Development of a Flow Cytometric Screening Assay for Serial Cytotoxicity by Natural Killer (NK) Lymphocytes
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"The annual number of new cancer cases in the USA has continued to increase and cancer remains a leading cause of death globally, stressing the need for improved therapeutics. NK cell immunotherapy is an emerging therapeutic option, which utilizes one's own immune cells to fight cancer and is therefore an important target for improvement. Most NK lymphocytes are one-time killers: they stop killing after destroying just one target (virally infected or tumor) cell. However, a small percent of NK cells is capable of sustained killing and one cell will destroy multiple target cells - ""serial killing"". The main goal of this project was to develop an improved screening assay to distinguish serial killers from one-time killers, using human NK cell-mediated cytotoxicity towards K562 tumor cells. This improved screening assay uses flow cytometry and an antibody panel to distinguish the NK cells from other blood cells (e.g., T & B cells, monocytes) and to detect a cell marker for killing. This marker, an intracellular vesicle protein (CD107a), is normally absent from the cell membrane of NK cells, but moves to the outer membrane after the NK cell kills. We hypothesized that one-time killers and sustained NK killers can be distinguished by the chronological re-location of CD107a with each round of killing. We proposed that the first and second rounds of killing could be identified by two different color fluors attached to anti-CD107a antibodies. Our data demonstrate evidence for K562 tumor killing. However, detection of CD107a post-killing was unsuccessful with primary NK cells and highlights an area for improvement. Once perfected, this new assay for serial killing can be used as the foundation to study the effects of pharmaceutical reagents that may induce serial killers and/or improve NK serial killing."