# Mutual Exclusion Analysis Shows that DUSP9 Negatively Regulates PD‐L1 Expression and Acts as a Target to Enhance Anti‐PD‐1 Efficacy

## TL;DR

This study identifies DUSP9 as a new target that can enhance the effectiveness of PD-1 immunotherapy by regulating PD-L1 expression.

## Contribution

The study introduces a novel approach using mutual exclusion analysis to identify negative regulators of PD-L1, with DUSP9 as a key discovery.

## Key findings

- DUSP9 negatively regulates PD-L1 expression by dephosphorylating STAT3 in multiple tumor cells.
- Combining DUSP9 targeting with PD-1 antibody improves therapeutic sensitivity in tumor models.
- High DUSP9 expression correlates with poor response to PD-1/PD-L1 antibody therapy in clinical data.

## Abstract

The expression level of PD‐L1 is one of the most widely used predictive markers of immune checkpoint blockade (ICB) efficacy in the clinic, suggesting the importance of regulating PD‐L1 expression. However, no published reports have addressed the systematic exploration of the regulation of immune checkpoint molecules from the perspective of mutual exclusion (ME) in gene expression. The ME analysis, based on gene plasticity, provides a novel perspective on the intergenic regulatory paradigm. Here, multiple negative regulators of PD‐L1 expression are identified, and dual‐specificity phosphatase 9 (DUSP9) is selected for intensive study. DUSP9 negatively regulates PD‐L1 expression in multiple tumor cells, and mechanistically, DUSP9 dephosphorylates STAT3 to mediate the inhibitory role. In syngeneic tumor models, the combination of DUSP9 targeting and PD‐1 antibody can enhance therapeutic sensitivity. The clinical data demonstrated that elevated DUSP9 expression is correlated with diminished PD‐1/PD‐L1 antibody response rates. Consequently, DUSP9 emerges as a promising target for enhancing treatment response in combination with PD‐1 antibody, and functions as a potential marker for predicting the efficacy of tumor immunotherapy. This research demonstrates an efficient method for identifying negative regulators of highly plastic genes (HPGs), which can predict immunotherapy responses and identify new targets for combination therapy with ICB.

A mutually exclusive screening system is established to identify negative regulators of highly plastic genes. Dual specificity phosphatase (DUSP9) is a novel negative regulatory molecule of PD‐L1 by dephosphorylating STAT3, and acts as a target molecule in combination with PD‐1 antibody for tumor immunotherapy and a new clinical biomarker for predicting responsiveness to ICB therapy.