Cancer-associated Fibroblasts Biology Research Articles

Abstract B071: Antigen-presenting cancer-associated fibroblasts are required for ICI-sensitivity in pancreatic ductal adenocarcinoma

Abstract Cancer-associated fibroblasts (CAFs) are a hallmark of many cancers and are particularly prevalent in pancreatic ductal adenocarcinoma (PDAC). This highly fibrotic environment is thought to play a role in resistance to therapy; however, attempts to target CAFs have been unsuccessful in clinical trials. Deeper insights into CAF biology have revealed that these cells are heterogeneous in origin, gene expression, and function. RNA sequencing studies have identified a subset of CAFs, antigen-presenting CAFs (apCAFs), which are defined by MHC-II and interact with CD4 T cells. Given the importance of CD4 T cells in the antitumor response in PDAC, understanding apCAF biology could demonstrate ways to promote their differentiation and enhance T cell activity.Methods: Two clones differing in sensitivity to ICIs, sKPC (sensitive) and rKPC (resistant), derived from the autochthonous KPC murine PDAC model, were implanted orthotopically into the pancreas of syngeneic C57BL/6 mice. Mice were untreated, treated with dual checkpoint inhibition, or immunized with a KRAS peptide vaccine. Tumors were harvested for TME characterization, functional assays, single-cell RNA sequencing (scRNAseq), and imaging mass cytometry (IMC). apCAFs, CD11c+, and CD4+ T cells were isolated for functional assays. Peptide-pulsed apCAFs and CD11c+ cells were cultured with naïve OT-II CD4+ T cells or sKPC tumor infiltrating CD4+ T cells. apCAF KO mice were generated by crossing PDGFRαCre and MHC-IIflx mice.Results: Immunosensitive sKPC tumors are characterized by higher immune cell and apCAF infiltration than rKPC tumors. These apCAFs activate tumor-infiltrating CD4 T cells and induce regulatory T cell (Treg) differentiation, but not production of immunosuppressive cytokines. IMC analysis shows greater proximity of apCAFs to CD4 T cells in sKPC tumors compared with rKPC tumors. Remarkably, apCAF KO mice implanted with sKPC tumors lose sensitivity to ICI. scRNAseq has uncovered a unique transcriptome of apCAFs depending on tumor of origin and time following tumor implantation, revealing potential targets by which to quantitatively and qualitatively modulate apCAFs and enhance the antitumor response. Furthermore, scRNAseq of CD4 T cells cocultured with apCAFs has shown a unique pattern of CD4 T cell gene upregulation depending on the TME from which apCAFs were isolated, which could yield strategies to modulate not only apCAFs but also CD4 T cell activity.Conclusions: apCAFs are more abundant and more proximal to CD4 T cells in immunosensitive tumors, and apCAF KO sKPC tumor-bearing mice lose sensitivity to ICI. Together these data implicate apCAFs as essential mediators of the antitumor immune response. The unique transcriptome of apCAFs and cocultured CD4 T cells depending on tumor of origin suggests multiple strategies to modulate their interactions. Although a small proportion of the TME, modulating apCAF number or function could provide a solution to the currently unmet need of new and more effective treatments for PDAC patients. Citation Format: Saumya Maru, Meredith Wetzel, Jacob T Mitchell, Nicole Gross, Lalitya Andaloori, Kathryn Howe, Emma Kartalia, Guanglan Mo, James Leatherman, Won Jin Ho, Luciane Kagohara, Elana Fertig, Edward J Pearce, Elizabeth M Jaffee. Antigen-presenting cancer-associated fibroblasts are required for ICI-sensitivity in pancreatic ductal adenocarcinoma [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 B071.

The Application of Nanoparticles Targeting Cancer-Associated Fibroblasts.

