The application of gene transfer techniques to organ transplantation offers the potential for modulation of immunity directly within an allograft without systemic side effects. Expression vectors and promoter elements are important determinants of gene transfer and expression. In this study, various vectors (naked plasmid DNA, retroviral vector, herpes simplex viral vector, and adenoviral vector) with various promoters (RSV-LTR, SV40, MuLV-LTR, HCMViel) were directly compared to demonstrate the successful gene transfer and expression of β-galactosidase in murine myoblasts in vitro and within murine heterotopic, nonvascularized cardiac isografts or allografts in vivo. Expression of transferred genes was not toxic to cells and strength of expression varied according to the type of vector. Plasmid DNA was expressed in myocytes, retroviral vector was expressed in the graft infiltrating cells, and herpes simplex and adenoviral vectors were expressed in both myocytes and graft-infiltrating cells. Preliminary studies evaluated the ability of these vectors to deliver immunologically important signals. Allografts injected with pSVTGF-β1, a plasmid-encoding transforming growth factor β1 (TGF-β1) under the control of the SV40 promoter, showed significant prolongation of graft survival of 26.3±2.5 days compared with 12.6±1.1 days for untreated allografts, and 12.5±1.5 days for the allografts injected with control plasmid (P<0.05). Allografts injected with MFG-vIL-10, a retroviral vector encoding viral interleukin-10 under the control of the MuLV-LTR, showed prolongation of graft survival of 36.7±1.3 days versus 12.6±1.1 days for the untreated allograft, and 13.5±2.0 days for the allografts injected with control retroviral vector (P<0.001). Roth vectors were transcriptionally active in vivo and did not appear to have toxic effects. Gene therapy for transplantation can induce transient expression of immunologically relevant molecules within allografts that impede immune activation while avoiding the systemic toxicity of conventional immunosuppression.