Discussion
Here, we investigated whether tet-226aa/N6-Ainv18 ES cells integrate and produce hFVIII at the transplant site. Cell infusion into the spleens of SCID mice caused increased hFVIII:Ag levels, ranging from $10% to $40% of the normal hFVIII:Ag level. However, teratomas developed in the spleens, even though the transplanted cells differentiated into liver EBs. Neoplastic transformation would facilitate the production of enormous amounts of hFVIII. Nevertheless, successful synthesis of hFVIII was encourag- ing, although few mice were used. Next, cell-transfer
experiments were conducted using hemophilia A-model mice. While transplanted cells might show low survival due to the hemophilia A mice having normal immunocompe- tence, it was expected that some of the engrafted cells would potentially produce hFVIII with low teratoma inci- dence. However, hFVIII was undetectable in hemophilia A mice using the same cell transplantation procedure as that used for SCID mice (not shown). Therefore, anticipating increased survival rates of transplanted cells in the pres- ence of liver-regeneration stimuli, cell transplantation was performed in WT mice after intraperitoneal CCl4 administra- tion. hFVIII was detected without teratoma formation in some, but not all mice administered a reduced number of transplant cells. Although intraperitoneal CCl4 administra- tion was lethal to most hemophilia A mice, hFVIII:Ag was detected in circulating blood and the periportal area of the liver of surviving hemophilia A mice, suggesting that tet-226aa/N6-Ainv18 ES cells are potentially useful for treating hemophilia A mice.
To establish ES cells, early embryos (blastocyst stage) are required as a source. Because ethical issues are associ- ated with using human ES cells experimentally, practical