Cancer-associated fibroblasts (CAF) are the most abundant stromal cells in the tumor microenvironment (TME), especially in solid tumors. It has been confirmed that it can not only interact with tumor cells to promote cancer progression and metastasis, but also affect the infiltration and function of immune cells to induce chemotherapy and immunotherapy resistance. So, targeting CAF has been considered an important method in cancer treatment. The rapid development of nanotechnology provides a good perspective to improve the efficiency of targeting CAF. At present, more and more researches have focused on the application of nanoparticles (NPs) in targeting CAF. These studies explored the effects of different types of NPs on CAF and the multifunctional nanomedicines that can eliminate CAF are able to enhance the EPR effect which facilitate the anti-tumor effect of themselves. There also exist amounts of studies focusing on using NPs to inhibit the activation and function of CAF to improve the therapeutic efficacy. The application of NPs targeting CAF needs to be based on an understanding of CAF biology. Therefore, in this review, we first summarized the latest progress of CAF biology, then discussed the types of CAF-targeting NPs and the main strategies in the current. The aim is to elucidate the application of NPs in targeting CAF and provide new insights for engineering nanomedicine to enhance immune response in cancer treatment.

Bioengineered Hydrogels Recapitulate Fibroblast Heterogeneity in Cancer.

Recently mapped transcriptomic landscapes reveal the extent of heterogeneity in cancer-associated fibroblasts (CAFs) beyond previously established single-gene markers. Functional analyses of individual CAF subsets within the tumor microenvironment are critical to develop more accurate CAF-targeting therapeutic strategies. However, there is a lack of robust preclinical models that reflect this heterogeneity in vitro. In this study, single-cell RNA sequencing datasets acquired from head and neck squamous cell carcinoma tissues to predict microenvironmental and cellular features governing individual CAF subsets are leveraged. Some of these features are then incorporated into a tunable hyaluronan-based hydrogel system to culture patient-derived CAFs. Control over hydrogel degradability and integrin adhesiveness enabled derivation of the predominant myofibroblastic and inflammatory CAF subsets, as shown through changes in cell morphology and transcriptomic profiles. Last, using these hydrogel-cultured CAFs, microtubule dynamics are identified, but not actomyosin contractility, as a key mediator of CAF plasticity. The recapitulation of CAF heterogeneity in vitro using defined hydrogels presents unique opportunities for advancing the understanding of CAF biology and evaluation of CAF-targeting therapeutics.

The Impact of Cancer-Associated Fibroblasts on the Biology and Progression of Colorectal Carcinomas.

(1) Colorectal cancer (CRC) is a leading cause of cancer-related deaths globally. Cancer-associated fibroblasts (CAFs) are major components of CRC's tumour microenvironment (TME), but their biological background and interplay with the TME remain poorly understood. This study investigates CAF biology and its impact on CRC progression. (2) The cohort comprises 155 cases, including CRC, with diverse localizations, adenomas, inflammations, and controls. Digital gene expression analysis examines genes associated with signalling pathways (MAPK, PI3K/Akt, TGF-β, WNT, p53), while next-generation sequencing (NGS) determines CRC mutational profiles. Immunohistochemical FAP scoring assesses CAF density and activity. (3) FAP expression is found in 81 of 150 samples, prevalent in CRC (98.4%), adenomas (27.5%), and inflammatory disease (38.9%). Several key genes show significant associations with FAP-positive fibroblasts. Gene set enrichment analysis (GSEA) highlights PI3K and MAPK pathway enrichment alongside the activation of immune response pathways like natural killer (NK)-cell-mediated cytotoxicity via CAFs. (4) The findings suggest an interplay between CAFs and cancer cells, influencing growth, invasiveness, angiogenesis, and immunogenicity. Notably, TGF-β, CDKs, and the Wnt pathway are affected. In conclusion, CAFs play a significant role in CRC and impact the TME throughout development.

Role of autophagy in cancer-associated fibroblast activation, signaling and metabolic reprograming.

