Myeloid Cell Populations Research Articles

The relationship between changes in inflammation and locomotor function in sensory phenotypes of central neuropathic pain after spinal cord injury.

Central neuropathic pain (CNP) commonly develops in patients after spinal cord injury (SCI), causing debilitating symptoms and sensory abnormalities to mechanical and thermal stimuli. The biological variability of pain phenotypes in individuals has limited the number of positive outcomes. Thus, it is necessary to investigate the physiological processes contributing to sensory changes that develop over time. To investigate the physiological processes contributing to neuropathic pain sensory changes and locomotor impairments with sensory phenotypes that develop over time. Using the tail flick and von Frey tests, we performed hierarchical clustering to determine the subpopulation of rats that developed thermal and mechanical sensory abnormalities. To measure inflammation as a potential mediator of CNP phenotypes, we used flow cytometry and immunohistochemistry. Finally, to assess the secondary effects on locomotor recovery, up to 8 weeks after injury, we used the CatWalk test to assess multiple parameters of gait. The von Frey test showed a subpopulation of SCI rats that were hyposensitive to mechanical stimuli from 6 to 8 weeks after injury. The tail flick test showed a subpopulation of SCI rats that were hypersensitive to thermal stimuli at 1 week and 3 to 8 weeks after injury. Although there were no differences in inflammatory cells between subpopulations, we did see significant changes in locomotor recovery between rats with and without sensory abnormalities. The myeloid cell population at large is not affected by mechanical or thermal phenotypes of pain in this model; however, locomotor recovery is impaired depending on the pain phenotype present. Further investigation into acute inflammatory cells may be insightful for predicting the development of pain phenotypes.

Scavenger Receptor CD36 in Tumor-Associated Macrophages Promotes Cancer Progression by Dampening Type I Interferon Signaling.

Tumor-associated macrophages (TAMs) are a heterogenous population of myeloid cells that dictate the inflammatory tone of the tumor microenvironment (TME). In this study, we unveiled a mechanism by which scavenger receptor CD36 suppresses TAM inflammatory states. CD36 was upregulated in TAMs and associated with immunosuppressive features, and myeloid-specific deletion of CD36 significantly reduced tumor growth. Moreover, CD36-deficient TAMs acquired inflammatory signatures including elevated type-I interferon (IFN-I) production, mirroring the inverse correlation between CD36 and IFN-I response observed in cancer patients. IFN-I, especially IFNβ, produced by CD36-deficient TAMs directly induced tumor cell quiescence and delayed tumor growth. Mechanistically, CD36 acted as a natural suppressor of IFN-I signaling in macrophages through p38 activation downstream of oxidized lipid signaling. These findings establish CD36 as a critical regulator of TAM function and the tumor inflammatory microenvironment, providing additional rationale for pharmacological inhibition of CD36 to rejuvenate anti-tumor immunity.

TMIC-78. CHEMOTHERAPY INDUCED IMMUNOGENIC RESPONSE IN GLIOMA AND IMPLICATIONS FOR THERAPEUTIC STRATEGIES

Abstract INTRODUCTION Many glioblastoma (GBM) treatments fail because they treat tumor cells in isolation and ignore the surrounding microenvironment. In our phase 1b clinical trial of delivery of Topotecan (TPT) via Convection Enhanced Delivery (CED) in glioma, we demonstrated effective tumor cell elimination accompanied by a robust inflammatory response. We hypothesized that TPT induces an immunogenic response resulting in an unfavorable inflammatory landscape. METHODS To characterize chemotherapy’s effect on myeloid cells, we analyzed pre- and post-treatment biopsies from our trial using bulk RNA sequencing to measure canonical myeloid markers. We validated survival benefit of CED in vivo in our tumor model and characterized post-treatment tissue using single cell RNA sequencing (scRNA seq) after 7 days of treatment. We treated slice cultures generated from surgical samples of GBM with TPT and performed scRNA seq and histologic analysis to assess microenvironment changes after 24 hours of treatment. We used several in vitro assays to characterize the direct and indirect mechanisms of myeloid activation. RESULTS Bulk RNA sequencing of post treatment biopsies demonstrates upregulation of markers associated with activated and exhausted immune cell populations such as IBA1, CD68, MSR1, MARCO and loss of markers associated with homeostatic microglia such as P2RY12 and TMEM119. Similar results are found within 7 days of treatment in vivo, however, are not found in human derived samples treated acutely. Treatment of in vitro mono and co-culture systems demonstrate a tumor cell death dependent activation of myeloid cell populations via immunogenic molecules. CONCLUSIONS Chemotherapies eliminate proliferating glioma cells but also induce inflammation. While many investigators have tried to leverage this activation, our results suggest that chronic inflammation contributes to poor prognosis and recurrence. The identification of molecules responsible for this activation point to new therapeutic targets aimed at controlling treatment-induced inflammation, as part of a combinatorial approach to treat GBM.

