Coordinated dynamics of circulating neutrophils, regulatory T lymphocytes, myeloid derived suppressor cells and...

Circulating immune cells serve as readily accessible biomarkers in cancer patients. Some of them, such as neutrophils, lymphocytes as well as the neutrophil to lymphocyte ratio (NLR), have been validated as prognostic indicators of disease outcome whereas the significance of others remains controversial due to conflicting findings. Moreover, the interplay and correlation among these markers have not been thoroughly investigated nor has their dynamic course during chemotherapy.

Blood was collected from 16 healthy donors and 90 patients receiving first line chemotherapy for metastatic colorectal cancer before, during and after chemotherapy. Neutrophils, lymphocytes, circulating CD4⁺CD25⁺FOXP3⁺ regulatory T lymphocytes (Tregs), monocytic myeloid derived suppressor cells (mMDSCs), polymorphonuclear myeloid derived suppressor cells (pMDSCs) and other exploratory myeloid subsets were immunophenotyped and quantified with flow cytometry. Their frequencies were compared between healthy donors and patients and correlated with each other and with clinical parameters. Associations with progression-free and overall survival were evaluated using Cox proportional hazards regression and longitudinal changes in immune cell populations during chemotherapy were analyzed using linear mixed-effects models.

Circulating Tregs were significantly reduced in patients with high neutrophil counts (7% vs 17%, p=0.04), increased significantly during treatment in responders, particularly in patients achieving complete or partial response (+16%, p = 0.003) but did not demonstrate prognostic significance. pMDSCs were further stratified by CD16 expression into a CD16⁺ subset associated with favorable outcome and a CD16^dim/- subset enriched in patients demonstrating poor prognosis. Frequency of circulating mMDSCs was modestly increased in patients but retained adverse prognostic significance (HR 1.98, CI 1.04-3.78, p=0.039) and correlated with the CD16^dim/- pMDSC fraction. Mature CD15⁺CD33^- polymorphonuclear cells were significantly expanded in patients (79% vs 73%, p=0.003) and correlated with adverse clinical features, whereas lower levels correlated with improved survival (HR 0.54, CI 0.3-0.98, p=0.045). Rare HLA-DR⁺CD16⁺ granulocytic subset demonstrated significantly reduced levels in patients compared to healthy donors while their kinetics during treatment also correlated inversely with disease burden.

Circulating immune cell subsets in metastatic colorectal cancer exhibit considerable baseline heterogeneity and distinct immune kinetics during chemotherapy. Our findings demonstrate that conventional leukocyte populations, when evaluated individually, together with detailed immunophenotyping provide complementary prognostic information, revealing previously unappreciated heterogeneity within major immune cell populations and a network of novel interrelationships among circulating immune cells. Together, these observations support comprehensive immune profiling as a promising approach for future biomarker development and immune-based patient stratification.