Human anti-pig NK cell and CD8 + T-cell responses in the presence of regulatory dendritic cells.

Background: Dendritic cells (DC) play a major role in natural killer (NK) cell and cytotoxic T lymphocyte (CTL) activation leading to cell-mediated xenogeneic responses. In contrast, the use of in vitro differentiated regulatory DC may represent an attractive approach to protect porcine endothelial cells (pEC) from human cell-mediated immune responses. In this study, we evaluated the potential of human regulatory DC to reduce xenogeneic NK cell and CTL responses to pEC. Methods: Human monocytes were differentiated into DC with GM-CSF and IL-4 in the absence or presence of rapamycin or IL-10. The effect of regulatory DC on xenogeneic NK cell and CTL responses was evaluated by analyzing phenotype, IFN gamma production, degranulation, and cytotoxicity by flow cytometry and cytotoxicity assays. Results: Upon maturation with LPS, Rapa-DC and IL-10-DC displayed different phenotypes and cytokine production profiles. In contrast to untreated DC, both Rapa-DC and IL-10-DC induced significantly less IFN gamma production and NK cell degranulation in response to pEC, but did not affect NK cell-mediated pEC lysis. Low production of IL-18 by Rapa-DC, and of IL-12 by IL-10-DC were linked to the deficient IFN gamma production by NK cells as shown by partial reversion of IFN gamma production upon cytokine reconstitution. In contrast to untreated DC efficiently generating xenoantigen-specific CTL, priming of CTL in the presence of IL-10-DC was impaired as shown by lower IFN gamma production and cytotoxicity of CTL in response to pEC. Conclusion: Both Rapa-DC and IL-10-DC controlled human anti-porcine NK cell responses, in particular IFN gamma production, whereas IL-10-DC presented stronger regulatory properties of anti-porcine CTL responses. These in vitro findings indicate that regulatory DC could be a useful tool to promote xenograft tolerance in vivo.