Suppression Of Antitumor Immunity Research Articles

CD8+ T cell-derived Fgl2 regulates immunity in a cell-autonomous manner via ligation of FcγRIIB

The regulatory circuits dictating CD8+ T cell responsiveness versus exhaustion during anti-tumor immunity are incompletely understood. Here we report that tumor-infiltrating antigen-specific PD-1+ TCF-1− CD8+ T cells express the immunosuppressive cytokine Fgl2. Conditional deletion of Fgl2 specifically in mouse antigen-specific CD8+ T cells prolongs CD8+ T cell persistence, suppresses phenotypic and transcriptomic signatures of T cell exhaustion, and improves control of the tumor. In a mouse model of chronic viral infection, PD-1+ CD8+ T cell-derived Fgl2 also negatively regulates virus-specific T cell responses. In humans, CD8+ T cell-derived Fgl2 is associated with poorer survival in patients with melanoma. Mechanistically, the dampened responsiveness of WT Fgl2-expressing CD8+ T cells, when compared to Fgl2-deficient CD8+ T cells, is underpinned by the cell-intrinsic interaction of Fgl2 with CD8+ T cell-expressed FcγRIIB and concomitant caspase 3/7-mediated apoptosis. Our results thus illuminate a cell-autonomous regulatory axis by which PD-1+ CD8+ T cells both express the receptor and secrete its ligand in order to mediate suppression of anti-tumor and anti-viral immunity.

Cutting Edge: LAG3 Dimerization Is Required for TCR/CD3 Interaction and Inhibition of Antitumor Immunity.

Lymphocyte activation gene 3 (LAG3) is an inhibitory receptor that plays a critical role in controlling T cell tolerance and autoimmunity and is a major immunotherapeutic target. LAG3 is expressed on the cell surface as a homodimer but the functional relevance of this is unknown. In this study, we show that the association between the TCR/CD3 complex and a murine LAG3 mutant that cannot dimerize is perturbed in CD8+ T cells. We also show that LAG3 dimerization is required for optimal inhibitory function in a B16-gp100 tumor model. Finally, we demonstrate that a therapeutic LAG3 Ab, C9B7W, which does not block LAG3 interaction with its cognate ligand MHC class II, disrupts LAG3 dimerization and its association with the TCR/CD3 complex. These studies highlight the functional importance of LAG3 dimerization and offer additional approaches to therapeutically target LAG3.

Radiotherapy and immunology.

The majority of cancer patients receive radiotherapy during the course of treatment, delivered with curative intent for local tumor control or as part of a multimodality regimen aimed at eliminating distant metastasis. A major focus of research has been DNA damage; however, in the past two decades, emphasis has shifted to the important role the immune system plays in radiotherapy-induced anti-tumor effects. Radiotherapy reprograms the tumor microenvironment, triggering DNA and RNA sensing cascades that activate innate immunity and ultimately enhance adaptive immunity. In opposition, radiotherapy also induces suppression of anti-tumor immunity, including recruitment of regulatory T cells, myeloid-derived suppressor cells, and suppressive macrophages. The balance of pro- and anti-tumor immunity is regulated in part by radiotherapy-induced chemokines and cytokines. Microbiota can also influence radiotherapy outcomes and is under clinical investigation. Blockade of the PD-1/PD-L1 axis and CTLA-4 has been extensively investigated in combination with radiotherapy; we include a review of clinical trials involving inhibition of these immune checkpoints and radiotherapy.

Functional remodeling of intraperitoneal macrophages by oncolytic adenovirus restores anti-tumor immunity for peritoneal metastasis of gastric cancer

Intraperitoneal tumor-associated macrophages (TAMs) are involved in evading anti-tumor immunity and promoting the peritoneal metastasis (PM) of gastric cancer (GC). Oncolytic viruses are known to induce the activation of host anti-tumor immunity in addition to tumor lysis. This study investigated whether a wild-type p53-loading telomerase-specific oncolytic adenovirus (OBP-702) could elicit the remodeling of intraperitoneal macrophages and enhance the efficacy of immune therapy. Increased numbers of CD163 TAMs and few CD8+ lymphocytes were immunohistochemically observed in clinical samples with PM, which suggested that TAMs were associated with the suppression of anti-tumor immunity. OBP-702 induced immunogenic cell death and upregulated PD-L1 expression in human and murine GC cell lines. Intraperitoneal administration of OBP-702 increased recruitment of CD8+ lymphocytes into the PM via the functional remodeling of intraperitoneal macrophages from TAM towards a pro-inflammatory phenotype, resulting in significantly suppressed tumor growth for the in vivo model. Furthermore, the combination of intraperitoneal OBP-702 with anti-PD-1 Antibody enhanced anti-tumor immunity and prolonged the survival of mice bearing PM. Intraperitoneal immunotherapy using OBP-702 restores anti-tumor immunity via the remodeling of intraperitoneal macrophages in addition to direct tumor lysis and cooperates with immune checkpoint inhibitors to suppress PM in GC.

