Blockade of Costimulation Between T Cells and Antigen-Presenting Cells: An Approach to Suppress Murine Graves' Disease Induced Using Thyrotropin Receptor-Expressing Adenovirus

Objective: Immune responses require costimulatory interactions between molecules on antigen-presenting cells and T cells: CD40 binding to CD40 ligand and B7 binding to CD28. Graves' hyperthyroidism is induced in BALB/c mice by immunization with thyrotropin receptor (TSHR) A-subunit adenovirus (Ad-A–subunit). We attempted to modulate Ad-A-subunit–induced Graves' disease using adenoviruses expressing costimulation"decoys": CD40-IgG-Fc (CD40-Ig) to block CD40:CD40-ligand interactions and CTLA4-Fc (CTLA4-Ig) to prevent B7:CD28 binding. Outcome: Unexpectedly, coimmunizing mice with Ad-A–subunit and excess control adenovirus(1:10 Ad-A–subunit:Ad-control) reduced TSHR antibody levels (thyrotropin binding inhibition [TBI]). Furthermore, only 15% of mice developed hyperthyroidism versus 75% using the same Ad-A–subunit dose (108 particles) without Ad-control. This effect was related to the dose of control adenovirus but not to the adenovirus insert, the timing or immunization site. Increasing the Ad-subunit dose (109 particles) and decreasing the control adenovirus dose (10:1 Ad-A–subunit:Ad-control) induced high TBI levels and 80% of mice were hyperthyroid. Coimmunization with Ad-CD40-Ig (but not Ad-CTLA4-Ig) reduced the incidence of hyperthyroidism to 40%. Conclusions: Using appropriate controls and adenovirus ratios, our data suggest the importance of CD40:CD40-ligand interactions for inducing Graves' hyperthyroidism by Ad-A–subunit. Furthermore, our observations emphasize the potential pitfalls of non-specific inhibition by coimmunization with two adenovirus species.