Background: Activation of T cells requires both the interaction of T-cell receptor with major histocompatibility complex on the antigen-presenting cell and costimulatory signals, for instance the B7 antigens expressed on antigen-presenting cells and the CD28 molecule expressed on T cells. A recombinant fusion protein, CTLA4-Ig, has been produced that contains the extracellular domain of human CTLA4 fused to IgG1 constant region and that binds the B7 molecule with high affinity. Blocking the CD28/B7 interaction with CTLA4-Ig inhibits T cell activation in vitro and in vivo.
Methods: We used CTLA4-Ig in a fully MHC-mismatched mouse keratoplasty model. The animals were divided into four groups: (1) no treatment, (2) intraperitoneal treatment with 130 micrograms CTLA4-Ig, (3) intraperitoneal treatment with 300 micrograms CTLA4-Ig, (4) subconjunctival treatment with 290 micrograms CTLA4-Ig.
Results: The allograft reaction occurred in untreated animals between days 12 and 16 (mean 13.5). While topical application of CTLA4-Ig seemed to shorten the graft survival (mean 11.6 days) and systemic application of 130 micrograms had no influence (mean 14.0), only intraperitoneal injection of 300 micrograms of CTLA4-Ig prolonged the survival of allografts (mean > 20 days) (P < 0.01).
Conclusion: CTLA4-Ig prolonged significantly the survival of corneal allografts in a fully MHC-mismatched mouse keratoplasty model, but the small antigen load of the corneal transplant and the anterior chamber-associated immune deviation (ACAID) may have a disadvantage to induce tolerance in this model of CTLA4-Ig therapy.