A study of HLA-G1 protection of porcine endothelial cells against human NK cell cytotoxicity

Human natural killer (NK) cells, which can directly lyse porcine endothelial cells, play an important role in xenotransplantation. HLA-G is a nonclassical major histocompatibility complex (MHC) class I molecules that has been implicated in protecting susceptible target cells from lysis by NK cells. The objective was to study the effect of protecting porcine endothelial cells transfected with HLA-G1 from human NK cell lysis. The recombinant expression vector pcDNA3-HLA-G1 was transfected into primary cultured porcine aortic endothelial cells (PAECs) by lipofection. Surface expression of HLA-G1 in transected PAECs was confirmed by an immunofluoresence technique. Peripheral blood mononuclear cells (PBMC) and NK cell line (NK92) were used as NK effects cells with pcDNA3-HLA-G1-transfected PAECs as targets in a MTT method using pcDNA3 transfection as a negative control. Expression of HLA-G1 on PAECs conferred significant protection against NK-mediated lysis. The rate of NK92 cytotoxicity was reduced to 41.5% ± 14.0% from 75.3% ± 10.5% in the control group ( P < .01). Similarly the rate of the PBMC cytotoxicity among different donors ( n = 7) was reduced to 45.4% ± 12.1% in contrast to 74.6% ± 11.2% in the control group ( P < .05). HLA-G1 molecules can directly protect xenogeneic PAECs against attack by human NK cells. These results indicate that the expression of HLA-G1 on the porcine cell surface may provide a new approach to overcome NK-mediated immunity to xenografts.