Costimulation blockade in pig artery patch xenotransplantation – a simple model to monitor the adaptive immune response in nonhuman primates

Abstract

Background CD154-blockade-based immunosuppression successfully prevents both humoral and cellular adaptive immune responses in baboons receiving α1,3-galactosyltransferase gene-knockout (GTKO) pig organs. Using a GTKO pig artery transplantation model in baboons, we evaluated the efficacy of CD28/B7 costimulatory pathway blockade in comparison to CD154-blockade. Methods Baboons received artery patch grafts from GTKO pigs, with either no (Group1), anti-CD154mAb-based (Group2), or CTLA4-Ig-based (Group3) immunosuppressive therapy. Anti-pig IgM and IgG antibody and cellular responses were monitored. Xenografts were immunohistologically evaluated for antibody and complement deposition, and cellular infiltration. Results Group1 baboons developed increased IgM and IgG antibody and cellular responses against GTKO antigens. In Group2, anti-CD154mAb alone prevented the development of both IgM and IgG antibody and cellular responses, but not cellular infiltration of the graft. In the single baboon that received ATG+MMF+anti-CD154mAb, cellular infiltration of the graft was not seen. In Group3, CTLA4-Ig with ATG+MMF inhibited the cellular proliferative response to pig antigens, but did not prevent the IgG response or cellular infiltration. Conclusions (i) Artery patch transplantation is a simple model to monitor the adaptive immune response to xenografts; (ii) anti-CD154mAb prevents sensitization, but not cellular infiltration (but, without anticoagulation, may result in early thrombosis of a pig xenograft); (iii) although in only one baboon, the addition of ATG and MMF prevents cellular infiltration, and (iv) replacement of anti-CD154mAb by CTLA4-Ig (at the doses used), even in combination with ATG and MMF, prevents the cellular proliferative response to GTKO pig antigens, but is insufficient to prevent the development of anti-pig antibodies.

Increased Soluble CD154 (CD40 Ligand) Levels in Xenograft Recipients Correlate With the Development of De Novo Anti-Pig IgG Antibodies

“…Platelet activation and deposition in xenografts is a major feature of the dysregulation of the coagulation system after organ xenotransplantation (23,24). Additionally, we have observed platelet deposition in GTKO pig artery patch xenografts (5).…”

“…As anti-CD154mAb is not available for clinical use, we investigated whether CD28/B7 costimulation pathway blockade using a CTLA4-Ig-based regimen can prevent sensitization to pig antigens after GTKO pig artery patch xenotransplantation in baboons (5). Both anti-CD154mAb-and CTLA4-Ig-based therapies were able to prevent cellular proliferation in response to pig cells and maintain low levels of CD4 + T cells and CD20 + B cells after transplantation.…”

“…Previously, we have shown that anti-CD154mAb-based (but not CTLA4-Ig-based) IS successfully prevents the development of de novo anti-GTKO pig IgG antibodies after pig artery patch xenotransplantation (5). In all recipients, pretransplant anti-pig IgG levels were negligible.…”

“…Previously, we have shown that, in the absence of IS (group 1), in mixed lymphocyte reaction, after transplantation there was an increased proliferation of baboon peripheral blood mononuclear cells in response to GTKO pig cells, while both anti-CD154mAb-based IS (group 2) and CTLA4-Ig-based IS (group 3) successfully prevented this proliferation (5).…”

Immunological Challenges and Therapies in Xenotransplantation

“…Using an anti-CD40 antibody associated with belatacept extended neonatal porcine islet survival (Thompson et al 2011b), although further studies are needed to confirm this finding. On the other hand, Ezzelarab et al (2012) found in an artery-patch xenotransplantation model that CTLA-4Ig therapy was probably not as efficacious as CD154/ CD40 inhibitors in preventing cellular and humoral response (Dons et al 2012).…”