Pancreatic Ductal Adenocarcinoma Tumor Microenvironment Research Articles

Pancreatic Cancer and Venous Thromboembolism

Pancreatic ductal adenocarcinoma (PDAC) accounts for more than 90% of all pancreatic cancers and is the most fatal of all cancers. The treatment response from combination chemotherapies is far from satisfactory and surgery remains the mainstay of curative strategies. These challenges warrant identifying effective treatments for combating this deadly cancer. PDAC tumor progression is associated with the robust activation of the coagulation system. Notably, cancer-associated thrombosis (CAT) is a significant risk factor in PDAC. CAT is a concept whereby cancer cells promote thromboembolism, primarily venous thromboembolism (VTE). Of all cancer types, PDAC is associated with the highest risk of developing VTE. Hypoxia in a PDAC tumor microenvironment also elevates thrombotic risk. Direct oral anticoagulants (DOACs) or low-molecular-weight heparin (LMWH) are used only as thromboprophylaxis in PDAC. However, a precision medicine approach is recommended to determine the precise dose and duration of thromboprophylaxis in clinical setting.

Multiomics integration reveals NETosis heterogeneity and TLR2 as a prognostic biomarker in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant neoplasm characterized by a poor prognosis and limited therapeutic strategy. The PDAC tumor microenvironment presents a complex heterogeneity, where neutrophils emerge as the predominant constituents of the innate immune cell population. Leveraging the power of single-cell RNA-seq, spatial RNA-seq, and multi-omics approaches, we included both published datasets and our in-house patient cohorts, elucidating the inherent heterogeneity in the formation of neutrophil extracellular traps (NETs) and revealed the correlation between NETs and immune suppression. Meanwhile, we constructed a multi-omics prognostic model that suggested the patients exhibiting downregulated expression of NETs may have an unfavorable outcome. We also confirmed TLR2 as a potent prognosis factor and patients with low TLR2 expression had more effective T cells and an overall survival extension for 6 months. Targeting TLR2 might be a promising strategy to reverse immunosuppression and control tumor progression for an improved prognosis.

Dual-crosslinking gelatin-hyaluronic acid methacrylate based biomimetic PDAC desmoplastic niche enhances tumor-associated macrophages recruitment and M2-like polarization

The tumor microenvironment (TME) of pancreatic ductal adenocarcinoma (PDAC) is characterized by deposition of desmoplastic matrix (including collagen and hyaluronic acid). And the interactions between tumor-associated macrophages (TAMs) and tumor cells play a crucial role in progression of PDAC. Hence, the appropriate model of tumor cell-macrophage interaction within the unique PDAC TME is of significantly important. To this end, a 3D tumor niche based on dual-crosslinking gelatin methacrylate and hyaluronic acid methacrylate hydrogels was constructed to simulate the desmoplastic tumor matrix with matching compressive modulus and composition. The bionic 3D tumor niche creates an immunosuppressive microenvironment characterized by the downregulation of M1 markers and upregulation of M2 markers in TAMs. Mechanistically, RNA-seq analysis revealed that the PI3K-AKT signaling pathway might modulate the phenotypic balance and recruitment of macrophages through regulating SELE and VCAM-1. Furthermore, GO and GSEA revealed the biological process of leukocyte migration and the activation of cytokine-associated signaling were involved. Finally, the 3D tumor-macrophage niches with three different ratios were fabricated which displayed increased M2-like polarization and stemness. The utilization of the 3D tumor niche has the potential to provide a more accurate investigation of the interplay between PDAC tumor cells and macrophages within an in vivo setting.

Targeted Therapy for Highly Desmoplastic and Immunosuppressive Tumor Microenvironment of Pancreatic Ductal Adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy with a very poor prognosis. Despite advancements in treatment strategies, PDAC remains recalcitrant to therapies because patients are often diagnosed at an advanced stage. The advanced stage of PDAC is characterized by metastasis, which typically renders it unresectable by surgery or untreatable by chemotherapy. The tumor microenvironment (TME) of PDAC comprises highly proliferative myofibroblast-like cells and hosts the intense deposition of a extracellular matrix component that forms dense fibrous connective tissue, a process called the desmoplastic reaction. In desmoplastic TMEs, the incessant aberration of signaling pathways contributes to immunosuppression by suppressing antitumor immunity. This feature offers a protective barrier that impedes the targeted delivery of drugs. In addition, the efficacy of immunotherapy is compromised because of the immune cold TME of PDAC. Targeted therapy approaches towards stromal and immunosuppressive TMEs are challenging. In this review, we discuss cellular and non-cellular TME components that contain actionable targets for drug development. We also highlight findings from preclinical studies and provide updates about the efficacies of new investigational drugs in clinical trials.

Collagen Lattice Model, Populated with Heterogeneous Cancer-Associated Fibroblasts, Facilitates Advanced Reconstruction of Pancreatic Cancer Microenvironment.

Pancreatic ductal adenocarcinoma (PDAC) is a solid-tumor malignancy. To enhance the treatment landscape of PDAC, a 3D model optimized for rigorous drug screening is essential. Within the PDAC tumor microenvironment, a dense stroma comprising a large extracellular matrix and cancer-associated fibroblasts (CAFs) is well-known for its vital role in modulating tumor growth, cellular heterogeneity, bidirectional paracrine signaling, and chemoresistance. In this study, we employed a fibroblast-populated collagen lattice (FPCL) modeling approach that has the ability to replicate fibroblast contractility in the collagenous matrix to build dense stroma. This FPCL model allows CAF differentiation by facilitating multifaceted cell-cell interactions between cancer cells and CAFs, with the differentiation further influenced by mechanical forces and hypoxia carried within the 3D structure. Our FPCL models displayed hallmark features, including ductal gland structures and differentiated CAFs with spindle shapes. Through morphological explorations alongside in-depth transcriptomic and metabolomic profiling, we identified substantial molecular shifts from the nascent to mature model stages and potential metabolic biomarkers, such as proline. The initial pharmacological assays highlighted the effectiveness of our FPCL model in screening for improved therapeutic strategies. In conclusion, our PDAC modeling platform mirrors complex tumor microenvironmental dynamics and offers an unparalleled perspective for therapeutic exploration.

