CD4 and neoplasm: Following the irradiation of lung tumors, preliminary clinical studies utilizing SBRT with regimens of 60 Gy in 8 fractions or 50 Gy in 4 fractions have demonstrated increases in immunoactive CD8+ cytotoxic T-cells in the peripheral blood samples of patients detected by differences in flow cytometry, while also showing a decrease in the levels of CD4+ regulatory T-cells and granulocytic myeloid-derived suppressor cells (MDSCs), which are thought to be integral to the immunosuppressive tumor microenvironment, and which play a significant role in tumor immune-cell invasion [18,19].