A solution for highly efficient electroporation of primary cytotoxic T lymphocytes

Abstract

Background Cytotoxic T lymphocytes (CTLs) are central players in the adaptive immune response. Their functional characterization and clinical research depend on efcient and reliable transfection. Although various methods have been utilized, electroporation remains the preferred technique for transient gene over-expression. However, the efciency of electroporation is reduced for human and mouse primary CTLs. Lonza ofers kits that efectively improve plasmid DNA transfection quality. Unfortunately, the removal of key components of the cell recovery medium considerably reduced the efciency of their kit for CTLs. Our aim was to develop a new recovery medium to be used with Lonza’s Nucleofector system that would signifcantly enhance transfection rates. Results We assessed the impact of diferent media in which the primary CTLs were placed to recover after electroporation on cell survival, transfection rate and their ability to form an immunological synapse and to perform exocytosis. We transfected the cells with pmax-GFP and large constructs encoding for either CD81-super ecliptic pHluorin or granzyme B-pHuji. The comparison of fve diferent media for mouse and two for human CTLs demonstrated that our new recovery medium composed of Opti-MEM-GlutaMAX supplemented with HEPES, DMSO and sodium pyruvate gave the best result in cell survival (>50%) and transfection rate (>30 and 20% for mouse and human cells, respectively). More importantly, the functionality of CTLs was at least twice as high as with the original Lonza recovery medium. In addition, our RM signifcantly improved transfection efcacy of natural killer cells that are notoriously hard to electroporate. Conclusion Our results show that successful transfection depends not only on the electroporation medium and pulse sequence but also on the medium applied for cell recovery. In addition, we have reduced our reliance on proprietary products by designing an efective recovery medium for both mouse and human primary CTLs and other lymphocytes that can be easily implemented by any laboratory. We expect that this recovery medium will have a signifcant impact on both fundamental and applied research in immunology.