Abstract LB426: Evidence for a role of GPR35 in IDO1-mediated tumor immune escape by regulating Hippo-YAP pathway

Abstract IDO1 is an immune checkpoint regulator and mediator of tumor immune evasion (1). The cellular and molecular mechanisms of IDO1-mediated immune suppression are not fully understood. We describe here that GPR35, the putative receptor for kynurenic acid (KYNA), a metabolite of IDO1-mediated tryptophan catabolism, couples to Hippo-YAP pathway. GPR35 activation, either by overexpression or by treatment with tryptophan metabolites resulted in Hippo inactivation and YAP-directed transcription via TEAD family of transcription factors. Recently, YAP is found to be essential for tumor immune escape. Yap1 deficiency in T-lineage-specific knockout mice, or by dosing a YAP inhibitor, impairs Treg formation and function, leading to tumor growth inhibition (2). YAP also plays an inhibitory role in CD8 T cell function, especially in activated CTL usually found in the TME [3,4]. Through medicinal chemistry design and a structure-vs-activity relationship study effort, we discovered a GPR35-selective inhibitor, here termed TMER1i. TMER1i potently blocks GPR35 in Hippo suppression and YAP activation. We showed that GPR35 is expressed in the T-cell lineage of the immune cells including naïve CD4 T cells, Treg and CD8 T cells. Treatment of purified human naïve CD4 T cells with anti-CD3/anti-CD28 under an IDO1+ TME-like culture condition in vitro induced a robust T cell activation and differentiation toward Treg phenotype, as shown previously using mouse naïve CD4 T cells by others (5). Importantly, TMER1i efficiently blocked the Treg differentiation under these conditions. When dosed in human-PBMC reconstituted NCG mice bearing HT29 tumors, TMER1i dose-dependently increased the infiltration of human CD8 T cells within tumors in a statistically significant manner, and a trending lower Treg cell infiltration, accompanied by a tumor growth inhibition. qPCR analysis of the HT29 tumors grown in the PBMC-NCG mice indicated that IDO1 was highly expressed in the tumors. These results indicated that GPR35 selective inhibitor TMER1i enhanced an anti-tumor immune activity in an IDO1+ tumor microenvironment. Taken together, these studies provided evidence for a role of GPR35 in mediating IDO1 immune suppression by regulating Hippo-YAP pathway in Treg and CTL cells in the immune system. Thus, GPR35 inhibitors have a potential to be novel immuno-therapeutic agents effective in treating patients with IDO1-positive tumors. Reference1.Munn, DH, and Mellor, AL. (2007) Indoleamine 2,3-dioxygenase and tumor-induced tolerance. J. Clin. Invest. 117:1147-11542.Ni, X. et al. Yap is essential for Treg-mediated suppression of antitumor Immunity. Cancer Discovery 2018; 8:1026-10433.Lebid, A. et al. (2020) YAP attenuates CD8 T cell-mediated anti-tumor response. Frontiers in Immunology 11:1-84.Stampouloglou, E. et al. (2020) YAP suppresses T-cell function and infiltration in the tumor microenvironment. PLoS Biol 18(1): e30005915.Fallarino, F. et al. (2006) The combined effects of tryptophan starvation and tryptophan catabolites down-regulate T cell receptor æ-chain and induce a regulatory phenotype in naïve T cells. J Immunol 176:6752-6761 Citation Format: Hongmei He, Nam Hee Kim, Sangdon Han, Zhi Liang Chu. Evidence for a role of GPR35 in IDO1-mediated tumor immune escape by regulating Hippo-YAP pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB426.

Deubiquitinase USP4 suppresses antitumor immunity by inhibiting IRF3 activation and tumor cell-intrinsic interferon response in colorectal cancer

Despite the approval of immune checkpoint blockade (ICB) therapy for various tumor types, its effectiveness is limited to only approximately 15% of patients with microsatellite instability-high (MSI-H) or mismatch repair deficiency (dMMR) colorectal cancer (CRC). Approximately 80%–85% of CRC patients have a microsatellite stability (MSS) phenotype, which features a rare T-cell infiltration. Thus, elucidating the mechanisms underlying resistance to ICB in patients with MSS CRC is imperative. In this study, we demonstrate that ubiquitin-specific peptidase 4 (USP4) is upregulated in MSS CRC tumors and negatively regulates the immune response against tumors in CRC. Additionally, USP4 represses the cellular interferon (IFN) response and antigen presentation and impairs PRR signaling-mediated cell death. Mechanistically, USP4 impedes the nuclear localization of interferon regulator Factor 3 (IRF3) by deubiquitinating the K63-polyubiquitin chain of TRAF6 and IRF3. Knockdown of USP4 enhances the infiltration of T cells in CRC tumors and overcomes ICB resistance in an MC38 syngeneic mouse model. Moreover, published datasets revealed that patients showing higher USP4 expression exhibited decreased responsiveness to anti-PD-L1 therapy. These findings highlight an essential role of USP4 in the suppression of antitumor immunity in CRC.

