Date of Award

2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Immunology

First Advisor

Andy J. Minn

Second Advisor

Carl H. June

Abstract

Immune therapies have significantly improved outcomes for cancer patients with

poor prognosis, but mechanisms that underlie response or resistance to therapy remain

elusive. Inflammatory cytokines such as interferon-gamma (IFNG) augment immune

function yet also promote T cell exhaustion through inhibitory ligands such as PDL1. How

these opposing effects are integrated in the tumor microenvironment is unclear. We show

that while inhibiting tumor IFNG signaling decreases interferon-stimulated genes (ISGs)

in cancer cells, it increases ISGs in immune cells by enhancing IFNG produced by

exhausted T cells (TEX). In tumors with favorable antigenicity, these TEX mediate rejection.

In tumors with neoantigen or MHC-I loss, TEX instead utilize IFNG to drive maturation of

innate immune cells, promoting tumor clearance. Thus, interferon signaling in cancer cells

and immune cells oppose each other to establish a regulatory relationship that limits both

adaptive and innate immune killing. In melanoma and lung cancer patients, perturbation

of this relationship is associated with response to immune checkpoint blockade

independent of tumor mutational burden.

In addition to these suppressive mechanisms, tumor infiltration and antigen loss

are common mechanisms that limit effectiveness of T cell responses in solid tumors, in

particular chimeric antigen (CAR) T cells. Delivery of pattern recognition receptor agonists

is one strategy to improve immune infiltration and prime adaptive immunity; however,

targeting these agonists to immune cells is challenging, and off-target signaling in cancer

cells can be detrimental as described above. Here, we engineer murine CAR-T cells to

deliver RN7SL1, an endogenous RNA that activates RIG-I/MDA5-dependent interferon

signaling. RN7SL1 is deployed in extracellular vesicles and preferentially transferred to

intratumoral immune cells. Unlike other RNA agonists, RN7SL1 restricts development of

myeloid-derived suppressor cells and decreases TGFB expression. In dendritic cells, it

fosters DC subsets with anti-viral and costimulatory features. Consequently, endogenous

effector-memory CD8 T cells expand, while exhausted T cells contract. Armed with the

ability to activate endogenous immune responses, these CAR-T cells effectively reject

solid tumors and tumors with CAR antigen loss by drawing on our insights into tumor

resistance mechanisms.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS