Myeloid-derived Suppressor Cells Populations Research Articles

Abstract IA09: Radiotherapy immunotherapy interactions: What determines success or failure?

Abstract Radiation therapy (RT) can both stimulate antitumor immunity and induce immunosuppressive responses, complicating its therapeutic efficacy. Data indicate that certain patient subsets—such as those undergoing combination treatment with radiation and immune-oncology drugs and/or targeted therapies may benefit from strategies that target immunosuppression or metastasis-promoting factors. One of the key challenges is the heterogeneous and context-dependent nature of myeloid suppressive states in the tumor microenvironment, which often leads to resistance to RT and immunotherapy. RT has been shown to skew myeloid plasticity towards immune suppression by expanding myeloid-derived suppressor cell (MDSC) populations, increasing their trafficking into tumor tissues, and promoting the development of suppressive macrophage subsets. Targeting myeloid cell plasticity post-RT presents a promising therapeutic strategy. Interventions that block the systemic induction of immunosuppressive myeloid cells to inhibit their trafficking to tumors, or those that promote the conversion of suppressive myeloid cells into anti-tumor populations could enhance the effectiveness of RT. Additionally, radiation-induced proteins that can be inhibited or amplified may provide a potential avenue to overcome the limitations of RT alone, and in combination with immunotherapy. Citation Format: Ralph R. Weichselbaum. Radiotherapy immunotherapy interactions: What determines success or failure?. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Targeted Therapies in Combination with Radiotherapy; 2025 Jan 26-29; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(2_Suppl):Abstract nr IA09

Distinct myeloid-derived suppressor cell populations in human glioblastoma.

The role of glioma-associated myeloid cells in tumor growth and immune evasion remains poorly understood. We performed single-cell RNA sequencing of immune and tumor cells from 33 gliomas, identifying two distinct myeloid-derived suppressor cell (MDSC) populations in isocitrate dehydrogenase-wild-type (IDT-WT) glioblastoma: an early progenitor MDSC (E-MDSC) population with up-regulation of metabolic and hypoxia pathways and a monocytic MDSC (M-MDSC) population. Spatial transcriptomics demonstrated that E-MDSCs geographically colocalize with metabolic stem-like tumor cells in the pseudopalisading region. Ligand-receptor analysis revealed cross-talk between these cells, where glioma stem-like cells produce chemokines attracting E-MDSCs, which in turn produce growth factors for the tumor cells. This interaction is absent in IDH-mutant gliomas, associated with hypermethylation and repressed gene expression of MDSC-attracting chemokines. Our study elucidates specific MDSCs that may facilitate glioblastoma progression and mediate tumor immunosuppression.

Intestinal Akkermansia muciniphila complements the efficacy of PD1 therapy in MAFLD-related hepatocellular carcinoma.

Immune checkpoint inhibitors are not effective for metabolic dysfunction-associated fatty liver disease (MAFLD)-hepatocellular carcinoma (HCC) patients, and identifying the key gut microbiota that contributes to immune resistance in these patients is crucial. Analysis using 16S rRNA sequencing reveals a decrease in Akkermansia muciniphila (Akk) during MAFLD-promoted HCC development. Administration of Akk ameliorates liver steatosis and effectively attenuates the tumor growth in orthotopic MAFLD-HCC mouse models. Akk repairs the intestinal lining, with a decrease in the serum lipopolysaccharide (LPS) and bile acid metabolites, along with decrease in the populations of monocytic myeloid-derived suppressor cells (m-MDSCs) and M2 macrophages. Akk in combination with PD1 treatment exerts maximal growth-suppressive effect in multiple MAFLD-HCC mouse models with increased infiltration and activation of Tcells. Clinically, low Akk levels are correlated with PD1 resistance and poor progression-free survival. In conclusion, Akk is involved in the immune resistance of MAFLD-HCC and serves as a predictive biomarker for PD1 response in HCC.

