Résumé :
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Clinical gene therapy studies have demonstrated the immunogenicity of AAV vectors since neutralizing antibodies and cytolytic T-cell responses have been elicited against the capsid, in some patients. For further clinical development, the immunogenicity of AAV vectors should be better understood in preclinical models. We are interested in rAAV2/1 vectors which are promising tools for gene transfer into skeletal muscle. We evaluated the innate and adaptive immune responses following a bolus intravenous (IV) administration in mice. Innate immune responses triggered by AAV vectors are thought to be weak, yet hepatic inflammatory reactions were described in mice following IV administration (Zaiss et al., J. Virol 2002). In our hands, the IV injection of 1011 vg endotoxin-free AAV2/1 vector did not trigger a detectable cytokine response. On the contrary, research-grade AAV2/1 preparations induced rapid but transient increases in TNFa, IL6, CCL5 and CXCL10 mRNAs, presumably an effect of the LPS contained in these preparations. Endotoxin-free AAV2/1 vectors triggered strong and neutralizing humoral responses initiated with IgM followed by IgG conversion peaking respectively at 1 and 2.5 weeks. A dose-dependent increase in IgG2a and IgG3 levels was observed with increasing amounts (1010, 1011 or 1012 vg) of vector whereas IgG2b were high at all doses and little IgG1 was detected. We found no evidence of CD4+ or CD8+ T-cell priming based on proliferation or activation markers. In conclusion, a bolus IV administration of rAAV2/1 vector in mice induces a strong humoral immune response against the capsid but little to no inflammation or cellular immunity. However, antibody isotype profiles suggest an underlying IFNg or TGFb-mediated T cell response. Our current prospects are (i) to further characterize the cellular immune response to the AAV1 capsid using reporter epitopes (ii) to assess the pro-inflammatory potential of AAV1 vector through activation of TLRs or others pathway of inflammasome.
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