Leukemic Microenvironment Research Articles

M6A-related lncRNAs predict prognosis and indicate immune microenvironment in acute myeloid leukemia

Acute myeloid leukemia (AML) is a complex hematologic malignancy. Survival rate of AML patients is low. N6-methyladenosine (m6A) and long non-coding RNAs (lncRNAs) play important roles in AML tumorigenesis and progression. However, the relationship between lncRNAs and biological characteristics of AML, as well as how lncRNAs influence the prognosis of AML patients, remain unclear. In this study. In this study, Pearson correlation analysis was used to identify lncRNAs related to m6A regulatory genes, namely m6A-related lncRNAs. And we analyzed their roles and prognostic values in AML. m6A-related lncRNAs associated with patient prognosis were screened using univariate Cox regression analysis, followed by systematic analysis of the relationship between these genes and AML clinicopathologic and biologic characteristics. Furthermore, we examined the characteristics of tumor immune microenvironment (TIME) using different IncRNA clustering models. Using LASSO regression, we identified the risk signals related to prognosis of AML patients. We then constructed and verified a risk model based on m6A-related lncRNAs for independent prediction of overall survival in AML patients. Our results indicate that risk scores, calculated based on risk-related signaling, were related to the clinicopathologic characteristics of AML and level of immune infiltration. Finally, we examined the expression level of TRAF3IP2-AS1 in patient samples through real-time polymerase chain reaction analysis and in GEO datasets, and we identified a interaction relationship between SRSF10 and TRAF3IP2-AS1 through in vitro assays. Our study shows that m6A-related lncRNAs, evaluated using the risk prediction model, can potentially be used to predict prognosis and design immunotherapy in AML patients.

HNE-mediated proinflammatory microenvironment in Acute Lymphoblastic Leukemia: Insights into the roles of extracellular vesicles and oxidative stress

HNE-mediated proinflammatory microenvironment in Acute Lymphoblastic Leukemia: Insights into the roles of extracellular vesicles and oxidative stress

Molecular Systems Architecture of Interactome in the Acute Myeloid Leukemia Microenvironment.

Simple SummaryAcute myeloid leukemia (AML) is a cancer of blood and bone marrow that causes rapid production of abnormal red and white blood cells. Once established, the cancer cells communicate through a complex set of molecular interactions with neighboring cells in order to survive, spread rapidly, and evade detection and destruction by the body’s immune system. In this study, a systematic review produced a comprehensive set of critical molecular interactions that was then organized into molecular “systems architecture” to map the communications between cancer cells and neighboring cells. This systems architecture may aid in identifying effective targets that disrupt communication between the cancer cells and the neighboring environment, leading to effective treatment strategies.A molecular systems architecture is presented for acute myeloid leukemia (AML) to provide a framework for organizing the complexity of biomolecular interactions. AML is a multifactorial disease resulting from impaired differentiation and increased proliferation of hematopoietic precursor cells involving genetic mutations, signaling pathways related to the cancer cell genetics, and molecular interactions between the cancer cell and the tumor microenvironment, including endothelial cells, fibroblasts, myeloid-derived suppressor cells, bone marrow stromal cells, and immune cells (e.g., T-regs, T-helper 1 cells, T-helper 17 cells, T-effector cells, natural killer cells, and dendritic cells). This molecular systems architecture provides a layered understanding of intra- and inter-cellular interactions in the AML cancer cell and the cells in the stromal microenvironment. The molecular systems architecture may be utilized for target identification and the discovery of single and combination therapeutics and strategies to treat AML.

Ferroptosis-related molecular patterns reveal immunological, inflammatory and lipid metabolism characteristics of the tumor microenvironment in acute myeloid leukemia

Ferroptosis-related molecular patterns reveal immunological, inflammatory and lipid metabolism characteristics of the tumor microenvironment in acute myeloid leukemia

Microenvironment and drug resistance in acute myeloid leukemia: Do we know enough?

Acute myeloid leukemia (AMLs), as the name suggests, often develop suddenly and are very progressive forms of cancer. Unlike in acute promyelocytic leukemia, a subtype of AML, the outcomes in most other AMLs remain poor. This is mainly attributed to the acquired drug resistance and lack of targeted therapy. Different studies across laboratories suggest that the cellular mechanisms to impart therapy resistance are often very dynamic and should be identified in a context-specific manner. Our review highlights the progress made so far in identifying the different cellular mechanisms of mutation-independent therapy resistance in AML. It reiterates that for more effective outcomes cancer therapies should acquire a more tailored approach where the protective interactions between the cancer cells and their niches are identified and targeted.

