Immunotyping of peripheral blood lymphocytes by flow cytometry reveals Th cell as a potential prognostic biomarker for extranodal NK/T-cell lymphoma

This study aimed to explore the distribution, characteristics and prognostic value of baseline peripheral blood lymphocyte subsets in patients with extranodal NK/T-cell lymphoma (NKTCL). We conducted this cross-sectional study of 205 newly-diagnosed NKTCL patients receiving first-line chemotherapy and radiation at our institute between 2010 and 2020. Baseline peripheral blood lymphocytes were detected using flow cytometry, and the clinical value was analyzed. Compared with healthy controls, patients with NKTCL presented with a distinct peripheral immunity with higher levels of cytotoxic CD8+ T cells (33.230 +/- 12.090% vs. 27.060 +/- 4.010%, p < 0.001) and NKT cells (7.697 +/- 7.219% vs. 3.550 +/- 2.088%, p < 0.001) but lower proportions of suppressive regulatory T cells (Treg, 2.999 +/- 1.949% vs. 3.420 +/- 1.051%, p = 0.003) and CD4+ helper T cells (Th, 33.084 +/- 11.361% vs. 37.650 +/- 3.153%, p < 0.001). Peripheral lymphocytes were differentially distributed according to age, stage, and primary site in patients with NKTCL. The proportion of Th cells/lymphocytes was associated with tumor burden reflected by stage (p = 0.037), serum lactate dehydrogenase (p = 0.0420), primary tumor invasion (p = 0.025), and prognostic index for NK/T-cell lymphoma (PINK) score (p = 0.041). Furthermore, elevated proportions of T cells (58.9% vs. 76.4%, p = 0.005), Th cells (56.3% vs. 68.8%, p = 0.047), or Treg cells (49.5% vs. 68.9%, p = 0.040) were associated with inferior 5-year progression-free survivals (PFS) via univariable survival analysis. Multivariate cox regression revealed elevated Th cells as an independent predictor for unfavorable PFS (HR = 2.333, 95% CI, 1.030-5.288, p = 0.042) in NKTCL. These results suggested the proportion of Th cells positively correlated with tumor burden and was a potential non-invasive biomarker for inferior survival for patients with NKTCL.