Effect of External Beam Radiation Therapy and Brachytherapy on Circulating Myeloid-Derived Suppressor Cell Populations in Patients Treated Definitively for Cervical Cancer

PurposeThe immunosuppressive function of myeloid derived suppressor cells (MDSCs) has been implicated in the regulation of immune responses against cancer and is associated with poor prognosis. Radiation treatment is known to alter immune cell populations within the tumor, however, whether this results in recruitment of immunosuppressive MDSC populations is not well understood. Here we evaluate the response of circulating MDSC populations in patients treated per standard of care cisplatin chemoradiation therapy (CRT) for locally invasive cervical cancer. Methods and MaterialsNewly diagnosed, treatment naïve patients with locally advanced cervical cancer were enrolled. Blood samples were collected from patients prior to starting CRT (T0), after external beam radiation therapy (EBRT) (T1), and after high-dose rate brachytherapy (T2). Samples from each timepoint were processed and prevalence of MDSC subsets were determined by flow cytometry. MDSC populations were identified by Live/Dead-CD11b+CD33+HLA-DR- staining. MDSC subsets were further subdivided into granulocytic (g-, CD15+CD14-), monocytic (m-, CD15-CD14+), or early-MDSCs (e-, CD15-CD14-). ResultsMost patients in our study were Caucasian non-smokers with HPV-associated squamous cell carcinoma of the cervix. We saw a trend for increased MDSC frequency in patients with more advanced stage disease at the time of initiating treatment. MDSCs increase in response to CRT and peak after brachytherapy (T2). In particular, the g-MDSC subset which increases 6.44x relative to baseline. There was no correlation between MDSC expansion and response to therapy. ConclusionOur study confirms other reports that circulating MDSCs in patients with cervical cancer increase in response to CRT and are associated with more advanced stage. Additionally, we show that MDSC expansion is driven by the g-MDSC subset. We did not see any correlation between MDSC expansion and treatment response, though this may be due to the limited sample size for this study

Cryptotanshinone alleviates immunosuppression in endometriosis by targeting MDSCs through JAK2/STAT3 pathway

BackgroundEndometriosis (EMS), a well-recognized chronic inflammatory disorder, characterized by significant immune dysregulation, in which myeloid-derived suppressor cells (MDSCs) are essential for facilitating immunosuppression and driving to disease progression. Cryptotanshinone (CTS) is an active compound capable of modulating MDSC-mediated immunosuppression; however, its therapeutic effects and mechanisms in the treatment of EMS remain unclear. PurposeThis study aims to investigate the therapeutic potential of CTS in modulating MDSCs through JAK2/STAT3 signaling pathway and to evaluate its effects on immune microenvironment and endometriotic lesion growth in EMS. MethodsTranscriptomic data (GSE141549) and single-cell RNA sequencing data (GSE213216) were analyzed to compare immune cell populations in control endometrium (CE), eutopic endometrium (EuE) and ectopic endometrium (EcE) of patients with EMS. Network pharmacology analysis, surface plasmon resonance (SPR) and cellular thermal shift assay (CETSA) were utilized to explore the molecular mechanism of CTS's effects on MDSCs. A C57BL/6J EMS mice model was established to evaluate CTS's influence on MDSC-mediated immune response in vivo. Flow cytometry and immunofluorescence were used to analyze the immune cell populations, particularly MDSCs and CD8+ T cells. Ex vivo bone marrow (BM)-derived MDSCs were prepared to investigate the modulatory activities of CTS on the frequency and function of MDSCs. The impacts of CTS on JAK2/STAT3 pathway were further examined by western blot. ResultsBioinformatic analysis revealed that, among the three progression stages (CE, EuE, and EcE), the EcE stage exhibited a relatively elevated level of MDSCs and a reduced level of CD8+ T cells. Network pharmacological analysis, along with SPR and CETSA identified that CTS potentially modulates MDSCs in EMS by targeting the JAK2/STAT3 pathway. In vivo studies demonstrated that a relatively high dose of CTS treatment (60mg/kg) effectively inhibited lesion growth, reduced the population of MDSCs, and enhanced CD8+ T cell infiltration. Ex vivo experiments showed that CTS decreased the BM-derived MDSC frequency and rescued the suppressive ability of MDSC upon CD8+ T cells in a dose-dependent manner. Further mechanism analysis confirmed that CTS modulates the expression of immunosuppressive genes and proteins associated with MDSCs through JAK2/STAT3 pathway. ConclusionThis study is the first to demonstrate that CTS is a promising natural compound for EMS treatment by inhibiting MDSC accumulation and modulating MDSC-mediated immune responses. Its therapeutic efficacy is linked to the modulation of the JAK2/STAT3 signaling pathway.

