Background: To understand changes in biological responses in nonhuman primate (NHP) recipients of xenotransplantation (XTP), we retrospectively investigated chronological changes in cytokine profiles of NHP recipients after solid organ XTP.

Methods: Plasma samples were collected from 7 NHP recipients of pig heart or kidney XTP with alpha-1,3-galactosyltransferase gene knockout (GTKO) under anti-CD154-based immune suppression at the following time points: immediately before; after 2 h, 3 d, and 7 d of XTP; and weekly thereafter until the graft failed. The plasma levels of the following cytokines were measured: interleukin (IL)-1α, IL-1β, IL-6, IL-12p70, IL-8, IL-10, IL-15, tumor necrotizing factor, interferon-gamma (IFN-γ), D-dimer, C3a, histone-complexed DNA fragments, and porcine high mobility group box 1.  For in vitro experiments, human natural killer (NK) cells were co-cultured with wild-type (WT)-porcine endothelial cells (PECs), GTKO-PECs, and human umbilical vein endothelial cells (HUVECs), with or without anti-CD154 antibody. IFN-γ levels in the culture supernatants were compared.

Results: IFN-γ levels peaked on day 7 or 10 of XTP and then decreased to basal levels, whereas proinflammatory cytokine levels increased along with the elevation of histone-complexed DNA fragments and were sustained until xenograft failure. In vitro, human NK cells produced more IFN-γ when in contact with WT-PECs than with HUVECs, which was not reduced by the use of GTKO-PECs or addition of anti-CD154 antibody into the mixture.

Conclusions: In NHP recipients of XTP, the early peak of IFN-γ priming subsequent inflammatory responses may be attributed to NK cell activation in response to xenografts.