Abstract 1602: Leukemia inhibitory factor (LIF)-factor XIIIA mediated macrophage-stromal crosstalk in pancreatic cancer

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy marked by a highly immunosuppressive tumor microenvironment (TME). Macrophages are known to promote immunosuppression and exhibit a profibrotic transcriptional profile with potential involvement in extracellular matrix (ECM) remodeling. Previously, we identified hyperactivation of cancer cell intrinsic cyclic AMP response element binding protein 1 (CREB) regulates leukemia inhibitory factor (LIF) to mediate macrophage infiltration and polarization within the TME of PDAC. Subsequently, we observed that disrupting LIF-LIF receptor (LIFR) signaling therapeutically not only diminishes the infiltration of tumor-associated macrophages (TAMs) but also results in a decrease in ECM deposition. This study delves into the potential regulatory pathway through which LIF induces remodeling of the ECM within the PDAC TME. Methods: We targeted LIF-induced macrophage-stromal crosstalk using the LIFR antagonist (EC359) in an orthotopically tumor implanted LSL-KrasG12D/+; Trp53 R172H/+; Pdx1Cre/+ (KPC) mice model of PDAC. Sirius red staining in tumor sections was performed to assess ECM (collagen) deposition. Moreover, we performed RNA transcriptomics-based analysis of recombinant (rLIF) induced bone marrow derived macrophages harvested from syngeneic C57BL/6 mice. The Cancer Genome Atlas (TCGA) pancreatic cancer (PAAD) data set along with single-cell RNA sequencing (scRNA seq) were employed to assess the expression of major downstream targets of LIF. To validate the RNA-seq results, we conducted immunohistochemical analysis (IHC) on mouse PDAC tissue sections and quantitative polymerase (qPCR) analysis on RAW 264 macrophage cell line treated with rLIF or KPC CREBWT PDAC tumor cells conditioned media. Results: We observed a drastic decrease in both TAM infiltration and, of note, ECM deposition in orthotopically implanted KPC pancreas tumor mice tissue treated with EC359 as compared to vehicle. Mechanistically, our RNA-seq analysis unveiled a significant upregulation of Factor XIIIA (FXIIIa), a major downstream target of LIF. Notably, TCGA data revealed that FXIIIa mRNA expression is upregulated across PDAC tumors marked by poor survival outcomes. Moreover, scRNA seq and IHC established that TAMs highly express FXIIIa in the PDAC TME. In exploring the effect of LIF-LIFR signaling in the ECM, mouse RAW 264.7 macrophage lines incubated in high LIF conditions confirmed transcriptional upregulation of ECM-associated proteins such as FXIIIa as well as fibronectin. Conclusion: Our investigation provides valuable insights into the possible mechanism by which LIF triggers ECM remodeling, thereby contributing to the desmoplastic stroma. Significantly, our findings propose that LIF-regulated FXIIIa signaling in macrophages serves as a plausible mediator of the LIF-induced ECM remodeling in PDAC. Citation Format: Nishah Jaferi, Siddharth Mehra, Varun Krishnamoorthy, Sudhakar Jinka, Anna Bianchi, Vanessa T. Garrido, Luis A. Nivelo, Ban Yuguang, Nagaraj S. Nagathihalli. Leukemia inhibitory factor (LIF)-factor XIIIA mediated macrophage-stromal crosstalk in pancreatic 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 1602.

Abstract 1577: Cancer associated fibroblast - tumor cell crosstalk enhances epithelial to mesenchymal transition and promotes a classical to basal switch in human pancreatic ductal adenocarcinoma

Abstract Introduction: Cancer associated fibroblasts (CAF) drive a complex tumor microenvironment (TME) in pancreatic ductal adenocarcinoma (PDAC) through incompletely understood interactions. Two major CAF subtypes, myofibroblastic (myCAF) and inflammatory (iCAF), dominate the tumor landscape and have been defined by gene expression profiles. There is significant plasticity between subtypes and alterations in CAF behavior likely drive changes in tumorigenicity and immune evasion. Additionally, PDAC tumor cells usually present with a predominant classical or basal phenotype that is associated with clinical outcomes. We hypothesized that CAF phenotype impacts tumor cell gene expression and alters the clinically-relevant tumor subtyping. Methods: We interrogated cellular crosstalk in the PDAC TME using a novel three-dimensional, patient-matched coculture system of patient-derived organoids (PDO) and CAFs, established from 12 patients undergoing surgical resection. Molecular characterization included bulk RNA sequencing, proteome profiling (107 factor), flow cytometry, multiplex RNA Scope, imaging mass cytometry (IMC), and RT-qPCR. Results: PDO gene expression analysis from bulk RNAseq demonstrated CAF coculture induced phenotypic shifts in the Moffitt subtype from a classical to a basal phenotype. Further, CAF coculture enhanced epithelial to mesenchymal transition (EMT) across all patients, even those with a baseline basal phenotype. We hypothesized this could be due to both cell-cell crosstalk and secreted factors. We therefore treated PDO with CAF-conditioned media (CM) and demonstrated that CM is sufficient to drive the observed classical-to-basal shift by RT-qPCR. Secretome analysis of CM derived from 3 CAF lines identified HGF, FGF19, and IL-8 as factors contributing to this transcriptional change. Next, we used spatial - omics (transcriptomics and proteomics) to examine the validity of these findings in source patient tissue. Using RNA Scope, we discovered distinct tumor neighborhoods expressing basal mRNAs KRT17 and KRT6a surrounded by CAFs compared to those expressing classical genes TFF1 and GATA6. We then used IMC to further explore CAF subtypes in patient tumors and found FAP+ myCAF regions corresponded to basal tumor regions, while CXCL12+ iCAFs were found in classical regions. Conclusions: PDAC tumor biology is likely driven by interactions between cancer cells and CAFs. Potential mediators of these interactions include both cell-cell contact and secreted factors. We introduce a novel approach combining in vitro coculture with tissue-based assays, demonstrating that modern culture techniques preserve cell type heterogeneity and plasticity. Together, these data demonstrate that a CAF-rich TME drives tumor cell plasticity not only towards EMT but also a more basal disease phenotype. Citation Format: Samantha Guinn, Brayan Perez, Jignasha Patel, Jae Lee, Daniel Zabransky, Won Ho, Elana J. Fertig, Emma Kartalia, Joseph Tandurella, Richard Burkhart, Jacquelyn W. Zimmerman, Elizabeth Jaffee. Cancer associated fibroblast - tumor cell crosstalk enhances epithelial to mesenchymal transition and promotes a classical to basal switch in human pancreatic ductal adenocarcinoma [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 1577.

