Abstract
Natural killer (NK) cells stand out as promising candidates for cellular immunotherapy due to their capacity to kill malignant cells. However, the therapeutic use of NK cells is often dependent on cell expansion and activation with considerable amounts of serum and exogenous cytokines. We aimed to develop an expansion protocol for NK-92 cells in an effort to generate a cost-efficient, xeno-free, clinical grade manufactured master cell line for therapeutic applications. By making functional assays with NK-92 cells cultured under serum-free conditions (NK-92SF) and comparing to serum-supplemented NK-92 cells (NK-92S) we did not observe significant alterations in the viability, proliferation, receptor expression levels, or in perforin and granzyme levels. Interestingly, even though NK-92SF cells displayed decreased degranulation and cytotoxicity against tumor cells in vitro, the degranulation capacity was recovered after overnight incubation with 20% serum in the medium. Moreover, lentiviral vector-based genetic modification efficiency of NK-92SF cells was comparable with NK-92S cells. The application of similar strategies can be useful in reducing the costs of manufacturing cells for clinical use and can help us understand and implement strategies towards chemically defined expansion and genetic modification protocols.
Highlights
Natural killer (NK) cells are potential candidates for adoptive immunotherapy against cancer [1].NK cells from different sources have been utilized in various clinical trials with a robust safety profile and varying degrees of success [1,2]
NK-92 cells are cultured in Good Manufacturing Practice (GMP)-grade, serum-free, xeno-free stem cell growth medium (CellGro SCGM) supplemented with 20% fetal bovine serum (FBS) and 1000 U/mL Proleukin or IL-2 in our laboratory
We used a serum reduction strategy in which serum levels were gradually reduced from 20% to 0% over a 4-week period which equals approximately 12 passages to obtain serum-free cultured NK-92 cells (NK-92SF) (Figure 1a)
Summary
Natural killer (NK) cells are potential candidates for adoptive immunotherapy against cancer [1].NK cells from different sources have been utilized in various clinical trials with a robust safety profile and varying degrees of success [1,2]. As an alternative to primary NK cells, the possibility of using cytotoxic cell lines as adoptive immunotherapy has been investigated [3,4,5,6,7]. NK-92 cells express high levels of activating receptors, such as NKG2D, NKp30, NKp46, and 2B4 [10], and are highly cytotoxic against a broad range of tumor cells [11,12,13,14]. This may be due to their lack of almost
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