Aves1, Lesley Ellies2, Erinn Rankin1, Albert Koong1, Amato Giaccia1 1 Stanford Department of Bone Morphogenetic Protein 1 Proteins supplier radiation Oncology, Stanford University School of Medicine, Stanford, CA, USA; 2Department of Pathology, University of California, San Diego, La Jolla, CA, USA Correspondence: Todd Aguilera ([email protected]) Journal for ImmunoTherapy of Cancer 2016, four(Suppl 1):P366 Background Hypofractionated high dose ionizing radiation (RT) can improve antitumor immune responses in numerous cancers. In some instances the mixture of RT and checkpoint immunotherapy suppress adaptive resistance top to a higher immunologic effect. On the other hand, quite a few tumors are unresponsive to the mixture making it essential to understand elements that render tumors immunologically inactive. We previously described immunologically responsive (Py117) and unresponsive (Py8119) syngeneic tumors from the PyMT mammary carcinoma model and applied these tumors to determine new targets to reverse T cell exclusion.P365 IL-10 blockade sensitizes ovarian cancer to anti-PD-1 antibody therapy by editing tumor-associated leukocyte populations Dallas B Flies1, Tomoe Higuchi2, Wojciech Ornatowski3, Jaryse Harris4, Sarah F Adams3 1 NextCure, Beltsville, MD, USA; 2University of New Mexico Comprehensive Cancer Center, Beltsville, MD, USA; 3University of New Mexico Comprehensive Cancer Center, Albuquerque, NM, USA; 4 University of New Mexico, Albuquerque, NM, USA Correspondence: Sarah F Adams ([email protected]) Journal for ImmunoTherapy of Cancer 2016, 4(Suppl 1):PJournal for ImmunoTherapy of Cancer 2016, four(Suppl 1):Page 195 ofMethods A reverse phase protein array was utilised to study variations in between the Py117 and Py8119 tumors. The CRISPR/Cas9 technology was used to knockout Axl, a TAM loved ones tyrosine kinase. We confirmed signal abrogation together with the loss of Axl by way of western blot, measured the intrinsic radiosensitivity by clonogenic survival, determined cellular proliferation, evaluated development in 3D tissue culture, implanted tumors to identify radiosensitivity in mice, and evaluated the response in immunodeficient mice. Offered the presence of an immunologic phenotype we measured the influence of Axl on antigen presentation and cytokine production. Lastly, we defined the antitumor immune response by dissociating tumors then immunophenotyping infiltrates, evaluating T cell function, and tumor cell responses. Lastly, we combined radiation, PD-1, and CTLA-4 therapy to demonstrate that loss of Axl sensitizes tumors to immunotherapy. Final results Through a RPPA, we identified differences in Axl Integrin alpha-IIb Proteins Storage & Stability expression a protein related together with the epithelial to mesenchymal transition (EMT). Then we knocked out Axl, which revealed no alterations in proliferation or intrinsic radiosenstivity but altered the EMT phenotype, resulted in higher tumor latency and enhanced radiosensitivity immediately after 20 Gy in mice. Key functions in the Axl knockouts were enhanced MHCI expression and decreased myeloid advertising cytokines and chemokines. The radiation response was decreased in mice carrying Axl knockout tumors suggesting the value of the immune response. Profiling the tumor microenvironment revealed higher immune infiltrates in Axl knockout tumors and higher CD8+ T cells at baseline. Ten days after radiation there was increased CD8 and CD4+ T cells and decreased macrophages. T cells remained functional but adaptive immune resistance was supported by improved PD-L1 and FoxP3+ T regs in Axl deficient tumors. We hypothesized and co.