Author ORCID Identifier
0000-0002-2124-8019
Date of Graduation
5-2024
Document Type
Thesis (MS)
Program Affiliation
Immunology
Degree Name
Masters of Science (MS)
Advisor/Committee Chair
Dr. Michael Curran
Committee Member
Dr. Tina Cascone
Committee Member
Dr. Jianjun Gao
Committee Member
Dr. Matthew Gubin
Committee Member
Dr. Gregory Lizee
Committee Member
Dr. Kristen Pauken
Abstract
Blockade of negative immune regulators for example CTLA-4, and PD-1/PD-L1 has proven to be a clinically effective strategy to enhance tumor specific immune responses. Recently discovered novel immunoglobulin superfamily ligand V-domain Ig suppressor of T-cell Activation (VISTA) is a new target for immunotherapy. VISTA expression is specifically upregulated on tumor infiltrating myeloid cells such as dendritic cells (DCs), tumor associated macrophages (TAMs) and myeloid derived suppressor cells (MDSCs). In addition, VISTA expression is increased on tumor-infiltrating regulatory T cells (Tregs) compared to those in the periphery. VISTA has been shown to suppress effector T cells through multiple mechanisms, primarily by inhibiting activation and effector function. Previous studies showed that antibody blockade of VISTA with clone (13F3) in multiple melanoma tumor models could reduce tumor growth and enhanced T cell responses within the tumor microenvironment (TME). Several limitations for antibody blockade of VISTA exist, including its rapid turnover on and off the cell surface, pH-dependent binding to its receptors, and potential toxicities resulting from VISTA blockade in non-myeloid tissues. To overcome rapid turnover of VISTA on the cell surface due to endosomal recycling, we used Antisense oligonucleotides (ASOs) to knockdown VISTA expression on myeloid cells. ASOs are synthetically generated single stranded oligonucleotides that alter messenger RNA to either diminish, recover, or adapt protein expression. We hypothesize that reducing VISTA expression on tumor-infiltrating myeloid cells via VISTA targeting ASOs will decrease the immune suppressive tumor stroma and improve anti-tumor T cell immunity. We tested the ability of multiple VISTA targeting ASOs in comparison to monoclonal antibody-mediated VISTA blockade for their impact on VISTA protein expression, immune infiltration of the TME, and evaluate their effect in vitro and in vivo. Our overall goal is to convert the TME from a suppressive myeloid population heavy milieu to a more pro- inflammatory microenvironment. Targeting VISTA can offer an attractive and unique opportunity for synergism with checkpoint blockade therapy due to its upregulation on tumor infiltrating MDSCs and TAMs suggesting that therapeutic approaches that effectively reduce VISTA protein (e.g., VISTA ASOs) may occupy a distinct compartment to evolve into a novel therapy for solid tumors such as melanoma, head and neck, and bladder cancer.
Keywords
Immunology, VISTA, Antisense Oligonucleotide, Checkpoint blockade, Tumor Immunology, Myeloid cell