The possible use of HLA-G1 and G3 in the inhibition of NK cell-mediated swine endothelial cell lysis

The splicing isoform of HLA-G that is expressed in xenogeneic cells, and it s effect on NK-mediated direct cytotoxicity was examined, using stable Chin ese hamster ovary (CHO) cell or swine endothelial cell (SEC) transfectants. cDNAs of HLA-G (G1 and G3) and human beta2-microglobulin were prepared and subcloned into the expression vector, pCXN. The transfected HLA-G1 was eas ily expressed on SEC, and co-transfection with human beta2-microglobulin le d to an enhanced level of HLA-G1 expression, as evidenced by flow cytometry . The expressed HLA-G1 significantly suppressed NK-mediated SEC cell lysis, which is an in vitro delayed-type rejection model of a xenograft. On the o ther hand, the swine leucocyte antigen (SLA) class I molecules could be up- regulated as the result of the transfection of human beta2-microglobulin, b ut did not down-regulate human NK-mediated SEC lysis. The HLA-G3 was not ex pressed on CHO and SEC in contrast to HLA-G1, as the result of the transfec tion. The gene introduction of HLA-G3 in SEC showed no protective effect fr om human NK cells. However, indirect evidence demonstrated that HLA-G3 tran sfection resulted in HLA-E expression, but not itself, when transfected to the human cell line, 721.221, thus providing some insight into its natural function in human cells. The present findings suggest that the expression o f HLA-G1 on the cell surface could serve as a new approach to overcoming NK -mediated immunity to xenografts.