Abstract 7528: Coordinated regulation of critical immune checkpoint proteins by the integrated stress response (ISR) pathway in lung cancer

Abstract Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related deaths worldwide. Despite recent advances, high rates of recurrence highlight the need for novel treatment options. Groundbreaking discoveries in identifying and exploiting the PD-1/PD-L1 (Programmed Death 1/Programmed Death Ligand 1) immune checkpoint have resulted in the approval of monoclonal antibodies that disrupt this interaction as a first-line therapy for lung cancer patients. However, only ~20% of NSCLC patients benefit from checkpoint blockade. A critical question remains as to what mechanisms facilitate resistance to PD-1/PD-L1 therapy and whether other immune checkpoints or pathways can be pursued clinically in combination with this therapy. The integrated stress response (ISR) pathway represents an emerging therapeutic vulnerability. The ISR is a generalized response to maintain cellular homeostasis, and is known to be activated by hypoxia, heme deprivation, amino acid starvation, and oncogenic activation. We previously demonstrated that ISR activation potently induces PD-L1 in NSCLC and suppression of anti-tumor immunity (Suresh et al, Nature Cancer, 2020). We discovered that ISR pathway activation enhances PD-L1 translation through the bypass of inhibitory upstream open reading frames (uORFs) in the PD-L1 5' UTR and a mechanistic link to the translation initiation factor eIF5B. Our latest studies demonstrate that the immune checkpoint protein, CD155 (Cluster of Differentiation 155), is induced by ISR activation. We find that both PD-L1 and CD155 are induced by multiple arms of the ISR pathway, and CD155 harbors inhibitory uORFs in its 5' UTR. Importantly, we observed a significant correlation between PD-L1 and CD155 expression in a panel of primary human lung adenocarcinomas. We further demonstrated that ISR activation inhibits T cell function in vitro and promotes tumor growth in the CMT167 syngeneic mouse model. Analysis of immune cell infiltration using mass cytometry in this in vivo model is ongoing. Currently, we are determining the extent to which ISR inhibition suppresses tumorigenesis by promoting anti-tumor immunity and whether this may synergize with existing immune checkpoint therapies. Overall, these studies will set the stage for determining whether inhibition of the ISR pathway alone or in combination with immune checkpoint blockade will benefit lung cancer patients. Our studies may also lead to new therapeutic approaches to trigger anti-cancer immune responses and improve current strategies. Citation Format: Shayna Elizabeth Thomas-Jardin, Shruthy Suresh, Cheryl Lewis, Chul Ahn, Bret M. Evers, John D. Minna, Kathryn A. O'Donnell. Coordinated regulation of critical immune checkpoint proteins by the integrated stress response (ISR) pathway in lung 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 7528.

Abstract 3186: An Erythrocyte-αPD-1 conjugate suppresses cancers resistant to checkpoint blockade immunotherapy: A first-in-human study

Abstract Background: Immune checkpoint blockade (ICB) therapy has revolutionized cancer treatment, yet resistance to this therapy can lead to immune escape and disease progression. Here, we introduce WTX-212, an erythrocyte-antibody conjugate covalently linking anti-PD-1 antibody to erythrocyte membranes. Unlike conventional antibodies, WTX-212 naturally accumulates in the spleen and remodels the splenic immune landscape in tumor-bearing mice. Pre-clinical studies have demonstrated that T cells activated by WTX-212 reduce the splenic reservoir of immunosuppressive myeloid cells, including those within tumors. This results in a systemic anti-tumor immune response and suppression of tumor growth in xenograft tumor models resistant to anti-PD-1 immunotherapies. A first-in-human (FIH) clinical trial is now investigating its potential in human cancer patients. Methods: The FIH trial (NCT05707325) is aimed to investigate the safety, pharmacokinetics, mechanisms and preliminary efficacy of WTX-212 in cancer patients with advanced malignancies. All of patients had previously received anti-PDs therapies and developed resistance to these treatments. By November 15th, 2023, 7 patients across two cohorts had received WTX-212 monotherapy (1 × 1011-2 × 1011 cells, Q3W IV). The tumor lesions were assessed using RECIST v1.1 criteria. Blood and tumor samples were collected for correlative analysis. Results: 7 patients with various solid tumors, having undergone a median of 3.1 prior lines of therapy (ranging from 1-6), received WTX-212 monotherapy. No dose-limiting toxicities or treatment-related adverse events greater than Grade 3 were reported. WTX-212 was detectable in peripheral blood at the end of cycle in a dose dependent manner. Disease control, including partial remission (PR) and stable disease (SD), was observed in 5/7 patients (DCR, 71%). One patient with esophageal cancer achieved a PR with a significant 44% reduction in target lesion size after two cycles of treatment. Two patients, one with esophageal cancer (3 lines prior therapies) and another with HPV-negative cervical cancer (4 lines prior therapies), maintained disease control for over 30 weeks after WTX-212 treatment. Consistent with preclinical findings, WTX-212 systemically induced anti-tumor responses, leading to a reduction of myeloid-derived suppressor cells (MDSCs) particularly the PMN-MDSC subset in 6/7 patients (reductions ranging from 24%-82% compared to baseline), and a median 1.5-fold increase of T cells in 7/7 patients in the peripheral blood after the 1st cycle of treatment. Conclusion: The initial promising data support further investigation and exploration of the combination therapy strategies to expand the therapeutic potential of WTX-212 in cancer patients. Erythrocyte-drug conjugation may serve as a unique strategy for targeting the peripheral immune system to treat cancers. Citation Format: Liu Yang, Xiaoqian Nie, Zheling Chen, Yuehua Liu, Jiawei Zheng, Xiaofei Gao. An Erythrocyte-αPD-1 conjugate suppresses cancers resistant to checkpoint blockade immunotherapy: A first-in-human study [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 3186.

