Fibroblast Subtypes Research Articles

Single-cell RNA sequencing analysis reveals the dynamic changes in the tumor microenvironment during NMIBC recurrence.

Due to the clinical characteristic of frequent recurrence in urothelial bladder cancer (UBC), patients face significant health impacts and economic burdens. Therefore, understanding the molecular mechanisms involved in UBC recurrence is crucial for reducing its recurrence rate. The aim of our study is to help urologists and clinical researchers gain a deeper understanding of the changes in the tumor microenvironment (TME) during UBC recurrence. We collected 10 samples from primary and recurrent non-muscle-invasive bladder cancer (NMIBC) and performed single-cell RNA sequencing. By distinguishing and annotating cell subpopulations, we identified tissue preferences of some novel cell subgroups. Next, pseudotime trajectory analysis, cell-cell communication analysis, and function enrichment analysis were applied to evaluate the dynamic changes in the TME and biological functions. Finally, we validated the distribution of some of these cell subgroups using multiplex immunofluorescence experiments. We identified a tumor-associated fibroblast (CAF) subtype with high COL18A1 expression that is highly expressed in recurrent NMIBC, suggesting that the stromal component of the tumor may play a crucial role in the recurrence process. Additionally, pseudotime trajectory analysis revealed a macrophage subtype with high IL-6 expression at the terminal stage of macrophage differentiation, exhibiting significant immunosuppressive features. This indicated the presence of immune exhaustion during NMIBC recurrence. Lastly, we found an upregulation of estrogen in recurrent urothelial cancer cells, which may partially explain the gender disparity observed in UBC. This study identified several cell subpopulations influencing NMIBC recurrence, which were heavily infiltrated in the TME of recurrent NMIBC. Additionally, the enrichment of estrogen in urothelial cancer cells from various sources suggested a role of sex hormones in NMIBC recurrence.

Differential activity of MAPK signalling defines fibroblast subtypes in pancreatic cancer

Fibroblast heterogeneity is increasingly recognised across cancer conditions. Given their important contribution to disease progression, mapping fibroblasts’ heterogeneity is critical to devise effective anti-cancer therapies. Cancer-associated fibroblasts (CAFs) represent the most abundant cell population in pancreatic ductal adenocarcinoma (PDAC). Whether CAF phenotypes are differently specified by PDAC cell lineages remains to be elucidated. Here, we reveal an important role for the MAPK signalling pathway in defining PDAC CAF phenotypes. We show that epithelial MAPK activity promotes the myofibroblastic differentiation of CAFs by sustaining the expression and secretion of TGF-β1. We integrate single-cell profiling of post-perturbation transcriptional responses from mouse models with cellular and spatial profiles of human tissues to define a MAPKhigh CAF (mapCAF) phenotype. We show that this phenotype associates with basal-like tumour cells and reduced frequency of CD8+ T cells. In addition to elevated MAPK activity, this mapCAF phenotype is characterized by TGF-β signalling, hypoxia responsive signatures, and immunoregulatory gene programs. Furthermore, the mapCAF signature is enriched in myofibroblastic CAFs from various cancer conditions and correlates with reduced response to immune checkpoint inhibition in melanoma. Altogether, our data expand our knowledge on CAF phenotype heterogeneity and reveal a potential strategy for targeting myofibroblastic CAFs in vivo.

Abstract A033: Integrating spatial transcriptomics and second harmonic generation imaging to identify targets of supermere-associated Discoidin Domain Receptor 1 involved in collagen alignment

Abstract Immune checkpoint blockade has been shown to be an effective treatment for colorectal cancers (CRCs) highly infiltrated by CD8+ T cells. However, there is a paucity of CD8+ T-cell infiltration in the majority of CRCs. We previously identified the collagen-activated receptor Discoidin Domain Receptor 1 (DDR1) as a member of a four-gene signature associated with T-cell exclusion in CRC. The cleaved ectodomain (cECD) of DDR1 induces collagen alignment, leading to T-cell exclusion in a breast cancer model. We found that almost all DDR1 cECD is found in supermeres, a novel secreted nanoparticle identified by our lab, and that DDR1 cECD is required for supermere signaling in recipient cells. We hypothesized that supermere-associated DDR1 cECD signals to CRC stromal cells, leading to collagen alignment. To test this hypothesis, we developed a method to determine which genes are associated with collagen alignment and DDR1 expression. To do this, 30 μm thick CRC sections are imaged using a Nikon AX multiphoton microscope by second harmonic generation imaging, which permits label-free imaging of collagen fibers. Spatial heatmaps of the collagen alignment are generated from the resulting images. Spatial transcriptomics is performed on a serial tumor section using the Visium v2 platform and the gene expression matrix is integrated with the collagen alignment heatmap data. As proof-of-principle, two CRC tumors have been analyzed using this method. Highly aligned regions were found to be associated with expression of genes involved in extracellular matrix organization, keloidal collagen and specific fibroblast subtypes. Genes which may be regulated by DDR1 cECD and be involved in collagen alignment will be confirmed at the protein level by multiplexed immunofluorescence on serial sections and in vitro experiments. This method will provide a rich dataset to elucidate the roles of supermeres and DDR1 cECD in T-cell exclusion and collagen fiber alignment and may support the discovery of new strategies to overcome immune exclusion in CRC. Citation Format: Maxwell S. Hamilton, Oleg Tutanov, Harsimran Kaur, Alan J. Simmons, Clark Massick, Kasey Vickers, Ken S. Lau, Ambra Pozzi, Robert J. Coffey. Integrating spatial transcriptomics and second harmonic generation imaging to identify targets of supermere-associated Discoidin Domain Receptor 1 involved in collagen alignment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr A033.

