In mixed lymphocyte reaction, human PBMC proliferative responses to GTKO pAEC alone (A), hMSC alone (B), GTKO pMSC alone (C), and GTKO/CD46 pMSC alone (D) were measured. The human PBMC response was significantly weaker to all three types of MSC (B, C, and D) than to GTKO pAEC (A). When GTKO pAEC were mixed with hMSC (E), GTKO pMSC (F), or GTKO/CD46 pMSC (G) at a 1:10 responder:stimulator ratio, each type of MSC significantly reduced the human PBMC proliferative response, with GTKO/CD46 pMSC reducing the response more significantly than hMSC. Data representative of three different experiments (*p<0.01 and **p<0.001 vs. GTKO pAEC [A]; #p<0.05 vs. GTKO pAEC + hMSC [E]). (Reproduced from Ezzelarab M, et al. Xenotransplantation 2011;18:183–195 [13] with permission).