Abstract 1582: Cabozantinib changes the tumor microenvironment to increase the efficacy of immunotherapy in refractory metastatic pancreatic ductal adenocarcinoma

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies. Tumors evade immune surveillance by expressing PD-L1 that interacts with the T cell protein PD-1, subsequently inhibiting CD8+ cytotoxic T lymphocyte proliferation and effector function. A plausible reason for this observation may be that other, redundant, immune suppressive mechanisms are at play. Our research team has shown that elevated infiltration of polymorphonuclear (PMN)-MDSCs within the PDAC tumor microenvironment (TME) inhibit T cell effector function, regardless of PD-1/PD-L1 inhibition (Holokai et al., 2020). Objective: A Phase II clinical trial was developed to identify the potential therapeutic benefit of combinatorial anit-PD-L1/PD-1 and cabozantinib (cabo) treatment in therapy-resistant (refractory and metastatic) PDAC patients. Methods: NanoString CosMx™ spatial molecular transcriptomic imaging (CosMx™ SMI) was performed using FFPE sections collected from a liver or lung metastatic target lesions at visit 1 (pretreatment) and visit 2 (9 weeks on combinatorial treatment) from individual patients. FFPE sections were prepared from the same target lesion, and fields of view were chosen on the H&E in consultation with GI pathologist. Seurat V 4.0 was used for the analysis and visualization by spatial mapping of each FOV showing identified cell population indicated by color coding in visit 1 and visit 2 within the same patient. Multiplex immunofluorescence (MxIF) of patient FFPE tissues and single cell RNA sequencing (scRNAseq) of PDAC organoids (PDOs) generated from the core biopsies collected at visit 1 and matched visit 2 from each patient were used to validate the CosMx™ SMI data. Results: A uniform manifold approximation and projection showed loss of tumor cell populations within the PDAC TME in response to combinatorial treatment compared to pretreatment visit 1. Comparison between spatial maps of visit 1 to visit 2 demonstrated a shift in cell populations within defined NICHES (local cellular TME) whereby there was 1) a loss of tumor cell populations, 2) increase in CTL infiltration, 3) increase in endothelial cells, 4) decrease immunosuppressive MDSCs, 5) decrease in antigen presenting CAFs, and 6) change in myCAFs to an inflammatory CAF phenotype. Within the iCAF population IL-6, CXCL1, LIFR, ACTA2 and FAK were expressed; correlating with an increase in CD8 perforin and granzyme B positive cells in response to cabo and checkpoint inhibition. MxIF, spectral flow cytometry and scRNAseq analyses of the matched in vitro PDO model showed tumor cell death that correlated with decreased MDSC viability, increased CTL proliferation and a shift in CAF phenotypes. Conclusion: These findings suggest that cabo induces a TME conducive to increased response to immunotherapy in PDAC patients with refractory metastatic disease. Citation Format: Jayati Chakrabarti, Pritha Adhikary, Jiang Wang, Davendra Sohal, Syed A. Ahmad, Junaid Arshad, Aaron J. Scott, Rachna T. Shroff, Yana Zavros. Cabozantinib changes the tumor microenvironment to increase the efficacy of immunotherapy in refractory metastatic pancreatic ductal adenocarcinoma [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 1582.

Abstract 1596: Disrupting local immunosuppression by combined myCAF/myeloid targeting in pancreatic cancer

Abstract Immunotherapy has revolutionized clinical care for many patients, but some cancers, such as pancreatic ductal adenocarcinoma (PDAC) remain stubbornly resistant. Local immunosuppression (LIS) is one of the striking hallmarks of PDAC due to the combined effects of multiple different immunosuppressive cell types in the tumor microenvironment (TME). There is great need for an increased understanding of the cellular crosstalk within tumors to understand how stromal cells coordinate in their suppression of immune responses. Oncogenic KRAS activation in tumor cells promotes the invasion and proliferation of tumor-supporting stromal cells, while excluding cancer-targeted cytotoxic T cells. Prior attempts to reverse LIS in PDAC by targeting individual stromal cell populations have been unsuccessful, alluding to the contributions of multiple distinct cell types. Here we examine the interactions of cancer-associated fibroblasts (CAFs) and myeloid-derived suppressor cells (MDSCs) and how they coordinate to suppress immune responses in the PDAC TME. We interrogate PDAC stromal cell biology by using targeted therapies to perturb various cell populations both in vivo using genetically engineered mouse models, and ex vivo using PDAC tumor explants. Explants are short-term slice cultures that enable experimental study of intact tumor sections with a full complement of cell types. 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 the 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 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 significantly elevates cytotoxic T cell numbers 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, Dafydd Thomas, Lukas Vlahos, Alvaro Curiel-Garcia, Amanda R. Decker-Farrell, Tanner C. Dalton, Stephen A. Sastra, Carmine F. Palermo, Andrea Califano, Kenneth P. Olive. Disrupting local immunosuppression by combined myCAF/myeloid targeting in pancreatic 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 1596.