Cancer-associated fibroblast subtypes modulate the tumor-immune microenvironment and are associated with skin cancer malignancy

Cancer-associated fibroblasts (CAFs) play a key role in cancer progression and treatment outcome. This study dissects the intra-tumoral diversity of CAFs in basal cell carcinoma, squamous cell carcinoma, and melanoma using molecular and spatial single-cell analysis. We identify three distinct CAF subtypes: myofibroblast-like RGS5+ CAFs, matrix CAFs (mCAFs), and immunomodulatory CAFs (iCAFs). Large-cohort tissue analysis reveals significant shifts in CAF subtype patterns with increasing malignancy. Two CAF subtypes exhibit immunomodulatory properties via different mechanisms. mCAFs sythesize extracellular matrix and may restrict T cell invasion in low-grade tumors via ensheathing tumor nests, while iCAFs are enriched in late-stage tumors, and express high levels of cytokines and chemokines to aid immune cell recruitment and activation. This is supported by the induction of an iCAF-like phenotype with immunomodulatory functions in primary healthy fibroblasts exposed to skin cancer cell secretomes. Thus, targeting CAF variants holds promise to enhance immunotherapy efficacy in skin cancers.

Extracellular Vesicles from Lung Adenocarcinoma Cells Induce Activation of Different Cancer-Associated Fibroblast Subtypes.

Background: Lung cancer, including the major subtype lung adenocarcinoma (LUAD), is the leading cause of cancer deaths worldwide, largely due to metastasis. Improving survival rates requires new treatment strategies and a deeper understanding of the mechanisms that drive tumor progression within the tumor microenvironment (TME). This study investigated the impact of extracellular vesicles (EVs) derived from LUAD cells on lung fibroblasts. Methods: EVs were isolated from LUAD cell lines via ultracentrifugation and characterized using nanoparticle tracking analysis and Western blotting. Lung fibroblasts were treated with PBS, TGFβ, or EVs, and their activation was assessed through protein (Western blotting) and RNA analyses (RNA seq and RT-qPCR). Results: The results confirmed the TGFβ induced activation and showed that LUAD EVs could also activate fibroblasts, increasing cancer-associated fibroblast (CAF) markers. While EV-induced CAF activation displayed unique features, like an increase in proliferation-related genes, the EV and TGFβ treatments also shared some differentially expressed genes. The EV groups induced a higher expression of ECM remodeling and EMT-associated genes, but some of those genes were also upregulated in the TGFβ group. Mesenchymal genes POSTN and SPOCK1 were significantly upregulated in TGFβ- and EV-treated fibroblasts. Their secretion as proteins from the TGFβ- and EV-induced CAFs was not significant, confirmed through ELISA. Conclusions: These findings suggest that LUAD EVs play a role in CAF activation through both shared and distinct pathways compared to canonical TGFβ activation, potentially identifying novel gene expressions involved in CAF activation. Additionally, optimal protein secretion conditions of confirmed CAF-upregulated genes need to be established to determine their contribution to the TME.

Single-cell RNA sequencing analysis reveals the role of TXNDC5 in keloid formation.

Thioredoxin domain-containing protein 5 (TXNDC5) is associated with fibrosis in a variety of organs, but its mechanism of action in keloid is unclear. In this study, we aimed to investigate the mechanism of TXNDC5 in keloid. Single-cell RNA sequencing data of keloid and normal scar samples obtained from public databases were normalized and clustered using the Seurat package. Pathway enrich analysis was conducted using biological process enrichment analysis and Gene Set Enrichment Analysis (GSEA). In addition, TXNDC5 expression and its effects on migration and invasion of keloid fibroblasts (KFs) were validated based on cell function experiments. A total of five cell types were obtained. The KF clusters were further clustered into two fibroblast subtypes (Fibroblast cells 1 and Fibroblast cells 2). Biological process enrichment analysis showed that transforming growth factor beta (TGF-β) signaling pathway was enriched in the two fibroblast subtypes. GSEA analysis demonstrated that genes in TGF-β signaling pathway were mainly enriched in Fibroblast cells 1, and that genes involved in cell proliferation, migration, and the TGF-β signaling pathway were all high-expressed in fibroblast cells 1. TXNDC5 was positively correlated with fibroblast proliferation, migration and TGF-β signaling pathway, and AUCell score. The cellular experiment confirmed that the messenger RNA and protein levels of TXNDC5 and TGF-β1 were high-expressed in KFs cells (P<0.001), and that knockdown of TXNDC5 downregulated TGF-β1 expression and inhibited migration and invasion of KFs (P<0.0001). Our study indicated that TGF-β signaling pathway was enriched in fibroblast cells, and TXNDC5 was positively correlated with proliferation, migration, and TGF-β signaling pathway. Cellular experiment demonstrated that knocking down TXNDC5 downregulated TGF-β1 expression, and suppressed migration and invasion of KFs. The current discoveries provided a new therapeutic strategy for the treatment of keloid.