IMMU-56. THE TIGIT/CD155 AXIS PLAYS A CRITICAL ROLE IN EXTRACELLULAR VESICLE-MEDIATED PROGRAMMING OF THE GLIOBLASTOMA MICROENVIRONMENT

Abstract Glioblastoma (GBM), the most common and deadly primary brain tumor, exerts profound local and systemic immunosuppressive effects through a variety of mechanisms. Tumor-derived extracellular vesicles (EVs) are increasingly appreciated as critical mediators of these effects. In surveying the tumor-immune microenvironment in samples of ultrasonic aspirate collected during surgical resection of GBM (n=13), we identified several key immunomodulatory markers expressed across a range of myeloid cell populations. Particularly, we found TIGIT, classically understood as a T cell inhibitory protein, expressed across a range of myeloid cell populations in patient samples, including in myeloid-derived suppressor cells (MDSCs, 46.84±16.78% of total monocytic MDSCs). Using EVs collected from patient-derived cell lines, we were able to recapitulate these effects upon co-culture with monocytes derived from the peripheral blood of healthy donors (n=7). Furthermore, Induced MDSCs significantly inhibit T cells proliferation (70.97±8.454%, compared to control 19.4±5.71; p<0.03), concomitant with a surge in Th2 immune responses via TIGIT/CD155 axis. This effect was reversed after TIGIT silencing, indicating a TIGIT-dependent immune suppression in the GBM microenvironment. Our study indicates EV-induced TIGIT upregulation in myeloid cells as a crucial immunosuppressive mechanism in glioblastoma, with potential therapeutic applications.

Differential T cell accumulation within intracranial and subcutaneous melanomas is associated with differences in intratumoral myeloid cells

Patients with metastatic brain melanomas (MBM) experience shorter-lasting survival than patients with extracranial metastases, and this is associated with a higher fraction of dysfunctional CD8 T cells. The goal of this study was to understand the underlying cause of T cell dysfunction in MBM. To accomplish this, we compared murine B16 melanomas implanted intracranially (IC) or subcutaneously (SC). CD8 T cell activation was not altered, but representation in IC tumors was lower. Transferred activated or naïve CD8 T cells accumulated in similar numbers in both tumors, suggesting that the vasculature does not differentially impair T cell presence. Surprisingly, we found no evidence for T cell activation in draining lymph nodes of SC or IC tumor-bearing mice, consistent with the fact that dendritic cells (DC) that had acquired tumor antigen showed an immature phenotype. Instead, T cell activation occurred within both tumors, where the majority of tumor antigen+ myeloid cells were found. While, the numbers of intratumoral DC were comparable, those in IC tumors acquired less tumor antigen, and were alternatively matured based on upregulation of MHCII without upregulation of CD86. Additionally, in IC tumors, the largest population of tumor antigen+ myeloid cells were microglia. However, their presence did not influence either antigen acquisition or the phenotype of other myeloid cell populations. Overall, our data suggest that diminished representation of CD8 T cells in IC tumors is a consequence of alternatively matured DC and/or microglia that induce distinctly activated T cells, which ultimately fail to continue to accumulate inside the tumor.

Metabolic pathways fueling the suppressive activity of myeloid-derived suppressor cells.

Myeloid-derived suppressor cells (MDSC) are considered an aberrant population of immature myeloid cells that have attracted considerable attention in recent years due to their potent immunosuppressive activity. These cells are typically absent or present in very low numbers in healthy individuals but become abundant under pathological conditions such as chronic infection, chronic inflammation and cancer. The immunosuppressive activity of MDSC helps to control excessive immune responses that might otherwise lead to tissue damage. This same immunosuppressive activity can be detrimental, particularly in cancer and chronic infection. In the cancer setting, tumors can secrete factors that promote the expansion and recruitment of MDSC, thereby creating a local environment that favors tumor progression by inhibiting the effective immune responses against cancer cells. This has made MDSC a target of interest in cancer therapy, with researchers exploring strategies to inhibit their function or reduce their numbers to improve the efficacy of cancer immunotherapies. In the context of chronic infections, MDSC can lead to persistent infections by suppressing protective immune responses thereby preventing the clearance of pathogens. Therefore, targeting MDSC may provide a novel approach to improve pathogen clearance during chronic infections. Ongoing research on MDSC aims to elucidate the exact processes behind their expansion, recruitment, activation and suppressive mechanisms. In this context, it is becoming increasingly clear that the metabolism of MDSC is closely linked to their immunosuppressive function. For example, MDSC exhibit high rates of glycolysis, which not only provides energy but also generates metabolites that facilitate their immunosuppressive activity. In addition, fatty acid metabolic pathways, such as fatty acid oxidation (FAO), have been implicated in the regulation of MDSC suppressive activity. Furthermore, amino acid metabolism, particularly arginine metabolism mediated by enzymes such as arginase-1, plays a critical role in MDSC-mediated immunosuppression. In this review, we discuss the metabolic signature of MDSC and highlight the therapeutic implications of targeting MDSC metabolism as a novel approach to modulate their immunosuppressive functions.