Abstract 5893: Crosstalk between sensory innervation and pancreatic ductal adenocarcinoma

Abstract In recent years, a growing body of research has illuminated the integral role of the nervous system in the initiation and progression of cancer, giving rise to the establishment of an emergent field known as cancer neuroscience. Pancreatic ductal adenocarcinoma (PDAC), constituting 90% of pancreatic cancers, manifests as a highly malignant solid tumor characterized by insidious onset, strong invasiveness, and a notable propensity for recurrence or metastasis. Consequently, the 5-year survival rate for PDAC remained dismally low at approximately 10% in 2021. Notably, PDAC is distinguished by perineural invasion (PNI), a phenomenon linked to postoperative recurrence and metastasis. A thorough exploration of the interplay between peripheral innervation and PDAC holds promise for identifying novel targets and therapies to enhance outcomes in PDAC. This study unveils a correlation between PDAC patients exhibiting high calcitonin gene-related peptide-positive (CGRP+) sensory innervation in the tumor microenvironment (TME) and diminished overall survival (OS) and disease-free survival (DFS) compared to those with lower CGRP+ nociceptive innervation. Concurrently, heightened CGRP+ sensory innervation corresponds to increased cancer pain, as assessed by Visual Analog Scale (VAS) scores. Further analysis reveals a negative association between CGRP+ nociceptive nerves and lymphatic metastasis, as well as tumor size in PDAC patients. In a murine PDAC model, the genetic or chemical ablation of CGRP+ sensory neurons significantly impedes disease progression. Additionally, sensory neuron ablation attenuates cancer-induced vesical pain and enhances the locomotor function of mice, suggesting an improvement in overall quality of life. Mechanically, within the TME of PDAC, the secretion of neuropeptides substance P (SP) and CGRP from sensory neurons is elevated, with CGRP exhibiting a more pronounced increase. Furthermore, the expression of the CGRP receptor—receptor activity modifying protein 1 (RAMP1)—surpasses that of the SP receptor in the TME. Subsequent blockade of the CGRP pathway using the RAMP1 antagonist Rimegepant significantly suppresses PDAC progression and alleviates cancer pain, accompanied by improved locomotor function. In summary, sensory innervation actively participates in the progression of PDAC through the secretion of CGRP. Consequently, the inhibition of the CGRP pathway emerges as a potential therapeutic strategy for both PDAC and cancer-induced pain. Citation Format: Kaiyuan Wang, Bo Ni, Xiuchao Wang, Jihui Hao. Crosstalk between sensory innervation and pancreatic ductal adenocarcinoma [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 5893.

Abstract 1579: Macrophage infiltration and polarization in pancreatic ductal adenocarcinoma following stereotactic body radiation therapy

Abstract Introduction: Stereotactic body radiation therapy (SBRT) has emerged as a promising treatment modality for pancreatic ductal adenocarcinoma (PDAC) due to its precise delivery and potential to improve local control. Beyond its direct impact on tumor cells, accumulating evidence suggests that SBRT may also modulate the tumor microenvironment (TME), influencing immune responses. Macrophages play a crucial role in the TME with their polarization into pro-inflammatory (M1) or pro-tumoral (M2) phenotypes significantly impacting cancer progression. Studying the TME and developing immune therapies may be helpful for metastatic PDAC, which currently only has non-curative treatment. The TME, in particular the polarization of macrophages, has not been well studied following radiation treatment. Therefore, our work aims to study how SBRT affects the infiltration and polarization of macrophages in the PDAC TME in a time-dependent manner. Methods: To establish and study PDAC C57BL/6J mice were orthotopically injected with a luciferase-labeled KPC tumor cell line. SBRT was administered to tumor-bearing mice following a schedule of 10Gy radiation per fraction in total of 5 fractions on days 10-14 post tumor implantation. Mice were euthanized on day 1, 3 and 7 after irradiation. Tumor tissues were collected for immunohistochemistry (IHC) staining and flow cytometry with antibodies targeting CD68, CD11b, CD86 (M1 marker), and CD206 (M2 marker). Images were analyzed and quantified using ImageJ and GraphPad Prism. Results: Via the use of IHC staining, we found no significant difference in the number of cells stained with the CD68 antibody (macrophage marker) when compared throughout groups. Additionally, we found no significant difference in the number of macrophages stained with the M2 marker. However, we did observe a significant increase in the number of macrophages stained with the M1 marker in the group receiving SBRT. Through flow cytometry of the tumor tissues we observed an increasing trend, as time passed, in the number of macrophages expressing the M1 marker. The same trend was observed in macrophages expressing both the M1 and M2 markers. However, a change in the total number of macrophages or those expressing only the M2 marker was not observed. Conclusions: SBRT does not affect the total number of infiltrated macrophages in the TME or the amount of M2 macrophages. However, we did observe that the percentage of M1 macrophage increases significantly as time passes after SBRT. We theorize that the increase in M1 macrophages may be due to an M2 to M1 transition in the M2 population. Our study provides preliminary rationale to use macrophage-targeted immune therapy to potentiate the efficacy of SBRT for PDAC treatment, though we understand that further follow-up studies with a larger sample size and longer time course are required to obtain significant and meaningful results. Citation Format: Emil D. Gonzalez Marrero, Liang Wang, Benjamin R. Schrank, Albert C. Koong. Macrophage infiltration and polarization in pancreatic ductal adenocarcinoma following stereotactic body radiation therapy [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 1579.

