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, IFNγ 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 IFNγ 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 IFNγ production by NK cells as shown by partial reversion of IFNγ 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 IFNγ 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 IFNγ 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.