Title: Tumor resection boosts therapeutic efficacy of encapsulated stem cells expressing a highly secretable variant of interferon-β in glioblastomas

To our knowledge, this is the first preclinical investigation on the potential of tumor debulking in combination with immune therapy in the setting of syngeneic orthotopic mouse model of GBM. In this study we developed syngeneic orthotopic mouse models of GBM resection and show that surgical tumor debulking evokes a characteristic, time-dependent peritumoral immune response in tumor-microenvironment. This immune response significantly enhanced the anti-tumor efficacy of encapsulated-mouse mesenchymal stem cells (MSC) engineered to release a highly secretable variant of a dual-functioning anti-proliferative and immunomodulatory-cytokine, interferon (IFN) β in the tumor-resection cavity. Given that ~75% of GBM patients undergo tumor-resection and systemically delivered drugs post-resection have been marginally successful in GBM patients, we envision a therapeutic modality in which at the time of primary GBM surgery, the main tumor mass will be removed and encapsulated stem-cells expressing IFN β will be introduced in the cavity and allowed to target the remaining GBM cells. Abstract Purpose: Despite tumor resection being the frontline clinical care for glioblastoma (GBM) patients, nearly all preclinical immune therapy models intends to treat established GBM tumor. Characterizing cytoreductive surgery-induced immune-response combined with the administration of immune cytokines has the potential of offering a new treatment paradigm of immune therapy for GBMs. Experimental design: We developed syngeneic orthotopic mouse GBM models of tumor-resection and characterized the immune response of intact and resected tumors. We also created a highly secretable variant of immune cytokine IFNβ to enhance the its release from engineered mouse mesenchymal stem cells (MSC-IFNβ) and assessed whether surgical resection of intracranial GBM tumor significantly enhance the anti-tumor efficacy of targeted on-site delivery of encapsulated-MSC-IFNβ. Results: We show that tumor debulking results in substantial reduction of myeloid-derived suppressor cells (MDSCs) and simultaneous recruitment of CD4/CD8 T cells. This immune response significantly enhanced the anti-tumor efficacy of locally delivered encapsulated-MSC-IFNβ. IFNβ enhanced selective post-surgical infiltration of CD8 T cells and directly induced cell-cycle arrest in tumor cells resulting in increased survival of mice. Utilizing encapsulated-MSC-IFNβ in resected orthotopic tumor xenografts of patient-derived GBM, we further show that IFNβ induces cell-cycle arrest followed by apoptosis resulting in increased survival in immune-compromised mice despite their absence of an intact immune system. Conclusions: This study demonstrates the importance of syngeneic tumor resection models in developing cancer immunotherapies and emphasizes the translational potential of local delivery of immune-therapeutic agents in treating cancer. tumors. Our results indicate that the resection-induced immune reaction can be further modulated towards a tumor-specific immune response via local delivery of IFNβ, leading to significantly increased survival of mice. human than mouse GBM cells by driving cells from cell cycle arrest towards apoptosis, which has great potential in future clinical translation. Single for in vitro analysis and mean ± s.e. m for BLI imaging analysis of tumor volumes. Differences were considered significant at P <0.05 (*); P <0.01 (**). Survival times of mouse groups were analyzed using Prism 5 software (GraphPad Software) and compared using a Mantel Cox GBM4 survival vs results reveal that human IFNβ has a greater direct anti-tumor activity than mouse IFNβ due to combined effects of cell cycle arrest and apoptosis. Given the lack of immune response in this xenograft model and the intact immune systems in human GBM patients, the use of MSC-hIFNβ offers a great potential for future clinical translation. As such, our findings serve as an excellent preclinical immuno-oncology model to study how current and/or developing immunotherapeutic agents alter different immune-related effector elements in the clinical context of post-resection tumor microenvironments. local