2016 Mentored Investigator Grant Recipient — Fan Zhao, PhD
Because of a lack of early symptoms and effective screening tests, many ovarian cancer patients are diagnosed at advanced stages and more than half of them die of recurrent disease within 5 years of diagnosis. However, the patients are found to gain dramatically increased survival if their surgical tumor specimens have the presence of tumor-infiltrating T cells, especially cytotoxic CD8+ T cells (a subtype of T cells). As you may guess from the name, cytotoxic T cells are the subgroup of T cells responsible for killing virus-infected cells and cancer cells. T cells recognize antigens via T cell receptors. The clinical observation strongly suggests that the prolonged survival could be mediated by the killing of ovarian cancer cells by the cytotoxic CD8+ T cells. The antigens that the cytotoxic T cells recognize can be extremely valuable targets because that’s what immune system use to distinguish ovarian cancer cell from normal cells. The existing data on the oligoclonality of the cytotoxic CD8+ T cells found inside ovarian tumors further supports that it is an antigen-driven activation process. Therefore, there is a lot to learn about the T cell response in ovarian cancer and it can also lead us to discover new ovarian cancer antigen candidates, which is immensely useful for various ovarian cancer immunotherapies. However, despite extensive studies in the past decade, our understanding of the T cell immune response in ovarian cancer is still very limited. But in the past few years, continuous effort has yielded a new generation of tools for T cell analysis that make this an opportune time to revisit this problem.
In this work, we want to understand the spontaneous immune response of ovarian tumor-infiltrating T cells. With the recent development of cytometry of Time of Flight (CyTOF), we can analyze single sample using up to 45 parameters, instead of only 12-15 parameters in the conventional cytometry. This allows us to analyze single T cells by what proteins that they express in a great detail, thus identifying important subtypes and populations of tumor-infiltrating T cells. Then we will implement another new technology – single T cell analysis to extract the complete T cell receptor sequences from the expanded cytotoxic CD8+ T cell clones, along with their functional information. Then we can use the complete T cell receptor sequences to reconstruct the T cell receptors of the identified clones and use the reconstructed T cell receptors to identify the cognate antigen using the third technology – yeast-displayed pHLA libraries.
This proposed study will deepen our understanding of T cell response landscape in ovarian cancer and help to identify important subgroups of T cells. Hopefully it will also provide new ovarian cancer antigen candidates as new targets for ovarian cancer immunotherapies, such as vaccines, adoptive immunotherapy and antibody-guided chemotherapeutic agents.
Fan Zhao is a postdoctoral fellow with Dr. Mark M Davis at the Department of Microbiology and Immunology at Stanford University School of Medicine. He obtained his B.Eng. in Biomedical Engineering at Sichuan University where he developed copper(II)-coordinated chitosan hydrogel beads for hemoperfusion under the supervision of Dr. Changsheng Zhao. Then He joined the laboratory of Dr. Bing Xu at Brandeis University where he received the Provost Award in 2013 and his Ph.D. in Chemistry with an additional specialization in Quantitative Biology in 2014. His doctoral research focused on immunomodulation by peptide-based self-assembled hydrogels. Currently, he is interested in designing new tools and improving existing tools to study the recognition of peptide-HLA antigen complex by T cell receptors and applying these tools to identify novel T cell antigens in ovarian cancer.