Prolongation of Islet Allograft Survival by Coexpression of CTLA4Ig and CD40LIg in Mice

Background: B7/CD28 and CD40/CD40L have been well established as important costimulatory pathways. Cytotoxic T lymphocyte-associated antigen-4 (CTLA4) delivers negative signals to antigen-presenting cells to down-regulate proinflammatory responses and competitively inhibits the binding of B7 and CD28. Signals from the CD40/CD40L costimulatory pathway also play an important role in acute rejection of organ grafts. Methods: Recombinant adenoviruses Ad-sCD40LIg-IRES₂-CTLA4Ig, Ad-CTLA4Ig, and Ad-sCD40LIg were constructed to express sCD40LIg and CTLA4Ig simultaneously or separately as described previously. Streptozocin-induced diabetic BALB/c mice were injected with recombinant adenovirus, receiving approximately 500 donor islets isolated from C57BL/6 mice under the left kidney capsule. Five groups were assigned according to the treatment: nontreated group, Ad-Shuttle-CMV-treated group, Ad-CTLA4Ig-treated group, Ad-sCD40LIg-treated group, and Ad-sCD40LIg-IRES₂-CTLA4Ig-treated group. The islet graft mean survival time (MST) was evaluated in the present study. Results: Compared to the islet graft MST of the nontreated group (7.3 ± 0.82 days) or Ad-Shuttle-CMV-treated group (7.2 ± 1.47 days), the Ad-CTLA4Ig-treated and Ad-CD40LIg-treated islet graft survivals in recipients were 56.3 ± 13.71 days (P < .01) and 47.3 ± 15.64 days (P < .05), respectively. The islet graft MST was dramatically prolonged to 116.3 ± 20.32 days in the Ad-sCD40LIg-IRES₂-CTLA4Ig-treated group (P < .01). Conclusion: Simultaneous blockade of the CD40/CD40L and B7/CD28 costimulatory pathways via coexpression of sCD40LIg and CTLA4Ig mediated by replication-defective adenovirus may be an acceptable method to induce immune tolerance.