Non-classical immune checkpoint CD137/CD137L and CD200/CD200R expressions are regulated by the tumor immune microenvironment in lymph node aspirates from lung cancer patients.

BACKGROUND

Immune escape is a hallmark of lung cancer, and limited responsiveness to PD-1/PD-L1 blockade highlights the need to identify additional immunoregulatory mechanisms in the mediastinal tumor microenvironment (TME). Non-classical immune checkpoints, including CD137/CD137L and CD200/CD200R, may interact with classical pathways but remain insufficiently defined in metastatic lymph nodes (LNs). We evaluated their expression on tumor cells and lymphocytes and their associations with PD-L1 and PD-L2.

METHODS

LN aspirates obtained during transbronchial needle aspiration biopsy (EBUS/TBNA) from 71 lung cancer patients were analyzed using cytology, hematological screening, and flow cytometry. Expression of CD137, CD137L, CD200, CD200R, PD-1, PD-L1, PD-L2 was assessed on tumor cells and lymphocytes.

RESULTS

Tumor cells showed high EpCAM and cytokeratin expression. CD137L was mainly detected on tumor cells, whereas CD137 was predominantly expressed on CD8+ T lymphocytes. CD200 expression was higher on tumor cells, while CD200R was enriched on lymphocytes, particularly CD8+ T cells. Correlation analysis revealed significant associations between non-classical and classical checkpoints, including positive correlations of CD200R and CD137 on tumor cells with PD-L2, and a positive correlation between CD137 on lymphocytes and PD-1.Checkpoint expression varied with histology:: NSCLC exhibited higher PD-L1, PD-L2, and CD137 expression. Tumor-rich LNs showed reduced tumor-cell expression of these markers, while lymphocyte profiles remained relatively stable.

CONCLUSION

CD137/CD137L and CD200/CD200R interact with PD-1-related pathways in metastatic LNs, forming an integrated immunoregulatory network predominantly shaped at the tumor cell level. Flow cytometric analysis of LN aspirates may help identify additional therapeutic targets in lung cancer.