Immunosuppression Factors PD-1, PD-L1, and IDO1 and Colorectal Cancer

Due to the low efficiency of immunotherapy for colorectal cancer (CRC), it is extremely promising and relevant to study the mechanisms of immunosuppression. In this work, a comprehensive study of the expression of soluble and tissue forms of PD-1 and PD-L1 in blood serum and tumors of patients with CRC, as well as IDO1 in tumors was performed for the first time. The diagnostic and prognostic significance of the studied parameters was determined. A statistically significant decrease in the number of soluble forms of PD-1 and PD-L1 in the blood serum and the association of the number of PD-L1+ cells in the stroma of tumors with the CRC stage were established. The absence of correlations between soluble and tissue forms of the studied proteins was shown, indicating the presence of independent mechanisms of immunosuppression in CRC, which may explain the ineffectiveness of immunotherapy for this type of tumor.