p-values were calculated using Graphpad using 1-way ANOVA with a Bonferroni correction. Transwell migration For migration through transwells JW74 (Corning Inc.), cells were seeded at 300,000 cells/cm2 onto the topside of the filter membrane and left to migrate in normal culture condition for either 9 or 24 hours. feature of this phenomenon is its delayed onset (days), in contrast to the acute DNA damage responses that occur in minutes to hours. Such dichotomous kinetics implicate additional rate limiting steps that are essential for DNA-damage induced inflammation. Here, we show that cell cycle progression through mitosis following DNA double-strand breaks (DSBs) leads to the formation of micronuclei, which precede activation of inflammatory signaling and are a repository for the pattern recognition receptor cGAS. Inhibiting progression through mitosis or loss of pattern recognition by cGAS-STING impaired interferon signaling. Moreover, STING loss prevented the regression of abscopal tumors in the context of ionizing radiation and immune checkpoint blockade (Fig 4a). Irradiation of B16 melanoma cells before injection caused significant reduction in the growth of abscopal tumors after anti-CTLA4 treatment (Fig 4b). In contrast, implanting irradiated B16 cells harboring STING deletion eliminated the radiation-mediated growth delay of the abscopal tumor after anti-CTLA4 (Fig 4b and Extended data 6aCb). Radiation in the absence of anti-CTLA4 was insufficient to induce the abscopal effect (Extended Rabbit Polyclonal to Shc (phospho-Tyr427) data 6c). The abscopal tumor volume reduction as measured at day 15 was not observed when the implanted cells were STING deficient (Fig 4c). Loss of STING in the irradiated tumor also significantly reduced overall survival in the mice (Extended data 6d). A similar impact on tumor size with STING loss was noted in abscopal tumors when the JW74 contralateral tumor was irradiated directly in the mice (Extended data 6e and 6f). Consistent with a requirement for T cell responses, STING knockout prevented the enrichment of intratumoral CD8 T cells in the abscopal tumor (Fig 4d) 24, 26. Thus, STING signaling is a critical component of host immune activation that drives regression of distal tumors in RT- and anti-CTLA4 combination therapy. Open in a separate window Figure 4 STING signaling is required for maximal anti-CTLA4 therapy driven abscopal responses in the B16 murine melanoma modela, Schematic of the modified RadVax procedure. b, Growth of Wild-type (B16) or STING Knockout (KO) abscopal tumors following injection of untreated cells, or cells treated with JW74 10Gy 3 days before implantation. All mice received 9H10 anti-CTLA4 antibody as described in a. p-value is from the mixed effect linear model. Number of mice for each group is indicated within parentheses. c, Static tumor volumes at day 15 as measured in (b). e, Fraction of CD8+ cytotoxic T cells as a percent of CD45+ cells infiltrating the abscopal tumor. f, Model as described in the text. Pairwise comparisons by Mann-Whitney test, all error bars are SEM of biological replicates. Checkpoint adaptation and insensitivity has been described in a wide range of eukaryotic organisms27, 28. Our data support a model in which imperfect cell cycle checkpoints allow passage through mitosis and accumulation of micronuclei where pattern recognition occurs (Fig 4f). This represents a situation in which actively cycling cells contribute to delayed onset inflammatory signaling in the context of DSB inducing therapies. These findings suggest possibilities to modulate the host immune system and ultimately the success of genotoxic therapies. METHODS Cell lines and tissue culture MCF10A cells were obtained from ATCC, stably transfected to express Cas9 as described below, and cultured in a 1:1 mixture of F12:DMEM media with 5% horse serum (Thermo Fisher Scientific), 20ng/mL human EGF (Peprotech), 0.5mg/ml hydrocortisone, 100ng/ml cholera toxin and 10g/mL recombinant human insulin (Sigma). MCF10A-IPpoI cells were previously described29 and U2OS-IPpoI and MCF10A-AsiSI cells were prepared with identical procedures. The AsiSI cDNA was a gift of from New England Biolabs and was cloned by PCR into the pLVX-PTuner vector (Clontech) with an Estrogen receptor tag derived by PCR from the pLVX-PTuner-IPpoI vector. B16-F10 and U2OS cells were purchased from ATCC and cultured in DMEM with 10% FBS. UWB1.289 and UWB1.289+BRCA1 cells were obtained from ATCC and cultured in a 1:1 mixture of RPMI1640 and MEGM (prepared from BulletKit, Lonza) with 10% FBS added. All cells were cultured in the.