Immune-relatedlncRNAs can predict the prognosis of acute myeloid leukemia.

The immune microenvironment in acute myeloid leukemia (AML) is closely related to patients’ prognosis. Long noncoding RNAs (lncRNAs) are emerging as key regulators in immune systems. In this study, we established a prognostic model using an immune‐related lncRNA (IRL) signature to predict AML patients’ overall survival (OS) through Least Absolute Shrinkage and Selection Operator (LASSO) and multivariate Cox regression analysis. Kaplan‐Meier analysis, receiver operating characteristic (ROC) analysis, univariate Cox regression, and multivariate Cox regression analyses further illustrated the reliability of our prognostic model. An IRL signature‐based nomogram consisting of other clinical features efficiently predicted the OS of AML patients. The incorporation of the IRL signature improved the ELN2017 risk stratification system's prognostic accuracy. In addition, we found that monocytes and metabolism‐related pathways may play a role in AML progression. Overall, the IRL signature appears as a novel effective model for evaluating the OS of AML patients and may be implemented to contribute to the prolonged OS in AML patients.

A novel ferroptosis-related gene signature can predict prognosis and influence immune microenvironment in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a highly heterogeneous hematopoietic malignancy that strongly correlates with poor clinical outcomes. Ferroptosis is an iron-dependent, non-apoptotic form of regulated cell death which plays an important role in various human cancers. Nevertheless, the prognostic significance and functions of ferroptosis-related genes (FRGs) in AML have not received sufficient attention. The aim of this article was to evaluate the association between FRGs levels and AML prognosis using publicly available RNA-sequencing datasets. The univariate Cox regression analysis identified 20 FRGs that correlate with patient overall survival (OS). The LASSO Cox regression model was used to construct a prognostic 12-gene risk model using a TCGA cohort, and internal and external validation proved the signature efficient. The 12 FRGs signature was then used to assign patients into high- and low-risk groups, with the former exhibiting markedly reduced OS, compared to the low-risk group. ROC curve analysis verified the predictive ability of the risk model. Functional analysis showed that immune status and drug sensitivity differed between the two risk groups. In summary, FRGs is a promising candidate biomarker and therapeutic target for AML.

Longitudinal Preclinical Imaging Characterizes Extracellular Drug Accumulation After Radiation Therapy in the Healthy and Leukemic Bone Marrow Vascular Microenvironment

Recent initial findings suggest that radiation therapy improves blood perfusion and cellular chemotherapy uptake in mice with leukemia. However, the ability of radiation therapy to influence drug accumulation in the extracellular bone marrow tissue is unknown, due in part to a lack of methodology. This study developed longitudinal quantitative multiphoton microscopy (L-QMPM) to characterize the bone marrow vasculature (BMV) and drug accumulation in the extracellular bone marrow tissue before and after radiation therapy in mice bearing leukemia. We developed a longitudinal window implant for L-QMPM imaging of the calvarium BMV before, 2 days after, and 5 days after total body irradiation (TBI). Live time-lapsed images of a fluorescent drug surrogate were used to obtain measurements, including tissue wash-in slope (WIStissue) to measure extracellular drug accumulation. We performed L-QMPM imaging on healthy C57BL/6 (WT) mice, as well as mice bearing acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). Implants had no effects on calvarium dose, and parameters for wild-type untreated mice were stable during imaging. We observed decreased vessel diameter, vessel blood flow, and WIStissue with the onset of AML and ALL. Two to 10 Gy TBI increased WIStissue and vessel diameter 2 days after radiation therapy in all 3 groups of mice and increased single-vessel blood flow in mice bearing ALL and AML. Increased WIStissue was observed 5 days after 10 Gy TBI or 4 Gy split-dose TBI (2 treatments of 2 Gy spaced 3 days apart). L-QMPM provides stable functional assessments of the BMV. Nonmyeloablative and myeloablative TBI increases extracellular drug accumulation in the leukemic bone marrow 2 to 5 days posttreatment, likely through improved blood perfusion and drug exchange from the BMV to the extravascular tissue. Our data show that neo-adjuvant TBI at doses from 2 Gy to 10 Gy conditions the BMV to improve drug transport to the bone marrow.

Single Cell RNA Sequencing Driven Characterization of Rare B/Myeloid and T/Myeloid Mixed Phenotype Acute Leukemia

Introduction: Pediatric mixed phenotype acute leukemia (MPAL), a rare subgroup of leukemia, contains features of both myeloid and lymphoid lineage blasts, which makes the disease more difficult to diagnose/treat. More information is needed to understand the origins of the major pediatric MPAL subtypes, B/Myeloid (B-MPAL) and T/Myeloid (T-MPAL), and how they relate to other leukemias. Single-cell RNA sequencing (scRNA-seq) analysis of bone marrow (BM) can provide in-depth information about the leukemia microenvironment and reveal differences/similarities between MPAL subtypes and other types of leukemia that could be exploited to develop novel diagnostics/therapies.Methods: We analyzed ~16,000 cells from five pediatric MPAL BM samples to generate a transcriptomic landscape of B-MPAL and T-MPAL blasts and associated microenvironment cells. Samples collected at the time of diagnosis (Dx) were used to generate scRNA-Seq data using a droplet-based barcoding technique (Panigrahy et al. JCI 2019, Tellechea et al. JID, 2020). After data normalization, cell clusters were identified using principal component analysis (PCA) and Uniform Manifold Approximation and Projection (UMAP) approach (Becht et al. Nat. Biotech 2018). Meta-analysis was performed using single cell samples from ongoing studies in the Bhasin lab (Bhasin, et al. Blood 2020 (ASH), Thomas et al. Blood 2020 (ASH)) and publicly available single cell data from GEO biorepository. Unsupervised analysis using UMAP and PCA was performed to determine the overall relationship among B-MPAL, T-MPAL and other leukemias (acute myeloid leukemia (AML), B-cell acute lymphoblastic leukemia (B-ALL), T-cell ALL (T-ALL)). Supervised differentially expressed gene (DEG) analysis was performed to identify B- and T- MPAL blast cell signatures (P value < 0.001 and log2 FC > 0.5). Transcriptomic profiles in MPAL samples and normal BM stem and immune cells were compared using data from the Human Cell Atlas Data Portal (humancellatlas.org). Gene set enrichment analysis (GSEA) was performed, and significantly enriched pathways were compared in MPAL subtypes (P value < 0.001).Results: PCA analysis showed transcriptome similarity between B-MPAL and both B-ALL and AML, while T-MPAL transcriptome correlated with T-ALL and AML (Fig. 1A). B- and T-MPAL subtype blasts clustered separately from each other in UMAP analyses, with T-MPAL blasts clustering with T-ALL blasts, and B-MPAL somewhat overlapping with B-ALL blasts. Subtype DEG analysis of leukemia blasts and healthy BM revealed distinct significantly upregulated gene signatures in B-MPAL (YBX3, SOCS2, BCL11A, and HIST1H1C) and T-MPAL (ITM2A, HPGD, PDLIM1, and TRDC) blasts (Fig. 1B). Pathway analysis showed upregulated gene activity related to TNFA signaling via NFKB, B-cell survival, and the AP1, FRA, and NGF transcription factors in B-MPAL blasts. In contrast, IL-17 and IL-12, T-cell apoptosis, and Stathmin pathways were upregulated in T-MPAL blasts (Fig. 1C). T-MPAL T-cells also expressed higher levels of T-cell exhaustion markers compared to T-cells in B-MPAL samples and healthy bone marrow.After filtering out genes that are significantly expressed in immune cells, we identified genes that are differentially expressed at diagnosis in MPAL blasts from patients that relapsed after treatment (Dx1) versus patients that achieved remission (Dx2). These genes are potential prognostic markers for B-MPAL and T-MPAL relapse/remission. These include MDM2 and NEIL1 from Dx1 and FOSL2 and CDKN1A in Dx2 B-MPAL blasts. In T-MPAL, expression of HES4 and SPINK2 is associated with Dx1 blasts and GNAQ and ITGA4 with Dx2 blasts. Pathway enrichment analysis on B-MPAL blasts revealed upregulation of interferon gamma and PD-1 signaling in Dx1 samples and increased HSP27 and Cell Cycle pathways in the Dx2 subset. T-MPAL Dx1 associated pathways included prostaglandin synthesis and IL-17, while cell-cell junction and extracellular matrix interactions were increased in T-MPAL Dx2 samples (Fig. 1D).Conclusion: Single-cell profiling was used to characterize the molecular landscapes of MPAL blasts and the bone marrow microenvironment and identified gene signatures and pathways that are specifically enriched in B- and T-MPAL subtypes. [Display omitted] DisclosuresDeRyckere: Meryx: Other: Equity ownership. Graham: Meryx: Membership on an entity's Board of Directors or advisory committees, Other: Equity ownership.

