Therapeutic regulation of systemic inflammation in xenograft recipients

Abstract

Inflammation is known to preclude tolerance after transplantation. We have previously shown that systemic inflammation in xenograft recipients (SIXR) precedes activation of coagulation in the absence of T cell responses. Accordingly, SIXR may amplify innate and adaptive immune responses against xenografts after pig-to-primate xenotransplantation, even with efficient immunosuppressive therapy. We evaluated the impact of anti-inflammatory agents on pro-inflammatory cytokines and chemokines in pig artery patch and heart xenograft recipients. Baboons received an artery patch (Group1, n=8) or heart (Group2, n=4) from genetically engineered pigs. All baboons received lymphodepletion with thymoglobulin (ATG) and costimulation blockade-based immunosuppression (anti-CD40 and/or CTLA4Ig). In Group1, baboons received either (i) no anti-inflammatory agents (n=2), (ii) cobra venom factor (CVF, n=2), (iii) α1-antitrypsin (AAT, n=2), or (iv) interleukin (IL)-6 receptor antagonist (IL-6RA, n=2). In Group2, all baboon received corticosteroids, either without (n=2) or with (n=2) IL-6RA. Serum IFN-γ, TNF-α, IL-1β, IL-17, IL-6, IL-8, MCP-1, and sCD40L levels were measured by Luminex. Fibrinogen, D-dimers, and C-reactive protein (C-RP) were also measured. Recipient baboon T cell proliferation was evaluated by mixed lymphocyte reaction (MLR) before and after transplantation. Pig and baboon tissue factor (TF) mRNA levels in heart xenografts were measured by RT-PCR. In no recipient was a marked increase in T cell response to pig cells observed after transplantation. In Groups 1 and 2, post-transplantation levels of IFN-γ, TNF-α, IL-1β, and IL-17 remained comparable to or lower than pre-transplant levels, except in one heart recipient that succumbed to CMV infection. In Group1, when no anti-inflammatory agent was administered, post-transplant levels of IL-6, IL-8, and MCP-1 were elevated. After CVF, IL-6, IL-8, and MCP-1 remained low. After IL-6RA, IL-6 and MCP-1 were elevated. After AAT, IL-8 was elevated. sCD40L became elevated intermittently in most recipients irrespective of the administered anti-inflammatory agent. In Group2, IL-6 was transiently elevated, particularly after IL-6RA administration. MCP-1 gradually increased by 2 months in Group2 recipients. sCD40L generally remained low except in one recipient. In Group1 and Group2 recipients, C-RP levels were elevated except after IL-6RA administration, while D-dimers were elevated regardless of administration of anti-inflammatory agent. In Group2, pig TF mRNA levels were increased in heart xenografts compared to naive pig hearts, irrespective of IL-6 receptor antagonist administration. Additionally, baboon TF mRNA levels were detectable in heart xenografts, but not in naive pig hearts. Some pro-inflammatory cytokines and chemokines are elevated in xenograft recipients, even with efficient T cell-directed immunosuppressive therapy. Persistent elevation of D-dimers, and individual cytokines and chemokines suggest a continuous inflammatory response, despite administration of anti-inflammatory agents. Systemic administration of combined anti-inflammatory agents as well as complement regulation may be essential to prevent SIXR after xenotransplantation.

Keywords: Xenotransplantation; chemokines; cytokines; heart; inflammation; pig.