The tumour microenvironment (TME) determines vital aspects of tumour development, such as tumour growth, metastases and response to therapy. Cancer-associated fibroblasts (CAFs) are abundant and extremely influential in this process and interact with cellular and matrix TME constituents such as endothelial and immune cells and collagens, fibronectin and elastin, respectively. However, CAFs are also the recipients of signals—both chemical and physical—that are generated by the TME, and their phenotype effectively evolves alongside the tumour mass during tumour progression. Amid a rising clinical interest in CAFs as a crucial force for disease progression, this review aims to contextualise the CAF phenotype using the chronological framework of the CAF life cycle within the evolving tumour stroma, ranging from quiescent fibroblasts to highly proliferative and secretory CAFs. The emergence, properties and clinical implications of CAF activation are discussed, as well as research strategies used to characterise CAFs and current clinical efforts to alter CAF function as a therapeutic strategy.

Patient-derived organoids (PDOs) are emerging as powerful models to capture the genetic heterogeneity of human tumors. However, the self-assembling nature of PDOs limits their use in studies of the impact of microenvironmental heterogeneity on tumor cell function. Here, a paper-based model, the Tissue Roll for Analysis of Cellular Environment and Response (TRACER) is adapted, using patterned polymer infiltration, to enable controlled assembly and disassembly of organoid structures to study the impact of both genetic and microenvironmental heterogeneity on tumor cell behavior. In the adapted platform (TRACER2), pancreatic cancer PDOs establish oxygen gradients across the tissue and in response exhibit graded cell viability, proliferation, hypoxiaresponse gene transcription, and response to gemcitabine therapy. Further, PDOs retrieved from the hypoxic regions of the TRACER2 cultures show graded transcriptional changes in immunosuppression-related genes and upon co-culture, after TRACER2 disassembly, induce graded functional changes in Jurkat cells and macrophage cells. Therefore, TRACER2 offers a novel platform to dissect the effects of microenvironmental parameters on tumor cell function.

Functional assessment of stem cell-mediated endogenous repair relies on animal studies. Here an in vitro assay is described that recapitulates important early steps of the in vivo skeletal muscle endogenous repair (MEndR) process. The assay is integrated with a custom semi-automated image analysis pipeline to enable high-content data analysis of donor-derived muscle fiber content and morphology. Myotube sheets, generated by infiltrating a cellulose scaffold with myoblasts, are engrafted with muscle stem cells (MuSCs), injured to induce a regenerative microenvironment, and muscle repair is assessed. Significantly, the spatiotemporal dynamics of in vitro repair closely matched those observed in vivo, when both stem cells and injury are present. By exploiting the easy imaging geometry of the engineered tissue, cellular mechanisms of action driving the MuSC response to the regenerative template are explored. In vivo outcomes of two known modulators of MuSC-mediated repair, measured by donor fiber production, MuSC niche repopulation, and response to a secondary injury, are phenocopied in the platform only when both the stem cells and injured 3D template are present. The MEndR platform represents a powerful opportunity to explore MuSC-mediated repair and potentially compress the discovery pipeline by combining drug screening and validation in one step.

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The spatial configuration of cells in the tumor microenvironment (TME) affects both cancer and fibroblast cell phenotypes contributing to the clinical challenge of tumor heterogeneity and therapeutic resistance. This is a particular challenge in stroma‐rich pancreatic ductal adenocarcinoma (PDAC). Here, a versatile system is described to study the impact of tissue architecture on cell phenotype using PDAC as a model system. This fully human system encompassing both primary pancreatic stellate cells and primary organoid cells using the TRACER platform to allow the creation of user‐defined TME architectures that have been inferred from clinical PDAC samples and are analyzed by CyTOF to characterize cells extracted from the system. High dimensional characterization using CyTOF demonstrates that tissue architecture leads to distinct hypoxia and proliferation gradients. Furthermore, phenotypic markers for both cell types are also graded in ways that cannot be explained by either hypoxia or coculture alone. This demonstrates the importance of using complex models encompassing cancer cells, stromal cells, and allowing control over architecture to explore the impact of tissue architecture on cell phenotype. It is anticipated that this model will help decipher how tissue architecture and cell interactions regulate cell phenotype and hence cellular and tissue heterogeneity.