Analysis Of Myeloid-derived Suppressor Cells Research Articles

Abstract 6864: Tumor suppressor function of the ubiquitin ligase Siah1a in melanoma is mediated by myeloid derived suppressor cells

Abstract Growing evidence supports the important role of myeloid-derived suppressor cells (MDSC) in melanoma progression and response to therapy. MDSC contributes to a pro-tumorigenic phenotype, yet the mechanistic basis for the immune suppressor properties acquired by MDSC remains largely unknown. Mammals have two homologous Siah genes, Siah1 (Siah1a and Siah1b in mice) and Siah2. In the context of melanoma, the ubiquitin ligases Siah1a and Siah2 have melanoma-intrinsic and -extrinsic (immune) functions. Correspondingly, ablation of Siah1a/2 in melanoma or its microenvironment attenuates melanoma development in a number of mouse melanoma models. Given that number of macrophage clusters infiltrated into melanoma when grown in Siah2 KO mice, we set to assess macrophage function in melanoma. Selective ablation of Siah1a or Siah2 in macrophages, using Lyz2Cre, revealed that Siah1a but not Siah2 elicits a tumor suppressor function in melanoma. Inoculation of mouse melanoma Yummer1.7 cells (Braf mutated and Pten deleted) in mice lacking Siah1a in macrophages, resulted in bigger melanoma tumors compared to melanoma grown in either WT or mice in which macrophages were ablated of Siah2. FACS analysis of melanoma tumors grown in mice harboring Siah1a mutant macrophages revealed a significant increase in MDSC, which coincided with a decrease in CD4+ and CD8+ cells, compared with WT mice. These observations suggest that a lack of Siah1a in macrophages leads to an expansion of MDSC that affects surrounding immune cells, including T cells. RNA-seq analysis of MDSC that were differentiated in vitro from bone marrow cells of WT or Siah1a ablated macrophage mice revealed increased expression of genes involved in proliferation and alternative macrophage activation in MDSC lacking Siah1a when compared to the WT genotype. Mapping mechanisms underlying Siah1a tumor suppressor function is expected to reveal novel regulatory cues in melanoma control by the MDSC population while mapping novel means for stratifications of melanoma to therapy, and possibly new means for therapy of this tumor type. Citation Format: Marzia Scortegagna, Yuanning Du, Yongmei Feng, Ze'ev Ronai. Tumor suppressor function of the ubiquitin ligase Siah1a in melanoma is mediated by myeloid derived suppressor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6864.

Myeloid-derived suppressor cell-derived osteoclasts with bone resorption capacity in the joints of arthritic SKG mice.

Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cells with immunosuppressive functions. It is known that MDSCs are expanded at inflammatory sites after migrating from bone marrow (BM) or spleen (Sp). In chronic inflammatory diseases such as rheumatoid arthritis (RA), previous reports indicate that MDSCs are increased in BM and Sp, but detailed analysis of MDSCs in inflamed joints is very limited. The purpose of this study is to characterize the MDSCs in the joints of mice with autoimmune arthritis. We sorted CD11b+Gr1+ cells from joints (Jo), bone marrow (BM) and spleen (Sp) of SKG mice with zymosan (Zym)-induced arthritis and investigated differentially expressed genes (DEGs) by microarray analysis. Based on the identified DEGs, we assessed the suppressive function of CD11b+Gr1+ cells from each organ and their ability to differentiate into osteoclasts. We identified MDSCs as CD11b+Gr1+ cells by flow cytometry and morphological analysis. Microarray analysis revealed that Jo-CD11b+Gr1+ cells had different characteristics compared with BM-CD11b+Gr1+ cells or Sp-CD11b+Gr1+ cells. Microarray and qPCR analysis showed that Jo-CD11b+Gr1+ cells strongly expressed immunosuppressive DEGs (Pdl1, Arg1, Egr2 and Egr3). Jo-CD11b+Gr1+ cells significantly suppressed CD4+ T cell proliferation and differentiation in vitro, which confirmed Jo-CD11b+Gr1+ cells as MDSCs. Microarray analysis also revealed that Jo-MDSCs strongly expressed DEGs of the NF-κB non-canonical pathway (Nfkb2 and Relb), which is relevant for osteoclast differentiation. In fact, Jo-MDSCs differentiated into osteoclasts in vitro and they had bone resorptive function. In addition, intra-articular injection of Jo-MDSCs promoted bone destruction. Jo-MDSCs possess a potential to differentiate into osteoclasts which promote bone resorption in inflamed joints, while they are immunosuppressive in vitro.

Integrated machine learning approaches for flow cytometric quantification of myeloid-derived suppressor cells in acute sepsis.

Highly heterogeneous cell populations require multiple flow cytometric markers for appropriate phenotypic characterization. This exponentially increases the complexity of 2D scatter plot analyses and exacerbates human errors due to variations in manual gating of flow data. We describe a semi-automated workflow, based entirely on the Flowjo Graphical User Interface (GUI), that involves the stepwise integration of several, newly available machine learning tools for the analysis of myeloid-derived suppressor cells (MDSCs) in septic and non-septic critical illness. Supervised clustering of flow cytometric data showed correlation with, but significantly different numbers of, MDSCs as compared with the cell numbers obtained by manual gating. Neither quantification method predicted 30-day clinical outcomes in a cohort of 16 critically ill and septic patients and 5 critically ill and non-septic patients. Machine learning identified a significant decrease in the proportion of PMN-MDSC in critically ill and septic patients as compared with healthy controls. There was no difference between the proportion of these MDSCs in septic and non-septic critical illness.

