Human TNF-related apoptosis-inducing ligand-expressing dendritic cells from transgenic pigs attenuate human xenogeneic T cell responses.

Background: Efficient and precise techniques for the genetic modification of pigs facilitate the generation of tailored donor animals for xenotransplantation. Numerous transgenic pig lines exist with the focus on inhibition of the complement system and of humoral immune responses. In addition, immune cell-based responses need to be controlled to prevent pig-to-primate xenograft rejection. Expression of human (hu) TNF-related apoptosis-inducing ligand (TRAIL) on porcine cells has the potential to ameliorate human T cell responses.

Methods: We generated transgenic pigs expressing human tumor necrosis factor (TNF)-related apoptosis-inducing ligand (huTRAIL) under the control of either the mouse H2K(b) promoter or a CMV enhancer/chicken β-actin (CAG) promoter, the latter one (CAG-huTRAIL) on a GGTA1 knockout/huCD46 transgenic background. The biological activity of huTRAIL was demonstrated by its apoptosis-inducing effect on Jurkat lymphoma cells. To clarify whether huTRAIL affects also primary immune cells and whether its effects depend on the presence of co-stimulatory molecules, we exposed human peripheral blood mononuclear cells (PBMC) or isolated T cells to huTRAIL-expressing porcine fibroblasts or dendritic cells in vitro.

Results: H2Kb-huTRAIL transgenic pigs express huTRAIL mainly in the spleen and secondary lymphoid tissues. The CAG-huTRAIL construct facilitated huTRAIL expression in multiple organs, the level being at least one order of magnitude higher than in H2Kb-huTRAIL transgenic pigs. Incubation with huTRAIL-expressing H2Kb-huTRAIL transgenic porcine dendritic cells decreased human T cell proliferation significantly without any signs of apoptosis. In spite of the high transgene expression level, CAG-huTRAIL transgenic fibroblasts did not affect proliferation of human PBMC, independent of their activation state.

Conclusions: These results suggest huTRAIL expression on porcine dendritic cells as a possible strategy to attenuate T cell responses against pig-to-primate xenografts.