Different radiosensitivity of CD4⁺CD25⁺ regulatory T cells and effector T cells to low dose gamma irradiation in vitro

Abstract

Purpose: To determine the radiosensitivity difference of human Cluster of Differentiation (CD)4⁺CD25⁺ regulatory T cells (Treg) and effector T cells to low dose gamma ray and elucidate the underlying mechanisms in vitro.

Materials and methods: Blood samples were collected from five health subjects and five patients with advanced hepatocellular carcinoma (HCC). Treg and CD4⁺CD25⁻ T cells were selected using magnetic microbeads. The proliferative profiles, cytokine secretion, and differential expressions of apoptosis-related proteins in Treg and CD4⁺CD25⁻ T cells were compared using [³H]-thymidine incorporation, Luminex assay and flow cytometry when treated with various low doses of γ-ray.

Results: A dose-dependent reduction of proliferation in response to irradiation which paralleled the induction of apoptosis existed in Treg and CD4⁺CD25⁻ T cells. Treg were more radiosensitive to low-dose irradiation (0.94 Gray [Gy]) than effector T cells. The interferon-γ (IFNγ) was significantly upregulated and interleukin 10 (IL-10) was significantly downregulated in irradiated Treg. An enhanced immune response to low dose gamma ray existed in the peripheral blood in patients with advanced HCC. Higher levels of active caspase-3, CD95, B cell lymphoma 2 (Bcl-2)-associated X protein (Bax) expression were observed in Treg compared to CD4⁺CD25⁻ T cells. In addition, gamma irradiation activated CD4⁺CD25⁻ T cells to express CD25.

Conclusions: These studies revealed that Treg were more radiosensitive than CD4⁺CD25⁻ T cells to low dose irradiation. Higher expressions of apoptosis-related proteins such as caspase-3, CD95 and Bax were observed in Treg when compared to CD4⁺CD25⁻ T cells. Our results suggest that treatment with low doses of gamma irradiation may be a viable strategy to enhance immune response in patients with advanced HCC.

Keywords:

• gamma irradiation
• regulatory T cells
• hepatocellular carcinoma
• apoptosis
• radiosensitivity

Acknowledgements

This work was supported by National Institutes of Health grant AI061158, DK 60443 and GCRC Grant (RR00082) (to D.N.).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.