Tumors not only consist of cancerous cells, but they also harbor several normal-like cell types and non-cellular components. cancer-associated fibroblasts (CAFs) are one of these cellular components that are found predominantly in the tumor stroma. Autophagy is an intracellular degradation and quality control mechanism, and recent studies provided evidence that autophagy played a critical role in CAF formation, metabolic reprograming and tumor-stroma crosstalk. Therefore, shedding light on the autophagy and its role in CAF biology might help us better understand the roles of CAFs and the TME in cancer progression and may facilitate the exploitation of more efficient cancer diagnosis and treatment. Here, we provide an overview about the involvement of autophagy in CAF-related pathways, including transdifferentiation and activation of CAFs, and further discuss the implications of targeting tumor stroma as a treatment option.

Medical Biology of Cancer-Associated Fibroblasts in Pancreatic Cancer.

Pancreatic cancer is one of the deadliest forms of cancer with one of the lowest 5-year survival rates of all cancer types. A defining characteristic of pancreatic cancer is the existence of dense desmoplastic stroma that, when exposed to stimuli such as cytokines, growth factors, and chemokines, generate a tumor-promoting environment. Cancer-associated fibroblasts (CAFs) are activated during the progression of pancreatic cancer and are a crucial component of the tumor microenvironment (TME). CAFs are primarily pro-tumorigenic in their activated state and function as promoters of cancer invasion, proliferation, metastasis, and immune modulation. Aided by many signaling pathways, cytokines, and chemokines in the tumor microenvironment, CAFs can originate from many cell types including resident fibroblasts, mesenchymal stem cells, pancreatic stellate cells, adipocytes, epithelial cells, endothelial cells, and other cell types. CAFs are a highly heterogeneous cell type expressing a variety of surface markers and performing a wide range of tumor promoting and inhibiting functions. Single-cell transcriptomic analyses have revealed a high degree of specialization among CAFs. Some examples of CAF subpopulations include myofibrotic CAFs (myCAFs), which exhibit a matrix-producing contractile phenotype; inflammatory CAFs (iCAF) that are classified by their immunomodulating, secretory phenotype; and antigen-presenting CAFs (apCAFs), which have antigen-presenting capabilities and express Major Histocompatibility Complex II (MHC II). Over the last several years, various attempts have been undertaken to describe the mechanisms of CAF-tumor cell interaction, as well as CAF-immune cell interaction, that contribute to tumor proliferation, invasion, and metastasis. Although our understanding of CAF biology in cancer has steadily increased, the extent of CAFs heterogeneity and their role in the pathobiology of pancreatic cancer remains elusive. In this regard, it becomes increasingly evident that further research on CAFs in pancreatic cancer is necessary.

A primer on cancer-associated fibroblast mechanics and immunosuppressive ability.

Cancer-associated fibroblasts (CAFs) are a major point of interest in modern oncology. Their interest resides in their ability to favor tumor growth without carrying genetic mutations. From a translational standpoint, they are potential therapeutic targets, particularly for hard-to-treat solid cancers. CAFs can be defined as non-tumor cells within the tumor microenvironment that have the morphological traits of fibroblasts, are negative for lineage-specific markers (e.g., leukocyte, endothelium), and enhance tumor progression in a multi-pronged manner. Two often-mentioned aspects of CAF biology are their ability to alter the mechanics and architecture of the tumor microenvironment, and also to drive local immunosuppression. These two aspects are the specific focus of this work, which also contains a brief summary of novel therapeutic interventions under study to normalize or eliminate CAFs from the tumor microenvironment.

Multiomic analysis reveals conservation of cancer-associated fibroblast phenotypes across species and tissue of origin.

Cancer-associated fibroblasts (CAFs) are integral to the solid tumor microenvironment. CAFs were once thought to be a relatively uniform population of matrix-producing cells, but single-cell RNA sequencing has revealed diverse CAF phenotypes. Here, we further probed CAF heterogeneity with a comprehensive multiomics approach. Using paired, same-cell chromatin accessibility and transcriptome analysis, we provided an integrated analysis of CAF subpopulations over a complex spatial transcriptomic and proteomic landscape to identify three superclusters: steady state-like (SSL), mechanoresponsive (MR), and immunomodulatory (IM) CAFs. These superclusters are recapitulated across multiple tissue types and species. Selective disruption of underlying mechanical force or immune checkpoint inhibition therapy results in shifts in CAF subpopulation distributions and affected tumor growth. As such, the balance among CAF superclusters may have considerable translational implications. Collectively, this research expands our understanding of CAF biology, identifying regulatory pathways in CAF differentiation and elucidating therapeutic targets in a species- and tumor-agnostic manner.

