Investigation of adenoviral gene transfer and associated complement-dependent inflammatory responses
Glycogen Storage Disease type II (GSDII) is caused by the lack of human acid-α-glucosidase (hGAA) activity to effectively reduce the lysosomal glycogen accumulation in striated muscle cells. Adenoviral (Ad) gene transfer vectors show potential for GSDII therapy. Previous studies demonstrated that a single intravenous injection of high-dose AdhGAA vector was able to correct glycogen accumulation, purely by hepatic transduction and secretion of hGAA to affected muscle groups. However, viral promoter shutdown and strong adaptive immune responses to hGAA curtailed the extent of efficacy. We sought to investigate whether the use of a fully deleted (FD) Ad vector expressing hGAA from liver specific promoter/enhancer elements could afford greater efficacy. Intravenous injection of this vector into GAA tolerant or nontolerant GAA-KO mice resulted in persistent, high-level hepatic GAA secretion, and complete glycogen correction in multiple muscle tissues for minimally 6 and 10 months respectively.
Despite the long-term efficacy and reduced adaptive immune response profile, toxicities resulting from Ad capsid interactions with the innate immune system limit Ad gene transfer in vivo. Ad vectors are able to activate complement pathways, which interact with Kupffer cells, platelets, and cytokines/chemokines. Since these same systems have been correlated with Ad associated toxicities, we hypothesized if these toxicities may be significantly diminished by preemptive complement system blockade.
High dose Ad injection into Ad wild-type (WT) and complement deficient (C3-KO) mice resulted in similar Ad transduction levels of liver hepatocytes, but altered the innate toxicity of Ads. The profound thrombocytopenia and elevated plasma cytokine/chemokine concentrations (KC, IL-5, IL-6, G-CSF, and GM-CSF) typically induced after Ad injections into WT mice were minimized after identical injections into C3-KO mice. Microarray analysis revealed that Ad injected WT mice livers as compared to Ad injected C3-KO mice livers, were marked by profound upregulation of genes in coagulation, metabolic, immune response, apoptosis related pathways. Our results confirm that complement inhibition strategies initiated prior to intravenous Ad vector administration should be investigated as a potential means to preemptively abrogate numerous Ad capsid induced toxicities and facilitate the known benefits of Ad mediated gene therapy and/or immunization applications.