Increased Levels of Circulating Monocytic- and Early-Stage Myeloid-Derived Suppressor Cells (MDSC) in Acute Myeloid Leukemia.

To investigate the levels of circulating myeloid-derived suppressor cells (MDSC) in patients with primary acute myeloid leukemia (AML), and to explore the relationship between the number of MDSC and AML. Peripheral blood samples from 29 patients with primary AML and 30 healthy controls were collected. CD33, CD11b, HLA-DR, CD14, and CD15 were used to label cells, and flow cytometry was used to analyze the numbers of total MDSC and subgroups eMDSC (early-stage MDSC), M-MDSC (monocytic MDSCs), PMN-MDSC (polymorphonuclear-MDSCs) or G-MDSC (granulocytic-MDSC) via two gating strategies. Presence of MDSC in AML was determined after assessment of clinical data. Phenotypic analysis of MDSC by the two gating strategies was consistent. Compared with healthy controls, the numbers of total MDSC (CD33+CD11b+ HLA-DR-) and G-MDSC (CD33+CD11b+ HLA-DR-CD14¬-CD15+ or CD14¬-CD15+ CD11b+) in peripheral blood of AML patients were lower (p < 0.05), while numbers of M-MDSC (CD33+CD11b+ HLA-DR-CD14+CD15- or HLA-DR-/LOWCD14+) and eMDSC (CD33+CD11b+ HLA-DR-/LOWCD14-CD15-) were higher (p < 0.05). The levels of G-MDSC in peripheral blood of AML-M2 patients were higher than those in other subtypes, along with total MDSC, while the levels of eMDSC and M-MDSC in AML-M3 patients were higher than those in other subtypes. The high frequency of HLA-DR-/LOWCD14+M-MDSC and CD33+CD11b+ HLA-DR-/LOWCD14-CD15- eMDSC in peripheral blood of AML patients indicates potential for MDSC as a diagnostic index in AML.

Analysis of canine myeloid-derived suppressor cells (MDSCs) utilizing fluorescence-activated cell sorting, RNA protection mediums to yield quality RNA for single-cell RNA sequencing

Fluorescence-activated cell sorting (FACS) is a branch of flow cytometry that allows for the isolation of specific cell populations that can then be further analyzed by single-cell RNA sequencing (scRNA-seq). When utilizing FACS for population isolation prior to sequencing, it is essential to consider the protection of RNA from RNase activity, environmental conditions, and the sorting efficiency to ensure optimum sample quality. This study aimed to optimize a previously published MDSC flow cytometry strategy to FACS sort canine Myeloid-Derived Suppressor Cells (MDSC) with various permutations of RNAlater ™ and RiboLock™ before and after FACS sorting. Concentrations of RNAlater™ greater than 2 % applied before flow analysis affected cell survival and fluorescence, whereas concentrations ≤ 2 % and time ≤ 4 h had little to no effect on cells. To shorten the procedural time and to enhance the sorting of rare populations, we used a primary PE-conjugated CD11b antibody and magnetic column. The combination of RiboLock™ pre- and post-sorting for FACS provided the best quality RNA as determined by the RNA integrity number (RIN ≥ 7) for scRNA-seq in a normal and dog and a dog with untreated oral melanoma dog. As proof of principle, we sequenced two samples, one from a normal dog another from a dog with untreated oral melanoma. Applying scRNA-Seq analysis using the 10X Genomic platform, we identified 6 clusters in the Seurat paired analysis of MDSC sorted samples. Two clusters, with the majority of the cells coming from the melanoma sample, had genes that were upregulated (> log2); these included MMP9, MMP1, HPGD, CPA3, and GATA3 and CYBB, CSTB, COX2, ATP6, and COX 17 for cluster 5 and 6 respectively. All genes have known associations with MDSCs. Further characterization using pathway analysis tools was not attempted due to the lower number of cells sequenced in the normal sample. The benefit deriving from the results of the study helped to gain data consistency when working with cells prone to RNase activity, and the scRNA-seq provided data showing transcriptional heterogeneity in MDSC populations and potentially identifying previously unreported or rare cell populations.

Frequency and Functional Analysis of Myeloid-Derived Suppressor Cells (MDSCs) in the Peripheral Blood and Bone Marrow of Patients with Chronic Idiopathic Neutropenia (CIN)

