# Phenotype of circulating tumor-reactive T cells predicts immune checkpoint inhibitor response in non-small cell lung cancer

## TL;DR

Circulating tumor-reactive T cells in blood change during cancer treatment, and these changes may predict treatment success in lung cancer patients.

## Contribution

Identified specific markers and phenotypic transitions of circulating tumor-reactive T cells associated with immune checkpoint inhibitor response in non-small cell lung cancer.

## Key findings

- Circulating TR-Ts in responders show low CD38 expression before treatment.
- After ICI treatment, responders' cTR-Ts transition to a TCF7+ stem-like phenotype.
- Phenotypic changes of cTR-Ts correlate with therapeutic outcomes in mouse tumor models.

## Abstract

Peripheral blood (PB) is a source of tumor-infiltrating tumor-reactive T cells (TR-T). Circulating TR-Ts (cTR-T) in PB are expected to contribute to the efficacy of immune checkpoint inhibitors (ICIs), but their phenotype remains poorly understood. Here we analyse paired tumor-infiltrating and peripheral CD8+ T cells from patients with non-small cell lung carcinoma (NSCLC), using single-cell RNA and T cell receptor (TCR) sequencing. Tumor-infiltrating TR-Ts are defined based on the reported TR-T-associated gene signatures. Using their TCR sequence as a barcode, we identify cTR-Ts and their specific surface markers, including CD49a, CD49b, and HLA-DR. Trajectory analysis assigns a progenitor-like phenotype to cTR-Ts, suggesting a potential developmental relationship with tumor-infiltrating TR-Ts. By single-cell transcriptomic and flow cytometric analysis on an ICI-treated cohort we show that pre-treatment cTR-Ts in responders are characterized by a relatively low expression of exhaustion-related CD38. Following the first dose, cTR-Ts of responders transit towards a TCF7+ stem-like phenotype. Additionally, we validate cTR-T’s phenotypic changes following PD-1 blockade therapy in mouse tumor models with artificial antigen. These findings suggest that the phenotypic state and transition of cTR-Ts may reflect their functional potential after tumor infiltration and are associated with therapeutic outcomes of ICIs.

Tumor-reactive T cells (TR-T) in the peripheral blood of cancer patients undergo phenotypic changes during immune checkpoint inhibitor (ICI) therapy, which might predict therapeutic outcomes. Here authors follow the phenotypes of paired tumor-infiltrating and peripheral CD8 + T cells longitudinally from patients with non-small-cell lung cancer undergoing ICI treatment by single-cell RNA and T cell receptor sequencing and identify specific markers for circulating TR-Ts and for ICI response.