Human T cells upregulate CD69 after coculture with xenogeneic genetically-modified pig mesenchymal stromal cells

• α1,3-Galactosyltransferase gene knock-out pigs expressing human CD46 (GTKO/CD46).
• GTKO/CD46 pig mesenchymal stromal cells (pMSC) regulate human T cell responses.
• GTKO/CD46 pMSC do not induce human T cell apoptosis or regulatory T cells.
• Human CD4+ and CD8+ T cells upregulate CD69 after coculture with GTKO/CD46 pMSC.
• CD69 upregulation on human T cells is associated with phosphorylation of STAT5.

Mesenchymal stromal cells (MSC) obtained from α1,3-galactosyltransferase gene knock-out pigs transgenic for the human complement-regulatory protein CD46 (GTKO/CD46 pMSC) suppress in vitro human anti-pig cellular responses as efficiently as allogeneic human MSC. We investigated the immunoregulatory effects of GTKO/CD46 pMSC on human CD4+ and CD8+ T cell proliferation in response to pig aortic endothelial cells (pAEC). pMSC efficiently suppressed T cell proliferation, which was associated with downregulation of granzyme B expression. No induction of CD4+CD25+Foxp3hi regulatory T cells or T cell apoptosis was documented. In correlation with T cell proliferation, CD25 expression was upregulated on T cells in response to pAEC but not to pMSC. In contrast, CD69 expression was upregulated on T cells in response to both pMSC and pAEC, which was associated with a significant increase in the phosphorylation of STAT5. GTKO/CD46 pMSC possibly regulate human T cell responses through modulation of CD69 expression and STAT5 signaling.