Myeloid-derived suppressor cells (MDSCs) are myeloid cells with immunoregulatory properties characterized mainly by suppression of T-cell responses (Bizymi et al, HemaSphere 2019). They are divided in HLA-DRlow/-/CD11b+/CD33+/CD15+ polymorphonuclear (PMN-MDSCs) and HLA-DRlow/-/CD11b+/CD33+/CD14+ monocytic (M-MDSCs) subsets and they are implicated in inflammatory and malignant diseases. Chronic idiopathic neutropenia (CIN), is a (usually benign) neutrophil disorder characterized by persistent and unexplained neutropenia following a detailed clinical/laboratory investigation including anti-neutrophil antibody testing, bone marrow (BM) biopsy and karyotype (Dale &amp; Bolyard, Curr Opin Hematol 2017). Previous studies have shown that neutropenia in CIN is associated with increased apoptosis of BM granulocytic progenitor cells due to an inflammatory BM microenvironment consisting of oligoclonal T-lymphocytes, proinflammatory monocytes and proapoptotic cytokines. The aim of the present study is to explore the possible involvement of the MDSCs in the pathophysiology of CIN by investigating their number in peripheral blood (PB) and BM in association with their functional characteristics. We have studied 100 CIN patients and 49 age- and sex-matched healthy controls. The patients fulfilled the previously described diagnostic criteria for CIN (Papadaki et al, Blood 2003) and had mean neutrophil counts 1095.67 ± 479.52 (median 1215, range 100-1700). MDSC subsets were quantitated by flow cytometry in the PB mononuclear cell (PBMC) fraction using the combination of CD33PC7/CD15PC5/HLA-DRECD/CD14PE/CD11bFITC monoclonal antibodies and the Kaluza analysis software. MDSC subsets were also studied in the BMMC fraction of 24 CIN patients and 8 healthy controls from the study population. The T-cell suppression function of patient MDSCs was evaluated in coculture experiments of immunomagnetically sorted, CFSE stained, normal CD3+ cells with immunomagnetically sorted M-MDSCs and PMN-MDSCs from 4 patients and 4 healthy donors using recombinant human IL-2 as activating factor. CFSE staining was detected in the CD3+ cells on day 0 and day 3 of coculture and analysis was performed with the Fcs Express 7 software. Statistical analysis was performed with the Statistica software. We found that the proportion of PB M-MDSCs was statistically significant lower in CIN patients (1.45% ± 1.82%) compared to controls (3.68% ± 3.12%, Mann-Whitney test, p &amp;lt; 0.0001) (Figure a) whereas the proportion of PB PMN-MDSCs, although lower in patients, did not differ significantly from the controls. The proportion of BM M-MDSCs did not differ significantly between CIN patients and controls whereas the proportion of BM PMN-MDSCs was statistically significant lower in patients (13.27% ± 11.27%) compared to controls (19.49% ± 4.46%; Mann-Whitney test, p = 0.0291) (Figure b). Paired analysis showed that the proportion of PMN-MDSCs were higher in the BMMC compared to PBMC fraction in both CIN patients (13.27% ± 11.27% vs 1.14% ± 1.64%, respectively; Wilcoxon test, p = 0.005) (Figure c) and healthy controls (19.49% ± 4.46% vs 9.92% ± 9.08%, respectively; Wilcoxon test, p = 0.0118). Interestingly, the proportion of increase of PMN-MDSCs (in BMMC vs PBMC fraction) was significantly higher in patients (86.71% ± 21.26%) compared to controls (55.95% ± 38.59%; Mann-Whitney test, p = 0.0357) (Figure d). The above data indicate low production of PMN-MDSCs in CIN patients compared to controls but a trend for accumulation of these cells in patients' BM. No statistically significant difference was documented in paired analysis of M-MDSCs between BMMC and PBMC fractions in either CIN patients or healthy controls. Patient PMN-MDSCs and M-MDSCs displayed normal capacity to suppress T-cell proliferation as was indicated by the T-cell generations in coculture experiments of normal CD3+ cells in the presence or absence of patient MDSCs (Figure e). In conclusion, CIN patients display low proportion of MDSCs in the PB and lower proportion of PMN-MDSC in the BM compared to normal individuals. Patient MDSCs display normal capacity to suppress T-cell activation. The low proportions of MDSCs may sustain the inflammatory process associated with CIN whereas the accumulation of PMN-MDSCs in the BM represents probably a compensatory mechanism to suppress the inflammatory processes within patients' BM microenvironment. Figure Disclosures Papadaki: Genesis pharma SA: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Early expansion of myeloid-derived suppressor cells inhibits SARS-CoV-2 specific T-cell response and may predict fatal COVID-19 outcome

The immunological mechanisms underlying the clinical presentation of SARS-CoV-2 infection and those influencing the disease outcome remain to be defined. Myeloid-derived suppressor cells (MDSC) have been described to be highly increased during COVID-19, however, their role remains elusive. We performed an in depth analysis of MDSC in 128 SARS-CoV-2 infected patients. Polymorphonuclear (PMN)-MDSC expanded during COVID-19, in particular in patients who required intensive care treatments, and correlated with IL-1β, IL-6, IL-8, and TNF-α plasma levels. PMN-MDSC inhibited T-cells IFN-γ production upon SARS-CoV-2 peptides stimulation, through TGF-β- and iNOS-mediated mechanisms, possibly contrasting virus elimination. Accordingly, a multivariate regression analysis found a strong association between PMN-MDSC percentage and fatal outcome of the disease. The PMN-MDSC frequency was higher in non-survivors than survivors at the admission time, followed by a decreasing trend. Interestingly, this trend was associated with IL-6 increase in non-survivors but not in survivors. In conclusion, this study indicates PMN-MDSC as a novel factor in the pathogenesis of SARS-CoV2 infection, and open up to new therapeutic options.

