Lab-Built Vascularized Liver Tissue Replicates Transplant Rejection Over 49 Days

Liver transplantation keeps alive patients whose livers have failed from cirrhosis, cancer, or acute injury. But transplanted livers are foreign tissue - the recipient's immune system recognizes them as such and mounts an attack. Managing that attack, calibrating immunosuppression carefully enough to prevent rejection without leaving patients dangerously exposed to infection, is one of the central challenges of transplant medicine. Progress has been constrained partly by the available research tools: animal models capture some aspects of human immune responses but miss others, and conventional cell culture systems cannot reproduce the structural and immunological complexity of actual liver tissue.

Researchers at the Terasaki Institute for Biomedical Innovation have built a platform that addresses some of those limitations. Their vascularized liver tissueoid-on-a-chip (LToC) contains multiple human liver cell types, forms a functional microvascular network through self-assembly, maintains hepatic function for 49 days, and - when deliberately exposed to immune cells from a mismatched donor - produces the molecular markers of cellular rejection.

Building the Tissueoid

The platform uses donor-matched human hepatic progenitor cells and intrahepatic portal vein endothelial cells. Within the first week of dynamic perfusion culture - flowing media through the system rather than keeping it static - the endothelial cells self-assembled into a perfusable microvascular network. This is a critical step: without functional vasculature, tissue models lack the mass transport needed to keep cells in the interior alive and metabolically active.

Over the following weeks, the tissueoid matured progressively into a structure containing the cell types present in native human liver: hepatocytes responsible for metabolic processing and protein synthesis, cholangiocytes lining bile ducts, Kupffer cells serving as resident immune macrophages, stellate cells involved in tissue remodeling, and endothelial cells forming the vascular network. This cellular diversity closely matches what is found in actual human liver tissue.

The platform sustained measurable hepatic function throughout the 49-day culture period. Albumin - a key liver-produced protein and a standard marker of hepatic function - was continuously secreted. The tissueoid also produced urea, complement factors, and hepatocyte growth factor, all consistent with functional liver tissue. Vascular integrity was maintained throughout.

Replicating Immune-Mediated Rejection

To model what happens when a transplanted liver is rejected, the team perfused the mature tissueoid with allogeneic T cells - immune cells from a genetically mismatched donor. The result was a reproducible pattern of damage: reduced tissue viability, disruption of the endothelial layer, loss of hepatic cell markers, and elevated expression of HLA class I antigens, which immune cells use to identify foreign tissue.

The cytokine profile matched what is observed during clinical transplant rejection. Levels of interleukin-6, tumor necrosis factor-alpha, interleukin-1-beta, interferon-gamma, granzyme A, granzyme B, and perforin all increased substantially. These molecules are produced by activated T cells and natural killer cells during the cellular attack on transplanted tissue, and their elevation in the model mirrors what clinicians see in rejection episodes in actual patients.

"This liver tissueoid-on-a-chip enables us to recreate key aspects of liver regeneration and immune-mediated rejection within a human-relevant, vascularized tissue architecture," said Dr. Abdul Rahim Chethikkattuveli Salih, first author of the publication.

Implications for Drug Development

"By integrating functional vasculature, multiple liver cell types, and immune responsiveness into a single platform, this system allows us to study transplant biology in a more physiologically meaningful way," added Dr. Vadim Jucaud, Principal Investigator at the Terasaki Institute. "This approach has the potential to support immunosuppressive drug evaluation and advance more personalized strategies for liver transplantation."

The platform's relevance for drug testing is significant. Immunosuppressive regimens currently used in transplantation - calcineurin inhibitors, mTOR inhibitors, corticosteroids - carry substantial side effects and do not prevent rejection in all patients. Testing candidate drugs requires a model that recapitulates human immune responses against human liver tissue. Animal models have provided some insight but diverge from human immunology in important ways. A human tissueoid system that reproducibly generates rejection responses offers a more direct testing environment.

Limitations and Next Steps

The tissueoid, while complex, is not a complete liver. It lacks the macroarchitectural organization of a full organ - the lobular structure, the zonation of metabolic functions, the portal-central vascular axis. The immune challenge tested was specific: allogeneic T cells added at a defined time point. The more complex dynamics of chronic rejection, involving persistent immune activation and progressive fibrosis over months, were not modeled. Translation from this laboratory system to clinical application will require extensive additional validation.