Abstract 2399: Inhibition of murine breast cancer growth by immunization with tumor cells transfected with a dominant negative vector of Stat3
Authors: Tkach Mercedes , Rosemblit Cinthia , Rivas Martín A. , Beguelin Wendy , Proietti Cecilia , Flaqué Celeste M. Diaz , Maronna Esteban , Charreau Eduardo H. , Elizalde Patricia V. , Schillaci Roxana 
Published: February 2011

Abstract
Stat3 is constitutively activated in several cancer types. Its activation in tumors promotes the transcription of genes associated with cell-cycle progression, cell survival, angiogenesis, and immune evasion. In particular in breast cancer, elevated activation levels of Stat3 are linked to breast tumorigenesis. We have already shown that progestins induce Stat3 activation in murine and human breast cancer cells. Moreover, we demonstrated that in the C4HD tumor that belongs to a progestin-dependent murine mammary tumor model, which requires medroxiprogesterone acetate (MPA) administration to proliferate, the presence of activated Stat3 is an absolute requirement for progestin stimulation of in vitro and in vivo breast cancer growth. Based on the evidence that disruption of Stat3 signaling in tumor cells can overcome tumor immune evasion, the present study focused on whether serial injection of irradiated C4HD cells expressing a dominant negative form of Stat3 (DNStat3), Stat3Y705F, could provide protection against C4HD wild-type tumor challenge, and focused as well on elucidating the mechanism mediating this effect. Our results showed that Balb/c mice immunized with DNStat3-transfected C4HD cells experienced significant inhibition of tumor growth with MPA (77%, 74% and 78% as compared with mice injected with PBS, with wild-type C4HD cells, or with empty vector-transfected C4HD cells, respectively). The lack of protection against tumor formation in nude mice suggested that T lymphocytes were involved in the antitumor response. Delayed-type hypersensitivity (DTH) assays in immunized Balb/c mice showed a strong increase in DTH reactivity in mice injected with DNStat3-transfected C4HD cells as compared to control groups, confirming that a cellular immune response was involved in the antitumoral effect. To evaluate this in vitro, we performed a 51Cr release assay to study the cytotoxic potential of the stimulated splenocytes towards C4HD cells. Only splenocytes isolated from mice injected with DNStat3-transfected C4HD cells were effective in lysing C4HD (37,9+0,6% cytotoxic activity at 50:1 effector-to-target ratio). We also assessed the capacity of splenocytes from immunized mice to proliferate in response to C4HD wild-type cells. Only splenocytes from mice injected with DNStat3-transfected C4HD cells proliferated strongly in response to mitomycin C-treated C4HD cells.
Induction of the immunogenic phenotype in DNStat3 C4HD cells occurred along with a dim increase of costimulatory molecule CD86 expression and with the secretion of pro-inflammatory cytokines like TNF-α, IL-6, IFN-γ and Rantes. In conclusion, our results demonstrate for the first time that breast cancer growth can be inhibited through induction of a specific protective immune response in vivo with tumor immunogens derived from DNStat3-transfected breast cancer cells.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2399.