Utilizing adenoviral E3 immunomodulatory genes for prevention of hepatocellular allograft rejection

Abstract

Hepatocyte transplantation is being explored as a life-saving treatment for patients with inherited liver diseases and liver failure. However, allograft rejection remains a major obstacle. Availability of genetically modified liver cells capable of evading immune rejection could obviate the need for long-term immunosuppression with its associated untoward side effects. Gene products of the early region-3 (AdE3) of the adenoviral genome are known to protect infected cells from immune recognition and destruction. Here we show that when immortalized rat hepatocytes are stably transduced with AdE3 and transplanted into the spleen or liver of fully MHC-mismatched rats, these cells are protected from allograft rejection. Quantitative real-time PCR analysis showed that a similar number of engrafted AdE3-transfected hepatocytes had survived in syngeneic and allogeneic recipients. Immunofluorescence studies revealed the presence of clusters of the transplanted allogeneic hepatocytes, demonstrating AdE3-mediated immunoprotection, as well as preferential proliferation of the engrafted hepatocytes. Cell surface expression of MHC class I on the donor hepatocytes was not reduced by AdE3 expression. Consistent with this, in vivo CTL alloresponse was attenuated, but not abolished in recipients of AdE3-transfected allogeneic hepatocytes. In contrast, AdE3 gene expression resulted in marked reduction of cell surface localization of Fas. Furthermore, expression of AdE3 genes in the donor hepatocytes inhibited TNF-alpha-induced degradation of IkappaB-alpha and phosphorylation of c-Jun, indicating inhibition of NF-kappaB and JNK/AP-1 pathways. Thus, the principle mechanism by which AdE3 gene products prevent allograft rejection appears to be related to the anti-apoptotic and anti-inflammatory functions of these proteins. Our results provide a rational for using the AdE3 genes as a target-specific immunomodulatory tool for facilitating allogeneic hepatocyte transplantation.