IMMU-58. BCAT1 TARGETED METABOLIC REPROGRAMMING PLAYS CRITICAL ROLES IN MODULATING MYELOID DERIVED SUPPRESSOR CELL FUNCTION IN GLIOBLASTOMA

Abstract A key component that has limited the efficacy of immunotherapy in glioblastoma (GBM) is the significant infiltration of immunosuppressive myeloid cells. Our previous work characterized myeloid derived suppressor cells (MDSCs) unique to GBM that drive tumor growth and immune suppression. Transcriptomic and flow cytometric analyses demonstrated that the most induced programs in these MDSCs are dominated by metabolic and mTOR pathways. Therefore, we aimed to understand the role of metabolic reprogramming in MDSC differentiation and immunosuppressive function. Using single cell RNA sequencing, we identified overexpression of enzymes and transporters involved in branched-chain amino acid (BCAA) metabolism, notably branched chain aminotransferase 1 (BCAT1), the first enzyme in the metabolic pathway. Intriguingly, this was only found in specific populations of early and monocytic MDSCs (E-MDSCs, M-MDSCs), and not polymorphonuclear MDSCs (PMN-MDSCs). Using established MDSC modeling systems, we found that M-MDSC differentiation and T cell suppressive function are dependent on BCAAs and can be hindered by pharmacological inhibition of BCAT1 activity or genetic knockout of BCAT1. We also establish that the influence of BCAA on M-MDSC function is specifically reliant on the BCAT1-mediated step of BCAA metabolism. To determine the underlying mechanism driving BCAT1’s impact on M-MDSC function, we evaluated the activity of signaling pathways known to be critical to M-MDSCs including the mTORC1 pathway. We found that the impact of BCAA and BCAT1 activity on M-MDSC function is abrogated by inhibition of mTORC1 pathway with reduction in M-MDSC differentiation and activity. Consistent with our single cell RNA sequencing analysis, modulation of BCAA levels and BCAT1 activity had no impact on PMN-MDSCs. Our results underscore the critical role of BCAT1 in preferentially modulating M-MDSC activity through mTORC1 signaling. Our finding paves the way for discovery of a targetable therapeutic approach to harness immunometabolism in myeloid cells to develop novel immune therapies.

Synovial Fluid Immune Cell Composition Following Intraarticular Fracture May Contribute to Posttraumatic Osteoarthritis.

Intra-articular ankle fracture (IAF) often leads to post-traumatic osteoarthritis (PTOA), resulting in significant long-term morbidity. While previous research has focused on the inflammatory cytokines and matrix metalloproteinases within the synovial fluid fracture hematoma (SFFH), the immune cell populations within SFFH that contribute to PTOA development remain underexplored. This study aimed to characterize the immune cell populations in SFFH to better understand their role in the inflammatory response and potential for inducing lasting cartilage damage. Twenty-four patients with IAF underwent surgical ankle aspiration to collect SFFH, which was analyzed using polychromatic flow cytometry. The analysis revealed that 72.8% of the CD45+ cells were lymphocytes, predominantly CD3+ T cells (76.5%), with 42.1% being CD4+ and 39.2% CD8+ T cells. Additionally, monocytes accounted for 21.2% of CD45+ cells, with small populations of natural killer cells and myeloid-derived suppressor cells also present. These findings emphasize the predominance of T cells, particularly CD4+ subsets, in the immune response following IAF. Understanding these dynamics is essential for developing targeted interventions to prevent PTOA. Future research should focus on elucidating the specific roles of these immune cell populations in PTOA progression and exploring potential therapeutic strategies.

Enhancing Anti-PD-1 Immunotherapy by Targeting MDSCs via Hepatic Arterial Infusion in Breast Cancer Liver Metastases.

Surgery, chemotherapy, and radiation often have limited utility for advanced metastatic disease in the liver, and despite its promising activity in select cancers, PD-1 blockade therapy similarly has minimal benefit in this setting. Curaxin, CBL0137, is an experimental anti-cancer drug that disrupts the binding of DNA to histones, destabilizes chromatin, and induces Z-DNA formation which may stimulate anti-tumor immune responses. Murine cell lines of colon (CT26) and breast (4T1) cancer were interrogated for survival and CBL0137-associated DNA changes in vitro. Immunocompetent models of liver metastases followed by CBL0137 hepatic arterial infusion (HAI) were used to examine in vivo tumor cell DNA alterations, treatment responses, and the immune contexture associated with CBL0137, both alone and in combination with anti-PD-1 therapy. CBL0137 induced immediate changes to favor tumor cell death in vitro and in vivo with an efficient tumor uptake via the HAI route. Toxicity to CBL0137 was minimal and anti-tumor treatment effects were more efficient with HAI compared to intravenous delivery. Immune effects were pronounced with CBL0137 HAI with concurrent depletion of a specific population of myeloid-derived suppressor cells and maintenance of effector T cell populations. Combination of CBL0137 HAI with PD-1 blockade improved survival in 4T1 tumors but not in CT26 tumors, and therapeutic efficacy relies on the finding of simultaneous and targeted depletion of myeloid-derived suppressor cells and skewing of T cell populations to produce synergy with PD-1 blockade therapy.