Interim subgroup analysis for response by PD-L1 status of CLASSICAL-Lung, a phase Ib/II study of pepinemab (VX15/2503) in combination with avelumab in advanced NSCLC.

3011 Background: Antibody blockade of semaphorin 4D (SEMA4D, CD100) promotes tumoral dendritic cell and CD8+ T cell infiltration and reduces function and recruitment of immunosuppressive myeloid cells. Importantly, these mechanisms to overcome immune exclusion and suppression have been shown to complement immune checkpoint therapies in preclinical models. Pepinemab is an IgG4 humanized monoclonal antibody targeting semaphorin 4D. The CLASSICAL-Lung clinical trial tests the combination of pepinemab with avelumab to couple T cell activation via checkpoint inhibition with beneficial modifications of the immune microenvironment via pepinemab. Methods: This phase 1b/2, single arm, first-in-human study is designed to evaluate the safety, tolerability and efficacy of pepinemab with avelumab in 62 patients (pts) with advanced (stage IIIB/IV) non-small cell lung cancer (NSCLC), including immunotherapy-naïve (ION) pts and pts whose tumors progressed following immunotherapy (IOF). Results: Among 21 evaluable ION pts, 5 experienced partial response (PR), 3 pts had clinical benefit ≥ 1 year, and the disease control rate (DCR) is 81%. Pts enrolled in this study were observed to have lower PD-L1 expression relative to prior single agent studies (likely due to approval of pembrolizumab for first line therapy). We, therefore, performed subgroup analysis for response by PD-L1 status. The objective tumor response (ORR) in the PD-L1 negative and low population ( &lt; 80% TPS by Dako 73-10 assay) appears to be approximately 2-2.5 fold greater with combination therapy than with historical single agent immune checkpoint controls. Notably, 97% of pts who experienced PR or SD were reported to have tumors with negative or low PD-L1 expression. Among 29 evaluable IOF pts, the combination resulted in 59% DCR, including 2 PR and 7 patients with durable clinical benefit of ≥ 23 weeks. Biomarker analysis of pre- and on-treatment biopsies confirmed increased CD8+ T cell density correlating with response. Surprisingly, analysis of myeloid-derived suppressor cells (MDSCs) revealed a relative paucity of these cells in pretreatment NSCLC biopsies as compared to other cancer indications such as HNSCC. Conclusions: This trial is nearing completion with only 5 of 62 subjects remaining on study. Preliminary data suggest the combination is well tolerated and shows signs of increased antitumor activity, particularly in PD-L1 negative or low tumors. Updated clinical response data and immunophenotypic analyses will be presented. Clinical trial information: NCT03268057 .

Association of myeloid suppressor cells with resistance to checkpoint blockade immunotherapy in urothelial carcinoma.

559 Background: Myeloid immune cells such as myeloid derived suppressor cells (MDSC) and tumor associated macrophages (TAM) have been hypothesized to cause resistance to immune checkpoint blockade (ICB). This is a pressing clinical problem for patients with bladder cancer. Here we determined if we could identify immune cells associated with resistance to ICB in the BBN963 mouse model, and if we could identify therapeutic strategies to target those same suppressor immune cells from patients with bladder cancer. Methods: BBN963 subcutaneous allografts were established in C57BL6/J mice. Response to anti-PD-L1 ICB was classified as partial or complete response according to RECIST criteria. Immune cell subsets with the tumors was evaluated by gene expression profiling and flow cytometry. Peripheral blood from patients with bladder cancer was collected under an IRB-approved protocol. MDSC were purified by flow sorting (CD11b+ CD33+ HLA-DRlow/neg) and screened for viability (Annexin-V staining) after 24 hours of exposure to a panel potential MDSC inhibitors. Results: 16/22 (72%) subjects met criteria for partial or complete response, while 6/22 (28%) were classified as anti-PD-L1 non-responders. Mice in the control group had a 0/10 (0%) response to isotype control (IgG) treatment. Monocytic MDSC (CD11b+ Ly6C+) were much more frequent among the intratumoral CD45+ cells of non-responding subjects as compared to control mice. Nanostring immune panel gene expression profiling revealed that combination treatment of tumor bearing mice with anti-PD-L1 plus ibrutinib (a putative MDSC inhibitor) decreased mRNA biomarkers of tumor-infiltrating macrophages. In vitro screening of patient-derived peripheral blood mononuclear cells showed that an inhibitor of the bromodomain and extraterminal domain (BET) family BRD4 specifically decreased MDSC viability. Conclusions: Monocytic MDSC appear to be associated with resistance to anti-PD-L1 ICB in a new murine model. Analysis of MDSC from patients with bladder cancer suggests that these myeloid suppressor cells can be specifically targeted.

