Macrophage Depletion via Clodronate Pretreatment Reduces Transgene Expression from AAV Vectors In Vivo

Abstract

Adeno-associated virus is a popular gene delivery vehicle for gene therapy studies. A potential roadblock to widespread clinical adoption is the high vector doses required for efficient transduction in vivo, and the potential for subsequent immune responses that may limit prolonged transgene expression. We hypothesized that the depletion of macrophages via systemic delivery of liposome-encapsulated clodronate would improve transgene expression if given prior to systemic AAV vector administration, as has been shown to be the case with adenoviral vectors. Contrary to our expectations, clodronate liposome pretreatment resulted in significantly reduced transgene expression in the liver and heart, but permitted moderate transduction of the white pulp of the spleen. There was a remarkable localization of transgene expression from the red pulp to the center of the white pulp in clodronate-treated mice compared to untreated mice. Similarly, a greater proportion of transgene expression could be observed in the medulla located in the center of the lymph node in mice treated with clodronate-containing liposomes as compared to untreated mice where transgene expression was localized primarily to the cortex. These results underscore the highly significant role that the immune system plays in influencing the distribution and relative numbers of transduced cells in the context of AAV-mediated gene delivery.

Macrophage inhibitor clodronate enhances liver transduction of lentiviral but not AAV vectors or mRNA lipid nanoparticlesin vivo

“…These molecules in turn promote immune cell induction and activation allowing the initiation and expansion of antitransgene and/or anti-capsid adaptive immune cells, primarily CD8+ T cells [86][87][88]. In line with our findings, the absence of AAV-mediated enhanced liver transduction following clodronate-induced macrophage inhibition was previously reported in 8-week-old C57BL6/J mice [50]. The different observations between lentiviral and AAV-mediated liver transduction In conclusion, our study shows that clodronate-induced macrophage inhibition enhances lentiviral-mediated liver transduction in vivo.…”

“…Pre-administration of clodronate liposomes followed by administration of adenoviral vectors depleted macrophages and allowed higher liver transduction in vivo [47][48][49]. In contrast, pre-administration of clodronate and AAV vector injection in vivo produced a considerable reduction in transgene expression in the liver [50].…”

Prevalence of antibodies against adeno-associated viruses (AAVs) in Göttingen Minipigs: Implications for Gene Therapy and Xenotransplantation

“…It has been reported that most people have already been exposed to wild-type AAVs [31], resulting in the development of an immune response against them. These patients, develop not only binding antibodies but also NAbs.…”

“…To address this, different strategies can be used, for example using modi ed capsids [29]. AAV vectors also may be altered by pseudo-typing, using the capsid of a heterologous AAV [31]. This could be tricky when using a recombinant vector developed from non-human primates (NHPs), for example when using AAVrh10, a virus originated in rhesus macaques, about 59% of healthy human adults had antibodies against it, and 21% had NAb's [32].…”