Changes in T Lymphocyte Subsets in Different Tumors Before and After Radiotherapy: A Meta-Analysis

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Radiation therapy (RT) induces an immune response, but the relationship of this response with tumor type is not fully understood.We searched English-language electronic databases including PubMed, EMBASE, and the Cochrane Library to collect studies about the changes in CD3+ T lymphocytes, CD4+ T lymphocytes, and CD8+ T lymphocytes before and after radiotherapy in tumor patients from January 2015 to December 2019. The quality of the included literature was evaluated using the NOS scale provided by the Cochrane Collaboration, and statistical software was used to analyze the included literature. P < 0.05 was considered to indicate statistical significance.A total of 17 studies in 15 articles involving 1735 tumor patients were included. All data were collected within 1 month before or after radiotherapy. Meta-analysis showed that numbers of CD3+ T lymphocytes were significantly reduced after radiotherapy compared with before treatment (standard mean difference [SMD]: -0.76; 95% CI [-1.46, -0.06]; P = 0.03), as were those of CD4+ T lymphocytes (SMD: -0.50; 95% CI: [-0.88, -0.12]; P = 0.01), but there was no statistically significant difference for CD8+ T lymphocytes (SMD: 0.19; 95% CI: [-0.23, 0.62]; P = 0.38). Subgroup analysis showed significant decreases in CD3+ T lymphocytes in liver cancer, esophageal cancer, head and neck cancer, pancreatic cancer and breast cancer after radiotherapy. Numbers of CD4+T lymphocytes increased after radiotherapy in breast cancer, and a decrease was observed in liver cancer, esophageal cancer, colorectal cancer, and head and neck cancer. CD8+ T lymphocyte numbers also increased compared with before radiotherapy in esophageal cancer, lung cancer, and colorectal cancer. But a decrease in liver cancer and head and neck cancer.Numbers of CD3+ and CD4+ T lymphocytes decreased after radiotherapy, whereas CD8+ T lymphocytes showed no significant change. Within 1 month of radiotherapy, the tumor microenvironment showed an immunosuppressive state. The degree of immune response induced by radiotherapy differed between tumor types.