Exploring the Biology of Cancer-Associated Fibroblasts in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy characterised by a stubbornly low 5-year survival which is essentially unchanged in the past 5 decades. Despite recent advances in chemotherapy and surgical outcomes, progress continues to lag behind that of other cancers. The PDAC microenvironment is characterised by a dense, fibrotic stroma of which cancer-associated fibroblasts (CAFs) are key players. CAFs and fibrosis were initially thought to be uniformly tumour-promoting, however this doctrine is now being challenged by a wealth of evidence demonstrating CAF phenotypic and functional heterogeneity. Recent technological advances have allowed for the molecular profiling of the PDAC tumour microenvironment at exceptional detail, and these technologies are being leveraged at pace to improve our understanding of this previously elusive cell population. In this review we discuss CAF heterogeneity and recent developments in CAF biology. We explore the complex relationship between CAFs and other cell types within the PDAC microenvironment. We discuss the potential for therapeutic targeting of CAFs, and we finally provide an overview of future directions for the field and the possibility of improving outcomes for patients with this devastating disease.

A review of the biology and therapeutic implications of cancer-associated fibroblasts (CAFs) in muscle-invasive bladder cancer.

Cancer-associated fibroblasts (CAFs) play a fundamental role in the development of cancers and their response to therapy. In recent years, CAFs have returned to the spotlight as researchers work to unpick the mechanisms by which they impact tumour evolution and therapy responses. However, study of CAFs has largely been restricted to a select number of common cancers, whereas research into CAF biology in bladder cancer has been relatively neglected. In this review, we explore the basics of CAF biology including the numerous potential cellular origins of CAFs, alongside mechanisms of CAF activation and their diverse functionality. We find CAFs play an important role in the progression of bladder cancer with significant implications on tumour cell signaling, epithelial to mesenchymal transition and the capacity to modify components of the immune system. In addition, we highlight some of the landmark papers describing CAF heterogeneity and find trends in the literature to suggest that the iCAF and myCAF subtypes defined in bladder cancer share common characteristics with CAF subtypes described in other settings such as breast and pancreatic cancer. Moreover, based on findings in other common cancers we identify key therapeutic challenges associated with CAFs, such as the lack of specific CAF markers, the paucity of research into bladder-specific CAFs and their relationship with therapies such as radiotherapy. Of relevance, we describe a variety of strategies used to target CAFs in several common cancers, paying particular attention to TGFβ signaling as a prominent regulator of CAF activation. In doing so, we find parallels with bladder cancer that suggest CAF targeting may advance therapeutic options in this setting and improve the current poor survival outcomes in bladder cancer which sadly remain largely unchanged over recent decades.

Cancer-Associated Fibroblasts: Tumorigenicity and Targeting for Cancer Therapy.

