Human Hepatocyte Transplantation: The Story So Far
Summary of Lecture by Anil Dhawan, MD
1. Main Clinical Topics Discussed
- Hepatocyte transplantation (HT) as an alternative or bridge to whole-organ liver transplantation
- Auxiliary liver transplantation as a proof-of-concept for partial liver replacement
- Applications in liver-based metabolic disorders (e.g., urea cycle defects, Crigler-Najjar syndrome, propionic acidemia) and acute liver failure (ALF)
- Challenges in clinical translation, including cell engraftment, GMP manufacturing, and regulatory requirements
2. Key Learning Points, Guidelines, and Recommendations
- Liver transplantation remains the gold standard for end-stage liver disease but is considered a treatment, not a cure — patients require lifelong immunosuppression, ongoing monitoring, and face long-term complications
- The regenerative capacity of the liver supports the theoretical basis for hepatocyte transplantation; even restoration of as little as 5% of enzyme function in urea cycle defect disorders may shift the clinical phenotype from severe to moderate or mild
- Auxiliary liver transplantation (transplanting one lobe while retaining the native liver) preserves the native liver as a future target organ for gene therapy — a key strategic advantage
- Hepatocyte infusion routes include:
- Percutaneous intraportal infusion
- Umbilical vein access (neonates)
- Hickman line via a tributary of the superior or inferior mesenteric vein
- Cell dose target: Up to 5–10% of native liver mass (approximately 10⁹ cells per infusion)
- Minimum cell viability threshold: >60% (assessed by trypan blue exclusion) required before clinical use
- ABO compatibility is maintained for all infusions
- Portal pressure monitoring is performed during infusion to reduce risk
3. Specific Clinical Data, Statistics, and Study Results
- Numerous single-gene metabolic defect models (Crigler-Najjar, OTC deficiency, Wilson disease, hyperlipidemia, MDR2 deficiency) have demonstrated successful outcomes following hepatocyte transplantation
- In a large animal (porcine) model of ALF (D-galactosamine/D-glycosamine model): controls died within 3 days; animals receiving porcine hepatocytes or reverted cells achieved >80% survival beyond 3 days
- Tyrosinemia animal models demonstrated up to 95% native liver repopulation following transplanted hepatocyte engraftment under selective pressure
- Clinical outcomes — Urea Cycle Defects (OTC deficiency):
- Multiple international centers (Pittsburgh, King's College London, Nebraska, Belgium, Germany, Spain, Virginia) have reported results
- No center has demonstrated cure; all have shown phenotype stabilization and successful bridging to liver transplantation, with avoidance of acute neurological injury
- Clinical outcomes — Crigler-Najjar Syndrome:
- Multiple groups have reported 50–60% reduction in serum bilirubin levels following hepatocyte transplantation
- Complete bilirubin normalization has not been achieved
- Patients remain candidates for liver transplantation and, notably, for emerging gene therapy (first trials reported in the U.S. and Europe showing early sustained bilirubin clearance in adults)
- Auxiliary transplantation — proof of concept:
- A 16-year follow-up case of a patient with propionic acidemia who received auxiliary transplantation at age 16 demonstrated sustained dual-liver architecture, preserving the native liver as a future gene therapy target organ
- Program timeline: The speaker's GMP hepatocyte program began in 1999, funded by a UK national charity
4. Practical Takeaways for Clinicians
- Hepatocyte transplantation should be considered a bridge, not a cure in current practice; it can stabilize metabolic disease, reduce disease burden, and allow patients to reach liver transplantation in better neurological condition
- Patient selection is critical: Best candidates are those with **single-gene, single-enzyme liver-based metabolic defects without cir