Prevention of acute vascular rejection by a functionally blocking anti-C5 monoclonal antibody combined with cyclosporine

Background. Inhibition of the complement cascade at C5 prevents formation of pro-inflammatory molecules C5a and C5b-9, which play a key role in allograft rejection. The present study was undertaken to determine whether blocking terminal complement with anti-C5 monoclonal antibody (mAb) alone or combined with cyclosporine (CsA) would prevent acute vascular rejection (AVR) in a mouse cardiac allograft model. Methods. C3H mouse hearts were transplanted into BALB/c mice and randomized into five groups with the following treatments: (1) no treatment; (2) CsA alone; (3) control mAb; (4) anti-C5 mAb alone; and (5) anti-C5 mAb and CsA. Results. Allografts in untreated or control mAb-treated recipients were rapidly rejected at 8.0 +/- 0.6 and 8.2 +/- 0.8 days, respectively. These grafts exhibited typical AVR, characterized by vasculitis, hemorrhage, and thrombosis. A high level of complement activity was also demonstrated in these animals. High-dose CsA was not able to inhibit complement activation or AVR, and grafts were rejected in 15.5 +/- 1.1 days. Anti-C5 monotherapy completely inhibited complement activation and attenuated AVR, but grafts were rejected in 8.3 +/- 0.5 days by acute cellular rejection. In contrast, a combination of anti-C5 mAb and CsA successfully achieved indefinite graft survival (> 100 days). This combined therapy completely inhibited terminal complement activation and prevented both humoral- and cellular-mediated rejection. Conclusions. Combination therapy of anti-C5 mAb and CsA achieves indefinite graft survival in a mouse cardiac allograft model. These data suggest that inhibition of terminal complement using anti-C5 mAb may be an effective therapeutic adjunct to prevent AVR in clinical transplantation.