Dendritic cells and the extracellular matrix: A challenge for maintaining tolerance/homeostasis

Patient-derived tumor explant models of tumor immune microenvironment reveal distinct and reproducible immunotherapy responses

Tumor-resident immune cells play a crucial role in eliciting anti-tumor immunity and immunomodulatory drug responses, yet these functions have been difficult to study without tractable models of the tumor immune microenvironment (TIME). Patient-derived ex vivo models contain authentic resident immune cells and therefore, could provide new mechanistic insights into how the TIME responds to tumor or immune cell-directed therapies. Here, we assessed the reproducibility and robustness of immunomodulatory drug responses across two different ex vivo models of breast cancer TIME and one of renal cell carcinoma. These independently developed TIME models were treated with a panel of clinically relevant immunomodulators, revealing remarkably similar changes in gene expression and cytokine profiles among the three models in response to T cell activation and STING-agonism, while still preserving individual patient-specific response patterns. Moreover, we found two common core signatures of adaptive or innate immune responses present across all three models and both types of cancer, potentially serving as benchmarks for drug-induced immune activation in ex vivo models of the TIME. The robust reproducibility of immunomodulatory drug responses observed across diverse ex vivo models of the TIME underscores the significance of human patient-derived models in elucidating the complexities of anti-tumor immunity and therapeutic interventions.

Hydrogel-Based Tumor Tissue Microarchitecture Reshapes Dendritic Cell Metabolic Profile and Functions

The extracellular matrix (ECM) plays a pivotal role in immunomodulation, providing structural and biochemical cues that shape immune cell function. In pathological conditions like cancer and chronic inflammation, dysregulated remodeling often results in altered ECM composition and architecture, with fibrillar alignment being a hallmark linked to disease progression. Here, how ECM alignment influences dendritic cell (DC) behavior using 3D biomimetic collagen matrices with controlled fibril anisotropy is investigated. This results show that immature DCs in aligned matrices exhibited increased expression of CD86 and HLA-DR with elevated secretion of CXCL8 and CCL2 chemokines, which may enhance immune cell recruitment. However, transcriptomic and metabolomic analysis revealed significant downregulation of oxidative phosphorylation and an insufficient compensatory shift toward glycolysis, resulting in reduced ATP production. This metabolic constraint correlated with impaired/reduced DC migratory speed and distance. In contrast, mature DCs displayed minimal sensitivity to ECM alignment, maintaining uniform differentiation and functional profiles across matrix conditions. T-cell coculture experiments revealed that ECM alignment dampens T-cell activation and proliferation, likely through direct modulation of T-cell behavior. These findings highlight the stage-specific effects of ECM alignment on DC function, highlighting its role in DC immunomodulation, with implications for therapeutic development in cancer and other pathological contexts.

Tug of war: Understanding the dynamic interplay of tumor biomechanical environment on dendritic cell function

Dendritic cells (DCs) play a pivotal role in bridging the innate and adaptive immune systems. From their immature state, scavenging tissue for foreign antigens to uptake, then maturation, to their trafficking to lymph nodes for antigen presentation, these cells are exposed to various forms of mechanical forces. Particularly, in the tumor microenvironment, it is widely known that microenvironmental biomechanical cues are heightened. The source of these forces arises from cell-to-extracellular matrix (ECM) and cell-to-cell interactions, as well as being exposed to increased microenvironmental pressures and fluid shear forces typical of tumors. DCs then integrate these forces, influencing their immune functions through mechanotransduction. This aspect of DC biology holds alternative, but important clues to understanding suppressed/altered DC responses in tumors, or allow the artificial enhancement of DCs for therapeutic purposes. This review discusses the current understanding of DC mechanobiology from the perspectives of DCs as sensors of mechanical forces and providers of mechanical forces.

Extracellular Matrix-Bioinspired Anisotropic Topographical Cues of Electrospun Nanofibers: A Strategy of Wound Healing through Macrophage Polarization

