Research Article Gene Electrotransfer of Plasmid-Encoding IL-12 Recruits the M1 Macrophages and Antigen-Presenting Cells Inducing the Eradication of Aggressive B16F10 Murine Melanoma Ursa Lampreht Tratar, 1 Luisa Loiacono, 2,3 Maja Cemazar, 1,4 Urska Kamensek, 1 Vito Michele Fazio, 2,3 Gregor Sersa, 1 and Emanuela Signori 2,5 1 Department of Experimental Oncology, Institute of Oncology Ljubljana, Zaloska 2, Ljubljana, Slovenia 2 Laboratory of Genetic and Clinical Pathology, University Campus Bio-Medico of Rome, Via Álvaro del Portillo 21, 00128 Rome, Italy 3 Laboratory of Oncology, IRCCS “Casa Sollievo della Sofferenza”, Viale dei Cappuccini, 71013 San Giovanni Rotondo, Italy 4 Faculty of Health Sciences, University of Primorska, Polje 42, Izola, Slovenia 5 National Research Council-Institute of Translational Pharmacology (CNR-IFT), Via Fosso del Cavaliere 100, Rome, Italy Correspondence should be addressed to Maja Cemazar; mcemazar@onko-i.si and Emanuela Signori; emanuela.signori@ift.cnr.it Received 9 January 2017; Revised 3 March 2017; Accepted 12 March 2017; Published 17 May 2017 Academic Editor: Rafael E. Marques Copyright © 2017 Ursa Lampreht Tratar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Cancer immunotherapy is currently one of the leading approaches in cancer treatment. Gene electrotransfer of plasmids encoding interleukin 12 (IL-12) into the cells leads to the production of IL-12, which drives immune cell polarization to an antitumoral response. One of the cell types that shows great promise in targeting tumor cells under the influence of IL-12 cytokine milieu is that of macrophages. Therefore, the aim of this study was to evaluate gene electrotransfer of antibiotic resistance-free plasmid DNA-encoding murine IL-12 (mIL-12) in mice bearing aggressive B16F10 murine melanoma. IL-12 electrotransfer resulted in the complete long-term eradication of the tumors. Serum mIL-12 and murine interferon γ (mIFNγ) were increased after IL-12 gene electrotransfer. Further on, hematoxylin and eosin (HE) staining showed increased infiltration of immune cells that lasted from day 4 until day 14. Immunohistochemistry (IHC) staining of F4/80, MHCII, and CD11c showed higher positive staining in the IL-12 gene electrotransfer group than in the control groups. Immune cell infiltration into the tumors and the high density of MHCII- and CD11c-positive cells suggest an antitumor polarization of macrophages and the presence of antigen-presenting cells that contributes to the important antitumor effectiveness of IL-12. 1. Introduction In the last decade, one of the main focuses of cancer research has been the involvement of immune system in the progres- sion of the disease. It is well established that the mechanisms of immune evasion play an important role in cancer progres- sion. Tumor cells are able to silence the immune system, reduce the expression of tumor antigens, inactivate immune cells, and induce the microenvironment to release immune suppressors [1]. Therefore, treatments aiming at modifica- tion of immune response have become a promising approach in treatment of tumors. Immunotherapy protocols can enhance the capacity of the immune system to fight cancer and counteract suppressing signals produced by tumor cells [2, 3]. Macrophages represent one of the main targets of immunotherapy, since they can be key actors in tumor progression. Tumor-associated macrophages (TAMs) are the most abundant cells in a tumor microenvironment. Schematically, two main TAM pheno- types could be identified in the complex shadows of their func- tional states: M1, with antitumor activity, and M2, with protumor activity. The protumor activities of M2 TAMs are assigned to specific subpopulations of macrophages and con- sist of suppression of T-cell response, angiogenesis, tumor cell invasion, motility, and intravasation [4]. M1 macrophages are activated by the granulocyte monocyte colony-stimulating factor (GM-CSF) and the tumor necrosis factor alpha (TNF-α). They express MHCII and produce IL-12 and Hindawi Mediators of Inflammation Volume 2017, Article ID 5285890, 11 pages https://doi.org/10.1155/2017/5285890