• ¹Walter Brendel Centre of Experimental Medicine, Ludwig-Maximilians-Universität München, Marchioninistr. 15, 81377 Munich, Germany.
• ²Department of Physics & Center for NanoScience, Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, 80539 Munich, Germany.
• ³Walter Brendel Centre of Experimental Medicine, Ludwig-Maximilians-Universität München, Marchioninistr. 15, 81377 Munich, Germany. Electronic address: markus.rehberg@lrz.uni-muenchen.de.

DNA-based nanoconstructs possess great potential for biomedical applications. However, the in vivo behavior of such constructs at the microscopic tissue/cell level as well as their inflammatory potential is largely unknown. Unmethylated CpG sequences of DNA are recognized by Toll-like receptor 9 (TLR9), and thus initiate an innate immune response. In this study, we investigated the use of DNA-based nanotubes as carrier systems for CpGdelivery and their effect on immune cells in vivo and in real time. DNA nanotubes were microinjected into skeletal muscle of anesthetized mice. Using in vivo microscopy, we observed that the DNA tubes were internalized within minutes by tissue-resident macrophages and localized in their endosomes. Only microinjection of CpG-decorated DNA nanotubes but not of plain DNA nanotubes or CpG oligonucleotides induced a significant recruitment of leukocytes into the muscle tissue as well as activation of the NF-ĸB pathway in surrounding cells. These results suggest that DNAnanotubes are promising delivery vehicles to target tissue macrophages, whereupon the immunogenic potential depends on the decoration with CpG oligonucleotides.