PROJECT ABSTRACT “This application is being submitted in response to the Notice of Special Interest (NOSI) identified as NOT-CA- 21-083.” This proposal is in response to the above recently announced Notice of Special Interest of the NCI for administrative supplemental funding to support development of an Immune Radiation Response Index (i-RRI). The Rutgers Cancer Institute of New Jersey is ideally suited for this supplemental funding with a strong Division of Radiation Cancer Biology program in the Department of Radiation Oncology and a strong immunology program. Our animal experiments will utilize a mouse breast cancer model that we have developed and have extensive experience in working with in studies focused on evaluating the regulation of effective antitumor immunity. In addition to having the full capabilities of conducting the proposed laboratory studies and develop the iRRI, a unique capability that the study provides is integration with a currently ongoing pre-operative radiation boost trial in breast cancer that has already enrolled its first patients. The mouse breast model we will be working with aligns with this human trial, allowing us to correlate the immune biomarkers from the mouse model experiments with immune biomarkers after a pre-operative radiation boost in human breast cancer patients. The specific aims of the current proposal are as follows: Specific Aim 1: Using a mouse breast cancer model developed in our group which allows for the evaluation of in-vivo immune analyses, we will conduct extensive immune analyses after several commonly employed radiation fractionation schemes to assess how each fractionation scheme influences the development of an immune radiation response index. Specific Aim 2: Determine if immune cells taken from control and tumor-bearing mice and expanded in-vitro replicates and allows the prediction of the radiation induced immune response seen in-vivo in our model. Specific Aim 3: Evaluate in an ongoing pre-operative radiation boost human breast cancer trial if the radiation induced immune response biomarkers assessed in the mouse model experiments from Specific Aim 1 correlate with the human breast cancer in-vivo pre-operative radiation. The proposed experimental studies are being performed in breast cancer cell lines and models where we have the radiation biology, clinical and immune biomarker expertise, and experience. Our expectation is that the information derived from the basic experiments will contribute to the definition and validation of an immune radiation response index that will in turn inform the clinical pre-operative boost protocol regarding the optimal fractionation scheme for pre-operative radiation.