NLRP3-activated bone marrow dendritic cells play antileukemic roles via IL-1β/Th1/IFN-γ in acute myeloid leukemia.

The bone marrow microenvironment of acute myeloid leukemia (AML) characterized by immunosuppressive features fosters leukemia immune escape. Elucidating the immunosuppressive mechanism and developing effective immunotherapeutic strategies are necessary. Here, we found that the Th1% and IFN-γ level were downregulated in bone marrow of AML and NLRP3-activated BMDCs promoted CD4+ T cell differentiation into Th1 cells via IL-1β secretion. However, IFN-γ-producing Th1 cells were not induced by NLRP3-activated BMDCs in the presence of the NLRP3 inflammasome inhibitor MCC950 or anti-IL-1β antibody in vitro unless exogenous IL-1β was replenished. This inhibitory effect on Th1 differentiation was also observed in Nlrp3-/- mice or anti-IL-1β antibody-treated mice. Notably, elevated Th1 cell levels promoted apoptosis and inhibited proliferation in leukemia cells via IFN-γ secretion in vitro and in vivo. Thus, NLRP3-activated BMDCs promote the proliferation of IFN-γ-producing Th1 cells with antileukemic effects and may provide insight into the basis for leukemia immunotherapy in patients with AML.

Mapping the evolution of Tcell states during response and resistance to adoptive cellular therapy.

To elucidate mechanisms by which Tcells eliminate leukemia, we study donor lymphocyte infusion (DLI), an established immunotherapy for relapsed leukemia. We model Tcell dynamics by integrating longitudinal, multimodal data from 94,517 bone marrow-derived single Tcell transcriptomes in addition to chromatin accessibility and single Tcell receptor sequencing from patients undergoing DLI. We find that responsive tumors are defined by enrichment of late-differentiated Tcells before DLI and rapid, durable expansion of early differentiated Tcells after treatment, highly similar to "terminal" and "precursor" exhausted subsets, respectively. Resistance, in contrast, is defined by heterogeneous Tcell dysfunction. Surprisingly, early differentiated Tcells in responders mainly originate from pre-existing and novel clonotypes recruited to the leukemic microenvironment, rather than the infusion. Our work provides a paradigm for analyzing longitudinal single-cell profiling of scenarios beyond adoptive cell therapy and introduces Symphony, a Bayesian approach to infer regulatory circuitry underlying Tcell subsets, with broad relevance to exhaustion antagonists across cancers.

Emerging Bone Marrow Microenvironment-Driven Mechanisms of Drug Resistance in Acute Myeloid Leukemia: Tangle or Chance?

Simple SummaryDespite high rates of remission obtained with conventional chemotherapy, the persistence of leukemic cells after treatments, eventually exiting in disease relapse, remains the main challenge in acute myeloid leukemia (AML). Increasing evidence indicates that, besides AML cell mutations, stromal and immune cells, as leukemic microenvironment components, may protect AML cells from therapies. Here, we will recapitulate emerging bone marrow (BM) microenvironment-dependent mechanisms of therapy resistance. The understanding of these processes will help find new drug combinations and conceive novel and more effective treatments.Acute myeloid leukemia (AML) has been considered for a long time exclusively driven by critical mutations in hematopoietic stem cells. Recently, the contribution of further players, such as stromal and immune bone marrow (BM) microenvironment components, to AML onset and progression has been pointed out. In particular, mesenchymal stromal cells (MSCs) steadily remodel the leukemic niche, not only favoring leukemic cell growth and development but also tuning their responsiveness to treatments. The list of mechanisms driven by MSCs to promote a leukemia drug-resistant phenotype has progressively expanded. Moreover, the relative proportion and the activation status of immune cells in the BM leukemic microenvironment may vary by influencing their reactivity against leukemic cells. In that, the capacity of the stroma to re-program immune cells, thus promoting and/or hampering therapeutic efficacy, is emerging as a crucial aspect in AML biology, adding an extra layer of complexity. Current treatments for AML have mainly focused on eradicating leukemia cells, with little consideration for the leukemia-damaged BM niche. Increasing evidence on the contribution of stromal and immune cells in response to therapy underscores the need to hold the mutual interplay, which takes place in the BM. A careful dissection of these interactions will help provide novel applications for drugs already under experimentation and open a wide array of opportunities for new drug discovery.