T-cell immunosuppression in sepsis is augmented by sciatic denervation-induced skeletal muscle atrophy.

Skeletal muscle atrophy is a known risk factor for immunosuppressive conditions and for a poor prognosis in sepsis. However, its immunopathology has not been experimentally elucidated. This study investigated the effects of skeletal muscle atrophy on the immunopathology of sepsis. Male C57BL/6J mice were subjected to sciatic denervation (DN) and caecal ligation and puncture (CLP) to induce muscle atrophy or sepsis. The macrophages, myeloid-derived suppressor cells (MDSC), and T-cells in peritoneal and spleen were analysed using flow cytometry. DN-induced muscle atrophy did not affect macrophage and MDSC populations. In contrast, the percentage of cytotoxic T-lymphocyte-associated antigen (CTLA)-4+ CD4+ T-cells, programmed death (PD)-1+ CD8+ T-cells, regulatory T-cells, and the CTLA-4+ regulatory T-cells was statistically significantly higher in DN-CLP mice than in sham-CLP mice. Skeletal muscle atrophy before sepsis triggers excessive Tcell immunosuppression, which may contribute to the exacerbation of sepsis under skeletal muscle atrophy.

Siwu decoction suppress myeloid-derived suppressor cells through tumour cells necroptosis to inhibit hepatocellular carcinoma

BackgroundHuman hepatocellular carcinoma (HCC) acquired resistance to anti-cancer agents due to the presence of immunosuppressive tumour microenvironment (TME) established by the interaction between tumour cells and immune populations. New treatment targeting the interaction is urgently needed and clinically beneficial to patients with HCC. This study aims to explore the anti-tumour effect of a Traditional Chinese Medicine formula Siwu Decoction (SWD) and its potential mechanism. Materials and methodsThe chemical profile of SWD was determined by high-performance liquid chromatography coupled with mass spectrometry. In vitro and in vivo effects of SWD in regressing HCC were assessed. The role of myeloid-derived suppressor cells (MDSCs) in mediating SWD-induced HCC inhibition was determined by adoptive transfer assay. The regulation of SWD-induced interaction between HCC cells and MDSCs was also confirmed both in vitro and in vivo. ResultsSWD dose-dependent inhibited the HCC growth and lung metastasis in an orthotopic growth tumour in mice, without significant toxicity and adverse side effect. SWD induced necroptosis in HCC cells, but did not directly inhibit in vitro culture of MDSCs, instead, SWD-treated HCC cell culture supernatant suppressed MDSCs by inducing its cell apoptosis. The necroptotic response of HCC cells can also suppress the MDSCs population in the TME without reducing circulating MDSCs infiltration into the tumours. Adoptive transfer of MDSCs recovered tumour growth and lung metastasis of HCC in SWD-treated mice. In HCC cells, SWD induced a necroptotic response, and blockade of necroptotic response in HCC cells recovered the MDSCs population in vitro and in vivo, and restored tumour growth and lung metastasis in SWD-treated mice. A combination of SWD improves the anti-HCC efficacy of sorafenib without inducing adverse side effects. Albiflorin, the effective compound of SWD, its anti-HCC manner has been verified to be consistent with that of SWD. ConclusionOur study observed for the first time that SWD can suppress HCC by regulating MDSCs through necroptosis of tumour cells in the TME. The main effective compound of SWD, albiflorin can be a potential adjuvant therapy in the clinical management of human HCC.

PRPS2-mediated modulation of the antitumor immune response in lung cancer through CCL2-mediated tumor-associated macrophages and myeloid-derived suppressor cells.

