RDP1258, a new rationally designed immunosuppressive peptide, prolongs allograft survival in rats: Analysis of its mechanism of action

Peptides derived from the HLA class I heavy chain (a.a. 75-84) have been sh own to modulate immune responses in vitro and in vivo in a non-allele-restr icted fashion. In vivo studies in rodents have demonstrated prolonged allog raft survival following peptide therapy. The immunomodulatory effect of the se peptides has been correlated with peptide-mediated modulation of heme ox ygenase 1 activity (HO-1). Recently, we used a rational approach for design ing novel peptides with enhanced immunosuppressant activity. These peptides were also more potent inhibitors of HO-1 activity in vitro. Here we evalua ted one of these peptides, RDP1258, for its ability to prolong heterotopic heart graft survival in rats. The peptide mediated effect on HO-1 was analy zed in vitro and in vivo. Peptide RDP1258 was shown to inhibit rat HO-1 in vitro in a dose-dependent fashion. However, RDP1258, like other MO-inhibito rs, when administered to rats, secondarily resulted in an up-regulation of splenic HO-1 activity. Up-regulation of HO-1 was associated with prolonged heart allograft survival (6.6 +/- 0.6 vs. 2/14 > 100 days and 12/14 16.2 +/ - 1.7 days; p < 0.001). The analysis of graft infiltrating cells on day 5 a fter transplantation showed a significant decrease in the number of graft i nfiltrating cells in RDP1258-treated recipients compared to untreated ones (14.8 vs. 32.7%; p < 0.01). In addition, grafts from peptide-treated animal s showed significantly decreased expression of TNF-alpha mRNA and increased levels of iNOS mRNA. Our results are consistent with the recent observatio n that up-regulation of HO-1 results in the inhibition of several immune ef fector functions. Modulation of HO-1 activity may enable the development of novel immunomodulatory strategies in humans.