Soluble forms of the immune check-point receptor PD-1 and its ligand PD-L1 in blood serum of patients with renal cell carcinoma: clinical and pathologic correlations

Background. Renal cancer is one of the most immunosensitive oncologic diseases. A prominent breakthrough in this field was gained with the development of medications directed to the suppression of PD-1/PD-L immune check-point signaling pathway that in normal physiologic conditions controls autoimmune reactions. Tumor PD-1 and/or PD-L1 expression is investigated both as a predictor of corresponding immunotherapy efficiency, and as molecular markers of overall prognosis and patients’ survival. This goal could be also attained by the measure­ment of soluble forms of these proteins (sPD-1 и sPD-L1) in blood serum. Objective of the study — comparative evaluation ofsPD-1 and sPD-L1 content in blood serum of practically healthy persons and patients with renal cancer and benign kidney tumors; analysis of the associations between these markers and clinical and pathologic characteristics of renal cancer. Materials and methods . 106 renal cancer (64 male and 42 female; age 33—81 years) and 11 patients with benign kidney tumors (3 male and 8 female; age 29—84 years) were included in the study. Control group comprised 19 men and 18 women of matching age. 57patients had stage I, 12 — II, 15 — III and 22 — stage IVrenal cancer. Serum sPD-L1 and sPD-1 concentrations were measured using standard enzyme immunoassay kits (Affimetrix, eBioscience, USA). Results. sPD-L1 levels in blood serum of patients with primary renal cancer and benign tumors were significantly higher than in control (p <0.0001 and p <0.05 respectively). sPD-L1 level significantly increased with disease stage (p <0.001), with T index increase from 1 to 3 declining at T4, was significantly higher in patients with lymph node metastases (both N1, and N2) than in those without such lesions (N0); it was also increased in М + patients, and in patients with grade III—IVin comparison to grade I—II tumors. sPD-1 levels did not differ sig­nificantly between study groups, did not depend on disease stage, presence of lymph node or distant metastases, but were decreased in patients with Т 4 as compared to those with less advanced primary tumor, and were significantly lower in patients with clear-cell than in those with chromophobic or papillary histologic variants. Conclusion . Serum sPD-L1 in renal cancer patients correlates with disease progression and tumor grade, and can be regarded as promising marker for monitoring of anti-PD1/PD-L1 treatment efficiency. Potential clinical implications of sPD-1 require further investigations and analysis.