Simple SummaryCancer-associated fibroblasts (CAFs) are found in the tumor microenvironment and exhibit several protumorigenic functions. Preclinical studies suggest that CAFs can be reduced, eliminated, or reprogrammed; however, clinical translation has not yet occurred. A better understanding of these cells and their functions will undoubtedly improve cancer treatments. In this review, we summarize current research, highlight major challenges, and discuss future opportunities for improving our knowledge of CAF biology and targeting.Cancer-associated fibroblasts (CAFs) are a heterogenous group of activated fibroblasts and a major component of the tumor stroma. CAFs may be derived from fibroblasts, epithelial cells, endothelial cells, cancer stem cells, adipocytes, pericytes, or stellate cells. These complex origins may underlie their functional diversity, which includes pro-tumorigenic roles in extracellular matrix remodeling, the suppression of anti-tumor immunity, and resistance to cancer therapy. Several methods for targeting CAFs to inhibit tumor progression and enhance anti-tumor immunity have recently been reported. While preclinical studies have shown promise, to date they have been unsuccessful in human clinical trials against melanoma, breast cancer, pancreas cancer, and colorectal cancers. This review summarizes recent and major advances in CAF-targeting therapies, including DNA-based vaccines, anti-CAF CAR-T cells, and modifying and reprogramming CAF functions. The challenges in developing effective anti-CAF treatment are highlighted, which include CAF heterogeneity and plasticity, the lack of specific target markers for CAFs, the limitations in animal models recapitulating the human cancer microenvironment, and the undesirable off-target and systemic side effects. Overcoming these challenges and expanding our understanding of the basic biology of CAFs is necessary for making progress towards safe and effective therapeutic strategies against cancers in human patients.

Cancer-Associated Fibroblasts: Mechanisms of Tumor Progression and Novel Therapeutic Targets.

Simple SummaryThe tumor microenvironment plays an important role in determining the biological behavior of several of the more aggressive malignancies. Among the various cell types evident in the tumor “field”, cancer-associated fibroblasts (CAFs) are a heterogenous collection of activated fibroblasts secreting a wide repertoire of factors that regulate tumor development and progression, inflammation, drug resistance, metastasis and recurrence. Insensitivity to chemotherapeutics and metastatic spread are the major contributors to cancer patient mortality. This review discusses the complex interactions between CAFs and the various populations of normal and neoplastic cells that interact within the dynamic confines of the tumor microenvironment with a focus on the involved pathways and genes.Cancer-associated fibroblasts (CAFs) are a heterogenous population of stromal cells found in solid malignancies that coexist with the growing tumor mass and other immune/nonimmune cellular elements. In certain neoplasms (e.g., desmoplastic tumors), CAFs are the prominent mesenchymal cell type in the tumor microenvironment, where their presence and abundance signal a poor prognosis in multiple cancers. CAFs play a major role in the progression of various malignancies by remodeling the supporting stromal matrix into a dense, fibrotic structure while secreting factors that lead to the acquisition of cancer stem-like characteristics and promoting tumor cell survival, reduced sensitivity to chemotherapeutics, aggressive growth and metastasis. Tumors with high stromal fibrotic signatures are more likely to be associated with drug resistance and eventual relapse. Clarifying the molecular basis for such multidirectional crosstalk among the various normal and neoplastic cell types present in the tumor microenvironment may yield novel targets and new opportunities for therapeutic intervention. This review highlights the most recent concepts regarding the complexity of CAF biology including CAF heterogeneity, functionality in drug resistance, contribution to a progressively fibrotic tumor stroma, the involved signaling pathways and the participating genes.

Roles of the Mesenchymal Stromal/Stem Cell Marker Meflin/Islr in Cancer Fibrosis.

Fibroblasts synthesise the extracellular matrix (ECM) such as collagen and elastin, the excessive accumulation of which can lead to fibrosis and organ dysfunction under pathological conditions. Cancer-associated fibroblasts (CAFs) are major constituents of the tumour microenvironment (TME) that accompany the desmoplastic reaction responsible for anti-cancer treatment resistance. Thus, it is important to dissect the roles of CAFs in the TME to develop new therapeutic strategies for refractory cancers. Recent progress in the studies of CAF biology suggests that the functions of CAFs are complicated and that they are composed of functionally distinct populations, including cancer-promoting CAFs (pCAFs) and cancer-restraining CAFs (rCAFs). We recently identified a new cell surface marker for rCAFs in pancreatic and colon cancers, designated as Meflin (mesenchymal stromal cell- and fibroblast-expressing Linx paralogue)/Islr (immunoglobulin super family containing leucine-rich repeat). Based on the distribution of Meflin/Islr-positive cells, we also considered it a specific candidate marker for mesenchymal stroma/stem cells. Meflin/Islr-positive CAFs have been shown to suppress cancer progression by being involved in regulating collagen structures and BMP signalling in the TME. This review describes the function of Meflin/Islr in cancer fibrosis as well as in cardiac and lung fibrosis and its potential in the development of new cancer therapeutics.

