HDAd6/35++-A new helper-dependent adenovirus vector platform for in vivo transduction of hematopoietic stem cells

In previous studies, we achieved safe and efficient in vivo he-matopoietic stem cell (HSC) transduction in mobilized mice and macaques with intravenously injected helper-dependent adenovirus HDAd5/35++ vectors. These vectors are derivatives of serotype Ad5-containing CD46-affinity enhanced Ad35 fiber knob domains. Considering the impact of anti-Ad5/HDAd5/ 35++ neutralizing serum antibodies present in the human pop-ulation, we generated HSC-retargeted HDAd6/35++ vectors derived from serotype 6. We found a lower prevalence and ti-ters of serum anti-HDAd6/35++ in human samples compared with HDAd5/35++. HDAd6/35++ vectors efficiently trans-duced human and rhesus CD34+ cells in vitro. Intravenous injection of HDAd5/35++-GFP or HDAd6/35++-GFP vectors after G-CSF/AMD3100 mobilization of mice with established human hematopoiesis or human CD46 transgenic mice re-sulted in comparable GFP marking rates in HSCs in the bone marrow and spleen. In long-term in vivo HSC transduction and selection studies with integrating vectors, stable GFP expression in >75% of PBMCs was show for both vectors. In contrast with HDAd5/35++, undesired transduction of hepa-tocytes was minimal with HDAd6/35++. Furthermore, HDAd6/35++ allowed for efficient in vivo HSC transduction in Ad5-pre-immune mice. These features, together with the straightforward production of HDAd6/35++ vectors at high yield, make this new HDAd vector platform attractive for clin-ical translation of the in vivo approach.

Automated summary

In previous studies, safe and efficient in vivo hematopoietic stem cell (HSC) transduction was achieved by intravenously injecting helper-dependent adenovirus HDAd5/35++ vectors in mobilized mice and macaques. To address the impact of anti-Ad5/HDAd5/35++ neutralizing serum antibodies in humans, HSC-retargeted HDAd6/35++ vectors derived from serotype 6 were generated. Compared with HDAd5/35++, HDAd6/35++ showed a lower prevalence and titers of serum anti-HDAd6/35++ in human samples. In vitro studies demonstrated efficient transduction of human and rhesus CD34+ cells by HDAd6/35++ vectors.