Original Articles Salmonella SL7207 application is the most effective DNA vaccine delivery method for successful tumor eradication in a murine model for neuroblastoma Elisa Berger a , Rocio Soldati a , Nicole Huebener b , Oliver Hohn c , Alexander Stermann d , Tahir Durmus e , Stephan Lobitz f , Ana C. Zenclussen a , Holger Christiansen g , Holger N. Lode d , Stefan Fest g,⇑ a Laboratory of Pediatric Immunotherapy, Department of Experimental Obstetrics and Gynecology, Medical Faculty, Otto-von Guericke University of Magdeburg, Germany b Genetics of Metabolic and Reproductive Disorders, Max-Delbrück Center for Molecular Medicine, Berlin, Germany c Robert Koch Institute, FG18-Division for HIV and other retroviruses, Berlin, Germany d Department of Pediatric Oncology, University Medicine of Greifswald, Greifswald, Germany e Department of Radiology, Charité, Berlin, Germany f Department of Pediatric Oncology, Hematology, BMT, Charité – Universitätsmedizin Berlin, Berlin, Germany g Department of Pediatric Oncology, University of Leipzig, Leipzig, Germany article info Article history: Received 7 November 2012 Accepted 25 December 2012 Available online xxxx Keywords: Neuroblastoma SL7207 Dendritic cells Gene gun Lentiviral particle abstract Attenuated Salmonella is an approved oral life vaccine that is currently entering pre-clinical cancer vac- cination studies as a promising DNA carrier. In a syngeneic mouse model for neuroblastoma, oral gavage of Salmonella typhimurium (SL7207) carrying recent generated survivin DNA vaccines induced a stronger cellular anti-NB immune response than gene gun application or injection of lentivirally transduced bone marrow-derived DCs. The level of Salmonella-associated side effects was not significant as indicated by unaffected survivin-mediated hematopoiesis and wound healing. We believe that our findings provide an important baseline to translate Salmonella-based DNA vaccination into a clinical application for neuroblastoma. Ó 2013 Elsevier Ireland Ltd. All rights reserved. 1. Introduction DNA vaccination is a versatile and cost-effective method to acti- vate the immune system against cancer [1,2]. The advantages of plasmid DNA vaccines are the continuous expression of antigens and likewise of co-stimulatory molecules, such as pro-inflamma- tory Th 1 cytokines [2]. Moreover, DNA plasmids provide immuno- stimulatory unmethylated CpG motifs, activating the TLR-9 receptor pathway [3,4] and the option to fuse the antigen sequence to upstream ubiquitin, thus facilitating proteasomal degradation, antigen presentation and effector cell activation [5–7]. These extraordinary characteristics favor the application of DNA vaccines over peptide or dendritic cell (DC) vaccination and prompted us to establish an effective DNA vaccination approach against neuroblas- toma (NB). This tumor of neuroectodermal origin is the most com- mon solid extracranial tumor during childhood and accounts for approximately 20% of cancer deaths in children between 1 and 10 years [8,9]. We generated DNA plasmids encoding for all well- known NB-associated antigens, i.e. tyrosine hydroxylase (TH), the first step enzyme of catecholamine synthesis, for peptide mimics of the disialoganglioside GD-2 and for the inhibitor of apoptosis protein survivin (SSV) [5,10–12]. All these DNA vaccines were effi- cient to induce a potent immune response eradicating NB in a pre- clinical immunocompetent mouse model. However, sufficient transfection of host antigen presenting cells (APCs) emerges as a major problem to translate DNA vaccination from animal models into clinical application [2]. This depends to great extend on the method of DNA delivery [13]. Most of the cur- rent vaccination phase I/II trails were performed with naked DNA injected into skin, muscle or lymph node resulting in a moderate stimulation of the immune system and a poor clinical response with no significant effect on event-free or overall survival rates (EFS, OS) [1,2,13]. Extensive efforts were made to improve DNA plasmid delivery into hosts using carrier systems known to be effective in membrane penetration and receptor-associated APC phagocytosis [14–17]. For these purposes the attenuated Salmo- nella typhimurium SL7207 strain was engineered [18]. SL7207 are not able to survive more than 2 cycles within a mammalian organ- 0304-3835/$ - see front matter Ó 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.canlet.2012.12.026 ⇑ Corresponding author. Address: Abt. für Pädiatrische Onkologie, Hämatologie und Hämostaseologie, Universitätsklinik und Poliklinik für Kinder und Jugendliche, Department für Frauen- und Kindermedizin, Liebigstr. 20a, D-04103 Leipzig, Germany. Tel.: +49 (0) 394 97 26510; fax: +49 (0) 394 97 26549. E-mail address: stefan.fest@medizin.uni-leipzig.de (S. Fest). Cancer Letters xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Cancer Letters journal homepage: www.elsevier.com/locate/canlet Please cite this article in press as: E. Berger et al., Salmonella SL7207 application is the most effective DNA vaccine delivery method for successful tumor eradication in a murine model for neuroblastoma, Cancer Lett. (2013), http://dx.doi.org/10.1016/j.canlet.2012.12.026