Cancer-associated fibroblasts in non-small cell lung cancer: Recent advances and future perspectives.

Non-small cell lung cancer (NSCLC) constitutes the majority of lung cancer, which is the leading cause of cancer-related deaths in the world. Nearly 70% of NSCLC patients were diagnosed at advanced stage with only 15% of five-year survival rate. Cancer-associated fibroblasts (CAFs) are the major component of tumor microenvironment and account for almost 70% of the cells in tumor tissues. By the crosstalk with cancer cells, CAFs reprogrammed cancer cell metabolism, remodeled extracellular matrix (ECM) and created a supportive niche for cancer stem cells. CAFs lead collective invasion of tumor cells and shape tumor immune microenvironment, promoting tumor metastasis and immune escape. In this review, we have summarized the progress of studies regarding CAFs influences on NSCLC in recent five years from the aspects of cell growth, metabolism, therapy resistance, invasion and metastasis and immune suppression. We have discussed the involved mechanisms and implications for the development of anti-NSCLC therapies. The current strategies of CAFs targeting and elimination have also been generalized. Only better understanding of the molecular biology of CAFs may contribute to the development of novel anti-NSCLC strategies.

Cancer-Associated Fibroblasts as Players in Cancer Development and Progression and Their Role in Targeted Radionuclide Imaging and Therapy.

Simple SummaryThe tumour microenvironment contains a unique population of cells, of complex origin and diverse functionality, known as Cancer associated fibroblasts (CAFs). In recent years there has been a growing interest in targeting CAFs to aid cancer diagnosis and therapy. Amongst the approaches utilized so far, targeting Fibroblast activation protein (FAP) has shown a lot of promise. In this review, we will focus on our current knowledge of the biology of CAFs as well as theranostic applications that will enhance cancer diagnosis and therapy in cancers carrying a distinct CAF signature.Cancer Associated Fibroblasts (CAFs) form a major component of the tumour microenvironment, they have a complex origin and execute diverse functions in tumour development and progression. As such, CAFs constitute an attractive target for novel therapeutic interventions that will aid both diagnosis and treatment of various cancers. There are, however, a few limitations in reaching successful translation of CAF targeted interventions from bench to bedside. Several approaches targeting CAFs have been investigated so far and a few CAF-targeting tracers have successfully been developed and applied. This includes tracers targeting Fibroblast Activation Protein (FAP) on CAFs. A number of FAP-targeting tracers have shown great promise in the clinic. In this review, we summarize our current knowledge of the functional heterogeneity and biology of CAFs in cancer. Moreover, we highlight the latest developments towards theranostic applications that will help tumour characterization, radioligand therapy and staging in cancers with a distinct CAF population.

Cancer-Associated Fibroblasts Suppress Cancer Development: The Other Side of the Coin.

Cancer-associated fibroblasts (CAFs) are the main stromal components of cancer, representing a group of heterogeneous cells. Many studies indicate that CAFs promote tumor development. Besides, evidence of the tumor suppression effects of CAFs keeps on merging. In the tumor microenvironment, multiple stimuli can activate fibroblasts. Notably, this does not necessarily mean the activated CAFs become strong tumor promoters immediately. The varying degree of CAFs activation makes quiescent CAFs, tumor-restraining CAFs, and tumor-promoting CAFs. Quiescent CAFs and tumor-restraining CAFs are more present in early-stage cancer, while comparatively, more tumor-promoting CAFs present in advanced-stage cancer. The underlying mechanism that balances tumor promotion or tumor inhibition effects of CAFs is mostly unknown. This review focus on the inhibitory effects of CAFs on cancer development. We describe the heterogeneous origin, markers, and metabolism in the CAFs population. Transgenetic mouse models that deplete CAFs or deplete CAFs activation signaling in the tumor stroma present direct evidence of CAFs protective effects against cancer. Moreover, we outline CAFs subpopulation and CAFs derived soluble factors that act as a tumor suppressor. Single-cell RNA-sequencing on CAFs population provides us new insight to classify CAFs subsets. Understanding the full picture of CAFs will help translate CAFs biology from bench to bedside and develop new strategies to improve precision cancer therapy.