BNIP3+ fibroblasts associated with hypoxia and inflammation predict prognosis and immunotherapy response in pancreatic ductal adenocarcinoma

BackgroundPancreatic ductal adenocarcinoma (PDAC) is one of the most malignant tumors that lacks effective treatment options. Cancer-associated fibroblasts (CAFs), an important component of the tumor microenvironment, associated with tumor progression, prognosis, and treatment response. This work aimed to explore the novel CAFs-associated target to improve treatment strategies in PDAC.MethodsThe PDAC single-cell sequencing data (CRA001160, n = 35) were downloaded and integrated based on GSA databases to classify fibroblasts into fine subtypes. Functional enrichment analysis and coexpression regulatory network analysis were used to identify the functional phenotypes and biological properties of the different fibroblast subtypes. Fibroblast differentiation trajectories were constructed using pseudochronological analysis to identify initial and terminally differentiated subtypes of fibroblasts. The changes in the proportions of different fibroblast subtypes before and after PDAC immunotherapy were compared in responsive and nonresponding patients, and the relationships between fibroblast subtypes and PDAC immunotherapy responsiveness were determined based on GSA and GEO database. Using molecular biology methods to confirm the effects of BNIP3 on hypoxia and inflammation in CAFs. CAFs were co cultured with pancreatic cancer cells to detect their effects on migration and invasion of pancreatic cancer.ResultsSingle-cell data analysis divided fibroblasts into six subtypes. The differentiation trajectory suggested that BNIP3+ Fibro subtype exhibited terminal differentiation, and the expression of genes related to hypoxia and the inflammatory response increased gradually with differentiation time. The specific overexpressed genes in the BNIP3+ Fibro subtype were significantly associated with overall and disease progression-free survival in the patients with PDAC. Interestingly, the greater the proportion of the BNIP3+ Fibro subtype was, the worse the response of PDAC patients to immunotherapy, and the CRTL treatment regimen effectively reduced the proportion of the BNIP3+ Fibro subtype. After knocking out BNIP3, the hypoxia markers and inflammatory factors of CAFs were inhibited. Co-culture of CAFs with pancreatic cancer cells can increase the migration and invasion of pancreatic cancer, but this could be reversed by knocking out BNIP3.ConclusionsThis study revealed the BNIP3+ Fibro subtype associated with hypoxia and inflammatory responses, which was closely related to the poor prognosis of patients with PDAC, and identified signature genes that predict the immunotherapy response in PDAC.

Immunotherapy and pan-apoptotic characterization of the tumor microenvironment in gastric cancer (STAD): a single-cell multidimensional analysis

BackgroundThe aim of this study was to elucidate the critical role of autophagy-related gene aggregation in gastric cancer tumor microenvironment cells and to investigate their major roles in cellular functions. In particular, the expression of these genes in tumor-associated fibroblast subtypes was scrutinized in an attempt to explain their cell-subpopulation-specific roles in cell–cell communication and regulation of cellular functions.MethodsIn this study, single-cell RNA sequencing data were first analyzed in multiple steps, including data preprocessing, cell clustering, and cell classification. Cell subpopulations and gene expression patterns were identified and analyzed using unsupervised non-negative matrix factorization (NMF) techniques. The dynamic expression of autophagy-related gene aggregates in various cell types was deciphered by pseudotime trajectory analysis (PTA). Intercellular communication analysis was performed using the CellChat R software package, revealing the intricate communication patterns and exchange of key signaling molecules between cell subpopulations, and SCENIC analysis was used to identify gene regulatory networks and reveal the mechanisms behind cellular heterogeneity.ResultCell subpopulations associated with pan-apoptosis were identified by NMF decomposition and SCENIC analysis. Cell–cell communication analysis revealed intricate communication patterns and exchange of key signaling molecules between cell subpopulations. Dynamic expression of autophagy-related genes aggregated in the pseudotemporal trajectory of STAD was observed by PTA. In the fibroblast subtype, different ligand-receptor interactions and their key roles in immunomodulation were observed.ConclusionBy deeply analyzing and comparing gene expression patterns within cellular subpopulations and intercellular communication, this study provides new insights into the role of pan-apoptosis-related genes in regulating immune responses and cellular functions in gastric cancer. These findings pave the way for further exploration of the role of these genes in tumorigenesis and immune regulation, as well as laying the foundation for potential therapeutic strategies.

