Combined inhibition of apoptosis and complement improves neural graft survival of embryonic rat and porcine mesencephalon in the rat brain.

To define potential mechanisms of cell death during neural cell transplantation, we investigated the role of intracellular caspase activation in combination with the activation of serum complement. We demonstrated that ventral mesencephalic (VM) cells are susceptible to complement-mediated cell lysis that can be blocked with an anti-C5 complement inhibitor (18A10). We also determined that incubating freshly isolated allogenic VM cells with the caspase inhibitor 1-3-Boc-aspartyl(Ome)-fluoromethyl ketone (BAF), followed by immediate striatal implantation, led to a 2.5-fold increase in tyrosine hydroxylase (TH) cell survival 12 weeks postimplantation (P < 0.05). In contrast, overnight incubation with BAF followed by striatal implantation led to a 2-fold reduction in TH cell survival at 12 weeks (P < 0.05). Using the optimal BAF treatment and complement inhibition, we tested the hypothesis that these treatments would lead to increased cell survival in both allogeneic and xenogeneic transplantation models. We transplanted cell suspensions of (a) rat E14 VM or VM treated with (b) BAF alone, (c) anti-C5, or (d) a combination of BAF and anti-C5. There was a significant increase in the relative number of TH-positive cells in the BAF/anti-C5 group versus control at 12 weeks posttransplantation. Similar results were achieved in a pig to rat xenotransplant paradigm. A neuronal xenograft marker (70-kDa neurofilament) also demonstrated relative increases in graft volume in the BAF/anti-C5 treatment group. These studies indicate that more than one mechanism can mediate cell death during neural cell transplantation and that a combined treatment using caspase and complement inhibition can significantly improve cell survival.