Splenic-Injection of Autologous Hepatocytes Genetically Modified to Express Soluble Donor-Mhc Class I Antigen Prolongs Heart Allograft Survival

881 Previous studies suggest that liver allografts can provide protection for other transplanted organs. In this respect heart allograft rejection can be prevented, and even reversed, with a liver transplant from the same donor. One possible explanation for this phenomenon is that hepatocytes produce relatively large amounts of potentially immunosuppressive soluble MHC class I antigen (Ag). In support of this theory we have recently shown that hepatocyte-secreted, soluble, allogeneic-MHC class I Ag downregulates both cytotoxic and helper T lymphocyte responses in vivo. In the present study we examined the potential immunosuppressive effects of hepatocyte-secreted donor-MHC Ag in a rat heart allograft model. Hepatocytes were obtained by collagenase digestion of a Lewis (RT11) liver. Cells were cultured and subsequently transfected by lipofection to express the soluble donor-MHC class I Ag, RT1.Aa (plasmid: pcRQ.B3). One day prior to ACI (RT1a) heterotopic heart allografting, Lewis recipients were injected with 1 × 107 pcRQ.B3-transfected hepatocytes via the spleen. Controls did not receive hepatocytes or were injected with hepatocytes transfected with a gene encoding firefly-luciferase (pCMVLux). All animals received a short-course of cyclosporin A (10 mg/kg/day, i.p.) on days 0 to +7, relative to heart transplantation. Graft survival results showed that recipients injected with hepatocytes expressing soluble donor-MHC class I Ag experienced a prolongation of ACI heart allograft survival, when compared to control. (Table)TableThese results suggest that the immunosuppressive effects of a single mismatched soluble donor-MHC class I Ag are sufficiently potent to promote heart allograft survival in a fully MHC-disparate, high-responder, rat-strain combination. This is one of the first steps in the development of a gene transfer-based system to deliver soluble donor-MHC class I molecules to organ transplant recipients. We are currently refining this gene transfer system to allow for more prolonged soluble donor-MHC expression in vivo, which we predict is a critical factor to provide for longer immunologic protection of heart allografts. Also, it is likely that delivery of a single type of mismatched donor-MHC Ag will be more effective between strain combinations where the MHC is not completely different. In summary, these results provide incentive to determine the full potential of soluble donor-MHC class I gene therapy in organ transplantation.