Both CD45RA+ and CD45RO+ human CD4+ T cells drive direct xenogeneic T-cell responses against porcine aortic endothelial cells: Human CD45RO+CD4+T recognize PAECs

Background: Xenogeneic cellular immune responses are mediated by either direct or indirect pathways depending on the participation of donor or host antigen presenting cells, respectively. The contribution of direct response of human T cells, especially memory T cells, to porcine antigen presenting cells is currently unknown. Here, we sought to determine whether human peripheral blood memory/activated phenotype T cells are directly responsive to porcine endothelial cells. Methods: Porcine aortic endothelial cells (PAECs) were prepared from Yorkshire or miniature pigs. Highly purified human T cells, including naive and memory/activated phenotype cells, were incubated with PAECs with or without the addition of exogenous cytokines. T-cell proliferation and T-cell receptor (TCR) V beta usage in response to PAECs were analyzed. Results: Both CD8+ and CD4+ T cells responded directly to PAECs and exhibited exclusive responsiveness to SLA class I and class II molecules, respectively. Naive and memory/activated phenotype CD4+ T cells responded against PAECs, whereas only naive phenotype CD8+ T cells contributed to such a response. In addition, both populations of xenogeneic human CD4+ T cells exhibited similar and diverse V beta usage. Conclusion: Due to the considerable contribution of human CD45RO+CD4+ T cells to the xenoreactivity against PAECs, effective control of xenogeneic memory/activated T-cell responses would significantly affect long-term survival of transplanted grafts.