Single-Cell Transcriptomics Reveals Cellular Heterogeneity and Drivers in Serrated Pathway-Driven Colorectal Cancer Progression

Serrated lesions are common precancerous pathways in colorectal cancer (CRC), but the process by which they progress to malignancy remains unclear. We aimed to elucidate this progression through a single-cell RNA landscape. We conducted single-cell RNA sequencing on three normal colonic tissues and fifteen SLs (including HPs, SSLs, SSLD, and TSAs) and integrated these data with datasets containing tumor samples. We identified three invasive malignant epithelial cell subtypes related to CRC progression: SLC1, SLC2, and tumor cell. SLC1, specific to SSLs, is involved in cell proliferation and shows a continuum of malignancy in gene expression. TSA-specific SLC2 exhibited FOXQ1 upregulation and active EMT, indicating invasiveness. The trajectory analysis showed that HPs do not progress to cancer, and different SL types are linked to the MSI status of advanced CRCs. We validated molecular drivers in premalignant lesions and later carcinogenesis. In the tumor microenvironment, CAF and pre-CAF fibroblast subtypes associated with progression were identified. During the premalignant stage, SLC1 triggered CD8+ T cell responses, while at the advanced stage, CAFs promoted tumor invasion and metastasis via FN1-CD44, influencing tumor progression and the treatment response. Our findings highlight transcriptional changes across serrated pathway stages, aiding in early CRC diagnosis and treatment.

Single cell analysis revealed SFRP2 cancer associated fibroblasts drive tumorigenesis in head and neck squamous cell carcinoma

Understanding the mechanisms of invasion and metastasis in head and neck squamous cell carcinoma (HNSCC) is crucial for effective treatment, particularly in metastatic cases. In this study, we analyzed multicenter bulk sequencing and comprehensive single-cell data from 702,446 cells, leading to the identification of a novel subtype of cancer-associated fibroblasts (CAFs), termed Secreted Frizzled-Related Protein2 CAFs (SFRP2_CAFs). These cells, originating from smooth muscle cells, display unique characteristics resembling both myofibroblastic CAFs and inflammatory CAFs, and are linked to poorer survival outcomes in HNSCC patients. Our findings reveal significant interactions between SFRP2_CAFs and SPP1 tumor-associated macrophages, which facilitate tumor invasion and metastasis. Moreover, our research identifies Nuclear factor I/X (NFIX) as a key transcription factor regulating SFRP2_CAFs behavior, confirmed through gene regulatory network analysis and simulation perturbation.

Cancer-Associated Fibroblast Subtypes Reveal Distinct Gene Signatures in the Tumor Immune Microenvironment of Vestibular Schwannoma.

Cancer-associated fibroblast (CAF) composition within the same organ varies across different cancer subtypes. Distinct CAF subtypes exhibit unique features due to interactions with immune cells and the tumor microenvironment. However, data on CAF subtypes in individuals with vestibular schwannoma (VS) are lacking. Therefore, we aimed to distinguish CAF subtypes at the single-cell level, investigate how stem-like CAF characteristics influence the tumor immune microenvironment, and identify CAF subtype-specific metabolic reprogramming pathways that contribute to tumor development. Data were analyzed from three patients with VS, encompassing 33,081 single cells, one bulk transcriptome cohort, and The Cancer Genome Atlas Pan-Cancer database (RNA sequencing and clinical data). Our findings revealed that antigen-presenting CAFs are linked to substantially heightened immune activity, supported by metabolic reprogramming, which differs from tumorigenesis. High expression of the stem-like CAF gene signature correlated with poor prognosis in low-grade gliomas within the pan-cancer database. This is the first study to classify CAF subtypes in VS patients and identify a therapeutic vulnerability biomarker by developing a stem-like CAF gene signature. Personalized treatments tailored to individual patients show promise in advancing precision medicine.

Universal and tissue-specific fibroblasts in chronic inflammation and cancer

In this issue of Cancer Cell, Gao etal. map fibroblast diversity across tumors and chronic inflammatory tissues. The authors uncover universal fibroblast subtypes such as LRRC15+ and MMP1+ myofibroblasts along with specialized tissue-specific subtypes. They reveal cellular roles of fibroblasts in immunosuppression through stromal niches and cell-cell interactions.

Unique Gene Expression Profiles within South Africa Are Associated with Varied Chemotherapeutic Responses in Conventional Osteosarcoma.