Abstract 233: Cabozantinib changes the landscape of the pancreatic tumor microenvironment and improves the efficacy of pembrolizumab

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy with an approximate 10% 5-year survival rate. PDAC patients rarely benefit from treatment with immune checkpoint inhibitors (ICIs) due to a tumor microenvironment (TME) associated with constrained effector T cell infiltration, and the presence of a suppressive myeloid cell population. Objective: To identify a combinatorial therapeutic strategy targeting the myeloid derived suppressor cells (MDSCs) and cancer associated fibroblasts (CAFs) within the PDAC TME to increase the efficacy of ICIs. Methods: C57BL/6 mice were orthotopically transplanted with syngeneic 7940b PDAC cells derived from transgenic KPC mouse. 7 days post-transplantation mice were treated with InVivoPlus anti-mouse PD-1 (CD279), cabozantinib (cabo, tyrosine kinase inhibitor) or a combination of drugs for a further 7 days. NanoString CosMx™ spatial molecular imaging (CosMx™ SMI) was performed using FFPE sections collected from core biopsies and surgically resected tissues. PDAC patient derived organoids (PDOs) were generated from the core biopsies or surgical biospecimens. Cancer-associated fibroblasts (CAFs) were isolated from the organoid cultures. Autologous immune cells (IMM) were cultured from patient peripheral blood mononuclear cells. PDO/CAF/IMM co-cultures were used to predict the patient response to cabo plus pembrolizumab combinatorial therapy. Results: Mice treated with a combination of anti-PD-1 and cabo exhibited significant EpCAM/PD-L1-expressing cell death that correlated with increased CTL proliferation and decreased PMN-MDSC death. Mice that were depleted of CD8+ CTLs using anti-CD8 antibody in vivo did not exhibit tumor cell death in response to combinatorial therapy and thus supporting the role of CTLs in driving effective immunotherapy in combination with cabozantinib treatment. Unexpectedly, a significant decrease in extracellular matrix protein fibronectin was observed. Human PDOs orthotopically transplanted into NSG mice developed pathology consistent with human PDAC with strong expression of CD44v9, IL6, vimentin and αSMA. Using PDAC PDO/CAFs/IMM co-cultures, pembro significantly induced tumor cell death in the presence CTLs, MDSCs significantly inhibited this response. Depletion of MDSCs using cabo in the PDO/CAFs/IMM co-cultures resulted in a significant increase in tumor cell death with a concomitant increase in CTL proliferation. Compared to core biopsies, surgical biospecimens collected post-standard of-care demonstrated a shift in cell populations within defined NICHES (local cellular TME) whereby there was 1) increases MDSCs, 2) change in CAFs phenotype and 3) increased expression of CD44v9. Conclusions: Cabozantinib depletes the PDAC TME of MDCSs leading to sensitization to ICI and tumor cell death and thus offers a potential combinatorial therapeutic approach. Citation Format: Pritha Adhikary, Jayati Chakrabarti, Meenu Priya Resmi, Jiang Wang, Davendra Sohal, Rachna T. Shroff, Syed A. Ahmad, Yana Zavros. Cabozantinib changes the landscape of the pancreatic tumor microenvironment and improves the efficacy of pembrolizumab [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 233.

Abstract 1597: CD144+cancer-associated fibroblasts drive the malignancy of pancreatic cancer via stimulating inflammatory paracrine

Abstract Purpose: Cancer-associated fibroblasts (CAFs) are highly heterogeneous in pancreatic ductal adenocarcinoma (PDAC). We previously reported that CAFs can acquire an endothelial phenotype under stress. Thus, we hypothesized that there are CAFs highly expressing endothelial markers and substantiated a novel subtype of CAFs promoting tumor progression. Experimental design: We performed single-cell RNA sequencing to identify the existence of CD144+CAFs. The prospective and retrospective analysis were combined to figure out the correlation between CD144+CAFs proportion and clinical outcome. The proliferation and invasion assay of cell lines, organoids and pancreatic cancer xenograft model were used to detect the effect of CD144+CAFs on tumor progression. Cytokine array assay, RNA-sequencing, IP-mass spectrum, Ch-IP and luciferase analysis were conducted to elucidate the underlying mechanism. siRNA delivery nanosystem was designed and administrated to precisely target CD144+CAFs in vivo. Results: CD144+CAFs were present in tumor microenvironment of PDAC and breast cancer and patients with a higher CD144+CAFs proportion have worse prognosis in PDAC. CD144+CAFs can promote the metastasis of PDAC through enhancing epithelial-mesenchymal transition. CD144-β-catenin-STAT3 signaling axis was activated and downstream inflammatory secreted cytokines were transcriptionally upregulated to maintain the functions and phenotype of CD144+CAFs. A novel CAF-targeting siRNA delivery nanosystem, loading FAPα and siCDH5, was designed and administrated to precisely target CD144+CAFs, which substantially inhibited the protumoral roles in vivo. Conclusion: CD144+CAFs can promote the growth and metastasis of PDAC by activating CD144-β-catenin-STAT3 signaling axis and stimulating inflammatory secretion. CAF-targeting siRNA delivery nanosystem can inhibit tumor progression by precisely targeting CD144+CAFs. Citation Format: Xugang Sun, Jun Yu, Tiansuo Zhao, Jihui Hao. CD144+cancer-associated fibroblasts drive the malignancy of pancreatic cancer via stimulating inflammatory paracrine [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 1597.

Abstract 445: Determining the molecular and biologic effects of HER3 and IDH1 antagonism on liver endothelium-PDAC crosstalk

