Serum EPO peaked at 2�C4 days post-transplantation http://www.selleckchem.com/products/BAY-73-4506.html and then fell to baseline within 1 month post-transplantation. We observed a subsequent and transient increase in hematocrit, showing that serum transgene�Cderived EPO isoforms were biologically active. Sustained expression of EPO by the transduced hepatocytes was proven both by protein detection and reverse transcription�CPCR in the liver biopsies up to 16 months after SLIT, suggesting the absence of cytotoxic immune response, as observed in previous experiments where transduced simian hepatocytes were eliminated within 5 weeks,16 and showing that mTTR promoter was not silenced. The decrease of serum EPO levels to baseline after 1 month may be explained by the following two hypotheses: 1. Low yield of engraftment of the transduced hepatocytes and subsequent low production of EPO.

Transplantation studies in rodents have shown that most transplanted hepatocytes (70�C80%) are entrapped in the portal system and are destroyed by phagocytic responses within 48 hours.17,18 In macaques, clearance of transplanted hepatocytes might be a slower process as compared to that observed in rodents because the peak of EPO was at 2�C4 days post-transplantation. Assuming a 70% transduction efficiency at the multiplicity of infection of 30 (ref. 19) and a 20�C30% engraftment efficacy,17 transduced and transplanted hepatocytes would amount to <1% of the total liver mass. In the long-term liver biopsies collected between 412 and 487 days post-transplantation, we detected vector DNA, with an average of 0.

15 copy number/diploid genome, confirming a low level of liver repopulation. 2. Humoral immune response against the isoforms of EPO produced by the transduced hepatocytes, which might specifically inactivate circulating exogenous EPO. We did not detect the presence of circulating immune complexes 15 days, 1 month, and 3 months after the procedure (data not shown), which seems to refute this hypothesis. We previously showed that the Gunn rat, an animal model of Crigler-Najjar syndrome type 1, was completely treated with <0.1 retroviral vector copies per diploid genome.20 Therefore, SLIT may provide enough functional cells in some inherited liver diseases like Crigler-Najjar syndrome type 1. For other liver diseases requiring a higher liver repopulation rate, SLIT has to be combined with strategies either to improve hepatocyte engraftment or to confer a selective proliferation of transduced hepatocytes. Interestingly, a recent study Cilengitide showed that a partial portal embolization before hepatocyte transplantation allowed repopulating 10% of the liver mass with transplanted Hoechst-labeled hepatocytes.