Immunologic Suppression Mediated by Genetically Modified Hepatocytes Expressing Secreted Allo-MHC Class I Molecules Christian Graeb, Marcus N. Scherer, Stuart J. Knechtle, and Edward K. Geissler ABSTRACT: Studies suggest that immunosuppression associated with liver transplantation may be related to the secretion of MHC class I antigen (Ag) by hepatocytes. To investigate this possibility, we developed a culture system whereby naive Lewis (RT1.A l ) splenocytes were cocul- tured with autologous hepatocytes transfected with plas- mids encoding either the membrane-bound or secreted allogeneic MHC class I Ag, RT1.A a . Cytotoxic T lym- phocyte (CTL) and helper T lymphocyte (HTL) limiting dilution assays were subsequently performed on precon- ditioned lymphocytes. Lymphocytes preconditioned with hepatocytes secreting RT1.A a showed an alloantigen spe- cific inhibition of CTL precursors (CTLp). In contrast, exposure of splenocytes to hepatocyte-expressed mem- brane-bound RT1.A a resulted in Ag-specific CTLp prim- ing. This CTLp priming effect by hepatocyte-expressed membrane-bound Ag could be effectively blocked when splenocytes were first preincubated with hepatocytes se- creting RT1.A a , before being exposed to hepatocytes ex- pressing membrane-bound RT1.A a . In contrast to CTLp, HTLp frequency, as determined by IL-2 production, was unaffected by either hepatocyte-expressed membrane- bound or secreted RT1.A a . Further studies on splenocytes conditioned with hepatocytes expressing secreted allo- MHC Ag suggest the possibility of suppressor cell devel- opment. This was demonstrated by prolongation of ACI (RT1 a ) heart allograft survival in Lewis recipients follow- ing adoptive transfer of splenocytes that were precondi- tioned in vitro with hepatocytes secreting alloantigen. Human Immunology 59, 415– 425 (1998). © American Society for Histocompatibility and Immunogenetics, 1998. Published by Elsevier Science Inc. ABBREVIATIONS Ag antigen CTLp cytotoxic T-lymphocyte precursor HTLp helper T-lymphocyte precursor MHC major histocompatibility complex pCMVLux control plasmid (encoding firefly luciferase) pcRQ.B3 plasmid encoding secreted MHC class I antigen, RT1.A a pcRT.45 plasmid encoding membrane-bound MHC class I antigen, RT1.A a sL-15 supplemented Leibovitz’s medium WF Wistar Furth rat strain INTRODUCTION A body of data has accumulated that suggests trans- planted livers have some immunologic privilege com- pared to other transplanted organs. This is evidenced in humans by data that show liver transplantation provides protection for kidney transplants [1] and cases of hyper- acute rejection [2]. Also, most patients that have been successfully removed from immunosuppressive drug therapy have been liver allograft recipients [3]. In animal models, rat liver transplants are spontaneously accepted between certain MHC disparate rat-strain combinations [4] and between unrelated pigs [5]. Spontaneously ac- This research was supported by Ortho Biotech and the American Society of Transplant Physicians, Grant-in-Aid; by the NIH (R15 AI39741-01), and by the Deutsche Forschungsgemeinschaft (GR 1478/2-1). From the University of South Alabama, Department of Clinical Labo- ratory Sciences, Mobile, AL, USA (C.G., M.N.S.,E.K.G), and University of Wisconsin, Department of Surgery, Madison, WI, USA (S.J.K). Current affiliation: University of Regensburg, Department of Surgery, Regensburg, Germany (C.G.). Address reprint requests to: Edward K. Geissler, University of South Alabama, Department of Clinical Laboratory Sciences, 1504 Springhill Ave., Room 2309, Mobile, AL 36604-3273, USA; Tel: (334) 434-3461; E-Mail: egeissle@jaguar1.usouthal.edu. Received March 3, 1998; revised April 13, 1998; accepted April 16, 1998. Human Immunology 59, 415– 425 (1998) 0198-8859/98/$19.00 © American Society for Histocompatibility and Immunogenetics, 1998 Published by Elsevier Science Inc. S0198-8859(98)00037-8