Age dependence of T-lymphocyte apoptosis induced by high-energy proton exposure

Peripheral blood samples from three donors of different ages were exposed t o 300 kVp x-rays or 138 MeV protons (0, 2, and 9 Gy dose). After 48 h incub ation, CD4 and CD8 T-lymphocytes were labelled with specific monoclonal ant ibodies and cellular DNA was stained by propidium iodine. Radiation-induced apoptosis was followed by flow cytometry and the data were processed by LY SIS II software. The data analysis revealed an age-dependent sensitivity to radiation-induced apoptosis by 300 kVp x-rays and 138 MeV protons, for bot h CD4 and CD8 T-lymphocytes. Radiation-induced apoptosis was about 4 times greater in CD4 lymphocytes from the youngest donor than the oldest donor an d was about 2 times greater in CD8 T-lymphocytes, both after x-ray and prot on exposures. RBE values for CD4 T-lymphocytes ranged from 0.9 to 1.4 and f or CD8-positive cells from 0.7 to 0.9. It is concluded that radiation-induc ed apoptosis of CD4 and CD8 T-lymphocytes, which is already exploited to pi -edict patient response in conventional radiotherapy, may also be used to p redict response in proton treatment planning.