Abstract 6531: Anti-tumor immune function of NR2F6, an orphan nuclear receptor, in stromal cells

Abstract Growing evidence points to the importance of the tumor microenvironment (TME) in tumor growth control, progression, and therapy response. Among those is the greater understanding of immune system components within the TME as mediators of tumor growth control. NR2F6 is an orphan nuclear receptor, which was shown to serve as an immune intrinsic checkpoint component and has been suggested to elicit tumor-intrinsic suppression of anti-tumor immunity. Correspondingly, genetic depletion of NR2F6 in CD8 T cells abrogates the immune-activating cytokines (e.g., IL-2, IFNg). In addition, genetic ablation of NR2F6 in melanoma cells activates CD8 T cell-mediated anti-tumor immunity partly by suppressing the expression of tumor-intrinsic immune repressors NACC1 and FKBP10. Notably, combined genetic ablation of tumor cells (NR2F6 KO melanoma) and stroma cells (NR2F6 KO mouse) resulted in a more pronounced inhibition of tumor growth compared with ablation of either tumor cells or TME. The latter provides the foundation for screening NR2F6 inhibitors, which are expected to have a strong systemic (tumor inhibition and immune cell activation) effect on tumor growth. Interestingly, single-cell transcriptomic data from human tumors identified high expression of NR2F6 in stroma cells, cancer-associated fibroblasts (CAFs), and tumor-associated endothelial cells (TAEs). Consistent with these, scRNAseq analysis of mouse melanoma revealed higher expression of NR2F6 in SMA+ immune suppressive myo-CAFs than in immune activating CAFs. Studies that directly reveal the role of stromal NR2F6 in anti-tumor immunity and tumor growth and the state of NR2F6 inhibitors will be discussed. Citation Format: Hyungsoo Kim, Yongmei Feng, Marria Radaeva, Eduard Sergienko, Artem Cherkasov, Ze'ev A. Ronai. Anti-tumor immune function of NR2F6, an orphan nuclear receptor, in stromal 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 6531.

Abstract A053: Dynamic regulation of pyruvate carboxylase is required for immune evasion and pulmonary metastasis

Abstract Metabolic plasticity is an important mediator of tumor cell survival, growth in various microenvironments, and immune evasion. We present a dimorphic role for for the metabolic enzyme pyruvate carboxylase (PC) in pulmonary metastatic versus primary mammary tumors. Specifically, we demonstrate that PC is essential for metastatic outgrowth in the lungs. In contrast, depletion of PC in tumor cells promotes primary tumor growth. This affect was only observed in immune competent animals, leading us to address the hypothesis that repression of PC can suppress anti-tumor immunity. Exploring key differences between the pulmonary and mammary environments we demonstrate that hypoxia potently downregulated PC. Metabolomic analyses demonstrated that in the absence of PC, tumor cells produce more lactate and undergo less oxidative phosphorylation. Inhibition of lactate metabolism was sufficient to restore T cell populations to PC-depleted mammary tumors and drastcially inhibited primary tumor growth. Along these line, forced overexpression of PC decreased lactate production, increased immune inflitation, and prevented initiation of pulmonary metastases. These findings highlight a key contextual role for PC-directed lactate production as a metabolic nexus connecting hypoxia and antitumor immune suppression in primary tumors and intiating pulmonary metastases. However, following immune evasion and initiation of metastasis the return of PC expression is required for propagation of macroscopic pulmonary metastases. Citation Format: Mike Coleman, Eylem Kulkoyluoglu Cotul, Dorothy Teegarden, Stephen Hursting, Mike K Wendt. Dynamic regulation of pyruvate carboxylase is required for immune evasion and pulmonary metastasis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A053.

