title: Pre-existing immunity to adeno-associated virus (AAV)2 limits transgene expression following intracerebral AAV2-based gene delivery in a 6-hydroxydopamine model of Parkinson's disease.
abstract: BACKGROUND
  Adeno-associated virus (AAV) vectors are used to deliver potentially therapeutic genes in clinical trials in Parkinson's disease (PD). Pre-existing immunity to AAV and a local neuroinflammatory response might negatively affect the efficacy of such AAV-mediated gene delivery.
  
  
  METHODS
  We pre-immunized rats with wild-type AAV-2. Three months later, we created PD-like lesions by intrastriatal injections of 6-hydroxydopamine (6-OHDA) in 50% of the animals. One month later, we injected AAV2 vector expressing enhanced green fluorescent protein (eGFP) in the striatum. Using immunohistochemistry, we assessed eGFP expression, microglia activation and CD8 T cell infiltration. We also measured AAV-2 specific neutralizing antibody titers in the serum.
  
  
  RESULTS
  The number of striatal cells transduced with AAV2 vector expressing eGFP was reduced by 71% in rats pre-immunized with wild-type AAV2 compared to non-immunized animals. We detected elevated numbers of OX6(+) activated microglia in the striatum and circulating AAV2-specific neutralizing antibodies in pre-immunized rats. We also observed that the intrastriatal 6-OHDA injection promoted CD8(+) T cell infiltration and enhanced microglia activation. Nevertheless, the 6-OHDA lesion did not alter AAV2-mediated expression of eGFP in either pre-immunized or non-immunized rats.
  
  
  CONCLUSIONS
  Our findings indicate that intracerebral AAV2-based gene therapy is compromised in rats with pre-existing immunity to AAV2. By contrast, a local neuroinflammatory response, caused by intrastriatal a 6-OHDA injection, does not affect viral vector-mediated transgene expression. Our results emphasize the importance of monitoring circulating AAV-specific neutralizing antibodies in patients undergoing intracerebral gene therapy using AAV vectors.
authors.affiliation: Neuronal Survival Unit, Department of Experimental Medical Science, Lund University, Lund, Sweden.
authors.forename: Shorena
authors.initials: S
authors.lastname: Janelidze
authors.forename: Ulrika
authors.initials: U
authors.lastname: Nordström
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kügler
authors.forename: Patrik
authors.initials: P
authors.lastname: Brundin
mesh_terms: D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood; D000914:Antibodies, Viral / Q000097:blood*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D045744:Cell Line, Tumor; D000229:Dependovirus / Q000235:genetics* / Q000276:immunology; D004195:Disease Models, Animal; D015870:Gene Expression; D018014:Gene Transfer Techniques; D015316:Genetic Therapy / Q000379:methods; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007114:Immunization; D017628:Microglia / Q000187:drug effects / Q000378:metabolism; D016627:Oxidopamine / Q000494:pharmacology; D010300:Parkinson Disease / Q000188:drug therapy / Q000628:therapy*; D051381:Rats; D014161:Transduction, Genetic; D019076:Transgenes
chemical_list: D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D016627:Oxidopamine
keywords: adenoassocated virus (AAV); immunology; inflammatory markers; neurodegenerative disease