# Antigen-specific T Cell precursor frequency influences the proliferation of stem-like T Cells in tumor-draining lymph nodes and anti-tumor immune responses

## TL;DR

This study shows that the number of initial T cells specific to a tumor antigen affects the development of stem-like T cells and the success of immunotherapy in mice.

## Contribution

First direct in vivo evidence that precursor T cell frequency influences stem-like T cell pool and immunotherapy response.

## Key findings

- Higher precursor frequency of antigen-specific T cells increases stem-like T cells in tumor-draining lymph nodes.
- Increased precursor frequency suppresses tumor growth and improves mouse survival.
- Higher precursor frequency enhances anti-PD-1 therapy effectiveness, leading to long-term survival.

## Abstract

While immune checkpoint blockade has transformed the landscape of cancer therapy, variability in patient responses constrains its therapeutic potential. Tumor-specific stem-like T (TSL) cells sustain durable immunity through self-renewal and differentiation. However, upstream regulators of TSL cells generation remain elusive, and direct evidence is still lacking regarding whether naïve tumor-specific T cell precursor frequency influences TSL cells pool establishment and immunotherapy response. This study aims to clarify the direct causal relationship between this precursor frequency and the number of TSL cells in tumor-draining lymph nodes, as well as the efficacy of anti-PD-L1 therapy.

We initially constructed a novel bone marrow cell chimeric model. Specifically, recipient mice of the wild-type C57BL/6 strain were subjected to lethal irradiation, after which they received intravenous adoptive transfer of a cell suspension (5 × 107 cells) comprising a blend of bone marrow cells derived from OT-I mice and wild-type mice in varying proportions. Subsequently, a subcutaneous transplanted tumor model was established by inoculating B16-OVA melanoma cells expressing the OVA antigen. Over the course of tumor progression, we evaluated tumor growth dynamics, mice survival outcomes, and T cell within the tumor-draining lymph nodes (TDLNs). Thereafter, we evaluated whether this divergence in precursor frequency of antigen-specific T cells modulates the efficacy of anti-PD-1 therapy.

The results of the bone marrow chimeric model demonstrated that: different precursor frequencies of antigen-specific T cell s significantly affect the abundance of stem-like T cells in the TDLNs of tumor-bearing mice. A higher precursor frequency of antigen-specific T cell could significantly suppress tumor growth and prolong the survival time of the mice. In the group with a higher precursor frequency, anti-PD-1 therapy effectively inhibited tumor growth, leading to long-term survival of the mice.

Our study provides the first direct in vivo evidence that the initial precursor frequency of tumor-antigen-specific T cell influences the stem-like T cell pool in TDLNs and thereby the efficacy of anti-PD-1 immunotherapy. This finding reveals a key upstream mechanism of response heterogeneity and offers a strategic rationale for overcoming ICB resistance.