ESTRO 2022 - Abstract Book

S435

Abstract book

ESTRO 2022

Figure 1. Survival during the 100-day observation period, with significant survival benefit in all groups compared to control animals. Conclusion Both conventional radiotherapy and FLASH could generate long-term anti-tumor effects in fully immune competent animals with high grade glioma cells on the flank.

PD-0484 Changes Of Immune Status In Patients With Different Pd-L1 Expression After SBRT Of Metastases

A. Zozulya 1 , S. Novikov 1 , I. Baldueva 2 , A. Artemyeva 3 , A. Muravceva 3 , D. Girdyuk 2 , N. Emelyanova 2 , E. Tuyryaeva 1 , E. Fedosova 1 , F. Antipov 1 , A. Arseniev 1 , S. Kanaev 1 , A. Belyaev 2 1 N.N. Petrov National Medical Research Centre of Oncology, Radiotherapy, Saint-Petersburg, Russian Federation; 2 N.N. Petrov National Medical Research Centre of Oncology, Oncoimmunology, Saint-Petersburg, Russian Federation; 3 N.N. Petrov National Medical Research Centre of Oncology, Pathomorphology, Saint-Petersburg, Russian Federation Purpose or Objective 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. Materials and Methods 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 ( χ 2) 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). Results 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+ ( χ 2 = 10,5, p < 0,01; pairwise p < 0,01); activated cytotoxic T-lymphocytes, CD3+ С D8+HLA-DR+ ( χ 2 = 10,5, p < 0,01; pairwise p < 0,01), T-lymphocytes, CD3+CD19- ( χ 2 = 7,8, p = 0,02; pairwise p = 0,02) and T-helpers, CD3+CD4+ ( χ 2 = 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 ( χ 2 = 6,7, p < 0,01; pairwise p = 0,04) and increased number of activated T-helpers ( χ 2 = 9,6, p < 0,01; pairwise p < 0,01) was detected 6-8 weeks after irradiation. Conclusion 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.

PD-0485 Dynamic of immune profile after SABR

S. Novikov 1 , A. Zozulya 2 , I. Baldueva 3 , A. Arsenev 1 , S. Kanaev 1 , N. Emelyanova 3