The combination of CD8 and TIM3 expression to predict survival outcomes in hepatocellular carcinoma.

543 Background: CD8+ T cells have anti-tumor immunity in a variety of cancers including hepatocellular carcinoma (HCC). Tumor-infiltrating CD8+ T cells express immune checkpoint proteins and focus on a therapeutic targeting. T cell immunoglobulin and mucin domain protein 3 (TIM3) has been reported to be associated with suppression of anti-tumor immunity, poor prognosis, and tumor progression in HCC, resulting in up-regulation on exhausted CD8+ T cells. As the exhausted T cells showed a decrease of effector cytokine production and cytolytic activity, leading to the tumor progression, TIM3 is one of the most important exhaustion markers. In the present study, we investigated the role of CD8 and TIM3 as a prognostic biomarker in HCC. Methods: We analyzed 474 HCC patients with clinical and transcriptomic data from The Cancer Genome Atlas (TCGA: n=359) and GSE 76427 (n=115) to examine associations between CD8, TIM3, and programmed death receptor-1/programmed cell death ligand 1 (PD-1/PD-L1) expression and survival outcomes. Each gene was divided into low- and high-expression groups using the tertiles of gene expression. Results: The patients with high CD8 and low TIM3 expression were associated with better overall survival (OS) (P=0.021 and P=0.025, respectively) in TCGA, while PD-1/PD-L1 were not associated with OS (P=0.306 and P=0.318, respectively). Moreover, the patients with high CD8 and low TIM3 expression were validated in GSE dataset (P=0.014 and P=0.009, respectively). The patients with high CD8 and low TIM3 expression were associated with improved OS compared with the overall HCC patient (P=0.008). Among the patients with high CD8 expression, low TIM3 expression (non-exhausted CD8+ T cells) was associated with better OS (P=0.009), but PD-1/PD-L1 were not associated with OS (P=0.491 and P=0.772, respectively). Finally, multivariate analysis showed that the patients withnon-exhausted CD8+ T cells were significantly superior for the survival outcomes (Hazard ratio=2.80, 95% CI=1.27–6.19, P=0.01). Conclusions: High CD8 and low TIM3 expression is associated with better OS in HCC than PD-1/PD-L1, suggesting that CD8 and TIM3 are useful biomarkers for predicting HCC prognosis. Restoring exhausted T cells via the suppression of TIM3 is a promising strategy for cancer treatment, which become a breakthrough in the cancer immunotherapy.

Inhibition of anti-tumor immunity by melanoma cell-derived Activin-A depends on STING.

The transforming growth factor-β (TGF-β) family member activin A (hereafter Activin-A) is overexpressed in many cancer types, often correlating with cancer-associated cachexia and poor prognosis. Activin-A secretion by melanoma cells indirectly impedes CD8+ T cell-mediated anti-tumor immunity and promotes resistance to immunotherapies, even though Activin-A can be proinflammatory in other contexts. To identify underlying mechanisms, we here analyzed the effect of Activin-A on syngeneic grafts of Braf mutant YUMM3.3 mouse melanoma cells and on their microenvironment using single-cell RNA sequencing. We found that the Activin-A-induced immune evasion was accompanied by a proinflammatory interferon signature across multiple cell types, and that the associated increase in tumor growth depended at least in part on pernicious STING activity within the melanoma cells. Besides corroborating a role for proinflammatory signals in facilitating immune evasion, our results suggest that STING holds considerable potential as a therapeutic target to mitigate tumor-promoting Activin-A signaling at least in melanoma.

Acquisition of suppressive function by conventional T cells limits antitumor immunity upon Treg depletion.

Regulatory T (Treg) cells contribute to immune homeostasis but suppress immune responses to cancer. Strategies to disrupt Treg cell-mediated cancer immunosuppression have been met with limited clinical success, but the underlying mechanisms for treatment failure are poorly understood. By modeling Treg cell-targeted immunotherapy in mice, we find that CD4+ Foxp3- conventional T (Tconv) cells acquire suppressive function upon depletion of Foxp3+ Treg cells, limiting therapeutic efficacy. Foxp3- Tconv cells within tumors adopt a Treg cell-like transcriptional profile upon ablation of Treg cells and acquire the ability to suppress T cell activation and proliferation ex vivo. Suppressive activity is enriched among CD4+ Tconv cells marked by expression of C-C motif receptor 8 (CCR8), which are found in mouse and human tumors. Upon Treg cell depletion, CCR8+ Tconv cells undergo systemic and intratumoral activation and expansion, and mediate IL-10-dependent suppression of antitumor immunity. Consequently, conditional deletion of Il10 within T cells augments antitumor immunity upon Treg cell depletion in mice, and antibody blockade of IL-10 signaling synergizes with Treg cell depletion to overcome treatment resistance. These findings reveal a secondary layer of immunosuppression by Tconv cells released upon therapeutic Treg cell depletion and suggest that broader consideration of suppressive function within the T cell lineage is required for development of effective Treg cell-targeted therapies.

