Research Article Immunosurveillance and Immunoediting of Breast Cancer via Class I MHC Receptors Megan M. Tu 1 , Mir Munir A. Rahim 2 ,C eline Sayed 1 , Ahmad Bakur Mahmoud 1,3 , and Andrew P. Makrigiannis 1,2 Abstract Ly49 receptors, which recognize "self" class I major histo- compatibility complex (MHC-I) molecules, enable natural killer (NK) cells to detect loss of MHC-I expression on transformed and virally infected cells. The impact of NK cell–mediated MHC-I surveillance on immunoediting of breast cancer is still not fully understood. This work assesses the impact of Ly49 receptors on tumor development in terms of cancer control and in driving immune-evading cancer muta- tions. Genetically modified Ly49-deficient mice and those lacking NK cells through antibody depletion were less able to control E0771-derived mammary tumors in an MHC-I–depen- dent fashion. Similarly, Ly49-deficient MMTV-PyVT–transgenic mice developed spontaneous mammary tumors faster than Ly49-sufficient MMTV-PyVT mice. Fewer CD69 þ and granzyme B þ NK cells were detected among the tumor-infiltrating lym- phocytes in Ly49-deficient than in Ly49-sufficient MMTV-PyVT mice. Furthermore, tumors from Ly49-deficient mice displayed reduced MHC-I expression, suggesting that tumors growing in these mice lacked an Ly49-derived pressure to maintain MHC-I expression. These same MHC-I-low tumors from Ly49-deficient mice were unable to flourish when transferred to Ly49-sufficient hosts, confirming that this tumor mutation was in response to an Ly49-deficient environment. This work demonstrates a role for Ly49 receptors in the control of mammary cancer, and provides evidence to support a model of tumor immunoediting, in which selective pressures from the immune system drive immune-evasive cancer mutations. Cancer Immunol Res; 5(11); 1016–28. Ó2017 AACR. Introduction Breast cancer is the leading cause of cancer-related deaths among women globally (1). Although detection and treatment of the primary tumors have yielded many successes, conventional therapies such as surgery, chemotherapy, and radiation do not address the risk of relapse and metastatic disease. Moreover, tumors are heterogeneous (2), and some of these tumor sub- populations are highly propagative and resistant to radiation (3–5). For these reasons, we are interested in exploring avenues of treatment that involve augmenting the immune system's response. In performing cancer immunosurveillance, the host immune system exerts pressure on a developing tumor, often eradicating cancerous cells before a tumor is established. However, this same immune pressure is believed to shape tumor development and select for mutations creating an immune-evasive cancer. This cancer-immune interaction proceeds in three phases, known as the "three Es" of cancer immunoediting. First, the immune system is able to eliminate many of the tumor cells. Next, the immune system enters equilibrium with those cancerous cells (6). Finally, the cancer cells develop enough resistance that they can escape the immune system, leading to a failure of immune-mediated cancer control. Immune-targeting clinical interventions seek to break the bleak pattern described by the three Es, allowing for control of a tumor by the immune system. Adaptive immunity, and par- ticularly the presence of tumor-infiltrating CD8 þ T cells, is crucial in the control of tumor cells and preventing overall cancer progression (7). For this reason, current immune ther- apies target these adaptive immune cells in an attempt to enhance their activity or longevity. The success of immune checkpoint inhibitors such as anti–CTLA-4 and anti–PD-1/ –PD-L1 in the clinic emphasizes the efficacy of immune-based cancer therapy. However, adaptive immunity is only one arm of the immune system, and there is mounting evidence for innate immune cells' involvement in cancer immunosurveillance. In particular, natural killer (NK) cells are involved in antitumor immunity, and the therapeutic potential of this population against cancer warrants study. In humans, NK cells comprise 10% to 15% of the lym- phocytes in the peripheral blood. In mice, NK cells can control various tumor cell lines, spontaneously arising tumors, and tumors induced by chemical carcinogens (8, 9). In humans, studies that correlate disease with NK-cell absence or dysfunction show the value of NK cells. Lessened NK cell–mediated cytotox- icity is associated with increased risk of cancer development (10). 1 Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Canada. 2 Department of Microbiology and Immunology, Dal- housie University, Halifax, Canada. 3 College of Applied Medical Sciences, Taibah University, Madinah Munawwarah, Saudi Arabia. Note: Supplementary data for this article are available at Cancer Immunology Research Online (http://cancerimmunolres.aacrjournals.org/). Corresponding Author: Andrew P. Makrigiannis, Dalhousie University, 5850 College St., Sir Charles Tupper Medical Building, room 7-C1, Halifax B3H 4H7, Canada. Phone: 902-494-2736; Fax: 902-494-5125; E-mail: amakrigiannis@dal.ca doi: 10.1158/2326-6066.CIR-17-0056 Ó2017 American Association for Cancer Research. Cancer Immunology Research Cancer Immunol Res; 5(11) November 2017 1016 on June 17, 2020. © 2017 American Association for Cancer Research. cancerimmunolres.aacrjournals.org Downloaded from Published OnlineFirst September 18, 2017; DOI: 10.1158/2326-6066.CIR-17-0056