We determined the predictive gene expression profiles associated with chemo-response in conventional osteosarcomas (COS) within South Africa. In 28 patients, we performed an RNA extraction, cDNA synthesis, and quantitative analysis using the RT-PCR 2-∆∆CT method to determine the fold change in gene expression alongside GAPDH (housekeeping gene). We observed a significant downregulation in the mRNA expression profiles of ABCB1-p-glycoprotein (p = 0.0007), ABCC3 (p = 0.002), ERCC1 (p = 0.007), p-53 (p = 0.007), and RFC1 (p = 0.003) in the COS patients compared to the healthy donors. Furthermore, ABCB1-p-glycoprotein (p = 0.008) and ABCC3 (p = 0.020) exhibited a significant downregulation in the COS tumour tissues when compared to the healthy donors. In our univariate logistic regression, the predictors of chemotherapeutic response comprised ERCC1 [restricted cubic spline (RCS) knot: OR -0.27; CI -0.504 to -0.032; p = 0.036]; osteoblastic subtype [OR -0.36; CI -0.652 to -0.092; p = 0.026); fibroblastic subtype [OR 0.91; CI 0.569 to 1.248; p < 0.001]; and mixed subtype [OR 0.53; CI 0.232 to 0.032; p = 0.032]. In our multivariable logistic regression, the significant predictors of chemotherapeutic response comprised age [RCS knot: OR -2.5; CI -3.616 to -1.378; p = 0.022]; ABCC3 [RCS knot: OR 0.67; CI 0.407 to 0.936, p = 0.016]; ERCC1 [RCS knot: OR 0.57; CI 0.235 to 0.901; p = 0.044]; RFC1 [RCS knot: OR -1.04; CI -1.592 to -0.487; p = 0.035]; chondroblastic subtype [OR -0.83; CI -1.106 to -0.520; p = 0.012]; and osteoblastic subtype [OR -1.28; CI -1.664 to -0.901; p = 0.007]. In this South African cohort, we observed the unique gene expression profiles of osteosarcoma tumourigenesis and chemotherapeutic responses. These may serve as prognostication and therapeutic targets. Larger-scale research is needed on the African continent.

Abstract A030: Modulation of lymphocyte adhesion and migration by iCAF and myCAF fibroblasts in PDAC

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) poses significant challenges in treatment due to its complex interaction with the tumour microenvironment (TME). Fibroblasts, a crucial component of the TME, influence tumour progression and therapeutic responses. This study explores the diversity of cancer-associated fibroblast (CAF) populations in PDAC tumours versus adjacent normal fibroblasts (ANFs), focussing on myofibroblasts (myCAFs) and inflammatory fibroblasts (iCAFs). These fibroblast subtypes exhibit distinct characteristics and localisation within the tumour. The research examines the impact of CAFs and ANFs on immune cell behaviour, particularly in relation to adhesion and migration. Methods: Tumour and juxta-tumoral tissue from patients were digested into single cell suspensions. Cells were stained with a 22-plex antibody panel by flow cytometry. Pseudo-emperipolesis assays were assessed by co-culture of lymphocytes with CAF and ANF fibroblasts. Furthermore, these were performed with or without stimulation of fibroblasts with by TGF-b or TNF-a/IFN-g, to promote myCAF or iCAF phenotypes respectively. Gene expression analysis of tumour-derived fibroblast subtypes was assessed by single-cell RNA sequencing using the 10X Genomics platform. The transcriptional profile of spatially resolved fibroblasts which were proximal or distant to tumour epithelium was determined by the NanoString GeoMx Digital Spatial Profiler (DSP) platform. Results: Flow cytometry analysis revealed that iCAFs predominated within the tumour stroma compared to myCAFs, although iCAF populations were less prevalent within ANF populations. Upon stimulation with inflammatory cytokines (TNF-α/IFN-γ), CAFs promoted lymphocyte migration in contrast to ANFs. However, TGF-β stimulation of CAF downregulated the migration of lymphocytes. As such, TGF-β or TNF-α/IFN-γ stimulation exhibited antagonistic effects on lymphocyte adhesion and migration in CAFs. Tumour-proximal fibroblasts exhibited myCAFs characteristics expressing α-SMA and PDPN, as well as ECM molecules such as collagen and integrins, suggesting a barrier to lymphocyte migration. Conversely, distal fibroblasts displayed an inflammatory profile, expressing cytokines and chemokines including CCL2, CXCL9, CXCL12, IL6, IL11 and LIF, thereby contributing to the inflammatory milieu within the tumour microenvironment. Additionally, iCAFs demonstrated higher transcription levels of hyaluronan synthase (Has1) and fibulin 2 (FBLN2) which are crucial for ECM formation and remodelling. This study identifies a differential role for iCAFs and myCAFs in the modulate of lymphocyte adhesion and migration within the PDAC microenvironment, highlighting the complex interplay between fibroblast subtypes and immune cell dynamics. Citation Format: Fouzia Zayou, Hayden Pearce, Wayne Croft, Samantha Nicol, Sandra Margielewska-Davies, Sarah Powell-Brett, Rachel Brown, Jianmin Zuo, Keith Roberts, Helen M. McGettrick, Paul Moss. Modulation of lymphocyte adhesion and migration by iCAF and myCAF fibroblasts in PDAC [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 A030.

