Project Summary Despite the establishment of obesity as a risk factor in the development of a multitude of cancer types including breast cancer, there is still a significant insufficiency of genetic evidence for implicating obesity in the initiation and progression of breast cancer development. While immunotherapeutic approaches such as the PD-1/PD-L1 blockade have shown promise in treating breast cancer, obesity causes substantial impairment of anti-tumor immunity. A significant challenge in the development of effective immunotherapeutic strategies for obesity- associated breast cancer lies in the characterization of the bone fide target genes that drive obesity-associated immune resistance. The emergence of noncoding RNAs as important biological molecules has provided the foundation for the development of next-generation treatment strategies. Our preliminary data demonstrated that a small nucleolar RNA (snoRNA), SNORD46, is upregulated in breast cancer and negatively correlated with the infiltration of cytotoxic leukocytes. We also indicated that obesity is associated with a chromatin variant of SNORD46. We collected genetic evidence indicating that the expression of SNORD46 leads to obesity and mammary gland tumors which are resistant to immunotherapy. Therefore, the goal of this proposal is to comprehensively characterize and implicate SNORD46 as a driver of obesity-associated breast cancer and demonstrate that targeting snoRNAs effectively improves the expansion and activation of CD8+ T-cells and NK cells and sensitizes obesity-associate breast cancer in immunotherapy. We will address our central hypothesis that snoRNAs act as essential gene targets that promote obesity and obesity-associated breast cancer initiation and immune resistance, which could be attenuated in vivo by an anti- sense oligonucleotide-based targeted therapy. In Specific Aim 1, we will define the molecular mechanism of SNORD46 inhibited, IL-15-dependent non-classic pathway in adipocytes, and IL-15-dependent expression of stimulatory checkpoints in CD8+ T cell and NK cells. In Specific Aim 2, we will ascertain the functional importance of snoRNAs in obesity-associated tumorigenesis and immune resistance using high-fat diet-induced obese mice and Snord46 mut/mut knockin obese mice. The proposed study will provide initial genetic evidence for defining the crucial role of adipocyte-expressed snoRNAs in promoting obesity and obesity-associated breast cancer. Mechanistically, we will elucidate the molecular mechanisms of the SNORD46-leukocyte interactions that drive obesity-associated breast cancer resistance to immunotherapy. Clinically, the proposed studies will delineate that targeting snoRNAs using locked nucleic acids (LNAs) effectively improves the proliferation/activation of CD8+ T-cells and NK cells in vivo, sensitizing obesity-associated breast cancer to immune checkpoint blockers.