Characterization of Immunosuppressive Cells Using MultiOmyx in Hematological Malignancies

Abstract Background Tumor associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC) can assist tumors to escape immune surveillance within the tumor microenvironment (TME). Based on phenotypical characteristics, MDSC can be further subdivided into granulocytic MDSC (G-MDSC) and monocytic MDSC (M-MDSC). These myeloid cell populations are well characterized and extensively studied in the solid tumors and their immunosuppressive function can be exerted via direct recruitment of Regulatory T cells (Treg). However, the role of these cells has been less studied in hematological malignancies (HM). Methods We report an analysis of MDSC, M2 macrophages and Treg using MultiOmyx multiplexed IF assay in clinical samples diagnosed with AML, HL and DLBCL. MultiOmyx technology enables detection and visualization of up to 60 protein biomarkers on a single FFPE slide. The FFPE sections were stained with a 13-marker panel including Arg1, CD11b, CD14, CD15, CD16, CD33, CD68, CD163, HLA-DR, CD3, CD4, CD8 and FOXP3. Results Both M-MDSC and G-MDSC were found to accumulate within the TME in different HM, with higher frequency of G-MDSC over M-MDSC. The data also revealed an abundant M2 macrophages present in the TME, especially in AML patient samples. Using the MultiOmyx proprietary algorithm, we quantified the counts and density of MDSC, TAM and Treg cells and studied the spatial correlations between different subsets of immunosuppressive cells. The results in the patient samples indicated that Treg was in closer proximity to M2 TAM than MDSC. Conclusions Targeting tumor-infiltrating myeloid cells has emerged as a new immunotherapeutic strategy. MultiOmyx 13-plexed panel has the potential to monitor the changes of immunosuppressive myeloid cells in response to immune modulating drugs such as MDSC-targeting drugs (e.g. PDE-5 inhibitors, COX-2 inhibitors), TAM-targeting agents (e.g. anti-CSF1R) and combination therapy in treatment of HM.

Characterization of Myeloid-Derived Suppressor Cells and Tumor Associated Macrophages Using MultiOmyxTM Hyperplexed Immunofluorescence Assay in Hodgkin Lymphoma

Tumor microenvironment (TME) consists of heterogeneous subsets of myeloid cells and plays a crucial role in promoting cancer development and metastasis. Tumor associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs) all contribute to an immunologically permissive microenvironment for cancer cells. On basis of the expression of surface markers, MDSC can be further subdivided into granulocytic MDSC (G-MDSC, polymorphonuclear MDSC) and monocytic MDSC (M-MDSC). In solid tumors, these different myeloid cell populations are well characterized and extensively studied. However, in hematological malignancies the role of myeloid cell subsets has been less studied. A recent study showed increase in MDSC in the bone marrow (BM) at time of diagnosis in acute myeloid leukemia (AML) patients (Sun H. et al. Int J Hematol. 2015). Significantly higher numbers of G-MDSC and M-MDSC were present at diagnosis in classic Hodgkin lymphoma (cHL) (Romano A. et al. Br J Haematol. 2015). The accumulation of TAMs was also reported to be associated with poor prognosis in cHL (Steidl C. et al. N Engl J Med. 2010). Collectively, these results indicate that the tumor-resident myeloid cells play an important clinical role, thus highlighting the need for monitoring and deeper characterization of various myeloid subsets in hematological malignancies, especially in the tumor FFPE sections.Herein, we report an analysis of MDSCs and ‘protumoral’ M2 macrophages using MultiOmyx hyperplexed immunofluorescence (IF) assay in 9 clinical samples diagnosed with HL. MultiOmyx is a proprietary multi ‘omic’ technology that enables detection and visualization of up to 60 biomarkers on a single 4µM FFPE slide (Gerdes MJ. et al. PNAS 2013). The HL FFPE sections were stained with a 13-marker panel including Arginase 1, CD11b, CD14, CD15, CD16, CD33, CD68, CD163, HLA-DR, CD3, CD4, CD8 and FOXP3. We observed that both M-MDSC (Fig 1A, characterized as CD11b+CD14+CD15-CD33+HLA-DR-) and G-MDSC (Fig 1B, identified as CD11b+CD14-CD15+CD33+HLA-DR-) accumulated within the TME in all 9 HL samples, with higher frequency of G-MDSCs over M-MDSCs. Arg1 expression was detected exclusively in G-MDSC population (Fig 1C). The data also revealed an abundant M2 macrophages (Fig 1D, characterized as CD68+CD163+) present in all HL samples. The detection of both MDSCs and M2 macrophages in HL samples supports the hypothesis that these cells contribute to the establishment of an immunosuppressive TME. Using the MultiOmyx proprietary algorithm, which takes into account the staining patterns, we will next quantify the counts and density of different tumor-resident myeloid subsets and measure the spatial distance between each subset of tumor-resident myeloid cells to the neoplastic Reed-Sternberg cells. Correlation study will also be performed to determine if significant correlations exist between MDSCs and TAMs and how these immunosuppressive myeloid cells are related to the Regulatory T cells (CD3+CD4+FOXP3+) in HL samples. In addition to HL samples, the same 13-plexed panel will be utilized to characterize the myeloid cell population from AML patients.TAMs and MDSCs are emerging as potential biomarkers for diagnosis and prognosis of cancer as well as therapeutic targets. The comprehensive myeloid cells phenotyping offered by MultiOmyx 13-plexed panel has the potential to monitor the changes of immunosuppressive myeloid cells in response to immune modulating drugs such as MDSC-targeting drugs (e.g. PDE-5 inhibitors, COX-2 inhibitors), TAM-targeting agents (e.g. anti-CSF1R) and combined therapy in treatment of lymphoma and leukemia. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Abstract LB-352: Identification of myeloid-derived suppressor cells in solid tumors by multiplex IHC