Mesenchymal Stem Cells With Cancer-Associated Fibroblast-Like Phenotype Stimulate SDF-1/CXCR4 Axis to Enhance the Growth and Invasion of B-Cell Acute Lymphoblastic Leukemia Cells Through Cell-to-Cell Communication.

Background: Bone marrow mesenchymal stem cells (BM-MSCs) are the stromal cells in the leukemia microenvironment, and can obtain cancer-associated fibroblast (CAF)-like phenotype under certain conditions to further promote leukemia progression. However, the mechanism of MSCs with CAF-like phenotype interacting with leukemia cells in B-cell acute lymphoblastic leukemia (B-ALL) and promoting the progression of B-ALL remains unclear.Methods: Mesenchymal stem cells with CAF-like phenotype were obtained by treating MSCs with recombinant human transforming growth factor-β (rhTGF-β), hereafter referred to as TGF-β conditioned MSCs. In vivo mouse model experiments, in vitro transwell chamber experiments, three-dimensional (3D) cell culture models, lentiviral transfection and other experimental methods were used to investigate the possible mechanism of the interaction between TGF-β conditioned MSCs and leukemia cells in promoting the growth, migration and invasion of B-ALL cells.Results: Compared with untreated MSCs, TGF-β conditioned MSCs significantly promoted the growth and proliferation of leukemia cells in mice, and increased the expression of CXCR4 in tumor tissues. In vitro cell experiments, TGF-β conditioned MSCs obviously promoted the migration and invasion of Nalm-6/RS4;11 cells, which were effectively blocked by the CXCR4 inhibitor AMD3100, thereby inhibiting the secretion of MMP-9 in TGF-β conditioned MSCs and inhibiting the activation of the PI3K/AKT signaling pathway in leukemia cells. Further, findings were made that the interaction between TGF-β conditioned MSCs and leukemia cells were mediated by the interaction between the integrin receptor α5β1 on the surface of leukemia cells and the increased expression of fibronectin on TGF-β conditioned MSCs. AMD3100 could weaken such effect by reducing the expression of integrin α5β1 on leukemia cells. Further regulation of integrin β1 could effectively interfere with the interaction between TGF-β conditioned MSCs and leukemia cells.Conclusion: Mesenchymal stem cells with CAF-like phenotype could be a key factor in promoting the growth and invasion of B-ALL cells, and the SDF-1/CXCR4 axis might be a significant factor in mediating the communication of MSCs with CAF-like phenotype and leukemia cells. To prevent the progression of B-ALL cells, blocking the SDF-1/CXCR4 axis with AMD3100 or targeting integrin β1 might be a potential therapeutic strategy.

Characteristics and clinical correlation of TIM-3 and PD-1/PD-L1 expressions in leukemic cells and tumor microenvironment in newly diagnosed acute myeloid leukemia

Dual targeting of TIM-3 and PD-1/PD-L1 pathways is currently under investigation for cancer immunotherapy. The interaction of these immune checkpoints remains unclear in the leukemic microenvironment of acute myeloid leukemia (AML). We performed an immunophenotypic study of bone marrow in 37 newly diagnosed AML patients. High levels of TIM-3 expression on AML blasts were correlated with first 7 + 3 induction failure (CR 16.2% vs. non-CR 36.4%, p = .038). In contrast, high TIM-3 levels on natural killer (NK) cells were associated with complete remission (CR) status after induction (CR 24.7% vs. non-CR 6.5%, p = .035). Few PD-L1 positive AML blasts and PD-1 or PD-L1 positive NK cells were observed. Although the exhausted PD-1 expressing T cells were detected in 28.3% of T cells, the double positive of PD-1 and TIM-3 T cells were rarely detected. In summary, the TIM-3 levels on AML blasts and NK cells are potentially the prognostic biomarkers in AML.

γδ T Cells for Leukemia Immunotherapy: New and Expanding Trends.

