ICTs from peripheral blood. Image:Summary/Conclusion: Similarities between TCE ICTs and CD3 ICTs in regards to TCR distributions and killing efficiencies suggest that the TCE reactivates leukemia-reactive T cells via a CD3-dependent mechanism rather than a more complex proximity mechanism. Our data further suggests that T cells in the AML bone marrow are highly heterogeneous and leukemia targeted to a very high degree. In summary, AML bone marrow ICTs are targeting and killing leukemic cells efficiently in a polyclonal fashion and our results highlight that boosting this mechanism can leverage the clinical impact of AML TCEs and be utilized in other novel AML immunotherapy approaches.

P742: TRANSCRIPTOMIC ANALYSIS OF ISOLATED CD4+ AND CD8+ T CELLS REVEALS DIFFERENCES IN TCR REPERTOIRE IN PATIENTS WITH HIGH RISK MDS COMPARED TO AML.

Background: Myelodysplastic syndrome (MDS) is a group of clonal disorders of hematopoietic progenitor cells, which often progresses towards acute myeloid leukemia (AML). Even though MDS is a clonal hematopoietic disease, bone marrow microenvironment and more specifically inflammation has been linked to its progression. Among other cell types, CD4+ and CD8+ T cells are major players in the regulation of the microenvironment in malignancies. Aims: In this study, we aimed to investigate the molecular signature of bone marrow CD4+ and CD8+ T cells from patients with high-risk MDS, AML and chronic myelomonocytic leukemia (CMML). Methods: RNA sequencing was performed on isolated CD4+ and CD8+ T cells from the bone marrow of six patients with high risk MDS (RAEB-II), six patients with CMML and four patients with AML, using cell sorting. Except from the analysis of gene expression, we performed TCR repertoire analysis using VDJtools, an open-source Java/Groovy-based framework that can analyze immune repertoire sequencing (RepSeq) data and allows applying a diverse set of post-analysis strategies. To do so, RNA sequencing data were used as input for the V-(D)-J junction mapping software and analysis was performed on the MiXCR platform. The output of MiXCR wereused as input for the VDJtools after running a convert routine with -S mixcr argument to prepare datasets in a format for VDJtools analysis. Results: Analysis of CD8+ T cells from patients with high risk MDS and AML identified 38 differentially expressed genes. We observed that the expression of the TCR variants TRAV20 and TRAV13-1 was increased in patients with AML compared to high risk MDS (Figure 1A). Further analysis of the TCR repertoire revealed that the diversity of TCR was higher in CD8+ T cells from patients with AML (Figure 1B), whereas multidimentional scaling analysis revealed a clear separation of the two groups (Figure 1C). To the same direction, clustering of the usage of TRAV-TRAJ further confirmed this finding (Figure 1D). On the other hand, we did not observe any difference in the TCR diversity of the variant usage when we compared CD8+ T cells from patients with CMML and AML (Figure 1E-F), or in the comparison between CD4+ T cells from patients with high risk MDS and AML (Figure 1G-I). Image:Summary/Conclusion: CD8+ T cells are a major cell population that exerts anti-tumour properties in cancer. Herein, we compared the TCR repertoire of CD8+ and CD4+ T cells in the bone marrow of patients with high risk MDS and AML and observed that despite the common features of these two disorders, there are significant differences in the TCR repertoire specifically in CD8+ T cells, especially concerning TCR diversity. These findings imply that there is more active T cell response in the bone marrow in AML compared to MDS. However, it is not clear to what degree this T cell response targets AML neo-antigens.

