Integration of reconstructed human skin (RhS) into organ‐on‐chip (OoC) platforms addresses current limitations imposed by static culturing. This innovation, however, is not without challenges. Microfluidic devices, while powerful, often encounter usability, robustness, and gas bubble issues that hinder large‐scale high‐throughput setups. This study aims to develop a novel re‐usable multi‐well microfluidic adaptor (MMA) with the objective to provide a flexible tool for biologists implementing complex 3D biological models (e.g., skin) while enabling simultaneous user control over temperature, medium flow, oxigen (O₂), nitrogen (N₂), and carbon dioxide (CO₂) without the need for an incubator. The presented MMA device is designed to be compatible with standard, commercially available 6‐well multi‐well plates (6MWPs) and 12‐well transwells. This MMA‐6MWP setup is employed to generate a skin‐on‐chip (SoC). RhS viability is maintained under flow for three days and their morphology closely resembles that of native human skin. A proof‐of‐concept study demonstrates the system's potential in toxicology applications by combining endothelialised RhS with flowing immune cells. This dynamic setting activates the monocyte‐like MUTZ‐3 cells (CD83 and CD86 upregulation) upon topical exposure of RhS to a sensitizer, revealing the MMA‐6MWP's unique capabilities compared to static culturing, where such activation is absent.

Invasion, immune modulation, and angiogenesis are crucial in melanoma progression. Studies based on animals or two-dimensional cultures poorly recapitulate the tumor-microenvironmental cross-talk found in humans. This highlights a need for more physiological human models to better study melanoma features. Here, six melanoma cell lines (A375, COLO829, G361, MeWo, RPMI-7951, and SK-MEL-28) were used to generate an in vitro three-dimensional human melanoma-in-skin (Mel-RhS) model and were compared in terms of dermal invasion and immune modulatory and pro-angiogenic capabilities. A375 displayed the most invasive phenotype by clearly expanding into the dermal compartment, whereas COLO829, G361, MeWo, and SK-MEL-28 recapitulated to different extent the initial stages of melanoma invasion. No nest formation was observed for RPMI-7951. Notably, the integration of A375 and SK-MEL-28 cells into the model resulted in an increased secretion of immune modulatory factors (e.g., M-CSF, IL-10, and TGFβ) and pro-angiogenic factors (e.g., Flt-1 and VEGF). Mel-RhS-derived supernatants induced endothelial cell sprouting in vitro. In addition, observed A375-RhS tissue contraction was correlated to increased TGFβ release and α-SMA expression, all indicative of differentiation of fibroblasts into cancer-associated fibroblast-like cells and reminiscent of epithelial-to-mesenchymal transition, consistent with A375′s most prominent invasive behavior. In conclusion, we successfully generated several Mel-RhS models mimicking different stages of melanoma progression, which can be further tailored for future studies to investigate individual aspects of the disease and serve as three-dimensional models to assess efficacy of therapeutic strategies.

Despite the recent impressive clinical success of immunotherapy against melanoma, development of primary and adaptive resistance against immune checkpoint inhibitors remains a major issue in a large number of treated patients. This highlights the need for melanoma models that replicate the tumor's intricate dynamics in the tumor microenvironment (TME) and associated immune suppression to study possible resistance mechanisms in order to improve current and test novel therapeutics. While two‐dimensional melanoma cell cultures have been widely used to perform functional genomics screens in a high‐throughput fashion, they are not suitable to answer more complex scientific questions. Melanoma models have also been established in a variety of experimental (humanized) animals. However, due to differences in physiology, such models do not fully represent human melanoma development. Therefore, fully human three‐dimensional in vitro models mimicking melanoma cell interactions with the TME are being developed to address this need for more physiologically relevant models. Such models include melanoma organoids, spheroids, and reconstructed human melanoma‐in‐skin cultures. Still, while major advances have been made to complement and replace animals, these in vitro systems have yet to fully recapitulate human tumor complexity. Lastly, technical advancements have been made in the organ‐on‐chip field to replicate functions and microstructures of in vivo human tissues and organs. This review summarizes advancements made in understanding and treating melanoma and specifically aims to discuss the progress made towards developing melanoma models, their applications, limitations, and the advances still needed to further facilitate the development of therapeutics.

Despite considerable advancements in cancer immunotherapy, advanced melanoma still presents a substantial clinical challenge. In an effort to explore treatment options, we examined the immunotherapeutic potential of effector Vγ9Vδ2-T cells in vitro in a three-dimensional (3D) human organotypic melanoma-in-skin (Mel-RhS) model. Vγ9Vδ2-T cells were introduced into Mel-RhS via intradermal injection and cultured within the tissue microenvironment for up to 3 days. Vγ9Vδ2-T cells remained viable for up to 3 days and were in close proximity to or within tumor nests. Upon Mel-RhS dissociation, a fraction was shown to be decorated by melanoma-associated chondroitin sulfate proteoglycan (MCSP), demonstrating their ability to actively navigate the tumor microenvironment and trogocytose cancer cells. Investigation into the apparent trogocytosis revealed an enhanced activated state of MCSP-decorated Vγ9Vδ2-T cells, evidenced by increased expression levels of 4-1BB, NKp44, programmed cell death protein-1 (PD-1), and programmed death-ligand 1 (PD-L1), compared with their MCSP⁻ counterpart. These findings suggest that Vγ9Vδ2-T cells, upon successfully contacting melanoma cells, actively recognize and acquire MCSP from these malignant cells. Evidence of actual tumor cell elimination, although not significant, was only obtained after preincubation of Mel-RhS with pamidronate, a phosphoantigen-inducing agent, indicating the need for additional T cell receptor-mediated signaling for Vγ9Vδ2-T cells to reach their full oncolytic potential. This study highlights the viability and persistence of Vγ9Vδ2-T cells within the 3D microenvironment, their migratory and antitumor functionality, and the suitability of the model for testing T cell-based therapies, contributing both to the understanding of Vγ9Vδ2-T cell biology and their application in cancer immunotherapy.