J. L. Chan1, A. K. Singh1, P. C. Corcoran1, M. L. Thomas2, B. G. Lewis2, K. A. Horvath1, M. M. Mohiuddin1 1National Institutes Of Health,Cardiothoracic Surgery Research Program/National Heart, Lung And Blood Institute,Bethesda, MD, USA 2National Institutes Of Health,Division Of Veterinary Resources/Office Of Research Services,Bethesda, MD, USA
Introduction:
Considerable progress has been achieved in xenotransplantation with genetic engineering and the inclusion of additional humanized transgenes appears to be associated with improved outcomes. Monocyte chemoattractant protein-1 (MCP-1), a potent chemotactic factor, has been implicated in transplant immune interaction and rejection. We report the novel use of six-transgene cardiac xenografts and characterize their impact on MCP-1.
Methods:
Heterotopic cardiac xenotransplantations were performed on baboons with swine donor hearts expressing three-gene modifications (GTKO.CD46.TBM) or six-gene modifications (GTKO.CD46.EPCR.DAF with TFPI.CD47 or CD39.TBM). Standard immunosuppressive therapy was administered. MCP-1 levels were measured by fluorescence intensity (FI) using Luminex assay.
Results:
No significant difference in MCP-1 levels were identified preoperatively. Within 48 hours of transplantation, recipients with six-gene modifications (n=3) had a significant reduction in MCP-1 compared to the three-gene cohort (n=3) (1376FI vs. 1928FI, p=0.03). The six-gene group continued to demonstrate decreased MCP-1 in the immediate 30-day postoperative period (1403FI vs. 1916FI, p=0.02) and remained sustained after three months (1159FI vs. 1761FI, p=0.004). Analysis of additional cytokines (IFNγ, TNFα, IL-6) and transmyocardial biopsy histology paralleled findings of a reduced inflammatory response in six-gene recipients. Elevations of MCP-1 to >10% above baseline were associated with transplant rejection within 30 days (odds ratio: 7.40, p=0.01).
Conclusion:
Expression of additional humanized factors in the six-gene cardiac xenografts, including DAF (complement inhibition), CD47 (cellular immune suppression), and CD39 (effector immune modulation), is associated with suppression of MCP-1 production. Decreased MCP-1 levels observed with use of these expanded multi-transgenic donors may reflect superior inflammatory regulation, reduced immunogenicity, and improved xenotransplantation outcomes.