BACKGROUND: Inhibition of chemokine receptor 5 (CCR5), a chemokine receptor expressed on activated T cells, is efficacious in modulating inflammation and immunity as well as in patients with human immunodeficiency virus infection. This study examined the effect and mechanism of CCR5 blockade in combination with cyclosporine in prolonging cardiac allograft survival in mice. METHODS: Hearts from BALB/c mice were transplanted into C57BL/10 recipients. They were administrated with anti-CCR5 antibody (Ab) or control Ab and cyclosporine or phosphate-buffered (PBS) saline, respectively. To investigate the role of regulatory cells, naive mice (secondary recipients) underwent adoptive transfer of splenocytes from anti-CCR5 Ab plus cyclosporine-treated recipients and cardiac allograft transplantation. RESULTS: Compared with recipients treated with control Ab plus PBS, allografts treated with anti-CCR5 Ab and cyclosporine showed significantly prolonged survival (p < 0.001), markedly decreased CD4+ and CD8+ T cells (p < 0.005), and increased frequency of CD4+CD25+Foxp3+ regulatory cells (23.98% +/- 1.55% vs 6.30% +/- 0.57%, p < 0.005). Adoptive transfer of CD4+CD25+ splenocytes from anti-CCR5 Ab plus cyclosporine-treated recipients induced significantly prolonged survival in secondary recipients (p < 0.01 vs adoptive transfer from naive mice and recipients depleted of CD25+ cells). CONCLUSIONS: CCR5 blockade combined with cyclosporine is effective in protecting the cardiac allograft in a robust murine model. This effect is partly mediated by regulatory cell recruitment and control of effector cell infiltration. J Heart Lung Transplant 2010;29:401-470 (C) 2010 International Society for Heart and Lung Transplantation. All rights reserved.