Researchers at China-based Tianjin Medical University reported that tumor-distal mediastinal lymph nodes (tdMLNs), long regarded primarily as anatomical structures for cancer staging, harbor functional progenitor exhausted CD8+ T cells (Tpex) that may contribute to sustained anti-tumor immunity following neoadjuvant chemoimmunotherapy in non-small cell lung cancer (NSCLC). The findings, published August 4 in Cell Reports Medicine, suggest that routine removal of these lymph nodes during surgery could potentially deplete an immune cell population important for postoperative responses to immune checkpoint inhibitors (ICIs).
Tpex cells are a stem-like subset of exhausted CD8+ T cells capable of self-renewal and differentiation into terminal effector cells following checkpoint blockade. Previous studies have largely focused on these cells within the tumor microenvironment. The new work extends that biology to tumor-distal mediastinal lymph nodes, indicating they may function as an immune reservoir rather than passive lymphatic tissue.
Using single-cell RNA sequencing together with paired T cell receptor (TCR) sequencing, the investigators profiled immune cells from primary tumors, adjacent normal tissue, tumor-proximal and tumor-distal mediastinal lymph nodes, and peripheral blood obtained from patients with lung squamous cell carcinoma who received neoadjuvant chemoimmunotherapy before surgery. The primary analysis included samples from five patients, with additional validation performed in eight patients using flow cytometry and functional assays.
The study found that Tpex cells within tumor-distal lymph nodes shared TCR clonotypes with terminally exhausted T cells infiltrating the primary tumor, indicating they originated from the same tumor-reactive immune response. Functional assays showed that these lymph node-derived Tpex cells retained the ability to produce interferon-γ, tumor necrosis factor-α and granzyme B following stimulation, consistent with preserved effector potential.
Further analysis suggested that stromal fibroblasts and endothelial cells within the lymph nodes provide chemokine and cytokine signals—including CCL19/CCR7, CCL21/CCR7 and IL-7/IL7R pathways—that help maintain the stem-like Tpex population. Neoadjuvant chemoimmunotherapy also appeared to increase interactions between dendritic cells and Tpex cells within both proximal and distal mediastinal lymph nodes, potentially supporting continued T-cell activation.
Longitudinal TCR sequencing performed in peripheral blood from three patients demonstrated persistence of tumor-associated T-cell clones for up to 18 months after surgery. Patients receiving adjuvant immune checkpoint inhibitors maintained or expanded these clonotypes, suggesting peripheral blood monitoring may provide a non-invasive method to track the durability of anti-tumor immune responses.