Phosphoribosyl pyrophosphate synthetase 2 (PRPS2) is known as an oncogene in many types of cancers, including lung cancer. However, its role in regulating tumor-associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC) remains unclear. Our study aimed to explore the involvement of PRPS2 in TAM and MDSC regulation. Stable Lewis lung cancer (LLC) cell lines were established using a lentivirus system. These LLC lines were then used to establish tumor model in mice. The levels of target genes were determined using qPCR, western blotting, and ELISA assays. The percentage of different immune cell types was analyzed using fluorescence-activated cell sorting. The chemotaxis ability of TAM and MDSC was evaluated using an in vitro transwell chemotaxis assay. Notably, PRPS2 was found to regulate the chemotaxis of TAM and MDSC in tumor cells, as evidenced by the positive correlation of PRPS2 expression levels and abundance of TAM and MDSC populations. In addition, the expression of CCL2, mediated by PRPS2, was identified as a key factor in the chemotaxis of TAM and MDSC, as evidenced by a significant reduction in macrophages and MDSC numbers in the presence of the CCL2 antibody. Furthermore, in vivo experiments confirmed the involvement of PRPS2 in mediating CCL2 expression. PRPS2 was also found to regulate immune cell infiltration into tumors, whereas knockdown of CCL2 reversed the phenotype induced by PRPS2 overexpression. In tumor tissues from mice implanted with LLC-PRPS2-shCCL2 cells, a notable increase in CD4+ and CD8+ T cell percentages, alongside a marked decrease in TAMs, M-MDSC, and PMN-MDSC, was observed. Taken together, PRPS2 plays a crucial role in modulating the antitumor immune response by reprogramming CCL2-mediated TAM and MDSC.

Unzippable Siamese Nanoparticles for Programmed Two-Stage Cancer Immunotherapy.

Epigenetic drugs (epi-drugs) can destruct cancer cells and initiate both innate and adaptive immunity, yet they have achieved very limited success in solid tumors so far, partly attributing to their concurrent induction of the myeloid-derived suppressor cell (MDSC) population. Here, dissociable Siamese nanoparticles (SIANPs) are developed for tumor cell-targeted delivery of epi-drug CM-272 and MDSC-targeted delivery of small molecule inhibitor Ibrutinib. The SIANPs are assembled via interparticle DNA annealing and detached via tumor microenvironment-triggered strand separation. Such binary regulation induces endogenous retrovirus expression and immunogenic cell death in tumor cells while restraining the immunosuppressive effects of MDSCs, and synergistically promotes dendritic cell maturation and CD8+ T cell activation for tumor inhibition. Significantly, immune microenvironment remodeling via SIANPs further overcomes tumor resistance to immune checkpoint blockade therapy. This study represents a two-pronged approach for orchestrating immune responses, and paves a new way for employing epi-drugs in cancer immunotherapy.

Decitabine suppresses MDSC-induced immunosuppression through dual functional mechanism and inhibits melanoma metastasis.

Myeloid-derived suppressor cells (MDSCs) play a crucial role in promoting melanoma metastasis. Reprogramming MDSCs into mature M1 macrophages has emerged as a strategy to inhibit metastasis. Decitabine (Dec) is known to eradicate MDSCs and suppress tumor growth. In this study, we provide evidence that Dec not only reduces the MDSC population by inducing apoptosis, arresting cell cycle, and impairing recruitment, but also suppresses their immunosuppressive function by downregulating related genes and facilitating differentiation into M1 macrophages. Transcriptomic analysis of Dec-treated MDSCs revealed a marked downregulation of immunosuppressive genes including S100a9, S100a8, Vegf, Cxcr2, and Nos2. Meanwhile, M1 macrophage-associated genes involved in immune activation were upregulated, such as Ddx58, Isg15, Tap1, Ccl5, Cxcl9, and Cxcl10. Further bioinformatic analysis indicated that Dec promotes MDSC-to-M1 macrophage differentiation and activates innate immune pathways including NOD-like signaling to enhance anti-tumor immunity. Time-course studies implied that Dec upregulates myeloid transcription factor Irf7 to initiate MDSC differentiation and orchestrate the anti-tumor immune response. Collectively, our study unveils a novel dual-functional mechanism of Dec as both a cytotoxic agent reducing MDSCs and an inducer of their differentiation into M1 macrophages, thereby alleviating immunosuppression. This highlights Dec's potential for clinical melanoma metastasis suppression.

LC-MS-based rheumatoid arthritis serum metabolomics reveals the role of deoxyinosine in attenuating collagen-induced arthritis in mice