Abstract C160: HMPL-653, a highly potent and selective CSF-1R inhibitor, targeting both tumor cells and tumor microenvironment

Abstract Background: Colony stimulating factor 1 receptor (CSF-1R) and its ligand CSF-1 (CSF-1R/CSF-1) signaling regulates the function and survival of tumor-associated macrophages (TAM), which are involved in tumor progression and suppression of anti-tumor immunity. Moreover, activation of CSF-1R/CSF-1 axis including CSF-1 fusions or CSF-1R activating mutations has also been implicated in the pathogenesis of certain tumors such as tenosynovial giant cell tumor and histiocytic neoplasms. HMPL-653 is a highly potent and selective CSF-1R small molecule inhibitor, discovered and being currently developed in phase I clinical trial (NCT05277454) by HUTCHMED. Methods: The inhibition on CSF-1R kinase was determined using Z-LYTE™ kinase assay. The selectivity of HMPL-653 was assessed against a panel of 413 kinases by Eurofins. Cellular target inhibition on phosphorylation of CSF-1R (p-CSF-1R) was detected by ELISA. In vitro cell viability was measured by CCK-8 assay. Multiple CSF-1/CSF-1R driven tumor models in Nu/Nu nude mice were applied to determine the anti-tumor activity of HMPL-653 as a single agent. To demonstrate the immunoregulatory effect of HMPL-653, a murine tumor model, B16F10, was established in C57BL/6J mice, and the combination regimen, HMPL-653 plus PCP (poly (I:C)+CpG+anti-PD-1) was evaluated. Results: HMPL-653 strongly inhibited CSF-1R kinase with IC50 of 5 nM, showing >7-fold potency than that of the approved CSF-1R inhibitor pexidartinib (IC50=39 nM). And the selectivity profiling in 413 kinase panels revealed that HMPL-653 was highly potent only against CSF-1R, indicating a lower off-target risk than paxidatinib reported. HMPL-653 potently inhibited CSF-1 stimulated p-CSF-1R in THP-1 cells with IC50 of 5 nM. In CSF-1/CSF-1R-dependent cell lines, M-NFS-60 (mouse myelogenous leukemia) and three cell lines stably expressed BCR-CSF-1R or CSF-1R mutations (Ba/F3-BCR-CSF-1R, Ba/F3-CSF-1RW450-E456del, and Ba/F3-CSF-1RY546-K551del), HMPL-653 significantly down regulated p-CSF-1R and its downstream signaling p-ERK and p-AKT. As a consequence, HMPL-653 robustly inhibited the cell viability of above cell models (IC50s: 3~40 nM). Besides the direct anti-tumor effect, HMPL-653 also demonstrated strong inhibition on macrophage survival and M2 macrophage polarization, indicating a potential effect on targeting tumor microenvironment. In vivo, oral administration of HMPL-653 induced remarkable and dose-dependent anti-tumor efficacies in M-NFS-60 ascites model and subcutaneous tumor models harboring above mentioned CSF-1R alterations. And the PK/PD analysis revealed that the anti-tumor effect correlated well with p-CSF-1R inhibition. Moreover, HMPL-653 significantly improved the anti-tumor activity of PCP regimen in B16F10 model by reducing TAMs including M2 macrophages and increasing the ratio of M1/M2 macrophages. Conclusion: HMPL-653 is a highly potent and selective CSF-1R small molecule inhibitor which targets both CSF-1/CSF-1R-dependent tumors and tumor associated macrophages, warranting further clinical evaluation. Citation Format: Jia Hu, Liang Ge, Hui Zhang, An Jiang, Juntao Yu, Weifang Xue, Jian Wang, Yang Sai, Na Yang, Weiguo Qing, Yongxin Ren, Michael Shi, Weiguo Su. HMPL-653, a highly potent and selective CSF-1R inhibitor, targeting both tumor cells and tumor microenvironment [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C160.

