# CX3CR1 identifies a potent effector CD8+ T cell subset associated with anti-PD-1 therapeutic efficacy in colorectal cancer

## TL;DR

This study identifies a specific type of immune cell, CX3CR1+CD8+T cells, that predicts better outcomes and response to immunotherapy in colorectal cancer patients.

## Contribution

The paper introduces CX3CR1+CD8+T cells as a novel effector subset linked to anti-PD-1 therapy efficacy in colorectal cancer.

## Key findings

- CX3CR1+CD8+T cells exhibit a terminal effector phenotype with high cytotoxicity and low exhaustion.
- Enrichment of CX3CR1+CD8+T cells is a strong predictor of improved survival in colorectal cancer.
- Anti-PD-1 therapy enhances the function and proliferation of CX3CR1+CD8+T cells via an ETS1, PRDM1, and STAT1 regulatory network.

## Abstract

The therapeutic landscape for deficient mismatch repair (dMMR) colorectal cancer (CRC) has been fundamentally transformed by the introduction of immune checkpoint inhibitors (ICIs). Yet, a significant fraction of patients exhibits primary or acquired resistance, underscoring a critical unmet need to decode the heterogeneity of tumor-infiltrating CD8+T cells. Identifying the effector subsets that truly drive tumor control will be essential for refining patient stratification and optimizing therapeutic interventions.

By leveraging a multi-dimensional approach that combined single-cell RNA sequencing (scRNA-seq), multiplex immunohistochemistry (mIHC), extensive clinical data mining, and in vivo murine models, we comprehensively delineated the phenotypic profile, regulatory networks, and clinical relevance of intratumoral CX3CR1+CD8+T cells.

We uncovered a unique CX3CR1+CD8+ T cell subset exhibiting a Temra-like terminal effector phenotype characterized by potent cytotoxicity (GNLY, PRF1) and low exhaustion. Clinically, enrichment of this population emerged as a strong, independent predictor of improved overall survival in CRC. Mechanistically, effective anti-PD-1 therapy revitalizes anti-tumor immunity by specifically promoting the proliferation and maintaining the function of these CX3CR1+ effector cells within the tumor. SCENIC analysis further revealed that this differentiation pathway is orchestrated by ETS1, PRDM1 and STAT1 driven regulatory network, which is markedly induced following PD-1 inhibition to enhance metabolic fitness and cellular recruitment.

This study characterizes CX3CR1+CD8+T cells as a key effector subset predicting prognosis and immunotherapy response in colorectal cancer. These insights not only support their use as a clinically meaningful biomarker but also highlight the regulatory network orchestrated by ETS1 and PRDM1 as a promising avenue for overcoming immune resistance.