Abstract In healthy individuals, immature myeloid cells undergo differentiation into Macrophages, Dendritic Cells or Neutrophils. In individuals with several types of cancers, Tumor-Derived Factors promote a pathological differentiation of these immature cells into Myeloid-Derived Suppressor Cells (MDSCs) that phenotypically resemble either Macrophages (M-MDSCs) or Neutrophils (PMN-MDSCs). Rather than supporting antitumoral immunity like their regular counterparts, these abnormal, highly immunosuppressive cells, impair antitumoral immunity and promote tumor development. In addition to MDSCs, the tumor micro-environment is also infiltrated by Tumor-Associated Macrophages (TAMs), which can be roughly divided in two main subgroups, M1- and M2-polarized Macrophages, that exhibit anti- or pro-tumor activity, respectively. Over the last years, MDSCs have been recognized as valuable prognostic and/or predictive biomarkers, and there is a raising need for methods to phenotype these cells in clinical trials. Myeloid cell subpopulations are all closely related, and as a consequence, the phenotyping of each subset is complex, due to the high number of markers needed to discriminate them from the others. Recent advances have been made to define standard protocols to discriminate M- and PMN-MDSCs from TAMs and physiological Macrophages or Neutrophils combining flow cytometry and T-cell suppression assays. There are differences in the composition of subpopulations at the systemic level and those that infiltrate the tumor micro-environment, and a method for accurate phenotyping of MDSCs on tissue sections by ImmunoHistoChemistry (IHC) still need to be defined, but has been hampered by the limited number of antibodies that could be associated on a single slide. Using multiplex IHC and multispectral imaging, we have designed an approach to phenotype each myeloid cell population in the tumor micro-environment, in different solid tumor types. Antibodies to cell surface markers, cytoplasmic proteins contributing to the immune-regulatory activity and transcription factors, have first been validated as simplex IHC markers, tested as parts of multiplex panels, and evaluated in various combinations, to define a phenotyping strategy. A new Image Analysis Software has been designed to assess the co-expression of each of the markers for individual cells even for stains that do not strictly colocalize at the pixel level (e.g. nuclear and membrane proteins). Using a successive gating strategy, cells displaying MDSCs and M1/M2-polarized macrophages phenotypes have been numbered in sections from various tumor types. Our method is compatible with standard automated IHC platforms and an automated multispectral scanner, and provides a solution for the analysis of MDSCs in FFPE samples in clinical trials. Citation Format: Renaud BURRER, Océane ARIBO, Assil BENCHAABEN, Maroua TLIBA, Domenico LAZZARO, Jean-Philippe COTON. Identification of myeloid-derived suppressor cells in solid tumors by multiplex IHC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-352.

Abstract 1582: The coupling of MDSCs with a computational neural network (NN) to detect solid tumors

Abstract The goal of this study was to create a non-invasive cancer detection assay that analyzes flow cytometry data in an objective method. By using an artificial neural network (NN), we were able to distinguish between cancer patients (CPs) and benign/healthy donors (HDs) based upon the flow cytometry profiles of MDSCs and other leukocytes. Myeloid-derived suppressor cells (MDSCs) are known to be key contributors in supporting tumor progression and tumor escape through their ability to suppress anti-tumor responses mediated through T cell and natural killer (NK) cell activity. Several studies have demonstrated their utility as indicators of tumor progression and possible predictors of clinical outcomes, but there is significant overlap with healthy individuals preventing discrete and accurate calls. We used standard multiparametric flow cytometry techniques to immunophenotype MDSCs and other leukocytes found in the peripheral blood of 65 biopsy-confirmed CPs with solid tumors and 84 HDs. A series of NNs utilizing pattern recognition computational algorithms are then created using three data sets: 1) the training set - this ‘teaches' the two output categories of cancer and not cancer, 2) the validation set - this uses backpropagation to improve the accuracy of the trained networks, and 3) the testing set - this is used to rank the trained networks against each other. Finally, a naïve testing set is then used to determine the overall sensitivity and specificity for the top-ranking networks. Using traditional flow cytometry gating methods to analyze MDSCs as a biomarker for cancer detection, it is difficult to achieve high sensitivity and specificity due to the substantial overlap with healthy individuals. Here, we incorporated a standard 12 marker flow cytometry assay with NN technology to achieve a sensitivity of 92% and a specificity of 89%. Pairing the advanced analytical capabilities of our NN with surface biomarker based analysis of MDSCs and certain leukocytes measured in peripheral blood has enabled us the ability to objectively identify patterns indicative for the existence of a solid tumor. Citation Format: George A. Dominguez, Kristen Maslar, Alexander Polo, Cyrus Sholevar, Anthony Campisi, John Roop, Dmitry Gabrilovich, Frank Rauscher, Amit Kumar. The coupling of MDSCs with a computational neural network (NN) to detect solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1582.

The coupling of MDSCs with a computational neural network (NN) to detect solid tumors.

