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Resistance to anti-xenogeneic response by combining alpha-Gal silencing with HO-1 upregulation
1Key Laboratory of Organ Transplantation, Ministry of Education and Health, Institute of Organ Transplantation, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
Background:
A major barrier to clinical xenotransplantation is preformed xenoreactive natural antibodies (XNA) found in higher primates which react to Galalpha(1,3)Gal (alpha-Gal) epitopes found on lower species. Accommodation of organs to xenogeneic recipients involves upregulation of cytoprotective genes and resistance to complement dependent cytotoxicity (CDC).
Methods:
To develop methods of increasing these organ-protective effects, we established an in vitro CDC model utilizing human serum as the source of XNA and porcine endothelial cells (pEC) as targets.
Results:
Using this system we demonstrated that downregulation of alpha-Gal epitopes by siRNA silencing of alpha1,3-galactosyltransferase (alpha-GT) led to marginal protection from CDC while alpha-Gal silencing combined with Griffonia simplicifolia isolectin B4 (GS-IB4), a lectin that specifically binds to alpha-Gal epitopes, led to complete protection. Interestingly, alpha-Gal silencing and GS-IB4 mediated effects were not associated with inhibition of XNA binding to cells, but with significant decreased E-selectin expression and cytoprotective gene HO-1 upregulation. PI3K inhibitor LY294002 could block the elevation of HO-1 protein expression and reverse the protective effect of alpha-Gal silencing and GS-IB4 against CDC.
Conclusion:
These data support the use of combination approaches targeting independent accommodation mechanisms to synergistically enhance donor organ survival in a xenogeneic setting.