Recently, many discoveries have elucidated the cellular and molecular diversity in the leukemic microenvironment and improved our knowledge regarding their complex nature. This has allowed the development of new therapeutic strategies against leukemia. Advances in biotechnology and the current understanding of T cell-engineering have led to new approaches in this fight, thus improving cell-mediated immune response against cancer. However, most of the investigations focus only on conventional cytotoxic cells, while ignoring the potential of unconventional T cells that until now have been little studied. γδ T cells are a unique lymphocyte subpopulation that has an extensive repertoire of tumor sensing and may have new immunotherapeutic applications in a wide range of tumors. The ability to respond regardless of human leukocyte antigen (HLA) expression, the secretion of antitumor mediators and high functional plasticity are hallmarks of γδ T cells, and are ones that make them a promising alternative in the field of cell therapy. Despite this situation, in particular cases, the leukemic microenvironment can adopt strategies to circumvent the antitumor response of these lymphocytes, causing their exhaustion or polarization to a tumor-promoting phenotype. Intervening in this crosstalk can improve their capabilities and clinical applications and can make them key components in new therapeutic antileukemic approaches. In this review, we highlight several characteristics of γδ T cells and their interactions in leukemia. Furthermore, we explore strategies for maximizing their antitumor functions, aiming to illustrate the findings destined for a better mobilization of γδ T cells against the tumor. Finally, we outline our perspectives on their therapeutic applicability and indicate outstanding issues for future basic and clinical leukemia research, in the hope of contributing to the advancement of studies on γδ T cells in cancer immunotherapy.

Editorial introductions.

Editorial introductions.

Myeloid cell‐based delivery of IFN‐γ reprograms the leukemia microenvironment and induces anti‐tumoral immune responses

The immunosuppressive microenvironment surrounding tumor cells represents a key cause of treatment failure. Therefore, immunotherapies aimed at reprogramming the immune system have largely spread in the past years. We employed gene transfer into hematopoietic stem and progenitor cells to selectively express anti‐tumoral cytokines in tumor‐infiltrating monocytes/macrophages. We show that interferon‐γ (IFN‐γ) reduced tumor progression in mouse models of B‐cell acute lymphoblastic leukemia (B‐ALL) and colorectal carcinoma (MC38). Its activity depended on the immune system's capacity to respond to IFN‐γ and drove the counter‐selection of leukemia cells expressing surrogate antigens. Gene‐based IFN‐γ delivery induced antigen presentation in the myeloid compartment and on leukemia cells, leading to a wave of T cell recruitment and activation, with enhanced clonal expansion of cytotoxic CD8+ T lymphocytes. The activity of IFN‐γ was further enhanced by either co‐delivery of tumor necrosis factor‐α (TNF‐α) or by drugs blocking immunosuppressive escape pathways, with the potential to obtain durable responses.

Imbalance of Chemokines and Cytokines in the Bone Marrow Microenvironment of Children with B-Cell Acute Lymphoblastic Leukemia.

In the hematopoietic microenvironment, leukemic cells secrete factors that imbalanced chemokine and cytokine production. However, the network of soluble immunological molecules in the bone marrow microenvironment of acute lymphoblastic leukemia (ALL) remains underexplored. Herein, we evaluated the levels of the immunological molecules (CXCL8, CCL2, CXCL9, CCL5, CXCL10, IL-6, TNF, IFN-γ, IL-17A, IL-4, IL-10, and IL-2) in the bone marrow plasma of 47 recently diagnosed B-cell acute lymphoblastic leukemia (B-ALL) patients during induction therapy using cytometric beads arrays. The results demonstrated that B-ALL patients showed high levels of CXCL9, CXCL10, IL-6, and IL-10 at the time of diagnosis, while at the end of induction therapy, a decrease in the levels of these immunological molecules and an increase in CCL5, IFN-γ, and IL-17A levels were observed. These findings indicate that B-ALL patients have an imbalance in chemokines and cytokines in the bone marrow microenvironment that contributes to suppressing the immune response. This immune imbalance may be associated with the presence of leukemic cells since, at the end of the induction therapy, with the elimination and reduction to residual cells, the proinflammatory profile is reestablished, characterized by an increase in the cytokines of the Th1 and Th17 profiles.