Abstract The goal of this study was to create a non-invasive cancer detection assay that analyzes flow cytometry data in an objective method. By using an artificial neural network (NN), we were able to distinguish between cancer patients (CPs) and healthy donors (HDs) based upon the flow cytometry profiles of MDSCs and other leukocytes. Myeloid-derived suppressor cells (MDSCs) are known to be key contributors in supporting tumor progression and tumor escape through their ability to suppress anti-tumor responses. Several studies have demonstrated their utility as indicators for tumor development, but there is significant overlap with healthy individuals. We used standard multiparametric flow cytometry techniques to immunophenotype MDSCs and other leukocytes found in the peripheral blood of 65 biopsy-confirmed CPs with solid tumors and 84 HDs. A series of NNs utilizing pattern recognition computational algorithms were created using three data sets: 1) the training set – this ‘teaches’ the two output categories of cancer and not cancer, 2) the validation set – this uses backpropagation to improve the accuracy of the trained networks, and 3) the testing set – this is used to rank the trained networks against each other. Finally, a naïve testing set is then used to determine the overall sensitivity and specificity for the top-ranking networks. Here, we incorporated a standard 12 marker flow cytometry assay with NN technology to achieve a sensitivity of 92% and a specificity of 89%. Pairing the advanced analytical capabilities of our NN with surface biomarker based analysis of MDSCs and certain leukocytes measured in peripheral blood has enabled us the ability to objectively identify patterns indicative for the existence of a solid tumor.

The coupling of MDSCs with a computational analytic method to detect solid tumors.

24 Background: Myeloid-derived suppressor cells (MDSCs) are key contributors in supporting tumor progression and tumor escape through their ability to suppress anti-tumor responses mediated through T cell and natural killer (NK) cell activity. Several studies have demonstrated their utility as indicators of tumor progression and possible predictors of clinical outcomes, but there is significant overlap with healthy individuals preventing discrete and accurate calls. The objective of our study was to create a non-invasive cancer detection assay that analyzes flow cytometry data in an objective method using an artificial neural network (NN) to distinguish between cancer patients (CPs) and healthy donors (HDs) based upon the flow cytometry profiles of MDSCs and other leukocytes. Methods: We used standard multiparametric flow cytometry techniques to immunophenotype MDSCs and other leukocytes found in the peripheral blood of 52 biopsy-confirmed CPs with solid tumors and 70 HDs. A series of NNs utilizing pattern recognition computational algorithms are then created using three data sets: 1) the training set - this ‘teaches’ the two output categories of cancer and not cancer, 2) the validation set – this uses backpropagation to improve the accuracy of the trained networks, and 3) the testing set – this is used to rank the trained networks against each other. Finally, a naïve testing set is then used to determine the overall sensitivity and specificity for the top-ranking networks. Results: Using traditional flow cytometry gating methods to analyze MDSCs as a biomarker for cancer detection, it is difficult to achieve both high sensitivity and specificity due to the substantial overlap with healthy individuals. Here, we incorporated a standard 12 marker flow cytometry assay with NN technology to achieve a sensitivity of 92.3% and a specificity of 90.0% with an area under the ROC curve (AUC) of 0.9477. Conclusions: Pairing the advanced analytical capabilities of our NN with surface biomarker based analysis of MDSCs and certain leukocytes measured in peripheral blood has enabled us the ability to objectively identify patterns indicative for the existence of a solid tumor.

The analysis of myeloid-derived suppressor cells in cancer patients with neutropenia to evaluate the effect of granulocytes colony stimulation factor

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population associated with immunosuppression andinflammation in cancer patients. Granulocytes colony stimulating factor (G-CSF) is frequently used in cancer patients withneutropenia. To evaluate the effect of G-CSF on patients being chemotherapy, we analyzed MDSCs in the peripheral blood.Peripheral blood was collected from 13 patients accompanied neutropenia during chemotherapy before and after G-CSFadministration. Flow cytometry was used to examine the percentage of MDSCs. The changes of MDSCs in the peripheral bloodaccording to G-CSF infusion were analyzed. The absolute neutrophil counts in patients before G-CSF administration were560±353 cells/uL (59-1,102 cells/uL). MDSCs were detected in the peripheral mononuclear cells with a cell percentage of2.74±4.02% (0.2-12.2%) and 5.48±8.56% (0.2-26.9%) before and after G-CSF infusion, respectively. Although there is nostatistically significance, G-CSF generally seems to move the MDSCs from the bone marrow to the peripheral blood to increaseMDSCs in the peripheral blood. It is necessary to study how the increased MDSCs affect the patient’s prognosis.

A Dynamic Metabolic Flux Analysis of Myeloid-Derived Suppressor Cells Confirms Immunosuppression-Related Metabolic Plasticity

Recent years have witnessed an increasing interest at understanding the role of myeloid-derived suppressor cells (MDSCs) in cancer-induced immunosuppression, with efforts to inhibit their maturation and/or their activity. We have thus modelled MDSCs central carbon metabolism and bioenergetics dynamic, calibrating the model using experimental data on in vitro matured mice bone marrow cells into MDSCs. The model was then used to probe the cells metabolic state and dynamics, performing a dynamic metabolic flux analysis (dMFA) study. Indeed, MDSCs maturation correlates with a high glycolytic flux contributing to up to 95% of the global ATP turnover rate, while most of the glucose-derived carbon enters the TCA cycle. Model simulations also reveal that pentose phosphate pathway and oxidative phosphorylation activities were kept at minimal levels to ensure NADPH production and anabolic precursors synthesis. Surprisingly, MDSCs immunosuppressive activity, i.e. L-arginine uptake, metabolism and endogenous synthesis, only consumes sparse quantities of energy-rich nucleotides (ATP and NADPH). Therefore, model simulations suggest that MDSCs exhibit a heterogeous metabolic profile similar to tumour cells. This behavior is probably an indirect immunosuppressive mechanism where MDSCs reduce the availability of carbon sources in the tumour periphery microenvironment, which could explain the dysfuntion and death of immune effector cells.