Abstract INTRODUCTION: Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy due to the lack of early diagnosis and limited response to treatments. Austere and nutrient-deprived conditions typically present in the PDAC tumor microenvironment (TME) induce chemotherapy resistance. Therefore, novel therapeutic strategies are needed. We have previously demonstrated the primary tumor expresses IDH1 which supports the pro-survival oxidative phosphorylation (OXPHOS) metabolism, and has been successfully targeted by ivosidenib, an IDH1 inhibitor, in preclinical studies. Meanwhile, endothelial cells (ECs) from the liver, the most common site of PDAC metastases, secrete soluble factors in the conditioned medium (CM) that activate HER3, a receptor tyrosine kinase, involved in cell proliferation and metabolism. OBJECTIVES: We sought to (1) uncover the mechanisms involved in driving the metabolic differences between primary and metastatic tumors through the utilization of ECs from the liver (2) conduct metabolic analyses to determine metabolic effects of HER3 activation, and (3) examine potential synergism of combination therapy against HER3 and IDH1 in primary and metastatic niches. METHODS: The effect of CM on PDAC cell growth was determined by PICO Green Assay. The effects of ECs HER3/IDH1 inhibitions on cellular metabolism were measured by multiple metabolic assays including Seahorse, CellTiter-Glo, lactate ELISA, and TMRE assays. HER3-specific antibody Seribantumab, HER3 inhibitor Sapitanib, and IDH1 inhibitor ivosidenib were used to block HER3 and/or IDH1. Moreover. A cell viability-based synergy study was performed to assess the effects of HER3-IDH1 combination. Effects of HER3 and IDH1 inhibitions on PDAC tumor growth and mouse survival in vivo were determined in syngeneic, orthotopic models with PDAC primary tumors and liver metastases. RESULTS: CM from liver ECs significantly increased cell growth in PDAC cells in vitro and increased glycolytic tropism in multiple HER3 positive PDAC cell lines measured by metabolic assays mentioned above. HER3 antibody and HER3 inhibitor both increased oxidative consumption rate (OCR), an indirect measure of OXPHOS, and decreased extracellular acidification rate (ECAR), a measure of glycolysis measured by Seahorse. Combination therapy utilizing HER3 and IDH1 inhibitors revealed synergy. In our in vivo tumor model, mice treated with combination therapy had significantly longer overall survival than those given either monotherapy or no treatment. CONCLUSIONS: Our results demonstrated a paracrine role of liver ECs in promoting cell growth via activating HER3 in PDAC cells as well as reprograming cellular metabolism from OXPHOS towards glycolysis. Identification of the metabolic shift that takes place in metastatic PDAC to the liver due to HER3 activation gives way for the development of a potentially lethal drug combination. Citation Format: Christina S. Boutros, Alexander W. Loftus, Moeez Rathore, Mehrdad Zarei, Kimberly Curry, Jordan M. Winter, Rui Wang. Determining the molecular and biologic effects of HER3 and IDH1 antagonism on liver endothelium-PDAC crosstalk [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 445.

Abstract 6631: Aging influences the pancreatic ductal adenocarcinoma tumor immune microenvironment to promote features of immunosuppression

Abstract Advancing age is the strongest independent risk factor for the development of pancreatic ductal adenocarcinoma (PDAC) and a negative prognostic factor. PDACs are typically immunologically “cold” tumors and do not often respond to currently approved immunotherapy treatment approaches. How aging may alter non-malignant cells, such as fibroblasts and immune cell populations, in the PDAC tumor microenvironment (TME) to decrease anti-tumor immune responses is not understood. We identified that aged microenvironments significantly alter the growth and progression of PDAC tumors. Orthotopic KPC and Panc02 mouse PDAC cell line injections into the pancreata of aged (>64-week-old) compared to young (6-8-week-old) C57BL/6 mice result in more rapid tumor growth and increased frequency of liver metastases in vivo. Tumors from aged mice have high expression of the TGFβ family member GDF-15 and hyperactivation of AKT signaling driven by the release of secreted factors from aged pancreatic fibroblasts. We found that in aged microenvironments there is a marked reduction in the number of CD8+ T cells and an increase in FoxP3+ regulatory T cells in primary orthotopic pancreatic tumors using the KPC and Panc02 models. In addition, we performed portal vein injections to establish liver metastases to study the differences in immune cell infiltration in metastases from young vs. aged microenvironments. Aged mice form more and larger liver metastases compared to young mice, and metastatic lesions in aged mice have decreased CD8+ T cell infiltration when compared to young mice. Since tumors in aged microenvironments have increased AKT activation compared to young microenvironments, we next tested if AKT signaling was sufficient to alter immune cell infiltration in PDAC tumors. In young mice, treatment with recombinant GDF-15, which activates AKT signaling, reduced CD8+ T cell infiltration into tumors. Conversely, in KPC tumors grown in aged mice treated with the AKT inhibitor MK-2206, there was a trend toward increased CD8+ T cell infiltration and a significant reduction in immunosuppressive FoxP3+ Tregs. Together, these data highlight age-dependent differences in the immune infiltration in PDAC tumors. They suggest that activation of AKT signaling can drive features of immunosuppression in PDAC, providing the rationale for targeting AKT signaling to improve antitumor immune responses in PDAC. Citation Format: Emma Kartalia, James M. Leatherman, Jae W. Lee, Elizabeth M. Jaffee, Ashani T. Weeraratna, Daniel J. Zabransky. Aging influences the pancreatic ductal adenocarcinoma tumor immune microenvironment to promote features of immunosuppression [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 6631.

Abstract 1587: Multimodal spatial transcriptomics uncover distinct tumor microenvironment states and cell-cell communication networks in molecular pancreatic cancer subtypes

Abstract The tumor microenvironment (TME) presents a complex ecosystem comprising a diversity of immune and stromal cell populations that influence tumor progression, drug delivery and therapy outcome. High levels of inter- and intra-tumor heterogeneity in TME state are driven by molecular tumor phenotypes. Pancreatic ductal adenocarcinoma (PDAC), one of the most lethal cancer types, displays a high genetic heterogeneity along with an immunosuppressive TME. However, it remains largely elusive how distinct TME states are mechanistically influenced, and which molecular processes dictate the emergence of different modes of immunosuppression within the TME of molecular PDAC subtypes.Here, we performed a systematic analysis of functional associations between the major molecular PDAC subtypes, the classical and mesenchymal subtype, and their TME states. We describe the TME composition and complex cell-cell communication networks within PDAC subtypes using a multimodal integration of spatial transcriptomics (ST) with complementary approaches, such as scRNA-seq, MS-based Secretomics and multiplexed histocytometry. We generated ST data sets (Visium) of a tumor cohort derived from a Kras-driven PDAC mouse model. To analyze TME composition as well as spatial niches and cell type communities, we computationally enhanced the spot-resolution of ST datasets, followed by cell type deconvolution and cell-cell communication analysis to identify subtype-specific TME communities and communication networks.To this end, we generated a large resource of PDAC mouse models which represent molecular subtypes of the disease and mimic the heterogeneity of TME states found in human PDAC cohorts. This analysis revealed that a set of subtype-specific secreted factors shape the immunosuppressive PDAC TME via direct and indirect communication networks with immunosuppressive myeloid and T cells in molecular PDAC subtypes. Multimodal ST analysis delineated spatial subtype-specific TME communities as well as spatial communication patterns. We functionally investigate the tumor cell intrinsic regulation of the identified subtype-specific secreted factors, providing potential therapeutic vulnerabilities for more effective combinatorial subtype-specific therapies including immunotherapeutic approaches. Citation Format: Stefanie Baerthel, Chiara Falcomatà, Vanessa Goelling, Daniele Lucarelli, Rushin Gindra, Constantin Schmitt, Jonathan Swietlik, Felix Meissner, Marc Schmidt-Supprian, Dieter Saur. Multimodal spatial transcriptomics uncover distinct tumor microenvironment states and cell-cell communication networks in molecular pancreatic cancer subtypes [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 1587.

