Myeloid derived suppressor cells (MDSC) represent one of the most powerful mechanisms used by tumors to evade the immune response and create T cell tolerance. During the previous cycle of this grant, we studied murine and human MDSC. Our data demonstrated that MDSC expressing arginase I deplete L-arginine from the microenvironment, triggering activation of the GCN2 kinase pathway which eventually leads to an arrest in T cell cycle progression, inhibition of IFN? production, and blocking of signaling through the T cell receptor. Other researchers have recently described three additional mechanisms by which MDSC may suppress T cell function, namely the production of peroxynitrites, the production of H2O2, and the induction of regulatory T cells. Therefore, it is essential to identify the primary mechanism by which MDSC induce T cell tolerance in vivo so targeted therapies that block MDSC function can be designed and tested. To achieve this goal, we developed a new strain of conditional arginase I knock-out mice (full knock-outs die soon after birth) in which arginase I is deleted only in the CD11b+ myeloid cells. We have also established additional murine knock-out colonies to study and compare the proposed mechanisms for the induction of T cell tolerance by MDSC. Our preliminary data continue to support the hypothesis that MDSC expressing arginase I deplete L-Arginine in the tumor microenvironment and thereby cause T cell tolerance. Inhibiting arginase I will result in the development of a protective anti-tumor T cell response. In addition, our data shows that human tumors activate and promote the survival of MDSC, allowing them to accumulate in cancer patients. Inhibiting these tumor derived signals may also represent a new therapeutic approach to blocking MDSC. To definitively identify the mechanisms by which MDSC induce T cell tolerance and determine how human tumors activate MDSC, we propose the following Specific Aims. 1. Test the hypothesis that the primary mechanism for the induction of T cell tolerance by MDSC is the production of Arginase I. 2. Determine the mechanism(s) by which MDSC induce T cell tolerance in vivo and determine its effect on the anti-tumor response. 3. Determine the mechanisms by which tumors promote the survival and inhibit apoptosis of human MDSC. 4. Determine which is the predominant mechanism for the induction of T cell tolerance by human MDSC.

Public Health Relevance

Cancer cells are capable of turning specific subsets of white blood cells that are normally protective against infection into efficient inhibitors of the host's anti-cancer response. These cells, called myeloid derived suppressor cells (MDSC), block the ability of lymphocytes to kill tumor cells. By determining how tumors activate MDSC and how MDSC block the protective anti-cancer response, the proposed research will enable us to develop new treatments that block the suppressive activity of MDSC and release the protective anti- tumor immune response in patients.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Cancer Immunopathology and Immunotherapy Study Section (CII)
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Mccarthy, Susan A
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Louisiana State Univ Hsc New Orleans
Schools of Medicine
New Orleans
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Lassak, Adam; Dean, Mathew; Wyczechowska, Dorota et al. (2018) Molecular and Structural Traits of Insulin Receptor Substrate 1/LC3 Nuclear Structures and Their Role in Autophagy Control and Tumor Cell Survival. Mol Cell Biol 38:
Al-Khami, Amir A; Zheng, Liqin; Del Valle, Luis et al. (2017) Exogenous lipid uptake induces metabolic and functional reprogramming of tumor-associated myeloid-derived suppressor cells. Oncoimmunology 6:e1344804
Sanchez, Maria Dulfary; Ochoa, Augusto C; Foster, Timothy P (2016) Development and evaluation of a host-targeted antiviral that abrogates herpes simplex virus replication through modulation of arginine-associated metabolic pathways. Antiviral Res 132:13-25
Fletcher, Matthew; Ramirez, Maria E; Sierra, Rosa A et al. (2015) l-Arginine depletion blunts antitumor T-cell responses by inducing myeloid-derived suppressor cells. Cancer Res 75:275-83
Hossain, Fokhrul; Al-Khami, Amir A; Wyczechowska, Dorota et al. (2015) Inhibition of Fatty Acid Oxidation Modulates Immunosuppressive Functions of Myeloid-Derived Suppressor Cells and Enhances Cancer Therapies. Cancer Immunol Res 3:1236-47
Dimitriades, Victoria; Rodriguez, Paulo C; Zabaleta, Jovanny et al. (2014) Arginase I levels are decreased in the plasma of pediatric patients with atopic dermatitis. Ann Allergy Asthma Immunol 113:271-5
Sierra, Rosa A; Thevenot, Paul; Raber, Patrick L et al. (2014) Rescue of notch-1 signaling in antigen-specific CD8+ T cells overcomes tumor-induced T-cell suppression and enhances immunotherapy in cancer. Cancer Immunol Res 2:800-11
Thevenot, Paul T; Sierra, Rosa A; Raber, Patrick L et al. (2014) The stress-response sensor chop regulates the function and accumulation of myeloid-derived suppressor cells in tumors. Immunity 41:389-401
Naura, Amarjit S; Kim, Hogyoung; Ju, Jihang et al. (2013) Minocycline blocks asthma-associated inflammation in part by interfering with the T cell receptor-nuclear factor ?B-GATA-3-IL-4 axis without a prominent effect on poly(ADP-ribose) polymerase. J Biol Chem 288:1458-68
Guo, Gang; Marrero, Luis; Rodriguez, Paulo et al. (2013) Trp53 inactivation in the tumor microenvironment promotes tumor progression by expanding the immunosuppressive lymphoid-like stromal network. Cancer Res 73:1668-75

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