Background

Xenotransplantation (XTx) involves the participation of innate immune system with natural antibody producing B cells, NK cells, macrophages and complement as well as adaptive immune system from T and B cells. Recently we have reported cardiac xenograft survival of over 2.5 years in a pig-to-baboon heterotopic transplantation model using a modified immunosuppression (IS) regimen, which includes depletion B cells and costimulation blockade by anti-CD40 antibody. In this study we demonstrate that continuous treatment of high dose of anti-CD40 antibody could prevent the xenograft rejection.

Methods

Heterotopic cardiac XTx was performed from GTKO.hCD46Tg (n=8) and GTKO.hCD46.hTBM (n=5) GE pigs into baboons using IS regimen that included ATG, anti-CD20 antibody, MMF, CVF, and co-stimulation blockade (anti-CD154 or anti-CD40) antibody. Telemetry, palpation and ultrasound (U/S) were used to evaluate the xenograft function. Baboon peripheral blood lymphocytes (PBLs) and serum were collected twice a week for the first two months post XTx and then monthly thereafter. Mixed lymphocyte reaction (MLR) and flow cytometry analysis was performed on PBLs to analyze the T cell response and the relative percentages of the B and T cells subsets. Non-gal IgG and IgM antibodies were measured in serum using their binding to pig endothelial cells (PAECs). Antibody secretion from stimulated PBLs of recipient baboon was also measured by ELISA.

Results and Conclusion

The GE pig cardiac xenografts along with modified IS (either anti- CD154 or CD40 antibody) survived up to 945 day.In MLR in-vitro T and B cells immune response was suppressed. The non-gal IgG and IgM antibodies were inhibited in long-term survivors. Regulatory T cell numbers were also maintained. After one and half or two year , anti-CD40 antibody was withdrawn from long-term xenograft survivors (n=2), which resulted in rejection of GE pig hearts over 8-10 week period. During this period serum levels of non-gal antibodies were progressively increased. These results demonstrate that the costimulation blockade by anti-CD40 antibody effectively suppresses adaptive immune response and xenograft rejection of GE pig hearts.

CITATION INFORMATION: Singh A, Chan J, Corcoran P, Lewis B, Thomas M, Ayares D, Horvath K, Mohiuddin M. Costimulation Blockade by Anti CD40 Antibody Prevents Humoral and Cellular Rejection of Heterotopic Pig Cardiac Xenograft. Am J Transplant. 2016;16 (suppl 3).

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