[Antisense TGF-beta 1 transfection decreases acute and chronic rejection in allografts]

The process of chronic rejection (CR) threatens long-term organ graft survival and is the major remaining barrier preventing successful clinical transplantation. The etiology of CR remains speculative, but its correlation with acute rejection episodes, HLA mismatch and immunosuppressive non-compliance suggests that active immune attack is responsible. The authors hypothesize that transforming growth factor beta-1 (TGF beta-1) plays a causal role in regulating and modulating both the acute and the chronic rejection. To investigate this hypothesis in rats, recombinant adenoviruses (rAdv)-mediated gene transfer encoding downregulating antisense--or upregulating bioactive TGF beta-1 transgene were used to infect orthotopic aortic grafts. In a high responder MHC class I histocompatibility difference (ACI to Lewis rat) and in syngeneic controls (Lewis to Lewis) both expression vectors were detected 1, 2 and 12 weeks following transplantation by intragraft cytokine transcription. Aortic segments were divided and processed for histology and RNA extraction. TGF beta-1 RNA expression was then evaluated by semi-quantitative RT-PCR (s26 standardized, HPLC quantitated). Histological evaluation was performed by a transplant pathologist in a blinded fashion. All analysis were prospective and repeated in triplicate. Untreated allografts were used as background controls for the acute and chronic rejection showing an endogenous up-regulation of TGF beta-1 at early time points (1 wk 2.7 +/- 0.5; 2 wk 9.2 +/- 6.1) and a decreased TGF beta-1/s26 ratio in chronic rejection (12 wk 1.2 +/- 0.11). Successful rAdv-transgene activity was, however, detected in low levels in all aortic layers showing a 25%-35% transfection rate whereas beta-galactosidase control gene expression was found as far as 35 days post transplant. Administration of down-regulating antisense TGF beta-1 gene into transplant segments significantly decreased the intragraft TGF beta-1 transcription (1 wk 0.8 +/- 0.2; 2 wk 1.9 +/- 0.5; 12 wk 0.7 +/- 0.15) and was correlated with absence of ongoing acute graft rejection in allografts (p < 0.01) during the first 2 weeks. The degree of intimal hyperplasia proliferation was also decreased by 40% in chronic allograft rejection. The transfection of upregulating bioactive TGF beta-1 vector led to clear increase of the TGF beta 1 gene expression but had no significant effect on immune response either on syngeneic nor allogeneic grafts. These data suggest that TGF beta-1 plays a key role in modulating the early stage of acute rejection and is a crucial mediator of the outcome of chronic rejection. Down regulation of intragraft TGF beta-1 gene expression shows immunosuppresisve property and could be used to develop clinically relevant strategies in transplantation.