Indoleamine 2,3-dioxygenase (IDO) is an endogenous immunosuppressant exerting its effects through tryptophan depletion and kynurenine generation. Kynurenine 3-monooxygenase (KMO) is a downstream enzyme from IDO further degrading kynurenine. Viral transfer of the human IDO gene, and generating an increase in the IDO protein prevents rejection (RJX) in rodent kidney transplant (KTx). Thus, the endogenous increase in IDO activity in rejecting allografts seen in our pig KTx model (JASN 27:723A) and in KTx patients (KI 77:60) is insufficient to prevent RJX. To address this question, we assessed both cytokine and feedback regulation of IDO, and their possible roles in acute rejection using a pig model of KTx.

Methods: Yorkshire pigs underwent orthotopic, allogeneic (Allo) (n=9) or auto renal transplants (Auto) (n=10), as we described (Trans Immunol, 42:40, 2017). Allos underwent swine leukocyte antigen testing and all pigs received mismatched kidneys. All animals had right nephrectomy (RNx) prior to closure, and left Nx at sacrifice after 72 hrs. No immunosuppression was used. In all kidneys, RJX was assessed using Banff criteria. IDO, cytokines, and KMO gene expressions were quantitated with qPCR. Tissue IDO activity was measured by HPLC; and tissue KMO expression was assessed by western blotting, and localized and quantitated with immunohistochemistry.

Results: Postop creatinine was higher in Allo vs Auto (8.12±1.50 vs 2.83±0.60 mg/dL) and all allografts showed acute RJX (Banff 1 to 3). Allo kidneys showed a 13 fold increase in IDO gene transcription, and 20 fold increase in IDO enzyme activity when compared to Auto. Allo showed an over 4-fold increase in tissue IFN-γ, with marked increases in TNF-α, TNF-β and IL1-β. Allo also showed significant down regulation of KMO gene transcription (55% of Auto) and protein expression by western (5% of Auto). In tissue sections, tubular epithelial cell KMO expression was silenced in Auto vs both Allo and RNx.

Conclusions: Increased allograft IDO expression with synchronous KMO down-regulation was observed in rejecting renal allografts, suggesting divergent cytokine regulatory pathways for the two enzymes. The pro-tolerant effects of IDO may be linked, at least in part, to KMO activity and the IDO-to-KMO signaling loop.

CITATION INFORMATION: Wang Y., Fang X., Kleven D., Ho C., Nahman S., Merchen T. Regulation of Indoleamine 2,3-Dioxygenase in Porcine Kidney Transplants Am J Transplant. 2017;17 (suppl 3).

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