Impact of the adenosine receptor A2BR expressed on myeloid cells on immune regulation during pregnancy.

During pregnancy, the maternal immune system must carefully balance protection against pathogens with tolerance toward the semiallogeneic fetus. Dysfunctions of the immune system can lead to severe complications such as preeclampsia, fetal growth restriction, or pregnancy loss. Adenosine plays a role in physiological processes and plasma-level increase during pregnancy. The adenosine receptor A2B (A2BR), which is expressed on both, immune and nonimmune cells, is activated by high adenosine concentrations, achieved during pregnancy. We investigated the impact of A2BR expressed on myeloid cells on immune regulation during pregnancy using a mouse model with myeloid deficiency for A2BR. We demonstrate systemic changes in myeloid and lymphoid cell populations during pregnancy in A2BR-KO (Adora2B923f/f-LysMCre) mice with increased monocytes, neutrophils, and T cells but decreased B cells as well as altered T-cell subpopulations with decreased Th1 cells and Tregs and increased Th17 cells. Lack of A2BR on myeloid cells caused an increased systemic expression of IL-6 but decreased systemic accumulation and function of MDSC and reduced numbers of uterine natural killer cells. The pregnancy outcome was only marginally affected. Our results demonstrate that A2BR on myeloid cells plays a role in immune regulation during pregnancy, but the clinical impact on pregnancy remains unclear.

Microglia and monocyte-derived macrophages drive progression of pediatric high-grade gliomas and are transcriptionally shaped by histone mutations

Pediatric high-grade gliomas (pHGGs), including hemispheric pHGGs and diffuse midline gliomas (DMGs), harbor mutually exclusive tumor location-specific histone mutations. Using immunocompetent de novo mouse models of pHGGs, we demonstrated that myeloid cells were the predominant infiltrating non-neoplastic cell population. Single-cell RNA sequencing (scRNA-seq), flow cytometry, and immunohistochemistry illustrated the presence of heterogeneous myeloid cell populations shaped by histone mutations and tumor location. Disease-associated myeloid (DAM) cell phenotypes demonstrating immune permissive characteristics were identified in murine and human pHGG samples. H3.3K27M DMGs, the most aggressive DMG, demonstrated enrichment of DAMs. Genetic ablation of chemokines Ccl8 and Ccl12 resulted in a reduction of DAMs and an increase in lymphocyte infiltration, leading to increased survival of tumor-bearing mice. Pharmacologic inhibition of chemokine receptors CCR1 and CCR5 resulted in extended survival and decreased myeloid cell infiltration. This work establishes the tumor-promoting role of myeloid cells in DMG and the potential therapeutic opportunities for targeting them.

Transformation of brain myeloid cell populations by SIV in rhesus macaques revealed by multiomics.

The primary immune constituents in the brain, microglia and macrophages, are the target for HIV in people and simian immunodeficiency virus (SIV) in nonhuman primates. This infection can lead to neurological dysfunction, known as HIV-associated neurocognitive disorder (HAND). Given the gaps in our knowledge on how these cells respond in vivo to CNS infection, we performed single-cell multiomic sequencing, including gene expression and ATAC-seq, on myeloid cells from the brains of rhesus macaques with SIV-induced encephalitis (SIVE) as well as uninfected controls. We found that the myeloid cell populations were significantly changed by SIVE. In SIVE microglia-like cells express high levels of chemoattractants capable of recruiting highly activated CAM-like cells to the site of infection/inflammation. A unique population of microglia-like cells was found in which the chromatin accessibility of genes diverged from their RNA expression. Additionally, we observed a dramatic shift of upstream gene regulators and their targets in brain myeloid cells during SIVE. In summary, this study further uncovers the transcriptome, gene regulatory events and potential roles of different brain myeloid phenotypes in SIVE.