Abstract 1395: Unraveling the interplay between tumor heterogeneity and microenvironment in pancreatic ductal adenocarcinoma evolution and its clinical implications

Abstract Intratumoral heterogeneity (ITH) and tumor microenvironment (TME) of pancreatic ductal adenocarcinoma (PDAC) play important roles in tumor evolution and patient outcomes. However, the precise characterization of diverse cell populations and their crosstalk associated with PDAC progression and metastasis is still challenging. We performed single-cell RNA sequencing of primary PDAC samples with and without paired liver metastasis samples to understand the interplay between ITH and TME in the PDAC evolution and its clinical associations. We discovered that even a small proportion (~30%) of basal-like ductal cells in primary PDAC was associated with poor chemotherapy response and patient survival and that epithelial-mesenchymal transition programs were largely subtype specific. The clonal homogeneity significantly increased with more prevalent and pronounced copy number gains of oncogenes, such as KRAS and ETV1, and losses of tumor suppressor genes, such as SMAD2 and MAP2K4, along PDAC progression. Diverse immune cell populations, including naive SELLhi regulatory T cells (Tregs) and activated TIGIThi Tregs, contributed to shaping immunosuppressive TMEs of PDAC through cellular interactions with malignant ductal cells. The proportion of basal-like ductal cells negatively correlated with that of immunoreactive cell populations, such as cytotoxic T cells, but positively correlated with that of immunosuppressive cell populations, such as Tregs. Overall, our study provides a valuable resource for better understanding the roles of ITH and TME in PDAC evolution and their clinical relevance in the treatment of PDAC. Citation Format: Hyemin Kim, Hyong-oh Jeong, Se-Hoon Lee, Kwang Hyuck Lee, Kyu Taek Lee, Jong Kyun Lee, Min Woo Lee, Semin Lee, Joo Kyung Park. Unraveling the interplay between tumor heterogeneity and microenvironment in pancreatic ductal adenocarcinoma evolution and its clinical implications [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 1395.

Abstract 1159: Machine learning integrating spatial omics uncovers humoral immunity patterns in intratumoral tertiary lymphoid structures in pancreatic cancer pathologic responders

Abstract Background: In pancreatic ductal adenocarcinoma (PDAC), rare long-term survivors correlate with high intratumoral tertiary lymphoid structure (TLS) density. This finding prompted our investigation of clinically viable strategies to induce TLS in patients with immune-excluded tumors. We previously reported the induction of intratumoral TLS following administration of a neoadjuvant GM-CSF-secreting allogeneic vaccine (GVAX) to PDAC patients (NCT00727441). However, no clinical benefit was observed, likely owing to immune tolerance mechanisms governing the PDAC tumor microenvironment (TME). We previously observed upregulation of both the PD-1 and 4-1BB pathways with GVAX, and thus in a subsequent neoadjuvant trial combined GVAX with PD-1 blockade and 4-1BB agonism (NCT02451982) which was associated with pathologic responses. We hypothesized this combination strategy induced TLS of higher maturity and anti-tumor activity compared to GVAX alone. Methods: To explore how this therapeutic strategy affected TLS morphology and intercellular crosstalk, we leveraged the Visium spatial transcriptomics platform and a 35-marker customized TLS panel for imaging mass cytometry. We generated cellular and molecular maps of the TME after neoadjuvant treatment in 26 PDAC patients (GVAX n=19, GVAX+aPD1 n=2, GVAX+aPD1+a41BB n=5). To compare TLS maturation in parallel with secondary lymphoid organ-mediated tumor immunity, we also profiled tumor-adjacent lymph nodes. We applied unsupervised learning with non-negative matrix factorization (NMF) and trained AI-enabled image classification models to characterize cellular states within tissue structures of interest. Results: We identified spatial gene expression NMF patterns in PDAC TLS spanning across distinct morphologies and neoadjuvant treatment arms. Intratumoral TLS after GVAX were found to propagate activated B cells expressing immunoglobulins that infiltrated into malignant cellular niches. TLS NMF patterns were also associated with autoimmune disease signatures, such as diabetes, in a subset of patients. We scored TLS using tumor-draining lymph nodes as a reference and found increased maturation of TLS after PD-1 blockade, while addition of 4-1BB agonism significantly boosted the cytotoxic NK/T cell compartment compared to GVAX alone. Conclusions: We present machine learning approaches for spatial multi-omics analysis to characterize the TLS-enriched TME. We mined genome-wide spatial TLS gene expression patterns elucidating the spatial dynamics of humoral immunity of rare immunotherapy pathologic responders in PDAC. Altogether our findings shed light on the plasticity of TLS in neoadjuvant immunotherapy and suggest future immunotherapy approaches should target both humoral and cytotoxic NK/T cell compartments to augment responses in solid tumors. Citation Format: Dimitrios N. Sidiropoulos, Sarah M. Shin, Alexander Girgis, Daniel H. Shu, Janelle Montagne, Atul Deshpande, Jeanette A. Johnson, Lucie Dequiedt, Victoria Jacobs, Aleksandra Ogurtsova, Guanglan Mo, Xuan Yuan, Genevieve Stein-O’Brien, Mark Yarchoan, Qingfeng Zhu, Ashley Kiemen, Elizabeth M. Jaffee, Lei Zheng, Won Jin Ho, Robert Anders, Elana J. Fertig, Luciane T. Kagohara. Machine learning integrating spatial omics uncovers humoral immunity patterns in intratumoral tertiary lymphoid structures in pancreatic cancer pathologic responders [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 1159.

