With recent impressive advancements in bioprinting, from printing a heart structure in zero gravity to successfully testing a bioprinter for stem cells, it is no surprise that the technology is actively being applied to medical trials with real-world applications, and yielding groundbreaking results for the community. In a recent study funded internally by Roche Pharmaceuticals and Organovo Holdings Inc., bioprinted 3D human liver tissues were evaluated for their potential use as durable, multi-cellular models of natural human liver tissue. As a result, the combination of patient-derived primary cells with bioprinting technology for the first time has confirmed superior performance in terms of mimicking human drug response in a known target organ at the tissue level.
Until recently, fabrication methods that enabled controlled spatial patterning of two or more cell types were limited to two-dimensional cultures or cultures that were a few cell layers thick. In a revolutionary feat, 3D bioprinting affords a means of fabricating tissue that is both spatially patterned and sufficiently three-dimensional, allowing for histological and biochemical assessments. Thusly, a fully human in vitro system comprising multiple liver cell types in a defined spatial pattern that can be used to gather both histopathological and biochemical data has the potential to provide important insights about the human tissue response in the pre-clinical setting, before costly human trials are initiated.
In this particular study, 3D liver tissues comprised of cryopreserved primary human hepatocytes, hepatic stellates, and human umbilical vein endothelial cells (HUVEC) cells were manufactured by Organovo. Separate high density bio-inks comprising parenchymal cells, made of 100% cellular paste, generated via compaction, were prepared and loaded into separate heads of the NovoGen Bioprinter®Instrument. Fabrication of the liver tissues was enabled by additive manufacturing, which allowed the cellular inputs, spatial distribution, and geometry to be defined with high precision. In this instance, the overall tissue structure does not fully recapitulate the native liver lobule, however the presence and organization of multiple cell types within the compartmentalized structure of the 3D liver tissues have proven to play a significant role in preserving liver-specific functions.
Throughout the trial, the bioprinted tissues retained the compartmentalization of parenchymal and non-parenchymal components established at the time of fabrication. The tissues also condensed and remodeled over time, yielding stable 3D structures, dense tissue-like cellularity, and no evidence of necrosis. Amazingly, lipid storage and glycogen storage, two functions associated with hepatocytes in vivo, were also demonstrated in the bioprinted liver tissues after maturation. Comparison of specific staining between bioprinted liver tissues and native human liver biopsy also showed similar patterns of expression. In addition, to investigate the ability of the tissues to be used as a model of drug induced liver injury (DILI), researchers also tested their response to a known hepatotoxicant compared to a non-toxic relative. Taken all together, the results suggest that 3D liver tissues could be a valuable addition to the pre-clinical toxicity pipeline.
These unprecedented results confirm the sustained viability and functionality of 3D liver tissues over time as well as their clear superiority over standard 2D cultures. Here, researchers have demonstrated that 3D bioprinted liver tissues can both effectively model DILI and distinguish between highly related compounds with differential profile. Overall, the trial has shown that this unique 3D model comprising multiple relevant liver cell types allows for the study of the tissue response to insult beyond simple cytotoxicity, enabling the measurement of cell type specific responses as well as in vitro histological assessment over extended time in culture.
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