Biological effects and irradiation dose induced in human lymphocytes in vitro by an intracellular radionuclide:99mTc.

Since lymphocyte radiolabeling is widely used for in vitro and in vivo studies and may interfere with the properties of the cells, the purpose of this work was to investigate the effects of 99mTc labeling on lymphocyte morphology and functions. Two ranges of 99mTc activity were used, 37 and 370 MBq, and their effects were compared to those produced by a graduated external irradiation. Electron microscopy was performed and T cells were studied using biological markers (E-Rosette formation, cell proliferation under lectin reactivity, and specific cell-mediated cytolysis). After 370-MBq labeling, an intense cytotoxic effect was observed on cell morphology, drastically impeding T-lymphocyte functions. Thirty-seven-megabecquerel labeling and sham procedure did not significantly affect cell functions. The external irradiation dose-response curve indicated a clear radiation-induced inhibitory effect, especially over 10 Gy. This effect was less intense than that obtained with 370-MBq 99mTc labeling. The labeling cytotoxic effect can then be attributed to a radiolesion due to a radiation dose which is probably higher than 10 Gy. In fact, the dose received by lymphocytes during the 370-MBq labeling procedure was estimated as 70 Gy by calculations, taking into account all emissions of 99mTc.