To observe the inhibitory effect of radiotherapy and monoclonal antibody-targeted blocking immune checkpoint molecule CEACAM1 (carcinoembryonic antigen-associated cell adhesion molecule) on glioma in situ in mice and its effect on immune response in mice.

We collected the clinical data of primary glioma patients who consecutively underwent operation and radiotherapy within 1 month in the Department of Neurosurgery of the First Hospital of Shanxi Medical University from March to December 2019. The expression of CEACAM1 on the surface of T lymphocytes in the peripheral blood of glioma patients before and after radiotherapy was detected respectively. GL261 glioma cells (stably transfected with luciferase gene) were implanted in the right caudate nucleus of the brain of C57BL/6 mice, and a small animal in vivo imaging system was used to observe the growth of the tumor. At the same time, the mice were divided into the isotype control group, the radiotherapy group, the anti-CEACAM1 group and the combined treatment group (n=5 in each group); the survival of the mice after treatment was observed. Immunohistochemical test was performed to detect the expression level of CEACAM1 in mouse brain gliomas before and after radiotherapy. Flow cytometry was performed to detect the expression levels of CD4⁺, CD8⁺ and regulatory T cells (Tregs) in mouse brain infiltrating T lymphocytes. The expression levels of serum interferon γ (IFN-γ) and interleukin 10 (IL-10) in mice were detected by enzyme-linked immunosorbent assay (ELISA).

Compared with before radiotherapy, the expression level of CEACAM1 on the surface of CD4⁺ T lymphocytes in the peripheral blood of glioma patients was significantly increased at 1 week after radiotherapy (P<0.05), and the expression level was further increased at 1 month after radiotherapy (P<0.05). There was no significant change in the expression level of CEACAM1 on the surface of CD8⁺ T lymphocytes 1 week after radiotherapy (P>0.05), and its expression level increased 1 month after radiotherapy (P<0.05). The combined treatment group could significantly inhibit the growth of gliomas in mice and prolong their survival period, and the survival period of some mice (2/5) in this group was more than 90 days (P<0.05). The results of immunohistochemistry showed that compared with before radiotherapy, there was no significant difference in the expression of CEACAM1 in mice 1 week after radiotherapy (P>0.05), but compared with before radiotherapy and 1 week after radiotherapy, the expression level of CEACAM1 increased significantly at 1 month after radiotherapy. high (both P<0.05). The results of flow cytometry showed that compared with the control group of the same type, the ratio of infiltrating CD8⁺ T lymphocytes in the brain of the mice in the combined treatment group increased, the ratio of Treg cells decreased, and the ratio of CD8⁺ T/Treg increased (all P<0.05). The ELISA results showed that the expression level of IFN-γ in the peripheral blood of mice in the combined treatment group increased, while the expression level of IL-10 decreased (both P<0.05).

Radiotherapy combined with CEACAM1 inhibitor therapy can generate a strong and durable anti-tumor immune response against gliomas in mice, and prolong the survival of some mice.

Glioma; Immunotherapy; Radiotherapy; Immune checkpoint; Immune escape; Mice