The skin serves as the body's outermost barrier and is the largest organ, providing protection not only to the body but also to various internal organs. Owing to continuous exposure to various external factors, it is susceptible to damage that can range from simple to severe, including serious types of wounds such as burns or chronic wounds. Macrophages play a crucial role in the entire wound-healing process and contribute significantly to skin regeneration. Initially, M1 macrophages infiltrate to phagocytose bacteria, debris, and dead cells in fresh wounds. As tissue repair is activated, M2 macrophages are promoted, reducing inflammation and facilitating restoration of the dermis and epidermis to regenerate the tissue. This suggests that extracellular matrix (ECM) promotes cell adhesion, proliferation, migrationand macrophage polarization. Among the numerous strategies, electrospinning is a versatile technique for obtaining ECM-mimicking structures with anisotropic and isotropic topologies of micro/nanofibers. Various electrospun biomaterials influence macrophage polarization based on their isotropic or anisotropic topologies. Moreover, these fibers possess a high surface-area-to-volume ratio, promoting the effective exchange of vital nutrients and oxygen, which are crucial for cell viability and tissue regeneration. Micro/nanofibers with diverse physical and chemical properties can be tailored to polarize macrophages toward skin regeneration and wound healing, depending on specific requirements. This review describes the significance of micro/nanostructures for activating macrophages and promoting wound healing.

TGF-β1-activated type 2 dendritic cells promote wound healing and induce fibroblasts to express tenascin c following corneal full-thickness hydrogel transplantation

We showed previously that 1-ethyl-3-(3-dimethylamino-propyl)-carbodiimide hydrochloride (EDC) cross-linked recombinant human collagen III hydrogels promoted stable regeneration of the human cornea (continued nerve and stromal cell repopulation) for over 4 years. However, as EDC cross linking kinetics were difficult to control, we additionally tested a sterically bulky carbodiimide. Here, we compared the effects of two carbodiimide cross linkers-bulky, aromatic N-cyclohexyl-N0-(2-morpholinoethyl)-carbodiimide (CMC), and nonbulky EDC-in a mouse corneal graft model. Murine corneas undergoing full-thickness implantation with these gels became opaque due to dense retro-corneal membranes (RCM). Corneal epithelial cytokeratin 12 and alpha smooth muscle actin indicative of functional tissue regeneration and wound contraction were observed in RCM surrounding both hydrogel types. However, quantitatively different levels of infiltrating CD11c⁺ dendritic cells (DC) were found, suggesting a hydrogel-specific innate immune response. More DC infiltrated the stroma surrounding EDC-N-hydroxysuccinimide (NHS) hydrogels concurrently with higher fibrosis-associated tenascin c expression. The opposite was true for CMC-NHS gels that had previously been shown to be more tolerising to DC. In vitro studies showed that DC cultured with transforming growth factor β1 (TGF-β1) induced fibroblasts to secrete more tenascin c than those cultured with lipopolysaccharide and this effect was blocked by TGF-β1 neutralisation. Furthermore, tenascin c staining was found in 40- to 50μm long membrane nanotubes formed in fibroblast/DC cocultures. We suggest that TGF-β1 alternatively activated (tolerising) DC regulate fibroblast-mediated tenascin c secretion, possibly via local production of TGF-β1 in early wound contraction, and that this is indirectly modulated by different hydrogel chemistries.

Activation of dendritic cells by crosslinked collagen hydrogels (artificial corneas) varies with their composition

Activated T cells are known to promote fibrosis, a major complication limiting the range of polymeric hydrogels as artificial corneal implants. As T cells are activated by dendritic cells (DC), minimally activating hydrogels would be optimal. In this study, we evaluated the ability of a series of engineered (manufactured/fabricated) and natural collagen matrices to either activate DC or conversely induce DC apoptosis in vitro. Bone marrow DC were cultured on a series of singly and doubly crosslinked hydrogels (made from recombinant human collagen III [RHCIII] or collagen mimetic peptide [CMP]) or on natural collagen-containing matrices, Matrigel^TM and de-cellularised mouse corneal stroma. DC surface expression of major histocompatibility complex Class II and CD86 as well as apoptosis markers were examined. Natural matrices induced low levels of DC activation and maintained a "tolerogenic" phenotype. The same applied to singly crosslinked CMP-PEG gels. RHCIII gels singly crosslinked using either N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide with the coinitiator N-hydroxy succinimide (EDC-NHS) or N-cyclohexyl-N-(2-morpholinoethyl)carbodiimide metho-p-toulenesulfonate with NHS (CMC-NHS) induced varying levels of DC activation. In contrast, however, RHCIII hydrogels incorporating an additional polymeric network of 2-methacryloyloxyethyl phosphorylcholine did not activate DC but instead induced DC apoptosis, a phenomenon observed in natural matrices. This correlated with increased DC expression of leukocyte-associated immunoglobulin-like receptor-1. Despite low immunogenic potential, viable tolerogenic DC migrated into and through both natural and manufactured RHCIII gels. These data show that the immunogenic potential of RHCIII gels varies with the nature and composition of the gel. Preclinical evaluation of hydrogel immunogenic/fibrogenic potential is recommended.