Determination of human γδ T cell-mediated cytotoxicity using a non-radioactive assay system.

The adoptive transfer of immune effector cells, such as CD8 killer αβ T cells, γδ T cells, NK (natural killer) cells, and genetically-modified T cells, has been receiving increasing attention. It is essential to determine cellular cytotoxicity so as to monitor the function and quality of ex vivo-expanded immune effector cells before infusion. The most common method is the [Cr]-sodium chromate release assay. It is, however, preferable to avoid the use of radioactive materials in clinical laboratories. In order to establish a non-radioactive alternative to the standard radioactive assay, we previously synthesized a chelate-forming prodrug (BM-HT) and demonstrated that a combination of BM-HT and europium (Eu) was useful to determine NK cell-mediated cytotoxicity. In the present study, we examined whether or not this improved assay system could be used to determine the cellular cytotoxicity exhibited by Vγ2Vδ2 γδ T cells. In addition, we compared Eu and terbium (Tb) in the measurement of cellular cytotoxicity. Our assay system using BM-HT could be used successfully for the analysis of both γδ T cell receptor (TCR)- and CD16-mediated cytotoxicity. When the intensity of fluorescence was compared between Eu and Tb, Tb chelate was more sensitive than Eu chelate, suggesting that the detection system using Tb is superior to Eu when tumor cells are not efficiently labeled with BM-HT. The method established herein is expected to promote the development of novel adoptive cell therapies for cancer.