Rab7 GTPase controls lipid metabolic signaling in myeloid-derived suppressor cells.

Lysosomal acid lipase (LAL) is a critical neutral lipid metabolic enzyme that regulates metabolic reprogramming in myeloid-derived suppressor cells (MDSCs) through over-activation of mammalian target of rapamycin (mTOR). Affymetrix GeneChip microarray analysis of MDSCs from LAL deficient mouse (lal−/−) revealed upregulation of Rab7 GTPase protein, which belongs to a superfamily of small-molecular-weight GTPase known to regulate intracellular membrane trafficking from early to late endosomes and lysosomes. Here, the physical protein-protein interaction between Rab7 GTPase and mTOR has been detected by co-immunoprecipitation in the cell extract of wild type HD1A and lal−/− MDSC-like HD1B myeloid cell lines. The GST pull down assay using the recombinant GST-Rab7 GTPase fusion protein showed that Rab7 GTPase interacts with the mTOR N-terminal heat repeat domain. Rab7 GTPase siRNA knocking down reversed the altered lysosome/mTOR distribution and expression levels in HD1B cells. Rab7 GTPase siRNA knocking down in isolated bone marrow lal−/− MDSCs or HD1B cells not only reduced over-activation of mTOR and its downstream effector S6, but also decreased glucose consumption, decreased ROS over-production, and increased healthy mitochondria by membrane potential measurement. Inhibition of Rab7 GTPase led to reduced lal−/− MDSCs differentiation from bone marrow Lin− progenitor cells, reduced lal−/− MDSCs trans-endothelial migration, and reversed lal−/− MDSCs suppression of T cell proliferation. Furthermore, inhibition of Rab7 GTPase reduced lal−/− MDSCs ability to stimulate tumor cell proliferation in vitro, tumor growth in vivo, and tumor invasion. Together, these results showed that Rab7 GTPase is critically involved in MDSCs homeostasis and pathogenic functions.

Interactome analysis of myeloid-derived suppressor cells in murine models of colon and breast cancer.

In solid cancers, myeloid derived suppressor cells (MDSC) infiltrate (peri)tumoral tissues to induce immune tolerance and hence to establish a microenvironment permissive to tumor growth. Importantly, the mechanisms that facilitate such infiltration or a subsequent immune suppression are not fully understood. Hence, in this study, we aimed to delineate disparate molecular pathways which MDSC utilize in murine models of colon or breast cancer. Using pathways enrichment analysis, we completed interactome maps of multiple signaling pathways in CD11b+/Gr1(high/low) MDSC from spleens and tumor infiltrates of mice with c26GM colon cancer and tumor infiltrates of MDSC in 4T1 breast cancer. In both cancer models, infiltrating MDSC, but not CD11b+ splenic cells, have been found to be enriched in multiple signaling molecules suggestive of their enhanced proliferative and invasive phenotypes. The interactome data has been subsequently used to reconstruct a previously unexplored regulation of MDSC cell cycle by the c-myc transcription factor which was predicted by the analysis. Thus, this study represents a first interactome mapping of distinct multiple molecular pathways whereby MDSC sustain cancer progression.

Abstract A102: Osteopontin produced by myeloid cells determines the outcome of breast cancer metastases

Abstract The matricellular protein osteopontin (OPN) combines regulatory and structural functions in the extracellular matrix and, when produced by tumor cells, concurs to progression, cell invasion and metastasis. Little is known about its activity when produced by host cells including that component of tumor stroma. Combining gene silencing in tumor cells and mice deficient for OPN we have dissected the role of tumor and host produced OPN in breast cancer metastasis using 4T1 and BJMC3879 spontaneously metastatic models. While tumor produced OPN favors lung metastasis promoting tumor cell survival in the blood stream, stromal OPN greatly affects the immusuppression at the metastatic site. Immunosuppression is often associated with the expansion of a heterogeneous myeloid population called myeloid derived suppressor cells (MDSC) comprising a granulocytic (Gr-1high) and a monocytic (Gr-1int/low) subset, the latter endowed with higher immune suppressive capacity and characterized by OPN expression. Analysis of MDSC showed that inhibition of lung metastases in OPN-deficient mice goes along with a skewing toward the Gr1high subset, whereas the Gr1int/low subset is more expanded in wild type mice. Moreover, the latter subset, in lungs of tumor-bearing OPN-deficient animals, is less suppressive than its wild type counterpart, and associated with a lower expression of arginase-1, IL-6 and phospho-STAT3. Our results find correlation with human tumors and underscore that different mechanisms characterize tumor- and host-produced OPN activities in breast cancer metastasis and reveal a new function for host-derived OPN as regulator of the local immune response in the metastatic lung niche. Citation Format: Mario P. Colombo, Claudia Chiodoni. Osteopontin produced by myeloid cells determines the outcome of breast cancer metastases. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A102.