Abstract A038: The hypoxic regulation of macrophage function in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is marked by an extensive fibroinflammatory stroma and a low-oxygen (hypoxic) microenvironment, which contribute to disease progression and therapeutic resistance. Within the PDAC stroma, macrophages and cancer-associated fibroblasts (CAFs) are the predominant cell types. Macrophages are a major immunosuppressive population in PDAC. These cells are highly plastic and, as a result, their environment plays an important role in regulating their function. Macrophages adapt to hypoxia primarily by stabilizing hypoxia-inducible factors (HIFs), which are oxygen-labile transcription factors. Although PDAC is profoundly hypoxic and both the tumor cells and stromal cells experience hypoxia, the effects of hypoxia and HIFs on macrophages and their interactions with other stromal cells in PDAC are not yet fully understood. We found that hypoxia promotes the acquisition of inflammatory cancer-associated fibroblasts (inflammatory CAFs), a fibroblast subtype that produces high levels of cytokines and chemokines. Utilizing a hypoxia marker in mouse models of PDAC, we have observed that inflammatory CAFs and macrophages are predominantly situated in hypoxic tumor regions compared with normoxic regions, while T cells are largely absent from these oxygen-poor regions. These preliminary data raise the possibility that inflammatory fibroblasts induced by hypoxia promote macrophage infiltration into hypoxic tumor regions and facilitate an immunosuppressive macrophage phenotype. We have also found that when macrophages are exposed to conditioned media derived from fibroblast cultures under either hypoxic or normoxic conditions, factors secreted from the hypoxia-exposed fibroblasts promote an immunosuppressive macrophage phenotype. We are currently identifying the factors released from hypoxic fibroblasts that drive the immunosuppressive macrophage phenotype. Future work will focus on evaluating the effects of macrophage-intrinsic responses to hypoxia through HIFs on pancreatic tumorigenesis in vivo. Citation Format: Sean Hannifin, Ashley M Mello, Tenzin Ngodup, Katelyn L Donahue, Marina Pasca di Magliano, Kyoung Eun Lee. The hypoxic regulation of macrophage function in pancreatic cancer [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 A038.

Abstract A048: Paricalcitol improves survival in tumor-permissive cancer-associated fibroblast subtype of pancreatic cancers

Abstract INTRODUCTION: Pancreatic ductal adenocarcinoma (PDAC) remains a deadly disease with poor survival and limited therapy options. While traditional cytotoxic agents target cancer cells, there has been growing interest in tumor microenvironment (TME) modulation given that desmoplastic stroma and immune suppression are hallmarks of PDAC. Recently, vitamin D agonism has been identified as a potential treatment to normalize the PDAC TME. We have previously described tumor-intrinsic and cancer-associated fibroblast (CAF) subtypes of PDAC that independently predict survival, but whether these subtypes are associated with outcomes after TME modulation has not been studied. METHODS: We evaluated the association of treatment outcomes in a Phase 2 trial of neoadjuvant nab-paclitaxel (A), gemcitabine (G), cisplatin (C), and paricalcitol (P) (NCT03138720) and a Phase 2 trial of A+G+C+hydroxychloroquine (HCQ) (NCT04669197) in patients with non-metastatic PDAC. RNA-sequencing was performed on 28 pretreatment biopsy samples. PurIST and DeCAF were used to determine tumor-intrinsic and CAF subtypes, respectively. Clinical variables such as CA19-9 levels, resectability, and overall survival (OS) were examined. RESULTS: For tumor-intrinsic subtypes, 5 tumors (18%) were basal-like and 23 (82%) were classical. For CAF subtypes, 11 (39%) were tumor-permissive (perm)CAF and 17 (61%) were tumor-restraining (rest)CAF. Neither tumor-intrinsic or CAF subtypes were associated with CA19-9 normalization or resectability at time of diagnosis in either trial. OS was available for NCT03138720; patients with basal-like tumors receiving A+G+C+P had worse median survival of 12.3 months compared to 20.9 months for those with classical tumors, although this difference did not reach statistical significance (log-rank P = 0.065). In two independent cohorts of 925 and 129 patients, those with permCAF tumors had an increased hazard ratio of at least 1.5 (P &amp;lt; 0.001) compared to patients with restCAF tumors for OS. Compared to this historical data, we did not find a difference in OS between patients with permCAF tumors (19.5 months) compared to restCAF tumors (19.7 months, log-rank P = 0.56). CONCLUSION: In the study of A+G+C+P, there was a disparity in OS between patients with basal-like vs. classical tumors, in contrast to the interim results of the COMPASS and PASS-01 trials, where patients with basal-like tumors receiving A+G had similar OS compared to patients with classical tumors. Compared to prior analysis, there was no difference in OS for patients with permCAF tumors vs. those with restCAF tumors, which may suggest that either paricalcitol (or the cytotoxic combination) may be of benefit for patients with permCAF tumors and normalize the CAF landscape. Single-agent studies with paired pre- and post-treatment samples are needed to better understand how to best tailor therapy regiments for patients based on tumor subtypes. Citation Format: Jaewon J Lee, Priscilla S Chan, Changfei Luan, Elena V Kharitonova, Naim U Rashid, Xianlu L Peng, Erkut H Borazanci, Jen Jen Yeh. Paricalcitol improves survival in tumor-permissive cancer-associated fibroblast subtype of pancreatic cancers [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 A048.

