Changes of Circulating Lymphocyte Populations and Its Association with Outcome after Hypofractionated Radiation Therapy in Patients with Non-small-cell Lung Cancer

Abstract

Hypofractionated radiation therapy may have significant immunomodulatory effects and could enhance anti-tumor immune effect. The purposes of this study were to investigate changes of peripheral blood lymphocytes at different time points during and after radiotherapy and their association with survival. We collected serial blood samples before treatment and about day 14 of radiotherapy, at the end of radiotherapy, 1 month and 3 months after radiotherapy from 42 patients with non-small-cell lung cancer from November 2016 to October 2018 . 40.5% (17/42) of the patients received 60-84Gy in 10-12 fractions of Stereotactic ablation radiotherapy. Other patients (59.5%, 25/42) were treated with Partial Stereotactic Ablative Boost Radiotherapy，the GTVb（GTV-boost）received 18-32Gy in 3-4 fractions, then the PTV was treated with conventional fractionated radiotherapy to a median dose of 55.44 Gy（48-60Gy）. We used flow cytometry to measure the changes of total CD3+, CD4+, CD8+ T cells, CD3+HLADR+ T cells, CD19+ B lymphocytes and CD16+CD56+ natural killer cells. The median follow up time was 10.6 months(range, 3.3 to 31.3). The one-year and two-year PFS was 73.0% and 58.0%, the one-year and two-year OS was 80.0% and 68.5%, and the one-year and two-year locoregional failure-free survival rate was 87.7% and 71.4%, respectively. The number of all the lymphocytes decreased gradually at the beginning of radiotherapy, reached the minimum at the end of radiotherapy, and gradually returned to the baseline level after radiotherapy. However, the fractions of CD3+HLADR+ T cells（activated T lymphocytes） decreased slightly at the beginning of radiotherapy, then gradually increased during radiotherapy until 3 months after radiotherapy. Moreover, 1 month after radiotherapy, the proportion of CD4+T cells was lower than the baseline, and the proportion of CD8+T cells was higher than the baseline, and the ratio of the two was lower than the baseline. Longer OS was significantly correlated with higher CD4+/CD8+Tcell ratio after radiotherapy (p＜0.05). And we found hypofractionated radiation therapy of patients with large tumor size produced more significant immune effects, while large tumor size may lead to worse OS, which still needs further exploration. The proportion of CD8+T cells and CD3+HLADR+ T cells（activated T lymphocytes）increased one month after the hypofractionated radiation therapy. We found longer OS was significantly correlated with higher CD4+/CD8+Tcell ratio after radiotherapy (p＜0.05), and this may be because the larger irradiation volume related to significant immunological effects of the tumor. These results may provide reference for future studies to determine the optimal treatment schedules when combining irradiation with specific immunotherapy approaches.