Rheumatoid arthritis (RA) is a persistent autoimmune condition with no identified cure currently. Recently, scientists have applied metabolomics to investigate altered metabolic profiles and unique diseases-associated metabolic signatures. Herein, we applied metabolomics approach to analyze serum samples of 41 RA patients and 42 healthy controls (HC) with the aim to characterize RA patients' metabolic profile, investigate related underlying pathological processes, and identify target metabolites. By utilizing ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry, we found 168 proposed metabolites and 45 vital metabolic pathways. Our analysis revealed that deoxyinosine (DI), a metabolite of the purine metabolic pathway, was the most significant reduced metabolite in RA patients. Furthermore, through targeted detection, we confirmed lower concentration of DI in RA patients' peripheral blood. Moreover, DI inhibited lipopolysaccharide-induced inflammation both in vitro and in vivo. We further assessed DI's therapeutic potential in a collagen-induced arthritis (CIA) murine model. The results revealed that DI attenuated CIA, as evidenced by significantly lowered clinical scores of arthritis, alleviated joint swelling, and mitigated bone destruction. Moreover, we elucidated the underlying mechanism by which DI increased the population of myeloid-derived suppressor cells (MDSCs) and suppressed the proliferation of induced T cells. Collectively, these findings suggested that DI potentially ameliorated RA by inducing immunosuppressive MDSCs. The study provides key observations on RA pathogenesis and may contribute to developing novel therapeutic strategies for this debilitating condition.

SIGLEC-3 (CD33) serves as an effective target in tumor progression

Abstract Human CD33 (Siglec-3) possesses an immune-receptor tyrosine-based inhibition motif (ITIM), which recruits Src homology 2 (SH2) containing phosphatases (SHP-1/2) and inositol phosphatase (SHIP) and exerts inhibitory effects. The structure and downstream signaling of CD33 bear similarity to programmed cell death protein-1 (PD-1), a promising target in cancer immune therapy. Previous studies indicate that CD33 serves as a therapeutic target in acute myeloid leukemia (AML), additionally, CD33 also acts as a prevalent surface marker of human myeloid-derived suppressor cells (MDSCs). According to the inhibitory signaling upon CD33 activation, CD33 may participate in tumor progression and the regulatory role of CD33 in solid tumors is still unclear. To investigate whether CD33 influences cancer progression, we established a melanoma tumor (B16F10) mouse model in monocyte/macrophage-specific human CD33 transgenic mice (hCD33 Tg mice, Cx3cr1cre/-hCD33M+/-). Compared to wild-type mice (WT), tumor growth and mortality were larger and higher in CD33 Tg mice. Moreover, an antagonistic anti-hCD33 monoclonal antibody (clone 4L3-46) treatment successfully attenuated tumor growth in hCD33 Tg mice and led to a restructuring of the infiltrating MDSCs population. These results indicate that human CD33 contributes to the advancement of tumors, and the blockade of CD33 represents a promising strategy in tumor therapy.

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.

Abstract 3065: Targeting of metabolic reprogramming in lung cancer by utilizing patient-derived organoid tissue for precision medicine

Abstract In a preliminary pilot study, we reported elevated activity of indoleamine 2,3-dioxygenase 1 (IDO1) in serum from cisplatin-resistant (CR) lung cancer patients compared to cisplatin-sensitive (CS) patients. This heightened IDO1 activity was associated with increased tryptophan (TRP) catabolism, resulting in the upregulation of kynurenine (KYN) production. The detection of KYN can now be readily achieved through immunohistochemistry (IHC). We demonstrated that this upregulation contributed to increased Treg (regulatory T cell) and MDSC (myeloid-derived suppressor cell) populations resulting in an immunosuppressive tumor microenvironment. To investigate this effect, we used dual inhibition of IDO1/TDO2 (tryptophan2,3-dioxygenase 2) in an orthotopic mouse model of CR-Lewis lung carcinoma. This resulted in a significant reduction in tumor volume compared to LLC-CS (n=7, p<0.01), confirming the role of TRP catabolism in CR tumorigenesis. To determine the relevance of the data derived from this mouse model to clinical settings, we established 50 patient-derived organoid tissues (PDOT) from patients with NSCLC. PDOT is an experimental ex vivo tissue model developed to recapitulate the intricate features of lung architecture, including the lung acinus. Upon optimizing our collection and growth protocols, each PDOT successfully developed into a spherical body within 14 days. Furthermore, through bulk RNA-seq analysis, we showed that PDOT closely mirrors the expression of key molecular markers (PD-L1 and mutations), as observed in the original tumor tissues. PDOT from patients possessing high levels of PD-L1 and KYN were exquisitely sensitive to dual inhibition with 2-3-fold greater sensitivity compared to patients with undetectable KYN expression in growth inhibition assays (GI50=20±5.5μM vs. 65±7.5μM). Increased lipid peroxidation was detected via flow cytometry by accumulation of the C11-BODIPY reporter dye in the dual inhibition treatment group. Moreover, we integrated PDOT with a novel 3D microfluidic culture that can be supplied with patient-matched peripheral blood mononuclear cells (PBMC) to assess immune response. Using CyTOF, we showed that dual inhibitors with Atezolizumab (anti-PD-L1) enhanced immune effector (CD8+, NK) and suppressed immunosuppressive (Treg, MDSC) populations. We believe that our swift progress in PDOT development may bridge the divide between cancer biomarker expression and patient trials by timely complementing conventional drug studies based on cell lines and xenografts to facilitate the design of personalized therapies. As a result, the extensive reporting that we have contributed for KYN expression profiling in CR has the potential to serve as a valuable companion diagnostic tool in the future. This can assist in applying precision oncology by finding the most appropriate patients for immunotherapies. Citation Format: Chunjing Wu, Jonathan D. Nguyen, George Theodore, Estelamari Rodriguez, Sydney Spector, Emily Kim, Taranatee Khan, Pablo Puente, Yujie Wang, Dao M. Nguyen, Cheng-Bang Chen, Diane Lim, Lynn G. Feun, Niramol Savaraj, Medhi Wangpaichitr. Targeting of metabolic reprogramming in lung cancer by utilizing patient-derived organoid tissue for precision medicine [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 3065.