Abstract A045: Disrupting local immunosuppression through combination myCAF/myeloid targeting in pancreatic cancer

Abstract Immunotherapy has revolutionized clinical care for many cancers, yet the approach has not been fully realized in immunologically cold tumors like Pancreatic Ductal Adenocarcinoma (PDAC). One striking hallmark of PDAC is local immunosuppression (LIS) which leads to cytotoxic T cell inactivation and exclusion. There is great need for an increased understanding of the cellular crosstalk within tumors and the identification of stromal and immune populations involved in shaping the tumor microenvironment (TME). Oncogenic KRAS activation in tumor cells promotes the invasion and proliferation of tumor-supporting stromal cells, while excluding cancer-targeted cytotoxic T cells. LIS is mediated by multiple subtypes of cancer-associated fibroblasts (CAFs) and myeloid cells resident within the tumor parenchyma. Multiple prior attempts to reverse LIS in PDAC by targeting individual stromal cell populations have been unsuccessful, alluding to the complexity of stromal crosstalk within the TME. The stromal diversity of PDAC complicates investigating paracrine cascades involving multiple cell types. To decipher diverse drug effects on altering the TME, we employ in vivo studies in mouse models recapitulating the human disease, as well as a novel tumor explant model that enables the short-term culture of intact human or murine PDAC. Importantly, PDAC explants maintain their histopathological architecture and cellular diversity over time. This medium-throughput platform allows for testing of multiple drugs and mechanistic hypotheses in the native PDAC TME. We show in preliminary data that Smoothened inhibition (SMOi) decreases proliferation and activity of myCAFs, but provokes the expansion of CD11b-positive myeloid cells in vivo. Thus, we hypothesize that LIS in PDAC is maintained by a delicate balance between myCAFs and myeloid cells, preventing effective T cell invasion. Single cell RNA-seq data comparing ctrl vs. SMOi-treated murine PDAC elucidates stromal subpopulations involved in the LIS phenotype and guides the identification of myeloid subtypes emerging after SMOi. Strikingly, we demonstrated that simultaneous SMOi and targeting myeloid cells via anti-Gr1 or CCR1 inhibition (CCR1i) significantly elevates cytotoxic T cell numbers up to 20x within the TME. We are currently investigating whether the activity of these T cells may be further potentiated through combination with immunomodulatory agents. By testing various treatment combination in the same TME, we will identify the best synergistic effects for future immunotherapy approaches in human PDAC. In summary, we are elucidating the complex mechanism behind LIS in PDAC by employing our novel explant culture system alongside in vivo studies. We aim to develop a translatable regimen to neutralize LIS, reactivating the cytotoxic T cells in the tumor periphery to invade, proliferate, and attack cancer cells. Citation Format: Marie C Hasselluhn, Lukas Vlahos, Dafydd Thomas, Quin T Waterbury, Alvaro Curiel Garcia, Amanda R Decker-Farrell, Tanner C Dalton, Stephen A Sastra, Carmine F Palermo, Timothy C Wang, Andrea Califano, Kenneth P Olive. Disrupting local immunosuppression through combination myCAF/myeloid targeting in pancreatic cancer [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 A045.

Abstract A044: Persistence of fetal splanchnic gene signature defines a tumor-restraining fibroblast subtype in pancreatic cancer

