Interest in combining radiotherapy and immune checkpoint therapy is growing rapidly. In this study, we explored a novel combination of this type to augment anti-tumor immune responses in preclinical murine models of melanoma, neuroblastoma, and head and neck squamous cell carcinoma. Cooperative effects were observed with local radiotherapy and intratumoral injection of tumor-specific antibodies, arising in part from enhanced antibody-dependent cell-mediated cytotoxicity (ADCC). We could improve this response by combining radiation with intratumoral injection of an IL-2-linked tumor-specific antibody (termed here an immunocytokine), resulting in complete regression of established tumors in most animals associated with a tumor-specific memory T cell response. Given the T cell response elicited by combined local radiation and intratumoral immunocytokine, we tested the potential benefit of adding this treatment to immune checkpoint blockade. In mice bearing large primary tumors or disseminated metastases, the triple-combination of intratumoral immunocytokine, radiation, and systemic anti-CTLA-4 improved primary tumor response and animal survival compared to combinations of any two of these three interventions. Taken together, our results show how combining radiation and intratumoral immunocytokine in murine tumor models can eradicate large tumors and metastases, eliciting an in situ vaccination effect that can be leveraged further by T cell checkpoint blockade, with immediate implications for clinical evaluation.

Background and Purpose We recently reported a time-sensitive, cooperative, anti-tumor effect elicited by radiation (RT) and intra-tumoral-immunocytokine injection in vivo. We hypothesized that RT triggers transcriptional-mediated changes in tumor expression of immune susceptibility markers at delayed time points, which may explain these previously observed time-dependent effects. Materials and Methods We examined the time course of changes in expression of immune susceptibility markers following in vitro or in vivo RT in B78 murine melanoma and A375 human melanoma using flow cytometry, immunoblotting, and qPCR. Results Flow cytometry and immunoblot revealed time-dependent increases in expression of death receptors and T cell co-stimulatory/co-inhibitory ligands following RT in murine and human melanoma. Using high-throughput qPCR, we observed comparable time courses of RT-induced transcriptional upregulation for multiple immune susceptibility markers. We confirmed analogous changes in B78 tumors irradiated in vivo. We observed upregulated expression of DNA damage response markers days prior to changes in immune markers, whereas phosphorylation of the STAT1 transcription factor occurred concurrently with changes following RT. Conclusions This study highlights time-dependent, transcription-mediated changes in tumor immune susceptibility marker expression following RT. These findings may help in the design of strategies to optimize sequencing of RT and immunotherapy in translational and clinical studies.

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We have identified a cooperative interaction between radiation and intratumoral injection of anti-GD2 immunocytokine (hu14.18-IL2) in murine tumor models. In a moderate size (~200 mm 3 ), single tumor, B78 melanoma model this combination results in complete tumor regression in 71% of animals and a memory T cell response. We hypothesized that intratumoral immunocytokine would improve local and abscopal response to combined radiation and anti-CTLA-4 antibody.Mice bearing large B78 tumors (~500mm 3

Radiation therapy (RT) may enhance tumor susceptibility to immune response. We and others have observed a cooperative interaction between RT and various immunotherapies, which appears dependent on the relative sequencing of each therapy. We reported a synergistic interaction between RT and the antibody-dependent cell-mediated cytotoxicity (ADCC) response to tumor-specific monoclonal antibodies (mAb) in murine melanoma. We reported enhanced cooperative effect when immunotherapy is administered 6-10 days after RT compared to administration on days 1-5 or 11-15. We hypothesized that this might reflect a delayed, transcriptionally-mediated effect of RT on the expression of tumor markers of immune susceptibility. In this study, we investigated the effect of RT on a variety of immune susceptibility markers at both transcriptional and post-translational levels to explore mechanisms behind the observed RT-induced changes. We used flow cytometry to examine the time course of phenotypic changes in immune susceptibility markers in B78 murine melanoma cells following in vitro RT. We observed a time- and RT dose-dependent increase in the expression of specific death receptors (Fas, DR5), as well as T cell co-stimulatory/co-repressor ligands (PD-L1, CD80). The timing of these changes correlated with tumor susceptibility to ADCC immune response in vivo. All protein expression changes observed by flow cytometry were found to occur over a similar time course by quantitative polymerase chain reaction (qPCR), suggesting that RT-induced protein expression changes were mediated by changes in transcriptional activity. Using high throughput qPCR, we observed a similar time course of transcriptional effects in additional markers of tumor cell immune susceptibility, including Fas, MHC I, CD40, and others. We compared the effect of RT on these markers in human and mouse melanoma cell lines and observed a comparable time course for transcript-level changes across species. This study sheds light on the mechanistic basis of time sensitivity in the interaction of RT with ADCC in vivo and suggests opportunities to enhance anti-tumor immune response by combining RT and immunotherapeutic agents. Such findings bear relevance for research investigating the potential role for RT in driving and optimizing the response to various cancer immunotherapies. Citation Format: Lauryn R. Werner, Monica Gressett, Maureen Riegert, Shyhmin Huang, Joseph G. Kern, Amy Erbe, Paul M. Harari, Paul M. Sondel, Zachary S. Morris. Transcriptionally mediated effects of radiation on the expression of immune susceptibility markers in murine and human melanoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4013.