OR1. Invisible organs made by genetic engineering to turn off MHC prior to allogeneic transplantation prevent a pro-inflammatory cytokine response in the recipient

Aim HLA and minor antigen mismatches are the main causes of allograft rejection and graft failure. We have shown in mice and rats that MHC silenced cells and tissues are protected against immune rejection. We also demonstrated in porcine lungs that SLA expression can be turned off in a complex vascularized organ. In this study we evaluated the effect of MHC I silencing prior to allogeneic lung transplantation (Tx) in an established porcine Tx model by monitoring the cytokine response during the first 12 weeks after Tx with immunosuppression given only in the first 4 weeks. Methods SLA I was permanently silenced during normothermic ex vivo perfusion with lentiviral vectors encoding short hairpin RNAs targeting b2m (n = 2). A lentivirally transduced non-specific shRNA was used in the control lung Tx group (n = 3). NanoLuc was used as a reporter gene in both groups. In each transplant experiment both donor lungs were genetically engineered with one lung being transplanted and the other lung used for quality control. Levels of b2m mRNA and SLA were quantified by RT-PCR and flow cytometry. SLA downregulation of endothelial cells was advisedly designed to not exceed 70%. Cytokines were monitored every second day after Tx and weekly after the post-operative day (POD) 7 by multiplex technology. Results Already 1 h after Tx the serum levels of IL-1b, IL-6 and IL-8 increased significantly in all animals by up to 0.263, 1.370 and 0.497 pg/ml, respectively. On POD 1, the cytokine secretion in the SLA silenced group decreased to pre-transplant levels whereas those of the control group remained significantly elevated (p  Conclusions These data strongly indicate that grafts silenced for MHC I are immunologically invisible supporting that MHC I and II silencing may successfully combat the burden of rejection and immunosuppression.