Adenoviral gene transfer into the normal and injured spinal cord: enhanced transgene stability by combined administration of temperature-sensitive virus and transient immune blockade

Abstract

This study characterized gene transfer into both normal and injured adult rat dorsal spinal cord using first (E1−/E3−) or second (E1−/E2A₁₂₅/E3−, temperature-sensitive; ts) generation of replication-defective adenoviral (Ad) vectors. A novel immunosuppressive regimen aimed at blocking CD4/CD45 lymphocytic receptors was tested for improving transgene persistence. In addition, the effect of gene transfer on nociception was also evaluated. Seven days after treatment, numerous LacZ-positive cells were observed after transfection with either viral vector. By 21 days after transfection, β-galactosidase staining was reduced and suggestive of ongoing cytopathology in both Ad-treated groups, despite the fact that the immunogenicity of LacZ/Ad_ts appeared less when compared with that elicited by the LacZ/Ad vector. In contrast, immunosuppressed ani- mals showed a significant (P ⩽ 0.05) increase in the number of LacZ-positive cells not displaying cytopathology. In these animals, a concomitant reduction in numbers of macrophages/microglia and CD4 and CD8 lymphocytes was observed. Only animals that received LacZ/Ad_ts and immunosuppression showed transgene expression after 60 days. Similar results were observed in animals in which the L4–L5 dorsal roots were lesioned before transfection. Gene transfer into the dorsal spinal cord did not affect nociception, independent of the adenovirus vector. These results indicate that immune blockade of the CD4/CD45 lymphocytic receptors enhanced transgene stability in adult animals with normal or injured spinal cords and that persistent transgene expression in the spinal cord does not interfere with normal neural function.