Bexmarilimab-induced macrophage activation leads to treatment benefit in solid tumors: The phase I/II first-in-human MATINS trial

Macrophage Clever-1 contributes to impaired antigen presentation and suppression of anti-tumor immunity. This first-in-human trial investigates the safety and tolerability of Clever-1 blockade with bexmarilimab in patients with treatment-refractory solid tumors and assesses preliminary anti-tumor efficacy, pharmacodynamics, and immunologic correlates. Bexmarilimab shows no dose-limiting toxicities in part I (n= 30) and no additional safety signals in part II (n= 108). Disease control (DC) rates of 25%-40% are observed in cutaneous melanoma, gastric, hepatocellular, estrogen receptor-positive breast, and biliary tract cancers. DC associates with improved survival in a landmark analysis and correlates with high pre-treatment intratumoral Clever-1 positivity and increasing on-treatment serum interferon γ (IFNγ) levels. Spatial transcriptomics profiling of DC and non-DC tumors demonstrates bexmarilimab-induced macrophage activation and stimulation of IFNγ and Tcell receptor signaling selectively in DC patients. These data suggest that bexmarilimab therapy is well tolerated and show that macrophage targeting can promote immune activation and tumor control in late-stage cancer.

The cross-talk between macrophages and tumor cells as a target for cancer treatment.

Macrophages represent an important component of the innate immune system. Under physiological conditions, macrophages, which are essential phagocytes, maintain a proinflammatory response and repair damaged tissue. However, these processes are often impaired upon tumorigenesis, in which tumor-associated macrophages (TAMs) protect and support the growth, proliferation, and invasion of tumor cells and promote suppression of antitumor immunity. TAM abundance is closely associated with poor outcome of cancer, with impediment of chemotherapy effectiveness and ultimately a dismal therapy response and inferior overall survival. Thus, cross-talk between cancer cells and TAMs is an important target for immune checkpoint therapies and metabolic interventions, spurring interest in it as a therapeutic vulnerability for both hematological cancers and solid tumors. Furthermore, targeting of this cross-talk has emerged as a promising strategy for cancer treatment with the antibody against CD47 protein, a critical macrophage checkpoint recognized as the "don't eat me" signal, as well as other metabolism-focused strategies. Therapies targeting CD47 constitute an important milestone in the advancement of anticancer research and have had promising effects on not only phagocytosis activation but also innate and adaptive immune system activation, effectively counteracting tumor cells' evasion of therapy as shown in the context of myeloid cancers. Targeting of CD47 signaling is only one of several possibilities to reverse the immunosuppressive and tumor-protective tumor environment with the aim of enhancing the antitumor response. Several preclinical studies identified signaling pathways that regulate the recruitment, polarization, or metabolism of TAMs. In this review, we summarize the current understanding of the role of macrophages in cancer progression and the mechanisms by which they communicate with tumor cells. Additionally, we dissect various therapeutic strategies developed to target macrophage-tumor cell cross-talk, including modulation of macrophage polarization, blockade of signaling pathways, and disruption of physical interactions between leukemia cells and macrophages. Finally, we highlight the challenges associated with tumor hypoxia and acidosis as barriers to effective cancer therapy and discuss opportunities for future research in this field.

The Special Role of JAK/STAT, and Notch Signaling Pathways in Cancer Pathogenesis

Cancer is essentially a genetic disease, characterized by unclear etiology in many cases, complex pathogenic mechanisms, since in the majority of cancer cases only risk or predisposing factors have been recognized, and unclarified observations concerning organs that are not often affected by malignant tumors such as the small intestine, spleen, heart, and the neurons of the Central Nervous System. A tumor’s appearance and progression presupposes a series of genetic and non-genetic alterations that characterize tumor cells, and are related to self-sufficiency in growth stimuli, insensitivity to anti-growth signals, unlimited replicative potential, angiogenesis promotion, ability to infiltrate surrounding tissues and induce distant metastases, and resistance to apoptosis. The mentioned characteristics are associated with signaling pathways that are involved in cell survival, cell death, cell growth and division, cell motility, and can be considered in the context of abnormalities of wider signaling networks that support cancer progression, such as tumor microenvironment alterations, angiogenesis, and inflammation. Among others, two signaling pathways, JAK/STAT and Notch, seem to play essential roles in tumorigenesis, despite the fact that are implicated in diverse cellular functions such as tissue formation and cell differentiation, proliferation, apoptosis, inflammation, self-renewal, antitumor immune response suppression, motility, stress response and other responses depending on the target tissue. Hyperactivation of those signaling pathways caused by mutations are able to transform cellular proto-oncogenes to oncogenes, whereas inactivation of tumor suppressor genes eradicates crucial negative regulators of signaling. Various anticancer agents target those signaling pathways in an attempt to inhibit those pathways including monoclonal antibodies and other agents in the context of targeted cancer therapy.

