Inhibition of Terminal Complement Components in Presensitized Transplant Recipients Prevents Antibody-Mediated Rejection Leading to Long-Term Graft Survival and Accommodation

Abstract

Ab-mediated rejection (AMR) remains the primary obstacle in presensitized patients following organ transplantation, as it is refractory to anti-T cell therapy and can lead to early graft loss. Complement plays an important role in the process of AMR. In the present study, a murine model was designed to mimic AMR in presensitized patients. This model was used to evaluate the effect of blocking the fifth complement component (C5) with an anti-C5 mAb on prevention of graft rejection. BALB/c recipients were presensitized with C3H donor skin grafts 7 days before heart transplantation from the same donor strain. Heart grafts, transplanted when circulating anti-donor IgG Abs were at peak levels, were rejected in 3 days. Graft rejection was characterized by microvascular thrombosis and extensive deposition of Ab and complement in the grafts, consistent with AMR. Anti-C5 administration completely blocked terminal complement activity and local C5 deposition, and in combination with cyclosporine and short-term cyclophosphamide treatment, it effectively prevented heart graft rejection. These recipients achieved permanent graft survival for >100 days with normal histology despite the presence of systemic and intragraft anti-donor Abs and complement, suggesting ongoing accommodation. Furthermore, double-transplant experiments demonstrated that immunological alterations in both the graft and the recipient were required for successful graft accommodation to occur. These data suggest that terminal complement blockade with a functionally blocking Ab represents a promising therapeutic approach to prevent AMR in presensitized recipients.

Molecules Great and Small

“…Documentation of impaired MAC complex (C5b-9) formation in the C6 2/2 recipients (73) supports the conclusion that terminal complement is a key effector mechanism. In work by others, anti-C5 mAb (inhibits C5 cleavage) plus cyclosporin and short-term cyclophosphamide resulted in prolonged heart allograft survival in presensitized mice, despite persistent antidonor IgG in the sera and the graft (74).…”

Deficiency of Capn4 Gene Inhibits Nuclear Factor-κB (NF-κB) Protein Signaling/Inflammation and Reduces Remodeling after Myocardial Infarction

“…Monocytes/macrophages were detected with a biotin-conjugated rat anti-mouse Mac-1 mAb (Cedarlane Laboratories) and then stained by a standard indirect avidin-biotin immunoperoxidase method using an Elite VECTASTAIN ABC kit (Vector Laboratories) as described previously (34). In addition, CD68 mRNA expression was determined as an additional marker of monocytes/macrophages.…”

Free Bone Graft Attenuates Acute Rejection and in Combination with Cyclosporin A Leads to Indefinite Cardiac Allograft Survival

“…Briefly, recipient mouse sera were obtained at the indicated time points from the various treatment groups, diluted 1/25 in PBS (determined by prior titration to be the most appropriate dilution for Ag-Ab recognition while avoiding Ag-Ab saturation), and incubated with C3H or C57BL/6 mouse splenocytes at 37°C for 30 min (40). Aliquots of washed cells were then incubated for 1 h at 4°C with either FITC-conjugated, affinity-purified goat Fab anti-mouse IgG (Caltag Laboratories) or anti-mouse IgM (Jackson ImmunoResearch Laboratories), as well as being simultaneously stained with rhodamine red-conjugated, affinity-purified goat Fab anti-mouse CD3.…”