In Vivo DC Editing by NK Cells Figure 1. Subcutaneous administration of MHC-negative cells results in an NK cell-dependent decrease of CD11cbright DCs in the draining lymph nodes. A: representative analyses of mononuclear cells isolated from either draining or controlateral (Control LN) lymph nodes of mice depleted or not of NK cells (Draining LN + anti-asialo GM1). B: NK cells are efficiently depleted in mice upon administration of anti-asialo GM1 mAbs. C: the percentage (left) and the absolute number (right) of DCs among mononuclear cells isolated from lymph nodes. Bars represents mean values and SD of five independent experiments (three mice per group). ** = p , 0,001; * = p , 0,005. doi:10.1371/journal.pone.0039170.g001 lower number of IFN-c producing T cells when compared to wild type mice that were also injected with TS/A plus YAC-1 (Figure 3,B). These results suggest that NK cell-mediated, perforin-dependent, lysis of DCs has a role in the optimal generation of antigen-specific T cells. However, the present results also offer, at least in part, an alternative interpretation, i.e. that NK cells can directly stimulate DC maturation, most likely by releasing pro-inflammatory cytokines (e.g. TNF-a), as previously demonstrated [21,35]. Indeed, in perforin-deficient mice, the activation of anti-tumor T cells was not as low as observed in NK cell-depleted mice using anti-asialo treatment (Figure 3,A). Thus, the enhanced antigen-specific T cell response, detectable upon NK cell-mediated DC editing could represent the outcome of both DC killing and cytokine-mediated DC activation. Finally, we also observed that vaccination with irradiated TS/A cells plus YAC-1 cells resulted in a significant increase of survival of mice upon challenge with a lethal dose of TS/A cells (Figure 4). 60% of mice pre-injected with irradiated TS/A plus YAC-1 survived 8 weeks after tumor challenge whereas, in the same time interval, only 20% of either NK cell-depleted mice or mice pre- injected with irradiated TS/A cells alone survived the tumor challenge. Altogether, these results support the concept that the PLoS ONE | www.plosone.org 3 June 2012 | Volume 7 | Issue 6 | e39170