Abstract The pancreas is composed of the epithelial and mesenchymal cells. While mesenchymal fibroblasts are a minor component of the normal pancreas, fibroblast population expands drastically during tumorigenesis. In pancreatic ductal adenocarcinoma (PDAC), cancer associated fibroblasts (CAFs) play critical and complex roles in the tumor microenvironment. This study sought to define the origin, heterogeneity and function of pancreatic cancer associated fibroblasts. Recently we performed a series of lineage tracing studies in genetically engineered mouse models. This identified the splanchnic mesenchyme (a tissue layer adjacent to the developing fetal pancreatic epithelium) as the fetal origin of the adult pancreatic resident fibroblasts and pancreatic CAFs. Single cell transcriptomic analysis indicated persistent and dynamic gene expressions along the pancreatic mesenchymal trajectory during development, homeostasis, precancer and cancer. Intriguingly, we found that two splanchnic transcription factors, GATA6 and FOXF1, are expressed in only subsets of adult pancreatic fibroblasts in temporally and spatially distinct patterns. Similar patterns were observed in both mouse models and human patient samples. To determine the role of GATA6 in fibroblasts during tumorigenesis, we constructed a dual DNA recombinase mouse genetic model. DNA recombinase FlpO directs expression of an oncogene Kras (G12D mutation) and loss of a tumor suppressor p53 in pancreatic epithelial cells to induce spontaneous tumor formation in the pancreas, and DNA recombinase Cre deletes Gata6 specifically in fibroblasts. This fibroblast specific Gata6 deletion resulted in altered number and gene expression of CAFs as well as increased tumor burden in the pancreas. This suggests a non-cell autonomous function of GATA6 within CAFs to restrain pancreatic cancer progression. In summary, this study delineated a continuous cell trajectory of the mesenchymal lineage in the pancreas across different life stages. Additionally, this study provides evidence that persistent and selective gene expressions along the mesenchymal trajectory contributes to pancreatic CAF heterogeneity and such persistence may constitute an inherent host defense mechanism to restrain pancreatic cancer. The enhancement of this mechanism could be explored further for therapeutic benefits. Citation Format: Lu Han, Tom Walter, Joseph Beaudet, Caroline Everett, Gustavo Leone, Michael Ostrowski. Persistence of fetal splanchnic gene signature defines a tumor-restraining fibroblast subtype in pancreatic cancer [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 A044.

FHL2 expression by cancer-associated fibroblasts promotes metastasis and angiogenesis in lung adenocarcinoma.

Cancer-associated fibroblasts (CAFs) contribute to the progression of lung cancer. Four and a half LIM domain protein-2 (FHL2) is a component of focal adhesion structures. We analyzed the function of FHL2 expressed by CAFs in lung adenocarcinoma. Expression of FHL2 in fibroblast subtypes was investigated using database of single-cell RNA-sequencing of lung cancer tissue. The role of FHL2 in the proliferation and migration of CAFs was assessed. The effects of FHL2 knockout on the migration and invasion of human lung adenocarcinoma cells and tube formation of endothelial cells induced by CAF-conditioned medium (CM) were evaluated. The effect of FHL2 knockout in CAFs on metastasis was determined using a murine orthotopic lung cancer model. The prognostic significance of stromal FHL2 was assessed by immunohistochemistry in human adenocarcinoma specimens. FHL2 is highly expressed in myofibroblasts in cancer tissue. TGF-β1 upregulated FHL2 expression in CAFs and FHL2 knockdown attenuated CAF proliferation. FHL2 knockout reduced CAF induced migration of A110L and H23 human lung adenocarcinoma cell lines, and the induction of tube formation of endothelial cells. FHL2 knockout reduced CAF-induced metastasis of lung adenocarcinomas in an orthotopic model in vivo. The concentration of Osteopontin (OPN) in CM from CAF was downregulated by FHL2 knockout. siRNA silencing and antibody blocking of OPN reduced the pro-migratory effect of CM from CAF on lung cancer cells. In resected lung adenocarcinoma specimens, positive stromal FHL2 expression was significantly associated with higher microvascular density and worse prognosis. In conclusion, FHL2 expression by CAFs enhances the progression of lung adenocarcinoma by promoting angiogenesis and metastasis.

Endothelial cells and fibroblasts mediate the microenvironmental regulatory network of carotid body paraganglioma

Objective:To explore the gene expression characteristics of endothelial cells and fibroblasts in the microenvironment of SDHD-mutated carotid body tumors（SDHD-CBT）, to fine the functional enrichment of each subcluster, and to further explore the network of cell-cell interactions in the microenvironment of SDHD-CBT. Methods:The bioinformatics analysis was used to download and reanalyze the single-nuclear RNA sequencing data of SDHD-CBT, SDHB mutated thoracic and abdominal paraganglioma（SDHB-ATPGL）, SDHB-CBT, and normal adrenal medulla（NAM）, to clarify the information of cell populations of the samples. We focused on exploring the gene expression profiles of endothelial cells and fibroblasts subclusters, and performed functional enrichment analysis based on Gene Ontology（GO） resources. CellChat was used to compare the cell-cell interactions networks of different clinical samples and predict significant signaling pathways in SDHD-CBT. Results:A total of 7 cell populations were profiled. The main subtypes of endothelial cells in SDHD-CBT are arterial and venous endothelial cells, and the main subtypes of fibroblasts are myofibroblasts and pericytes. Compared to NAM, SDHB-CBT and SDHB-ATPGL, cell communication involving endothelial cells and fibroblasts in SDHD-CBT is more abundant, with significant enrichment in pathways such as FGF, PTN, WNT, PROS, PERIOSTIN, and TGFb. Conclusion:Endothelial cells and fibroblasts in SDHD-CBT are heterogeneous and involved in important cellular interactionprocesses, in which the discovery of FGF，PTN，WNT，PROS，PERIOSTIN and TGFb signals may play an important role in the regulation of microenvironment of SDHD-CBT.