Abstract B062: Low dose dual epigenetic therapy utilizing hypomethylating agents and HDAC inhibitors prolong survival in an orthotopic PDAC model and alter the tumor microenvironment

Abstract Background: We have previously studied the effect of hypomethylating agent Decitabine (5- aza-dC; DAC) on pancreatic cancer using the KPC model (KrasG12D/+;Trp53R172H/+;Pdx1- Cre) and observed increased CD4+/CD8+ TILs, greater PD1 expression and slowed tumor growth with increased tumor necrosis. Subsequently we showed a significant survival benefit with DAC+αPD1 compared to either single agent. However, we identified a specific myeloid cell population initially identified by Chi3l3 expression that may be responsible for treatment resistance or escape. Based on prior observations of synergy specifically affecting tumor infiltrating myeloid and lymphoid cells, we focused on identifying a dual epigenetic strategy (a combination of DAC plus histone deacetylase inhibitors (HDACi)) to enhance immunological synergy and test their treatment efficacy with αPD1. Methods: We used a combination primary KPC-derived cell lines, bone marrow (BMDM) and peritoneum derived (PM) myeloid cells and T cells in co-culture systems to assess cytotoxic synergy (Bliss/Lowe consensus) and immune effects (cytokine release, myeloid cell polarization and T cell activation) to evaluate combinations of DAC+HDACi. The KPC orthotopic model relying on US monitoring of tumor size for standardized initiation of therapy was used for survival analysis and profiling in treatment combinations of DAC+HDACi+αPD1. Results: We showed that hypomethylation therapy exerts a primarily paracrine effect on myeloid cells and this polarization results in a decrease in DAC–induced T cell activation. We therefore selected HDAC inhibitors that in combination with DAC alter this paracrine effect. We selected specific HDAC inhibitors based on induction of class of HDAC expression following hypomethylation therapy, highest Bliss synergy scores at low doses and reversal of cytokine release, M2 polarization and T cell inactivation. Three HDAC inhibitors were chosen for in vivo testing, Domatinostat, Pracinostat and Entinostat. Using the treatment paradigm of ultra-low dose DAC+ HDACi (mainly to minimize toxicity) combined with αPD1 in the KPC orthotopic model we show that the triple combination (DAC + Entinostat + αPD1) is well-tolerated and results in a significant survival benefit compared to single and dual agent combinations. In addition, we also demonstrate a reduction in the Chi3l3 expressing myeloid cell population. Conclusions: Our results show that the combination of hypomethylating agent plus HDAC inhibitor has several beneficial effects on the tumor immune response in PDAC. HDAC inhibitors specifically reduce the suppressive myeloid cell population we previously identified after DAC therapy. The combination of dual low dose epigenetic therapy using a hypomethylating agent plus HDAC inhibitor followed by αPD1 results in significant survival benefit in the orthotopic KPC model. Citation Format: Stephen Muzyka, Arturo Orlacchio, Amanda Ackermann, Yasmine Chinda, Yoona Shim, Igor Dolgalev, Tamas Gonda. Low dose dual epigenetic therapy utilizing hypomethylating agents and HDAC inhibitors prolong survival in an orthotopic PDAC model and alter the tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B062.

A comprehensive and longitudinal evaluation of the different populations of lymphoid and myeloid cells in the peripheral blood of patients treated with chemoradiotherapy for head and neck cancer

BackgroundImmunotherapy provided significant survival benefits for recurrent and metastatic patients with head and neck cancer. These improvements could not be reproduced in patients treated with curative-intent chemoradiotherapy (CRT) and the optimal radio-immunotherapy (RIT) concepts have yet to be designed. Exploration and analysis of the pre-therapeutic immune status of these patients and the changes occurring during the treatment course could be crucial in rationally designing future combined treatments.MethodsBlood samples were collected from a cohort of 25 head and neck cancer patients treated with curative-intended (C)-RT prior to therapy, after the first week of treatment, and three months after treatment completion. Peripheral blood mononuclear cells (PBMCs) or all nucleated blood cells were isolated and analyzed via flow cytometry.ResultsAt baseline, patients showed reduced monocyte and lymphocyte counts compared to healthy individuals. Although overall CD8+ T-cell frequencies were reduced, the proportion of memory subsets were increased in patients. Radiotherapy (RT) treatment led to a further increase in CD8+ effector memory T-cells. Among myeloid populations, tumor-promoting subsets became less abundant after RT, in favor of pro-inflammatory cells.ConclusionThe present study prospectively demonstrated a complex interplay and distinct longitudinal changes in the composition of lymphocytic and myeloid populations during curative (C)-RT of head and neck cancer. Further validation of this method in a larger cohort could allow for better treatment guidance and tailored incorporation of immunotherapies (IT) in the future.