Upregulation of exosome secretion from tumor-associated macrophages plays a key role in the suppression of anti-tumor immunity

Macrophages play a pivotal role in tumor immunity. We report that reprogramming of macrophages to tumor-associated macrophages (TAMs) promotes the secretion of exosomes. Mechanistically, increased exosome secretion is driven by MADD, which is phosphorylated by Akt upon TAM induction and activates Rab27a. TAM exosomes carry high levels of programmed death-ligand 1 (PD-L1) and potently suppress the proliferation and function of CD8+ Tcells. Analysis of patient melanoma tissues indicates that TAM exosomes contribute significantly to CD8+ Tcell suppression. Single-cell RNA sequencing analysis showed that exosome-related genes are highly expressed in macrophages in melanoma; TAM-specific RAB27A expression inversely correlates with CD8+ Tcell infiltration. In a murine melanoma model, lipid nanoparticle delivery of small interfering RNAs (siRNAs) targeting macrophage RAB27A led to better Tcell activation and sensitized tumors to anti-programmed cell death protein 1 (PD-1) treatment. Our study demonstrates tumors use TAM exosomes to combat CD8 Tcells and suggests targeting TAM exosomes as a potential strategy to improve immunotherapies.

Tumors recycle glucocorticoids to drive Treg-mediated immunosuppression.

Suppression of antitumor immunity is a prominent feature of the tumor microenvironment. In this issue of the JCI, Taves, Otsuka, and authors show that glucocorticoids (GCs), which are potent immunosuppressive hormones mainly produced by the adrenals, can be reconverted from their inactive form to active metabolites via the 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) enzyme expressed by murine tumor cell lines. In the tumor microenvironment, GCs acted on CD4+ regulatory T cells to enhance their immunosuppressive function and promote tumor growth. The findings suggest that targeting GC recycling as a strategy for modulating tumor immunosuppression has the potential to improve therapeutic efficacy of immune checkpoint blockade.

Abstract PO-089: Opioid-mediated suppression of anti-tumor immunity via peripheral OPRM1 signaling in head and neck squamous cell carcinoma

Abstract Head and Neck squamous cell carcinoma (HNSCC) causes severe pain, beyond what is reported in other cancer types. Opioids are the current backbone of HNSCC pain treatment but may have an immunomodulatory effect in the presence of cancer; T cells express opioid receptors. We recently demonstrated that opioids may affect the efficacy of anti-PD1 monoclonal antibody (mAb) treatment in recurrent/metastastic HNSCC patients; opioid usage was associated with significantly lower progression free survival and overall survival as well as decreased CD8 T cells in the tumor microenvironment. We hypothesized that cancer immunosurveillance is impaired by the immunosuppressive actions of exogenous opioids via peripheral mu-opioid receptor (OPRM1) signaling. A syngeneic mouse oral cancer model was used to determine if analgesic morphine impacted the tumor-associated immune response during tumor progression and in response to anti-PD1 mAb; mouse oral cancer cell line 1 (MOC1) tumor-bearing mice were treated with vehicle or morphine (10mg/kg i.p., 2x daily for 4.5 days) and the tumor-associated immune infiltrate was assessed between groups using flow cytometry. Anti-PD1 mAb (250µg/mouse, 3 × 2 day interval) was initiated directly following morphine treatment. Co-administration of methylnaltrexone (MNTX), a peripheral OPRM1 antagonist used to confirm specificity and site of action of the morphine-induced effects. Finally, any direct effects of morphine on tumor cells were investigated in oral cancer cell lines using quantitative PCR and colorimetric proliferation assays. Morphine induced a 75±5% reduction in CD8+ T cells and a 90±3% reduction in CD19+ B cells in MOC1 compared to sham mice (n=6/group); morphine-induced immunosuppression was completely blocked with co-treatment of MNTX. Studies involving morphine administration prior to anti-PD1 treatment are currently underway but given the substantial suppression in infiltrating lymphocyte populations, efficacy is expected to be lessened. Lastly, Oprm1 expression was not detected at the mRNA level in mouse oral cancer cell lines. In vitro, 10µM morphine did not induce cell proliferation (proliferation relative to vehicle after 48hr; vehicle=100±8.3%, morphine=115.7±9.6%) or improve wound healing (wound closure after 24hr; vehicle=76.2±11.6%, morphine=78.5±11.4%). Taken together, our data suggest that morphine suppresses anti-tumor immunity via peripheral OPRM1 signaling in immune cells but not tumor cells. Further investigation is warranted to determine whether peripheral opioid blockade (i.e. MNTX) can slow tumor progression and improve response to cancer treatments while preserving centrally-mediated analgesia. Citation Format: Lisa A. McIlvried, Mona Yuan, Nicole L. Horan, Megan A. Atherton, Marci L. Nilsen, Dan P. Zandberg, Nicole N. Scheff. Opioid-mediated suppression of anti-tumor immunity via peripheral OPRM1 signaling in head and neck squamous cell carcinoma [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Innovating through Basic, Clinical, and Translational Research; 2023 Jul 7-8; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2023;29(18_Suppl):Abstract nr PO-089.