Determinants and Functions of CAFs Secretome During Cancer Progression and Therapy.

Multiple lines of evidence are indicating that cancer development and malignant progression are not exclusively epithelial cancer cell-autonomous processes but may also depend on crosstalk with the surrounding tumor microenvironment (TME). Cancer-associated fibroblasts (CAFs) are abundantly represented in the TME and are continuously interacting with cancer cells. CAFs are regulating key mechanisms during progression to metastasis and response to treatment by enhancing cancer cells survival and aggressiveness. The latest advances in CAFs biology are pointing to CAFs-secreted factors as druggable targets and companion tools for cancer diagnosis and prognosis. Especially, extensive research conducted in the recent years has underscored the potential of several cytokines as actionable biomarkers that are currently evaluated in the clinical setting. In this review, we explore the current understanding of CAFs secretome determinants and functions to discuss their clinical implication in oncology.

Cancer-Associated Fibroblasts: Versatile Players in the Tumor Microenvironment

Simple SummaryCancer-associated fibroblasts (CAFs) are key players in the tumor microenvironment. They are responsible for potentiating growth and metastasis through versatile functions, including maintenance of the extracellular matrix, blood vessel formation, modulation of tumor metabolism, suppression of antitumor immunity, and promotion of chemotherapy resistance. As such, CAFs are associated with poor prognosis and have emerged as a focus of anticancer research. In this review, we discuss the origins of CAFs, their heterogenous subtypes and their properties. We then detail the current state of preclinical and clinical research targeting CAF activities. We believe the limited efficacy of current cancer therapeutic approaches is driven by an incomplete understanding of CAF functions and by a nonstandardized CAF classification system. Therefore, we suggest a unified CAF classification based on specific functions to develop a new class of therapies that will focus on targeting the pro-tumorigenic properties of CAFs during tumor progression.Cancer-associated fibroblasts (CAFs) are indispensable architects of the tumor microenvironment. They perform the essential functions of extracellular matrix deposition, stromal remodeling, tumor vasculature modulation, modification of tumor metabolism, and participation in crosstalk between cancer and immune cells. In this review, we discuss our current understanding of the principal differences between normal fibroblasts and CAFs, the origin of CAFs, their functions, and ultimately, highlight the intimate connection of CAFs to virtually all of the hallmarks of cancer. We address the remarkable degree of functional diversity and phenotypic plasticity displayed by CAFs and strive to stratify CAF biology among different tumor types into practical functional groups. Finally, we summarize the status of recent and ongoing trials of CAF-directed therapies and contend that the paucity of trials resulting in Food and Drug Administration (FDA) approvals thus far is a consequence of the failure to identify targets exclusive of pro-tumorigenic CAF phenotypes that are mechanistically linked to specific CAF functions. We believe that the development of a unified CAF nomenclature, the standardization of functional assays to assess the loss-of-function of CAF properties, and the establishment of rigorous definitions of CAF subpopulations and their mechanistic functions in cancer progression will be crucial to fully realize the promise of CAF-targeted therapies.