CCN4 (WISP-1) reduces apoptosis and atherosclerotic plaque burden in an ApoE mouse model

Background and aimsCCN4/WISP-1 regulates various cell behaviours that contribute to atherosclerosis progression, including cell adhesion, migration, proliferation and survival. We therefore hypothesised that CCN4 regulates the development and progression of atherosclerotic plaques. MethodsWe used a high fat fed ApoE−/− mouse model to study atherosclerotic plaque progression in the brachiocephalic artery and aortic root. In protocol 1, male ApoE−/− mice with established plaques were given a CCN4 helper-dependent adenovirus to see the effect of treatment with CCN4, while in protocol 2 male CCN4−/−ApoE−/− were compared to CCN4+/+ApoE−/− mice to assess the effect of CCN4 deletion on plaque progression. ResultsCCN4 overexpression resulted in reduced occlusion of the brachiocephalic artery with less apoptosis, fewer macrophages, and attenuated lipid core size. The amount of plaque found on the aortic root was also reduced. CCN4 deficiency resulted in increased apoptosis and occlusion of the brachiocephalic artery as well as increased plaque in the aortic root. Additionally, in vitro cells from CCN4−/−ApoE−/− mice had higher apoptotic levels. CCN4 deficiency did not significantly affect blood cholesterol levels or circulating myeloid cell populations. ConclusionsWe conclude that in an atherosclerosis model the most important action of CCN4 is the effect on cell apoptosis. CCN4 provides pro-survival signals and leads to reduced cell death, lower macrophage number, smaller lipid core size and reduced atherosclerotic plaque burden. As such, the pro-survival effect of CCN4 is worthy of further investigation, in a bid to find a therapeutic for atherosclerosis.

Targeting CNS myeloid infiltrates provides neuroprotection in a progressive multiple sclerosis model

Demyelination and axonal injury in chronic-progressive Multiple Sclerosis (MS) are presumed to be driven by a neurotoxic bystander effect of meningeal-based myeloid infiltrates. There is an unmet clinical need to attenuate disease progression in such forms of CNS-compartmentalized MS. The failure of systemic immune suppressive treatments has highlighted the need for neuroprotective and repair-inducing strategies. Here, we examined whether direct targeting of CNS myeloid cells and modulating their toxicity may prevent irreversible tissue injury in chronic immune-mediated demyelinating disease. To that end, we utilized the experimental autoimmune encephalomyelitis (EAE) model in Biozzi mice, a clinically relevant MS model. We continuously delivered intracerebroventricularly (ICV) a retinoic acid receptor alpha agonist (RARα), as a potent regulator of myeloid cells, in the chronic phase of EAE. We assessed disease severity and performed pathological evaluations, functional analyses of immune cells, and single-cell RNA sequencing on isolated spinal CD11b+ cells. Although initiating treatment in the chronic phase of the disease, the RARα agonist successfully improved clinical outcomes and prevented axonal loss. ICV RARα agonist treatment inhibited pro-inflammatory pathways and shifted CNS myeloid cells toward neuroprotective phenotypes without affecting peripheral infiltrating myeloid cell phenotypes, or peripheral immunity. The treatment regulated cell-death pathways across multiple myeloid cell populations and suppressed apoptosis, resulting in paradoxically marked increased neuroinflammatory infiltrates, consisting mainly of microglia and CNS / border-associated macrophages. This work establishes the notion of bystander neurotoxicity by CNS immune infiltrates in chronic demyelinating disease. Furthermore, it shows that targeting compartmentalized neuroinflammation by selective regulation of CNS myeloid cell toxicity and survival reduces irreversible tissue injury, and may serve as a novel disease-modifying approach.

Mutant IDH Modulates Suppressive Myeloid Populations in Malignant Glioma.