Abstract 1531: TIL analysis demonstrates different mechanisms underlying PD-1 resistance in animal models

Abstract Despite the tremendous success of PD-1 immunotherapy in treating cancer, resistance to the therapy is an inevitable risk. One of the major mechanisms underlying this resistance is alterations in the tumor microenvironment, including tumor-infiltrating lymphocyte (TIL) profiling changes after anti-PD1 treatment. To better understand the mechanism of PD-1 resistance, characterization of TILs in the tumor microenvironment was explored. First, immune cell profiling was performed in syngeneic tumor models established by 19 cancer cell lines without anti-PD-1 treatment. Depending on the tumor model, absolute numbers of CD45+ cells and immune cell subsets varied. Moreover, stratifying the analysis based on tumor size (100 mm3 to 3000 mm3) revealed alterations in the proportion of immune cell percentages in MC38 tumors, which implies alterations in TIL frequency during cancer progression. Next, we investigated the TIL profile in two PD-1 resistant models: a hPD-1 antibody-induced resistant model and a syngeneic model in aged mice. The hPD-1 antibody resistant model was induced by multiple rounds of hPD-1 antibody retreatment on MC38 tumor-bearing humanized B-hPD-1/hPD-L1 mice. Efficacy results from this model further validated their resistance to hPD-1 treatment (0% tumor growth inhibition (TGI)), while the control group, which was not serially treated, showed substantial tumor inhibition (82.2% TGI). Next, mPD-1 antibody resistance was evaluated in aged wild-type mice. While mPD-1 efficacy on MC38-bearing young mice was approximately 85.5% TGI, the efficacy of this treatment in aged mice yielded only 6% TGI. TIL analysis in these models was subsequently performed: in the hPD-1-treated control mice that were responsive to anti-PD1 treatment, the numbers of total T cells, cytotoxic T cells (CD8+) and MHC II positive cells were increased, while the anti-tumor effector cells in the serially treated resistant mice were either unchanged (total T cells and MHC II positive cells) or decreased (CD8+ cells); strikingly, an increase in inhibitory myeloid-derived suppressor cell (MDSC) populations was also observed in the resistant model post-treatment. In the anti-PD1 treated aged mice, the frequency of TILs was unchanged upon mPD-1 treatment, suggesting that resistance in aged mice may be due to non-responsiveness of the immune cells. In sum, our results demonstrate different mechanisms underlying anti-PD-1 resistance, and suggest that a more thorough analysis of the TILs present in the tumor microenvironment could predict the responsiveness to PD-1 therapy and inform treatment strategies. Citation Format: Sha Qiao, Yujia Liu, Wei Liu, Wenqian Pan, Xiaofei Zhou, Linlin Wang, Mengya Chai, Yujie Liu, Hao Yang, Zhaoxue Yu. TIL analysis demonstrates different mechanisms underlying PD-1 resistance in animal models [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 1531.

