Peripheral infection with adenovirus causes unexpected long-term brain inflammation in animals injected intracranially with first-generation, but not with high-capacity, adenovirus vectors: toward realistic long-term neurological gene therapy for chronic diseases.

Although adenoviral vectors provide prolonged gene expression in the brain by comparison to peripheral organs, expression is eliminated by a severe inflammatory infiltration (i.e., activated macrophages/microglia and T-lymphocytes) after peripheral infection with adenovirus. Here, we demonstrate that high-capacity adenoviral (HC-Ad) vectors succeed in maintaining long-term transgene expression in the brain, even in the presence of an active peripheral immunization with adenovirus that completely eliminates expression from first-generation vectors within 60 days. Importantly, even 60 days after the peripheral infection, brains injected with first-generation vectors exhibited evidence of a chronic infiltration of CD8(+) cells, macrophage/microglial activation, and up-regulation of brain MHC-I expression. No inflammation was observed in the brains injected with the HC-Ad vector. Thus, these results demonstrate that HC-Ad vectors will allow safe, stable, and long-term transgene expression in the brain, even in the presence of peripheral infection with adenovirus. This markedly improves the prospects for the use of adenoviral vectors for long-term gene therapy of neurological disorders.