The tumor microenvironment has long-been known to be immunosuppressive. Many specific proteins have been identified that prevent adequate activation of infiltrating immune cells. It is not known, however, how tumor cells initiate an environment that allows survival in the presence of effector cells that have evolved to eliminate them. One such effector cell in the antitumor response is the natural killer (NK) cell, which secretes inflammatory cytokines and directly kills transformed cells. There is significant evidence to support the involvement of NK cells in the elimination of transformed cells in the early stages of tumor development. At some point, through an unknown mechanism, transformed cells establish a method to escape recognition by these cells and a solid tumor develops. Once a tumor is established, the ability of cytotoxic immune cells to eliminate tumor targets is severely diminished, allowing tumor growth and further suppression of local and systemic immunity. There is also extensive recruitment of myeloid cells, believed to promote angiogenesis and metastasis, and prevent immune cell activation. Using cellular and molecular biological techniques, we will study the complex interactions between tumor cells, the myeloid cells that they recruit and NK cells in patients with glioblastoma. We hypothesize that myeloid cells are recruited to protect tumor cells from immune recognition, and may serve as decoy targets for NK cells in patients with cancer. My research plan details my immediate and long-term career goals in understanding the cellular and molecular mechanisms that govern tumor suppression of local and systemic immunity. My immediate goals are to define the impact of a tumor on NKG2D-ligand expression by myeloid cells and how these myeloid cells can, in turn, regulate the function of NK cells. We hypothesize that through induction of NKG2D ligands on the surface of myeloid cells, NK cell killing is redirected from tumor cells to the massive infiltration of myeloid cells. If these NKG2D ligand positive myeloid cells serve as decoy targets for NK cells, a tumor will have created a physical barrier and promote survival, angiogenesis and metastasis shielded from the cytotoxic cells of the immune system. We have shown that NKG2D ligand-positive myeloid cells can be targets for NK cells, and that tumor- derived soluble proteins induce NKG2D ligand expression on myeloid cells. In this proposal, we will first evaluate NK cell function in response to NKG2D ligand expressing myeloid cells from patients (Aim 1). We will next determine if NKG2D ligand expression by myeloid cells in patients with cancer can be used as a diagnostic or prognostic tool (Aim 2). Furthermore, we will isolate and identify the tumor-derived soluble protein or proteins that induce NKG2D ligands on myeloid cells (Aim 3). Altogether, this research effort will have important clinical relevance and will influence clinical management of patients with brain, hepatocellular, prostate, and breast cancer. My long-term goals after becoming an assistant professor include forming an interdisciplinary basic and clinical research program to explore how a tumor influences innate and adaptive immune responses in patients. Using animal models and patient samples, I aim to discover mechanisms of tumor immunosuppression and develop improvements to current immunotherapy for patients with cancer. I will complete the mentored phase of this proposal under the guidance of Drs. Andrew Parsa and Lewis Lanier and look forward to completing the independent phase of this project as an assistant professor at another university.

Public Health Relevance

The focus of my research has been aimed at defining the impact of tumor burden on the function of cytotoxic immune cells in patients with glioblastoma. This work will have broad implications in the development of novel patient therapies that capitalize on improvements of Natural Killer and CD8+ T cell function. The work proposed in this application will identify a potential mechanism of immune evasion by glioblastoma. This project may also be widely applicable to monitoring at risk patient populations using a novel biomarker for cancer. Finally, this project will identify a novel soluble protein target for immune therapy in glioblastoma and possibly in other cancer patients. By gaining a better understanding of how tumors can systemically and locally impact cells of the immune system, and mechanisms for tumor escape of immune recognition, we hope to improve preventative and therapeutic approaches in the battle against cancer.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Transition Award (R00)
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Special Emphasis Panel (NSS)
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Howcroft, Thomas K
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Seattle Children's Hospital
United States
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