Abstract
We have recently demonstrated that adeno-associated virus serotype 9 (AAV9)-mediated human erythropoietin (hEPO) gene delivery into the brain protects dopaminergic (DA) neurons in the substantia nigra in a rat model of Parkinson's disease. In the present study, we examined whether pre-exposure to AAV9-hEPO vectors with an intramuscular or intrastriatal injection would reduce AAV9-mediated hEPO transduction in rat brain. We first characterized transgene expression and immune responses against AAV9-hEPO vectors in rat striatum at 4 days, 3 weeks and 6 months, and with doses ranging from 1011 to 1013 viral genomes. To sensitize immune system, rats received an injection of AAV9-hEPO into either the muscle or the left striatum, and then sequentially an injection of AAV9-hEPO into the right striatum 3 weeks later. We observed that transgene expression exhibited in a time course and dose dependent manner, and inflammatory and immune responses displayed in a time course manner. Intramuscular, but not intrastriatal injections of AAV9-hEPO resulted in reduced levels of hEPO transduction and increased levels of the major histocompatibility complex (MHC) class I and class II antigen expression in the striatum following AAV9-hEPO re-administration. There were infiltration of the cluster of differentiation 4 (CD4)-and CD8-lymphacytes, and accumulation of activated microglial cells and astrocytes in the virally injected striatum. In addition, the sera from the rats with intramuscular injections of AAV9-hEPO contained greater levels of antibodies against both AAV9 capsid protein and hEPO protein than the other treatment groups. hEPO gene expression was negatively correlated with the levels of circulating antibodies against AAV9 capsid protein. Intramuscular and intrastriatal re-administration of AAV9-hEPO led to increased numbers of red blood cells in peripheral blood. Our results suggest that pre-immunization with an intramuscular injection can lead to the reduction of transgene expression in the striatal re-administration.
Highlights
Adeno-associated virus (AAV) vectors show promise for gene therapy of chronic neurological disorders including Parkinson’s disease (PD) [1,2], due to their non-pathogenic, ability to transduce non-dividing cells and dividing cells, long-term transgene expression [3,4], no detected toxicity and minimal immune responses in transduced regions [4,5]
At 4 days, immunocytochemical staining showed that AAV9mediated human erythropoietin (hEPO) gene transduction in the injected striatum was at a low level. hEPO immunostaining was light in the injected striatum, and hEPO-immunoreactive (IR) cells were barely detected in low magnification images of striatal sections (Fig. 2A)
We used associated virus serotype 9 (AAV9)-mediated hEPO gene transfer into the rat brain as a model system to systematically characterize inflammatory and immune responses to intrastriatal AAV9-hEPO vectors when recipient rats were at different immune status with intrastriatal or intramuscular injections of AAV9hEPO vectors
Summary
Adeno-associated virus (AAV) vectors show promise for gene therapy of chronic neurological disorders including Parkinson’s disease (PD) [1,2], due to their non-pathogenic, ability to transduce non-dividing cells and dividing cells, long-term transgene expression [3,4], no detected toxicity and minimal immune responses in transduced regions [4,5]. We have recently shown that intrastriatal injections of AAV9 carrying a human erythropoietin (hEPO) gene result in a robust hEPO transduction in the striatum and protect nigral DA neurons from 6-hydroxydopamine (6-OHDA) toxicity in a rat model of PD, suggesting its therapeutic potential for PD [12]. Clinical studies have shown that the translations of AAV-mediated gene therapy into humans unexpectedly result in only short-term expression of the therapeutic. It suggests that an immune response against AAV vectors plays a very important role in the obstacle for successful translations to humans. The AAVmediated transgene expression may be precluded because of the preexisting neutralizing antibodies and AAV capsid-specific T cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
