# Tackling Treg mediated resistance to radiation and anti-PDL1 in HNSCCs

> **NIH NIH R01** · UNIVERSITY OF COLORADO DENVER · 2020 · $439,092

## Abstract

Abstract
Current treatment of head and neck squamous cell carcinoma (HNSCC) with immune checkpoint inhibitors and
radiotherapy (RT) are initially effective, but relapse is common. The goal of our research is to understand
mechanisms of response and resistance and to use this knowledge to improve therapy. We show that during
the response phase to treatment, RT increases STAT1 phosphorylation, CXCL9/10 secretion, and PDL1
expression on cancer cells, and increases CD8 and CD4 infiltration and activation. These effects, however,
dissipate in the resistance phase, and a significant increase in regulatory T cells (Tregs), STAT3, and TGF1
are observed. Treg depletion and anti-STAT3 targeting restores response to RT and anti-PDL1, resulting in
suppression of plasma levels of TGF1, activation of T effector cells (Teff, Cd44+, IFN-G+ CD4 and CD8 T
cells) and complete tumor eradication in an orthotopic model of HNSCC. This effect is unachievable with the
addition of anti-CTLA4, anti-Tim3, or with hypofractionation of RT. Our in vitro preliminary data show that RT
enhances STAT3 phosphorylation on CD4 T cells, leading to increased Treg conversion. This is reversed with
STAT3 inhibitors. CD4 T cell conversion toward a Treg phenotype represents an important mechanism of
immune evasion. TGF1 has been established as a necessary growth factor for conversion of naïve CD4 T
cells to Tregs through induction of FoxP3 expression. In addition, STAT3 is a necessary transcription co-factor
for FoxP3 expression. Our central hypothesis is that during the response phase, RT induces a distinct
cancer cell STAT1-mediated CXCL9/10 secretion which recruits and activates Teff resulting in
enhanced synergy with anti-PDL1. RT, however, also promotes CD4 conversion to Treg cells by
phosphorylation of STAT3, which leads to the development of treatment resistance by inhibiting Teff
function. Using knockdown constructs of STAT1 and CXCL9/10 on cancer cells and a CXCR3-/- mouse
model, we will determine the effect of RT-induced chemokines in Teff chemotaxis, proliferation, and TCR
activation (Aim1). To determine how RT affects CD4 T cell conversion and how that feeds back to negatively
affect Teff function, we will use the CD4-Cre/ Stat3flox/flox mice with knockdown of STAT3 on CD4 T cells as well
as STAT3 inhibitors (Aim2). Finally, we will use tissue and blood samples from a Phase I clinical trial aimed at
using neoadjuvant combination RT and anti-PDL1 and will examine whether that changes the immune
landscape to increase Teff/Treg ratio and enhance Teff activation profile (Aim3). We expect these studies to
elucidate molecular and cellular parameters of RT plus immune checkpoint blockade and to help develop more
effective therapy for HNSCC.

## Key facts

- **NIH application ID:** 9898356
- **Project number:** 5R01DE028529-02
- **Recipient organization:** UNIVERSITY OF COLORADO DENVER
- **Principal Investigator:** SANA D KARAM
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $439,092
- **Award type:** 5
- **Project period:** 2019-04-01 → 2024-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9898356

## Citation

> US National Institutes of Health, RePORTER application 9898356, Tackling Treg mediated resistance to radiation and anti-PDL1 in HNSCCs (5R01DE028529-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9898356. Licensed CC0.

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