Mutations in the isocitrate dehydrogenase (IDH) genes IDH1 and IDH2 have critical diagnostic and prognostic significance in diffuse gliomas. Neomorphic mutant IDH activity has been previously implicated in T-cell suppression; however, the effects of IDH mutations on intratumoral myeloid populations remain underexplored. In this study, we investigate the influence of IDH status on the myeloid compartment using human glioma specimens and preclinical models. We performed RNA sequencing and quantitative immunofluorescence on newly diagnosed, treatment-naive IDH-mutant grade 4 astrocytoma and IDH-wild-type (IDH-WT) glioblastoma (GBM) specimens. We also generated a syngeneic murine model, comparing transcriptomic and cell-level changes in paired isogenic glioma lines that differ only in IDH mutational status. Among patient samples, IDH-mutant tumors displayed an underrepresentation of suppressive myeloid transcriptional signatures, which was confirmed at the cellular level with decreased numbers of intratumoral M2-like macrophages and myeloid-derived suppressor cells. Introduction of the mutant IDH enzyme into murine glioma was sufficient to recapitulate the transcriptomic and cellular shifts observed in patient samples. We provide transcriptomic and cellular evidence that mutant IDH is associated with a quantitative reduction of suppressive myeloid cells in gliomas and that introduction of the mutant enzyme is sufficient to result in corresponding cellular changes using an in vivo preclinical model. These data advance our understanding of high-grade gliomas by identifying key myeloid cell populations that are reprogrammed by mutant IDH and may be targetable through therapeutic approaches.

A phase Ib/II study of pacritinib, an interleukin 1 receptor associated kinase 1 (IRAK1) inhibitor, in patients (pts) with solid tumors harboring the 1q21.3 copy number amplification (CNA).

43 Background: The role of IRAK1 pathway in inflammatory and immune response is established in autoimmune diseases but less well-understood in cancer. Chromosome 1q21.3 CNA detected in plasma cell-free DNA was observed in pts with advanced solid tumors, and associated with IRAK1 upregulation. In preclinical animal models, IRAK1 upregulation promoted tumorigenesis, while its inhibition led to decreased tumor growth. Pacritinib is a JAK2/FLT3 inhibitor that is FDA approved for treatment in myelofibrosis, but also have known activity against IRAK1. We hypothesize that pacritinib may be effective in disease control of pts with plasma 1q21.3 CNA. Methods: A phase Ib/II clinical trial was designed to investigate the efficacy of pacritinib in pts with treatment (rx) refractory solid tumors harboring 1q21.3 CNA. Serial pt tumor and blood samples were collected and analyzed to elucidate the effect of IRAK1 inhibition on tumor microenvironment and systemic immune modulation. Results: 330 patients were screened, 1q21.3 CNA was detected in 30.1% of pts. Highest incidence of 1q21.3 CNA positivity was detected in breast cancer (39.8%), colorectal cancer (39.7%) and lung cancer (36.1%). 12 pts were commenced on rx over 3 dose levels (DL) (DL1: n=6, DL2: n=3, DL3: n=3). At DL1 (200mg BID), no DLTs were observed, but 2 pts had G3 transaminitis attributed to drug/disease, and 1 pt had intolerable G2 rash; decision was made for dose reduction. At DL2 (200mg OM, 100mg ON), no DLTs were observed. Reescalation to 200mg BID (DL3) was carried out with no DLT observed. Pacritinib at 200mg BD was declared the recommended phase II dose in pts with solid tumors. In the dose expansion cohort, 8 pts (4 colorectal cancer, 3 hepatobiliary [HPB] cancer, 1 lung cancer) have been enrolled thus far. No objective responses were observed. Within pts with HPB tumors, 1 pt with pancreatic cancer had a progression-free survival (PFS) of 25.0 weeks, and 1 pt with cholangiocarcinoma had a PFS of 15.9 weeks. Preliminary analysis of serial tumor biopsy samples suggest an expansion of CD8+ T cell population with pacritinib rx. Serial peripheral blood mononuclear cells analysis showed no significant trend in change in CD8+ T cell population, but a predominance of PD-1+ T cells with rx, and also an increase in CD4+ T cell population. In the myeloid cell population, there appears to be decrease in dendritic cell population, but no significant change in trend of macrophage was observed. Conclusions: Pacritinib at 200mg BID is safe and tolerable in pts with solid tumors. IRAK1 inhibition appears to modulate immune cell populations both in the tumor microenvironment and systemic circulation. Dose expansion is underway, with potential signal of disease control in HPB tumors. Clinical trial information: NCT04520269 .

Abstract Or108: The role of SARM1 in regulation of immune response in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is an unmet medical need. Recent studies have shown that HFpEF is associated with immune dysregulation and decline in nicotinamide adenine dinucleotide (NAD + ) levels. However, the molecular mechanisms linking these factors in HFpEF are not completely understood. Sterile alpha and TIR motif-containing 1 (SARM1) is a NAD + consuming enzyme that may regulate immune response and NAD + metabolism. Here, we investigated the role of SARM1 in HFpEF pathophysiology. We utilized a two-hit diet model to induce HFpEF in mice (HFpEF diet: high-fat diet and L-NAME). Wild-type (WT) mice on HFpEF diet showed progressive decline in diastolic function (e.g. decreased E’/A’, increased relaxation time, IVRT) at 5- and 15-week, associated with unchanged systolic function and increased cardiac hypertrophy. Despite decline in NAD + levels as previously reported in HFpEF hearts, qPCR analysis showed no significant differences in the expression of enzymes involved in NAD + biosynthesis including the salvage, Preiss-Handler and de novo pathways. We employed RNA-sequencing to identify cardiac gene signatures that are associated with HFpEF. Gene ontology analysis showed activation of various immune pathways in HFpEF hearts. Using flow cytometry analysis, we observed around 66% increase in total leukocytes (CD45+) number, along with infiltration of both T cells (CD3+ CD4+/CD8+) and myeloid cell populations (CD11b+) in HFpEF hearts. To understand the role of SARM1 in HFpEF pathogenesis, we subjected global SARM1 knock out (KO) mice to HFpEF diet. SARM1 KO hearts had improved diastolic function and reduced hypertrophy after 15-week HFpEF diet. RNA-sequencing of SARM1 KO-HFpEF hearts showed downregulations of transcripts in immune activation pathways, compared to WT-HFpEF hearts. In summary, our findings suggest that SARM1 may regulate immune activation pathways and promote HFpEF pathogenesis. We plan to determine the intricate relationships between immune dysregulation, metabolic stress, and cardiac dysfunction in HFpEF pathogenesis. The future direction may identify potential avenues for targeted therapeutic interventions aimed at modulating immune responses for HFpEF.

Helminth induced monocytosis conveys protection from respiratory syncytial virus infection in mice.

Respiratory syncytial virus (RSV) infection in infants is a major cause of viral bronchiolitis and hospitalisation. We have previously shown in a murine model that ongoing infection with the gut helminth Heligmosomoides polygyrus protects against RSV infection through type I interferon (IFN-I) dependent reduction of viral load. Yet, the cellular basis for this protection has remained elusive. Given that recruitment of mononuclear phagocytes to the lung is critical for early RSV infection control, we assessed their role in this coinfection model. Mice were infected by oral gavage with H. polygyrus. Myeloid immune cell populations were assessed by flow cytometry in lung, blood and bone marrow throughout infection and after secondary infection with RSV. Monocyte numbers were depleted by anti-CCR2 antibody or increased by intravenous transfer of enriched monocytes. H. polygyrus infection induces bone marrow monopoiesis, increasing circulatory monocytes and lung mononuclear phagocytes in a IFN-I signalling dependent manner. This expansion causes enhanced lung mononuclear phagocyte counts early in RSV infection that may contribute to the reduction of RSV load. Depletion or supplementation of circulatory monocytes prior to RSV infection confirms that these are both necessary and sufficient for helminth induced antiviral protection. H. polygyrus infection induces systemic monocytosis contributing to elevated mononuclear phagocyte numbers in the lung. These cells are central to an anti-viral effect that reduces the peak viral load in RSV infection. Treatments to promote or modulate these cells may provide novel paths to control RSV infection in high risk individuals.

Non-viral-mediated gene transfer of OX40 ligand for tumor immunotherapy.