P436: TARGETED DELIVERY OF T22-PE24-H6 TO CXCR4 POSITIVE CELLS FOR ACUTE MYELOID LEUKEMIA TREATMENT

Background: Acute myeloid leukemia (AML) is a malignant heterogeneous group of hematological diseases that originates from a hematopoietic progenitor with altered maturation capacity. Recently, considerable advances have been made in the development of targeted therapies for distinct molecularly defined subtypes. Although many AML patients initially respond to current treatment, the majority of them relapse. Therefore, new targeted therapies are needed to overcome drug resistance and improve treatment effectiveness. CXCR4 is a chemokine receptor that is expressed in over 20 cancer types, both hematologic cancers and solid tumors. CXCR4 receptor and its ligand CXCL12 are key mediators of the interactions between AML cells and the bone marrow (BM) microenvironment. Moreover, CXCR4 is highly expressed in around 50% of AML patients. Thus, we have generated a nanoparticle (T22-PE24-H6) that selectively delivers the exotoxin A from Pseudomonas aeruginosa to CXCR4+ leukemic cells. Aims: To assess the selectivity of T22-PE24-H6 cytotoxicity in CXCR4+ AML cell lines as well as in BM samples from AML patients. In addition, we evaluated the antineoplastic effect of the nanoparticle in a CXCR4+ AML disseminated mouse model. Methods: OCI-AML-3, MONO-MAC-6 and HEL cell lines were characterized for CXCR4 expression using flow cytometry and immunohistochemistry (IHC). The in vitro antineoplastic effect of T22-PE24-H6 was determined by cell viability assays. Competition assays with the CXCR4 antagonist AMD3100 were performed to demonstrate the CXCR4-dependent cytotoxicity of the nanoparticle. In vivo effect was assessed in NSG mice intravenously injected with 1x106 luminescent MONO-MAC-6 cells. Animals were treated with 5 μg T22-PE24-H6 or Buffer (166 mM NaCO3H pH 8) daily for 10 doses. Bioluminescence signal (BLI) was monitored to quantitatively measure and evaluate in vivo disease progression. Animal tissue samples were collected after mice euthanasia and used to analyze AML dissemination and toxicity. CXCR4 expression levels and T22-PE24-H6 effect were also determined in BM samples from 10 newly-diagnosed AML patients. Results: T22-PE24-H6 nanoparticle demonstrated a potent in vitro anticancer effect in MONO-MAC-6 cell line. The specific cytotoxic activity of the nanoparticle was CXCR4 dependent as demonstrated by performing competition assays with AMD3100. Furthermore, T22-PE24-H6 intravenous administrations showed significant BLI reduction in a CXCR4+ AML disseminated mouse model compared to buffer-treated mice. In addition, no differences between groups in mouse body weight, biochemical parameters or histopathological changes in normal tissues were detected. Finally, T22-PE24-H6 causes a significant cell viability reduction in AML patient samples with high CXCR4 expression. In contrast, the nanoparticle has no effect in AML patient samples with low expression of CXCR4. Summary/Conclusion: T22-PE24-H6 selectively kills AML cell lines and BM samples from AML patients with CXCR4 overexpression. The nanoparticle also induces a high antineoplastic effect in a CXCR4+ AML disseminated mouse model without detectable systemic toxicity. These data strongly support that T22-PE24-H6 may obtain therapeutic benefit for AML patients with high CXCR4 expression.

P1402: ALTERATIONS OF HUMAN BONE MARROW NICHE IN CLONAL HEMATOPOIESIS AND AML

Background: Acute myeloid leukemia (AML) is a heterogeneous disease, predominantly caused by acquisition of mutations in the hematopoietic stem and progenitor cells. Some of these mutations are acquired in a preleukemic state termed clonal hematopoiesis of indeterminate potential (CHIP). Recent studies show that alterations in the bone marrow niche can support progression and therapy resistance of myeloid neoplasia. To date, it is unclear when these niche alterations occur and how they contribute to disease progression. In our study, we aim to elucidate alterations in the bone marrow niche, in particular in mesenchymal stem cells (MSC), during the evolution from healthy to CHIP and further to AML. Aims: Primary goal of this project is to examine how hematopoietic and niche cells from different health status (healthy, CHIP and AML) interact with each other and to what extent the presence of clonal hematopoiesis and leukemia have an impact on function and structure of the bone marrow niche. Methods: We collected primary human bone marrow (BM) and peripheral blood (pB) from hematologically healthy individuals who underwent hip replacement surgery at the LMU University Hospital. BM samples from AML patients are provided by the Laboratory for Leukemia Diagnostics, LMU University Hospital. Individuals are assigned to non-CHIP or CHIP cohorts based on targeted mutation analyses on pB samples. To study transcriptional changes in the bone marrow compartments, non-CHIP, CHIP and AML BM samples were FACS-sorted for 10 hematopoietic and non-hematopoietic cell types, and further processed for bulkRNA sequencing. MSC from donor BM samples were isolated via plastic adherence over 10-14 days of in vitro culture. MSC were characterized regarding their surface marker expression (FACS), differentiation (osteogenic, adipogenic, chondrogenic) potential and metabolic activity (Seahorse XF). Results: So far, we have included 98 healthy individuals and 64 have undergone targeted sequencing, revealing 19 individuals (30%) with CHIP. While there was no difference between the gender of the non-CHIP and CHIP groups, individuals with CHIP tended to be of older age (median, 64 y non-CHIP vs. 73.5 y CHIP). Most common mutations were DNMT3A (10/19), TET2 (7/19), ASXL1 (2/19), with variant allele frequencies varying between 1.0% and 16.8%, and 1.42 mutations per individual on average. The amount of mutations per individual increased with age. Analysis of MSCs from non-CHIP (n=5) and CHIP (n=5) individuals revealed no difference in surface marker expression over 10 passages. Differentiation assays of MSCs (non-CHIP=4, CHIP= 2) showed no difference in adipogenic and chondrogenic differentiation after 21 days. For osteogenesis, we noticed a trend towards an increased differentiation potential in the MSCs of CHIP individuals. To gain deeper insights into the BM niche we sorted 4 non-hematopoietic and 6 hematopoietic cell populations from non-CHIP (n=3), CHIP (n=4) and AML (n=4) individuals and performed bulkRNA sequencing on each population. So far changes in the composition of the bone marrow niche were only detected in the AML samples. Summary/Conclusion: Currently, we are analyzing the bulkRNA sequencing data and performing further experiments on cultured MSC to increase group sizes, as well as MSC and HSPC co-cultures in vitro to gain more insight into the bone marrow niche in non-CHIP, CHIP and AML. Additionally, we are continuously recruiting new individuals into our study. A comprehensive update on our cohort, sequencing data and MSC characterization will be shown at the conference.

