Measurement of Average Telomere Length in Ex Vivo Expanded Natural Killer Cells by Fluorescence In Situ Hybridization (FISH) and Flow Cytometry.

Natural killer (NK) cells are a subset of cytotoxic lymphocytes that play a critical role in innate immune surveillance against infections and tumors through cytokine secretion and target cell lysis. NK cells function without any need for prior antigen exposure. Thus, more recently NK cells are considered a promising source of lymphocytes for adoptive tumor therapy. However, because NK cells represent only a small lymphocyte fraction, expand poorly ex vivo, and have limited life spans, clinical scale generation of NK cells for tumor immunotherapy was a challenging issue. To overcome this challenge, numerous expansion platforms have been developed. However, ex vivo expansion of NK cells could lead to proliferation-induced senescence. Telomeres at the end of chromosomes play a crucial role in maintaining the integrity of the chromosome and are lost at each cell division in somatic cells and have emerged as important cellular elements in aging and cancer. Because telomere length is known to decrease in adult human NK cells and is associated with proliferation-induced senescence, it is important to determine the effect of NK cell expansion systems on telomere length. In this chapter, a detailed protocol is provided to analyze the telomere length of expanded NK cells using a commercially available Flow FISH kit.