Abstract 505: Oral azacitidine modulates the immune microenvironment in acute myeloid leukemia (AML) patients in remission: A subanalysis from the QUAZAR AML-001 Trial

Abstract BACKGROUND The immunologic effects of maintenance therapy in patients (pts) with AML in remission are not well-characterized but of high clinical interest, as rapid recovery of bone marrow (BM) after intensive chemotherapy (IC) may help delay relapse. Post IC, immunological interactions in the BM microenvironment present several immunosuppressive mechanisms. PD-L1 is commonly overexpressed on AML blasts, which is associated with worse prognosis. Oral azacitidine (Oral-AZA [CC-486]) is a hypomethylating agent recently approved in the US for pts with AML in complete remission (CR) or CR with incomplete hematologic recovery (CRi). To better understand the effects of Oral-AZA on immune cells, checkpoint expression of PD-L1/2 on AML blasts and normal myeloid progenitors (MPs), and the kinetics of T cell recovery and activation/exhaustion (eg, PD1, TIM3) were assessed. METHODS Biomarker-evaluable pts aged ≥ 55 years with AML were randomized 1:1 to Oral-AZA 300 mg (n=56) or placebo (PBO, n=52) post IC within 4 months of achieving CR. Flow cytometry evaluations of BM aspirates were performed at screening (ie, baseline [BL]), every 3 cycles until cycle 24 and every 6 cycles thereafter to cycle 36, or as clinically indicated. Correlative analyses of baseline immune parameters with median (med) relapse-free survival (RFS) were computed using Kaplan-Meier methods. RESULTS In the biomarker-evaluable pts, PD-L1 and PD-L2 expression at BL were higher on AML blasts (med intensity 7.1 and 2.9) than normal MPs (0.7 and 1.6). Most AML blasts were PD-L2+ (79%), whereas only 1.9% were PD-L1+. When stratified by the med, higher BL CD3 T cell numbers (as a % of total BM ) were associated with favorable RFS in both Tx arms (Oral-AZA: ≥ med, 562 days[d] and &amp;lt; med, 235d [P = .0308]; PBO: ≥ med, 325d and &amp;lt; med, 155d [P = .0391]). At cycle 3, pts in the Oral-AZA arm had a 1.7-fold increase in CD3 T cells from BL (PBO, 1.1; P = .0450), suggesting Oral-AZA can promote immunologic recovery during early Tx cycles. There was an inverse correlation between T cell exhaustion marker phenotypes (PD1/TIM3+) with CD4 (r = -.5967; P &amp;lt; .0001) and CD8 (r = -.2484; P = .0095) T cell numbers. An increase in RFS was seen in the PBO arm with lower PD1/TIM3+ CD4 numbers (&amp;lt; med, 429d; ≥ med, 155d; P = .0037), with a nominal increase observed in the Oral-AZA arm (&amp;lt; med, 428d; ≥ med, 303d; P = .6764). In a subset of pts, Oral-AZA appeared to suppress CD4 T cell exhaustion (PD1/TIM3+) compared with PBO. CONCLUSIONS Pts in CR/CRi post-IC have a unique immune profile defined by high expression of PD-L1 on a subset of blasts and a high % of PD-L2+ blasts. A higher BL CD3 T cell count after IC in BM was prognostic. Additionally, Oral-AZA appears to contribute to an increase in T cells while also suppressing exhaustion, potentially promoting T cell signaling that could activate functional immune-mediated responses against residual leukemic cells. Citation Format: Daniel L. Menezes, Wendy L. See, Alberto Risueno, Jianglin Ma, Ignazia La Torre, Barry Skikne, CL Beach, Keshava Kumar, Anjan Thakurta. Oral azacitidine modulates the immune microenvironment in acute myeloid leukemia (AML) patients in remission: A subanalysis from the QUAZAR AML-001 Trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 505.

Mining the Microenvironment for Therapeutic Targets in Chronic Lymphocytic Leukemia

Abstract The leukemia cells of patients with chronic lymphocytic leukemia (CLL) are highly fastidious, requiring stimulation by soluble factors and interactions with accessory cells within the supportive niches of lymphoid tissue that comprise the leukemia microenvironment. The advent of therapies that can disrupt some of the stimulatory signaling afforded by the microenvironment has ushered in a new era of targeted therapy, which has dramatically improved clinical outcome and patient survival. Future advances are required for patients who develop intolerance or resistance to current targeted therapies. These may be found by investigating novel drugs that can inhibit identified targets, such as the pathways involved in B-cell receptor signaling, or by developing agents that inhibit additional targets of the leukemia microenvironment. This review describes some of the molecules involved in promoting the growth and/or survival of CLL cells and discusses targeting strategies that may become tomorrow’s therapy for patients with CLL.