Cytotoxic T Lymphocyte Responses to Transgene Product, Not Adeno-Associated Viral Capsid Protein, Limit Transgene Expression in Mice

Department of Immunotherapy Research, Genzyme, Framingham, MA 01701, USA.
Human gene therapy (Impact Factor: 3.76). 11/2008; 20(1):11-20. DOI: 10.1089/hum.2008.055
Source: PubMed


The use of adeno-associated viral (AAV) vectors for gene replacement therapy is currently being explored in several clinical indications. However, reports have suggested that input capsid proteins from AAV-2 vector particles may result in the stimulation of cytotoxic T lymphocyte (CTL) responses that can result in a loss of transduced cells. To explore the impact of anti-AAV CTLs on AAV-mediated transgene expression, both immunocompetent C57BL=6 mice and B cell-deficient muMT mice were immunized against the AAV2 capsid protein (Cap) and were injected intravenously with an AAV-2 vector encoding alpha-galactosidase (alpha-Gal). C57BL=6 mice, which developed both CTL and neutralizing antibody responses against Cap, failed to show any detectable alpha-Gal expression. In contrast, serum alpha-Gal levels comparable to those of naive mice were observed in muMT mice despite the presence of robust CTL activity against Cap, indicating that preexisting Cap-specific CTLs did not have any effect on the magnitude and duration of transgene expression. The same strategy was used to assess the impact of CTLs against the alpha-Gal transgene product on AAV-mediated gene delivery and persistence of transgene expression. Preimmunization of muMT mice with an Ad=alpha-Gal vector induced a robust CTL response to alpha-Gal. When these mice were injected with AAV2=alpha-Gal vector, initial levels of alpha-Gal expression were reduced by more than 1 log and became undetectable by 2 weeks postinjection. Overall, our results indicate that CTLs against the transgene product as opposed to AAV capsid protein are more likely to interfere with AAV transgene expression.

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Available from: Johanne M Kaplan
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    • "Transduction efficiency can be also be increased by mutating surface exposed tyrosine residues on the capsid, which is thought to reduce proteasomal degradation, increasing trafficking to the nucleus (Zhong et al., 2008; Markusic et al., 2010). Though a variety of mechanisms are involved in these studies, they, along with other studies in animals, are united by a common theme: in current murine models, functional CD8+ T cell infiltrates in AAV transduced tissues are primary directed against the transgene product rather than the capsid, while an antibody response is often observed to both potential immunogens (Siders et al., 2009). "
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