Abstract 6674: Fungi utilizes exocytosis pathway to facilitate the release of DAMPs from pancreatic cancer cells

Abstract Recent studies overwhelmingly show that microbiome is pervasive to tumor and play key role in immunotherapy response and reprograming tumor immune microenvironment (TIME). However, it remains unknown how microbiome facilitates the host-immune cell crosstalk and promote tumorigenesis. Our recent study in pancreatic ductal adenocarcinoma (PDAC) show that intratumor fungal microbiome facilitate the release of a damage associated molecular pattern (DAMP) molecule IL-33 from cancer cells. The secreted IL33 from cancer cells in turns recruits ILC2 and TH2 cells which promotes PDAC tumorigenesis. However, the mechanism of fungal mediated IL-33 release from PDAC cells remains unknown. Our follow up studies using high throughput integrated proteomic profiling and immunoprecipitation revealed a group of exocyst complex proteins interacting with IL-33 in the presence of fungus. The exocyst complex consists of eight sub-unit proteins that tethers the secretory vesicles to the plasma membrane and implicated in cellular exocytosis. We found EXOC6B a component of exocyst complex, modulates IL-33 release via exocytosis pathway from the PDAC cells. Genetic depletion of EXOC6B resulted in shunted IL-33 release and significantly abrogated PDAC tumor progression. Mechanistically, we found that mycobiome activates a non-canonical TLR2-CARD9 pathway, thereby driving IL-33 nucleocytoplasmic transport and exocytosis. This study identifies a unique mechanism of EXOC6B mediated release of IL-33 that expands our knowledge on how host-mycobiome interaction shapes PDAC tumor microenvironment by intricate molecular mechanism. Our study identifies EXOC6B as a new therapeutics target involved in the mycobiome driven IL-33 secretion in pancreatic cancer. Citation Format: Aftab Alam, Shyamananda Singh Mayengbam, Sharon Senchanthisai, Bektas Irmak, Prasenjit Dey. Fungi utilizes exocytosis pathway to facilitate the release of DAMPs from pancreatic cancer 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 6674.

Abstract 3983: Antigen-presenting cancer-associated fibroblasts provide an alternate mechanism for CD4 T cell activation in murine pancreatic ductal adenocarcinoma

Abstract Despite the advent of immune checkpoint inhibitors (ICI) that have markedly changed the treatment landscape for select tumors, pancreatic ductal adenocarcinoma (PDAC) remains unresponsive to such an approach. Features of the PDAC tumor microenvironment that contribute to treatment resistance, including the influence of cancer-associated fibroblasts (CAF) on immune and tumor cells, remain poorly understood. Antigen-presenting CAFs (apCAFs) express MHC-II and activate CD4 T cells in genetically engineered PDAC mouse models, but are rarely found in human PDAC. In a human PDAC atlas consisting of six published single-cell RNA-sequencing datasets, we identified 370 apCAFs out of 8736 total CAFs, the majority of which were from one dataset. Understanding apCAF regulation can reveal how to promote their differentiation and enhance T cell activating capacity in PDAC. Methods: Two KPC clones that differ in sensitivity to ICIs, sKPC (sensitive) and rKPC (resistant), derived from the autochthonous KPC murine model of PDAC, were implanted orthotopically into the pancreas or subcutaneously into the flank of syngeneic C57BL/6 mice. Tumors were harvested at 14-28 days post implantation for quantification of T cells, dendritic cells, and CAFs. To evaluate function, apCAFs were sorted and CD11c+ and CD4+ T cells were isolated from tumors. Naïve CD4+ T cells were also isolated from OT-II mice. apCAFs and CD11c+ cells were pulsed with OVA and co-cultured with OT-II CD4+ T cells, or co-cultured with sKPC tumor infiltrating CD4+ T cells in the presence of endogenous peptides. Results: Total CAFs are equivalent between tumors, but apCAFs are significantly more abundant in sKPC tumors. Furthermore, the apCAF to dendritic cell ratio within these tumors ranged from 5:1 to 50:1. CD11c+ dendritic cells sorted from sKPC tumors and pulsed with OVA peptide robustly activate naïve OT-II CD4+ T cells, as expected from professional APCs; sorted apCAFs also activate naïve OT-II CD4+ T cells, although to a lesser degree. When apCAFs or CD11c+ dendritic cells are cultured with tumor-infiltrating CD4+ T cells, however, they upregulate CD4 activation markers to a similar extent. Conclusions: apCAFs are more abundant in tumors derived from ICI-sensitive KPC clones and greatly outnumber dendritic cells. Functionally, apCAFs from sKPC tumors stimulate tumor-derived CD4 T cells to the same degree as CD11c+ dendritic cells, implicating a role in activation of the immune response in ICI-sensitive tumors. Although a small proportion of the tumor microenvironment, the apCAF subset may be enhanced in number and function by CAF-targeted modulators to affect the antitumor response; transcriptomics analyses are currently underway to identify regulators of apCAFs. Such a strategy could provide a solution to the currently unmet need for new and more effective treatments for PDAC patients. Citation Format: Saumya Maru, Lalitya Andaloori, Kathryn Howe, Kabeer Munjal, James Leatherman, Edward J. Pearce, Elizabeth M. Jaffee. Antigen-presenting cancer-associated fibroblasts provide an alternate mechanism for CD4 T cell activation in murine pancreatic ductal adenocarcinoma [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 3983.