Session Item

To study the influence of PD-L1 expression on the dynamics of immunological changes before and at different intervals after stereotactic body radiation therapy (SBRT) of metastatic lesions in patients with metastatic forms of solid tumors.

In 21 patients with metastatic lesions in the lungs and/or liver SBRT was performed as 4 fractions of 10-13.5Gy or 3 fractions of 15Gy-20Gy. A quantitative assessment and analysis of blood immunological parameters was conducted before SBRT, 3-4 weeks and 6-8 weeks after the end of SBRT. Peripheral blood samples were analyzed by flow cytometry. We used morphological material (primary tumor or metastasis) obtained before SBRT for determination of PD-L1 expression using CPS-index. Statistical analysis was performed using Friedman (χ2) and Nemenyi criteria. Depending on the PD-L1 status, we divided patients in two groups: PD-L1 negative, CPS<1 (12 patients) and PD-L1 positive, CPS≥1 (9 patients).

3-4 weeks after the end of SBRT in PD-L1 negative group we observed statistically significant increase of activated T-helpers, CD3+CD4+HLA-DR+ (χ2 = 10,5, p < 0,01; pairwise p < 0,01); activated cytotoxic T-lymphocytes, CD3+СD8+HLA-DR+ (χ2 = 10,5, p < 0,01; pairwise p < 0,01), T-lymphocytes, CD3+CD19- (χ2 = 7,8, p = 0,02; pairwise p = 0,02) and T-helpers, CD3+CD4+ (χ2 = 6,7, p = 0,04; pairwise p = 0,03). Statistically significantly increased levels of activated T-helpers and activated cytotoxic T-lymphocytes were also mentioned 6-8 weeks after SBRT (pairwise p < 0,01 in both indicators). While T-lymphocytes, CD3+CD19- and T-helpers, CD3+CD4+ returned to the initial (pre-SBRT) levels without statistical significance (p>0,05). Different changes in immune profile were revealed in PD-L1 positive group: 3-4 weeks after SBRT we mentioned decreased level of T-regulatory lymphocytes, CD4+CD25brightCD127low (χ2 = 6,7, p < 0,01; pairwise p = 0,04) and increased number of activated T-helpers (χ2 = 9,6, p < 0,01; pairwise p < 0,01) was detected 6-8 weeks after irradiation. 

In PD-L1 negative (CPS<1) patients SBRT induced significant activation of antitumor T-cell immune response while in PD-L1 positive (CPS≥1) patients SBRT was mainly associated with reduction of T-regulatory lymphocytes.