Abstract 179: Identification of a novel crosstalk between MDSC and NKregs in immunotherapy resistant triple negative breast cancer

Abstract Triple-negative breast cancer (TNBC) is one of the most aggressive forms of breast cancer and lacks standard treatment options. Although immunotherapy shows some response in these patients along with chemotherapy, heterogeneity of tumor cells and immune cells results in significant low response to immunotherapy treatment. Based on single cell sequencing which enables identity of heterogenous population at single cell level and functional studies involving preclinical mouse models, our laboratory recently identified distinct CD56brightSOCS3highCD11b−CD27− immature NK cells subpopulations, with diminished cytotoxic granzyme signatures that promote TNBC tumor progression. However, the precise characterization and functionality of these rogue tumor promoting NK cells remains unclear in clinical samples. Here, we aimed to illustrate mechanistic insight of these novel immature NK subpopulation in context of immunotherapy resistant TNBC patient samples. The scRNA seq analysis of TNBC patient samples identified four specific subclusters of NK cells in TNBC. We further found that NK2 and NK3 subclusters are CD56dim Granzymehigh cytotoxic NK cells and the other two subclusters (NK0 and NK1) are CD56bright immature NKs. Interestingly, the NK0 and NK1 subcluster specifically exhibit distinctive characteristics and functions. Notably, CD56bright immature NK1 cells, identified as tissue-resident NK cells, were engaged in direct communication with myeloid-derived suppressor cells (MDSCs). The CD56bright NK0 possesses moderate to low SOCS3 expression and moderate to high granzyme expression with elevated early NK activation markers and inhibitory receptor expressions, suggesting its regulatory property (NKregs). scRNA seq and flow cytometry analysis showed higher NKregs and immunosuppressive MDSC population, specifically with high monocytic-MDSCs (mMDSCs) in non-responder TNBC (to adjuvant combinational treatment of chemo and immunotherapy) patient samples rather than responder patients’ tissue. Based on in silico analysis, we further found a potential crosstalk between these mMDSC & NKreg within the tumors of non-responsiveness of TNBC patients. Overall, our studies show a connection of MDSCs and NKregs in TNBC patients, who do not respond to immunotherapy, highlighting a possible mechanism for immunotherapy resistance, which could be targeted in near future for better treatment options in TNBC. Citation Format: Megha Das, Samantha Henry, Shailesh Singh, Camila Dos Santos, Rumela Chakrabarti. Identification of a novel crosstalk between MDSC and NKregs in immunotherapy resistant triple negative breast cancer [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 179.

Abstract 105: Understanding the role of β2-adrenergic receptor signaling on type II innate lymphoid cells in cancer

Abstract Increased norepinephrine (NE) due to chronic stress can activate adrenergic receptors, specifically β2-adrenergic receptors (β2AR), to produce an immunosuppressive tumor microenvironment (TME). Previous work by our lab demonstrated that tumor burden can be reduced by blocking β2AR signaling. Immune cells express β2AR and we have shown that the increased β2AR signaling leads to increased T cell exhaustion and increased inhibitory activity of myeloid-derived suppressor cells (MDSCs). In general, the resulting immunosuppression leads to a modest but significant reduction in tumor growth. However, the lack of a dramatic reduction in tumor growth reveals the complex nature of adrenergic signaling dependent regulation of the cancer immune response. Recent literature revealed that innate lymphoid cells (ILCs), especially type II ILCs (ILC2s), express high levels of β2AR. Therefore, we evaluated whether β2AR regulates ILC2s within the TME and how that affects tumor prognosis. We generated a genetic conditional knockout murine model where β2AR expression in ILC2s was deleted by crossing IL5cre expressing mice to β2ARflox/flox mice (IL5creβ2ARf/f). AT3 breast cancer cell line was injected into the 4th mammary fat pad and tumor volume was measured every 2-3 days. Tumor infiltrating ILC2s (CD45+Lineage−CD90.2+CD127+ST2+) were analyzed by flow cytometry at D36 post-tumor implantation. Notably, IL5creβ2ARf/f mice had increased AT3 breast cancer tumor growth compared to control mice. Flow cytometric analysis of the tumor revealed an increased frequency of GATA3+ ILC2s within the TME. These GATA3+ ILC2s lacking β2AR expressed higher levels of the IL33 receptor, ST2, and a higher percentage of IL13+ cells compared to WT GATA3+ ILC2 cells. We also observe a trend toward increased MDSC population within the TME of mice lacking β2AR in ILC2s. These results reveal an anti-tumor function of β2AR signaling through the suppression of ILC2 activity within the TME that warrants further investigation. This work has been in part supported by NIH Grants F30 CA284763 (to J.C.), K99 HL155792 (to H.M.), and RO1 CA205246 (to E.R.) Citation Format: Jee Eun Choi, Cameron R. MacDonald, Saeed Daneshmandi, Jianmin Wang, Nathan T. Roberts, Caitlin M. James, Philip L. McCarthy, Hemn Mohammadpour, Elizabeth A. Repasky. Understanding the role of β2-adrenergic receptor signaling on type II innate lymphoid cells in cancer [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 105.