Transplantation of human hepatocytes into tolerized genetically immunocompetent rats

AIM To determine whether normal genetically immunocompetent rodent hosts co uld be manipulated to accept human hepatocyte transplants with long term su rvival without immunosuppression. METHODS Tolerance towards human hepatocytes was established by injection of primary human hepatocytes or Huh7 human hepatoma cells into the peritoneal cavities of fetal rats. Corresponding cells were subsequently transplanted into newborn rats via intrasplenic injection within 24 h after birth. RESULTS Mixed lymphocyte assays showed that spleen cells from non-tolerized rats were stimulated to proliferate when exposed to human hepatocytes, whi le cells from tolerized rats were not. Injections made between 15 d and 17 d of gestation produced optimal tolerizaton. Transplanted human hepatocytes in rat livers were visualized by immunohistochemical staining of human alb umin. By dot blotting of genomic DNA in livers of tolerized rats 16 weeks a fter hepatocyte transplantation, it was found that approximately 2.5 x 10(5 ) human hepatocytes survived per rat liver. Human albumin mRNA was detected in rat livers by RT-PCR for 15 wk, and human albumin protein was also dete ctable in rat serum. CONCLUSION Tolerization of an immunocompetent rat can permit transplantatio n, and survival of functional human hepatocytes.