IL-10 and TNFα are associated with decreased survival in low-risk pediatric acute myeloid leukemia; a children’s oncology group report

Pediatric acute myeloid leukemia (AML) is a devastating disease with a high risk of relapse. Current risk classification designates patients as high or low risk (LR) based on molecular features and therapy response. However, 30% of LR patients still suffer relapse, indicating a need for improvement in risk stratification. Cytokine levels, such as IL-6 and IL-10, have been shown to be prognostic in adult AML but have not been well studied in children. Previously, we reported elevated IL-6 levels in pediatric AML bone marrow to be associated with inferior prognosis. Here, we expanded our investigation to assess cytokine levels in diagnostic peripheral blood plasma (PBP) of pediatric AML patients and determined correlation with outcome. Diagnostic PBP was obtained from 80 patients with LR AML enrolled on the Children’s Oncology Group AAML1031 study and normal PBP from 11 controls. Cytokine levels were measured and correlation with clinical outcome was assessed. IL-6, TNFα, MIP-3a, and IL-1β were significantly higher in AML patients versus controls when corrected by the Bonferroni method. Furthermore, elevated TNFα and IL-10 were significantly associated with inferior outcomes. Our data demonstrate that in diagnostic PBP of LR pediatric AML patients, certain cytokine levels are elevated as compared to healthy controls and that elevated TNFα and IL-10 are associated with inferior outcomes, supporting the idea that an abnormal inflammatory state may predict poor outcomes. Studies are needed to determine the mechanisms by which these cytokines impact survival, and to further evaluate their use as prognostic biomarkers in pediatric AML.

LC3-associated phagocytosis in bone marrow macrophages suppresses acute myeloid leukemia progression through STING activation.

The bone marrow (BM) microenvironment regulates acute myeloid leukemia (AML) initiation, proliferation, and chemotherapy resistance. Following cancer cell death, a growing body of evidence suggests an important role for remaining apoptotic debris in regulating the immunologic response to and growth of solid tumors. Here, we investigated the role of macrophage LC3–associated phagocytosis (LAP) within the BM microenvironment of AML. Depletion of BM macrophages (BMMs) increased AML growth in vivo. We show that LAP is the predominate method of BMM phagocytosis of dead and dying cells in the AML microenvironment. Targeted inhibition of LAP led to the accumulation of apoptotic cells (ACs) and apoptotic bodies (ABs), resulting in accelerated leukemia growth. Mechanistically, LAP of AML-derived ABs by BMMs resulted in stimulator of IFN genes (STING) pathway activation. We found that AML-derived mitochondrial damage–associated molecular patterns were processed by BMMs via LAP. Moreover, depletion of mitochondrial DNA (mtDNA) in AML-derived ABs showed that it was this mtDNA that was responsible for the induction of STING signaling in BMMs. Phenotypically, we found that STING activation suppressed AML growth through a mechanism related to increased phagocytosis. In summary, we report that macrophage LAP of apoptotic debris in the AML BM microenvironment suppressed tumor growth.

Metformin sensitizes AML cells to chemotherapy through blocking mitochondrial transfer from stromal cells to AML cells

Interaction between stromal cells and acute myeloid leukemia (AML) cells in bone marrow (BM) is known to contribute importantly to chemoresistance and disease recurrence. Therefore, disruption of a crosstalk between AML cells and BM microenvironment may offer a promising therapeutic strategy for AML treatment. Here, we demonstrate that in a niche-like co-culture system, AML cells took up functional mitochondria from bone marrow stromal cells (BMSCs) and inhibition of such mitochondrial transfer by metformin, the most commonly prescribed drug for type 2 diabetes mellitus, significantly enhanced the chemosensitivity of AML cells co-cultured with BMSCs. The chemo-sensitizing effect of metformin was acted through reducing the mitochondrial transfer and mitochondrial oxidative phosphorylation (OXPHOS) in the recipient AML cells. In addition, metformin potentiated the antitumor efficacy of cytarabine (Ara-C) in vivo in an NCG immunodeficient mouse xenograft model by inhibiting the mitochondrial transfer and OXPHOS activity in the engrafted human AML cells. Altogether, this study identifies a potential application of metformin in sensitizing AML cells to chemotherapy and unveils a novel mechanism by which metformin executes such effect via blocking the mitochondrial transfer from stromal cells to AML cells.