Fig 1: Tumor only SBRT increases immune responses in canines and humans with HNSCC.A Complete blood count from B16-OVA mice from Supplemental Fig. 2B (ENI, n = 7; tumor only, n = 3). B Complete blood count from LY2 mice from Fig. 5D (Sentinel LN, n = 3; ENI, n = 3). C Schematic of the clinical trial conducted in dogs diagnosed with sinonasal cancer and treated with SBRT with or without ENI. D Quantitation of CD4 (CD5+CD4+) and CD8 (CD5+CD8+) T cells from nasal lavages of dogs (ENI, n = 3; tumor only, n = 3). E Schematic of human phase I/Ib clinical trial using neoadjuvant SBRT and Durvalumab. F Quantitation of the percentage of CD45+ cells that are CD3+ T cells in the blood of patients before and after treatment with SBRT and durvalumab (Responders, n = 9; Non-responders, n = 3). G Representative multispectral fluorescent images of lymph nodes from patients and normal control nodes. IFNg is in orange. H MultiPLIER quantification of genes involved in TCR activation and genes downstream of TCR activation (n = 14 patients). I Quantification of cells within the TME of patients before and after treatment. J Quantification of cancer cells (CK+) in patients before and after treatment (n = 18). K Model of how SBRT triggers a systemic immune response and how ENI reduces that response. 1. SBRT increases antigen in the TME, 2. antigen is acquired by DCs, which 3. present antigen to T cells in DLNs. These activated T cells act on the local tumor, but also 4. enter systemic circulation and go to the distant tumor site and 5. kills cancer cells which 6. release new antigen upon cell death. 7. These new antigens are presented to T cells in the distant DLN and triggers additional antigen-specific T cells to distant tumor only antigens. ENI decreases this systemic immune response by decreasing DC activation of antigen-specific T cells in the DLNs by radiation induced cell death. A two-tailed un-paired Student’s t test was used for mouse and canine data. A two-tailed paired Student’s t test was used for the human data. Significance was determined if the p-value was <0.05*, <0.01**, and <0.001***. The error bars represent the standard error of the mean (±SEM). Source data are provided as a Source Data file. p-values are indicated for figures A. **0.0071, D. CD4 *0.0375, CD8 *0.0451, H. *0.0346, and J. ***0.0002. Panels (C, E and K) created with BioRender.com.