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T cell-directed immunosuppressive therapy prevents development of natural anti-AB and anti-pig antibodies in infant baboons

Eefje Dons¹, Claudia Montoya¹, Hidetaka Hara¹, Cassandra Long¹, Gabriel Echeverri¹, Burcin Ekser¹, Corin Ezzelarab¹, Dasha Roa¹, Roman Wolf², Mohamed Ezzelarab¹, Lori West³, David Cooper¹

¹Thomas E. Starzl Transplantation Institute, Department of Surgery, University of Pittsburgh, Pittsburgh, PA, United States; ²Division of Animal Resources, Oklahoma University Health Sciences Center, Oklahoma City, OK, United States; ³Department of Pediatrics, Cardiac Transplant Research, University of Alberta, Edmonton, AB, Canada

Introduction: We attempted to determine whether B cell tolerance to incompatible A/B (AB-I) allo-antigens and wild-type (WT) pig xeno-antigens could be achieved in infant baboons before production of anti-AB and anti-pig antibodies (Abs) begins during the first few months of life.

Methods: We implanted artery patch grafts in the aorta in 3m baboons using either AB-I or WT grafts. Gp1 (n=2) received either AB-I or WT graft without immunosuppressive therapy (IS). Gp2A received AB-I+IS (n=2); Gp2B received WT+IS (n=2). IS (ATG, anti-CD154mAb, MMF) was discontinued at 8m of age. Gp3 (n=2) received either anti-CD154mAb or CTLA4-Ig only, but no graft. A control group (Gp4, n=6) received no IS and no graft. Follow-up (except in Gp1) was for 12-18m. Anti-AB and anti-Gal IgM and IgG were measured by ELISA; anti-pig Abs by flow cytometry. The cellular response was measured by MLR.

Results: In Gp 4, anti-AB and anti-pig IgM (but not IgG) increased steadily throughout follow-up. Gp1 became sensitized only to donor-specific A or B or pig antigens within 2 weeks (increase in IgG Abs and proliferation in MLR), and were euthanized at 4 weeks. Gp2 and Gp3 that received anti-CD154mAb did not make either anti-AB or anti-pig Abs while receiving IS (irrespective of the presence or type of graft), but both anti-AB and anti-pig IgM (but not IgG) began to increase steadily after ceasing IS.

Conclusions: The production of natural anti-AB and anti-pig Abs was inhibited by IS with anti-CD154mAb (but not CTLA4-Ig), even in the absence of an allograft or xenograft, suggesting that natural Abs may be T cell-dependent. These data contrast to clinical experience with AB-I allotransplantation in infants, who cease producing only donor-specific Abs, and may be related to the IS agent used. Lack of Ab production to a pig g.