Immune checkpoint blockade (ICB) is rapidly becoming a standard of care in the treatment of many cancer types. However, the subset of patients who respond to this type of therapy is limited. Another way to promote antitumoral immunity is the use of immunostimulatory molecules, such as cytokines or T cell co-stimulators. The systemic administration of immunotherapeutics leads to significant immune-related adverse events (irAEs), therefore, the localized antitumoral action is needed. One way to achieve this is intratumoral non-viral gene-immune therapy, which allows for prolonged and localized gene expression, and multiple drug administration. In this study, we combined the previously described non-viral gene delivery system, PEG-PEI-TAT copolymer, PPT, with murine OX40L-encoding plasmid DNA. The resulting OX40L/PPT nanoparticles were characterized via gel mobility assay, dynamic light scattering analysis and in vitro transfection efficiency evaluation. The antitumoral efficacy of intratumorally (i.t.) administered nanoparticles was estimated using subcutaneously (s.c.) implanted CT26 (colon cancer), B16F0 (melanoma) and 4T1 (breast cancer) tumor models. The dynamics of stromal immune cell populations was analyzed using flow cytometry. Weight loss and cachexia were used as irAE indicators. The effect of combination of i.t. OX40L/PPT with intraperitoneal PD-1 ICB was estimated in s.c. CT26 tumor model. The obtained OX40L/PPT nanoparticles had properties applicable for cell transfection and provided OX40L protein expression in vitro in all three investigated cancer models. We observed that OX40L/PPT treatment successfully inhibited tumor growth in B16F0 and CT26 tumor models and showed a tendency to inhibit 4T1 tumor growth. In B16F0 tumor model, OX40L/PPT treatment led to the increase in antitumoral effector NK and T killer cells and to the decrease in pro-tumoral myeloid cells populations within tumor stroma. No irAE signs were observed in all 3 tumor models, which indicates good treatment tolerability in mice. Combining OX40L/PPT with PD-1 ICB significantly improved treatment efficacy in the CT26 subcutaneous colon cancer model, providing protective immunity against CT26 colon cancer cells. Overall, the anti-tumor efficacy observed with OX40L non-viral gene therapy, whether administered alone or in combination with ICB, highlights its potential to revolutionize cancer gene therapy, thus paving the way for unprecedented advancements in the cancer therapy field.

Cell of origin alters myeloid-mediated immunosuppression in lung adenocarcinoma.

Solid carcinomas are often highly heterogenous cancers, arising from multiple epithelial cells of origin. Yet, how the cell of origin influences the response of the tumor microenvironment is poorly understood. Lung adenocarcinoma (LUAD) arises in the distal alveolar epithelium which is populated primarily by alveolar epithelial type I (AT1) and type II (AT2) cells. It has been previously reported that Gramd2 + AT1 cells can give rise to a histologically-defined LUAD that is distinct in pathology and transcriptomic identity from that arising from Sftpc + AT2 cells1,2. To determine how cells of origin influence the tumor immune microenvironment (TIME) landscape, we comprehensively characterized transcriptomic, molecular, and cellular states within the TIME of Gramd2 + AT1 and Sftpc + AT2-derived LUAD using KRASG12D oncogenic driver mouse models. Myeloid cells within the Gramd2 + AT1-derived LUAD TIME were increased, specifically, immunoreactive monocytes and tumor associated macrophages (TAMs). In contrast, the Sftpc + AT2 LUAD TIME was enriched for Arginase-1+ myeloid derived suppressor cells (MDSC) and TAMs expressing profiles suggestive of immunosuppressive function. Validation of immune infiltration was performed using flow cytometry, and intercellular interaction analysis between the cells of origin and major myeloid cell populations indicated that cell-type specific markers SFTPD in AT2 cells and CAV1 in AT1 cells mediated unique interactions with myeloid cells of the differential immunosuppressive states within each cell of origin mouse model. Taken together, Gramd2 + AT1-derived LUAD presents with an anti-tumor, immunoreactive TIME, while the TIME of Sftpc + AT2-derived LUAD has hallmarks of immunosuppression. This study suggests that LUAD cell of origin influences the composition and suppression status of the TIME landscape and may hold critical implications for patient response to immunotherapy.

Targeting polymorphonuclear myeloid-derived suppressor cells in the immunosuppressive tumor microenvironment for cancer immunotherapy.

Tumor-driven immune suppression is a critical mechanism by which cancer cells evade the host immune system, leading to tumor growth and metastasis. The tumor immune microenvironment contains a large population of immune-suppressing myeloid cells, which play a key role in tumor development and drug resistance to existing immunotherapy. Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) are important components of the immunosuppressive microenvironment. Uncovering the molecular mechanisms of PMN-MDSCs and finding specific targets for PMN-MDSCs to regulate tumor immune microenvironment is the focus and challenge of current immunotherapy. In a recent issue of Nature, Wang and colleagues revealed that CD300ld on PMN-MDSCs is required for tumor-driven immune suppression(1), this provided a new target for cancer immunotherapy, The study identified CD300ld as a novel, highly conserved tumor immunosuppressive receptor. CD300ld is highly expressed specifically on PMN-MDSCs and is a key receptor in regulating the recruitment and immunosuppressant function of PMN-MDSCs. Targeting CD300ld can reshape the tumor immune microenvironment by inhibiting the recruitment and function of PMN-MDSCs, resulting in broad-spectrum anti-tumor effects. CD300ld target shows good safety, conservation, anti-tumor effectiveness, and synergism with the Programmed death-1 target, which is expected to become a new ideal target for tumor immunotherapy.