Expression of immune checkpoints on peripheral blood cells in patients with prostate cancer

Introduction. The first clinical trials of the treatment of patients with prostate cancer with checkpoint inhibitors show that only a few patients benefit from this type of treatment. This implies the need to find predictive biomarkers that would help identify patients for whom treatment with checkpoint inhibitors could be effective. Our study aimed to assess the level of PD-1, PD-L, and CTLA-4 expression on peripheral blood mononuclear cells of patients with primary prostate cancer and to demonstrate their applicability in clinical practice. Material and methods. Fifty men with primary prostate cancer were enrolled in the study. The control group consisted of 20 healthy men. The material for the study was peripheral blood from which mononuclear cells were isolated by flow cytometry, and the expression of PD-1, CTLA-4, and PD-L1 on them was assessed. Results. High PD-L1 expression on lymphoid dendritic cells has been demonstrated in patients with prostate cancer in comparison to the control group (p = 0.015) and high PD-L1 expression has been demonstrated in the following groups: high risk (p = 0.026), T2/T3 (p = 0.011), and Gleason 7 (p = 0.027). There was no high PD-1 expression on T lymphocytes among patients with prostate cancer in comparison to the control group, but positive correlations were found between PD-1 expression on CD3+ T cells and PSA (p = 0.049), risk group (p = 0.002), and TNM (p = 0.050). Low CTLA-4 expression was found on CD3+ lymphocytes among patients with prostate cancer in comparison to the control group (p = 0.006). Conclusions. Several groups of patients with prostate cancer have been identified, showing high PD-L1 and PD-1 expression on peripheral blood mononuclear cells, and a relationship between PD-1 and PD-L1 expression and the tumor aggressiveness potential has been demonstrated. This means that the assessment of PD-1 and PD-L1 expression can be used as a prognostic and predictive biomarker in prostate cancer.