Abstract 5110: Cancer-associated fibroblast phenotypes vary across colorectal cancers and correlate with CD8+ T-cell infiltration

Abstract BACKGROUND: Cancer-associated fibroblasts (CAFs) play an important role in the tumor microenvironment (TME). This has been correlated with changes in cancer biology, including tumor progression and treatment response. CAFs exhibit divergent phenotypes differentiated by their expression profiles and function. Across cancer types, two CAF subsets have been consistently identified: myofibroblastic and non-myofibroblastic. Here we examine podoplanin (PDPN), α-smooth muscle actin (αSMA), and collagen as potential CAF subtype markers in the stromal compartment of colorectal cancers (CRCs). These markers were compared with versican (VCAN), an immunoregulatory proteoglycan associated with an immune excluded TME. METHODS: A tissue microarray containing representative tumor and normal tissue from 122 CRC patients was stained using Masson's Trichrome (collagen) or immunohistochemistry for αSMA, PDPN, VCAN and versikine (Vkine, a proteolytic fragment of VCAN). Quantification of the stains (0 to 3+) was performed by at least two observers in consultation with a surgical pathologist. Smooth muscle from the muscularis propria was excluded from quantification in the αSMA stain. CD8 staining was quantified as the number of tumor infiltrating CD8+ lymphocytes (TILs) per high power field (HPF). Separate tissue cores were sequenced for 107 of these patients using the Qiagen Comprehensive Cancer Panel. Mutations were identified using Strelka; SNPs and indels were cross-referenced to ClinVar. RESULTS: Stromal staining for αSMA, PDPN, and collagen varied across CRC sections. The abundance and intensity of staining was independent of disease stage. Those cancers with 3+ collagen or αSMA had reduced TILs (collagen 0-1+: 8.0 TILs/HPF vs 2-3+: 3.0, p=0.02; αSMA 0-1+: 7.4 vs 2-3+: 3.6, p=0.04). There was a similar trend observed for PDPN (0-1+: 6.5 vs 2-3+: 3.5, p=0.1). VCAN proteolysis predominant (VPP; VCAN 0-1+ and Vkine 2-3+) samples, previously reported to associate with higher CD8+ TILs, had lower collagen vs VCAN proteolytic weak (VPW; mean collagen score 1.6 vs 2.2, p=0.002) and lower αSMA (VPP: 1.7 vs VPW: 2.1, p=0.02). PDPN was not associated with proteolysis (p=0.4). In VPP tumors, stromal marker abundance did not correlate with CD8+ TILs; however, in VPW tumors, CD8+ TILs were higher in low PDPN (4.1 vs 1.5 TILs/HPF, p = 0.02) and low αSMA tumors (4.8 vs 1.6; p = 0.009). The trend was similar for low collagen tumors (3.7 vs 1.9, p = 0.1). Collagen was more abundant in TP53-mutant cancers (p=0.03, Chi-Square Test). CONCLUSIONS: The stromal microenvironment of CRC is highly variable across patients with diverse CAF densities and phenotypes. The makeup of this microenvironment has potential clinical impacts, as it correlates with immune cell infiltration. Further investigation into CAF biology in the TME could reveal therapeutic targets to alter immune surveillance of cancers. Citation Format: Katherine A. Johnson, Philip B. Emmerich, Cheri A. Pasch, Linda Clipson, Kristina A. Matkowskyj, Dustin A. Deming. Cancer-associated fibroblast phenotypes vary across colorectal cancers and correlate with CD8+ T-cell infiltration [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5110.

Diversity and Biology of Cancer-Associated Fibroblasts.

Efforts to develop anti-cancer therapies have largely focused on targeting the epithelial compartment, despite the presence of non-neoplastic stromal components that substantially contribute to the progression of the tumor. Indeed, cancer cell survival, growth, migration, and even dormancy are influenced by the surrounding tumor microenvironment (TME). Within the TME, cancer-associated fibroblasts (CAFs) have been shown to play several roles in the development of a tumor. They secrete growth factors, inflammatory ligands, and extracellular matrix proteins that promote cancer cell proliferation, therapy resistance, and immune exclusion. However, recent work indicates that CAFs may also restrain tumor progression in some circumstances. In this review, we summarize the body of work on CAFs, with a particular focus on the most recent discoveries about fibroblast heterogeneity, plasticity, and functions. We also highlight the commonalities of fibroblasts present across different cancer types, and in normal and inflammatory states. Finally, we present the latest advances regarding therapeutic strategies targeting CAFs that are undergoing preclinical and clinical evaluation.