The ratio of CD8 + lymphocytes to tumor-infiltrating suppressive FOXP3 + effector regulatory T cells is associated with treatment response in invasive breast cancer

PURPOSE: FOXP3 + and CD8 + are recognized markers of tumor-infiltrating lymphocytes (TILs) for breast cancer. FOXP3 + TILs are composed of effector Tregs (eTregs) and other subpopulations that are classified by their differences in suppressive function. In this prospective study, we evaluated Treg subpopulations and CD8 + TILs in breast cancer. METHODS: 84 patients with breast cancer were enrolled. Fresh TILs were extracted andTregs were classified into eTregs (CD4(+)FOXP3(high)CD45RA(−)), other FOXP3(+) Treg subsets (naïve and non-Tregs), and total CD8(+)CD4(−) TILs using flow cytometry. The suppression strength of each Treg subpopulation was analyzed. The association between TIL subpopulations, clinicopathological characteristics, and response to chemotherapy was evaluated. RESULTS: The mean CD8/eTreg ratio value was 7.86 (interquartile range: 4.08–12.80). The proliferation function of eTregs was significantly suppressed compared with that of the other subpopulations (proliferation rates: control: 89.3%, + naiiveTreg: 64.2%, + non-Treg: 78.2% vs eTreg 1.93%; all P < 0.05). The patients with high with a high CD8 + /eTreg ratio achieved excellent pathological complete response (pCR) rate of neoadjuvant chemotherapy (90.2%) and the CD8/eTreg ratio were independent predictive factors for pCR (odds ratio:18.7(confidence interval 1.25–279) P < 0.05). A detailed assessment of the CD8/eTreg ratio for each patient who underwent NAC revealed that high CD8/eTreg ratio showed a significantly higher pCR rate compared to patients with a low CD8/FOXP3 ratio (39.6% vs 13.3, P < 0.05) in triple negative subtype patients with stromal TILs < 50%. CONCLUSIONS: A high CD8/eTreg ratio enhances pCR rate in patients with invasive breast cancer.