Recruitment of human NK cells to porcine tissues has been demonstrated in pig organs perfused ex vivo with human blood in the early 1990s. Subsequently the molecular mechanisms involved in human NK cell-porcine endothelial cell (pEC) interactions have been elucidated in order to identify targets for therapeutic interventions. Human NK cell adhesion to pEC is mediated by CD49d/CD106 (VCAM-1), CD62L and b2-integrin/ICAMs interactions. Human NK cytotoxicity against pEC depends on: (1) the absence of interactions between inhibitory human NK receptors and porcine MHC class I molecules, (2) cross-species binding of activating human NK receptors (NKp44 and NKG2D) to ligands on pEC such as porcine ULBP-1, whereas (3) the expression of aGal on pEC does not play a role in direct xenogeneic NK cell recognition. While pharmacological therapies using immunosuppressive drugs have some effect on NK responses, specific molecular strategies to overcome human anti-pig NK cell responses include: (1) blocking of the molecular events leading to recruitment (chemotaxis, adhesion, transmigration), (2) expression of human MHC class I molecules on pEC, and (3) elimination or blocking of pig ligands for activating human NK receptors. Finally, cell-mediated strategies including regulatory T cells and tolerogenic dendritic cells (DC) have been proposed to control NK cell responses. Previously, we have demonstrated partial protection from xenogeneic NK cytotoxicity in vitro by the expression of several human MHC class I molecules including HLA-E on pEC. This strategy was now tested under physiological conditions using human blood in an ex vivo perfusion system of pig forelimbs stemming from HLA-E/CD46 expressing transgenic pigs. Human NK cells were rapidly recruited and disappeared from the circulating blood. Transgenic expression of HLA-E seems to provide partial protection from pig muscle infiltration. This perfusion system represents a powerful tool to study the early cell-mediated rejection mechanisms taking place in the setting of vascularized pig-to-human xenotransplantation. In addition, the potential of tolerogenic monocyte-derived DC to protect xenografts from xenogeneic NK cells responses was studied. Whereas, HLA-G expression on pEC did not induce tolerogenic DC in cellular co-cultures, induction by rapamycin and IL-10 inhibited xenogeneic NK cells responses. Thus, these data support the notion that eventually a combination of specific strategies may promote xenograft tolerance against xenogeneic NK cells responses.