Fatty acids promote the expansion of NK-92 cells in vitro by improving energy metabolism

Polyvinyl alcohol, N-acetylcysteine, and methyl-β-cyclodextrin exhibit albumin functions in natural killer cell culture

Albumin is a crucial component of serum-free media, playing a significant role in ex vivo cell culture as a lipid carrier and antioxidant. However, purified albumin contains undefined substances, making it challenging to achieve clinical application standards for effector cell culture. This study used natural killer (NK)-92 cells as a model to investigate the effects of the albumin substitute replacing bovine serum albumin (BSA) on cell expansion and metabolism in an in-house-designed, chemically defined, serum-free medium. We selected polyvinyl alcohol (PVA), N-acetylcysteine (NAC), and methyl-β-cyclodextrin (M-β-CD) as an albumin substitute combination and optimized their concentrations by using response surface methodology. The optimized albumin substitute was named PVA-NAC-M-β-CD (PNM). After 8 days of culture, NK-92 cells cultured with the PNM exhibited phenotype and cytotoxic function comparable to cells cultured with different concentrations of BSA. The expansion fold was 89.22 ± 3.55, significantly higher than the 51.23 ± 6.57 observed in the 0.75 g/L BSA group (p < 0.05). Further verification of functions of PNM showed that intracellular fatty acid levels, cholesterol consumption rates, and the pSTAT5 level in the PNM group were significantly higher than those in the 0.75 g/L BSA group (p < 0.05). Reactive oxygen species levels remained controlled, and mitochondrial membrane potential was similar. These findings suggested that the PNM can effectively replace the functions of BSA as a fatty acid carrier, antioxidant, and, to some extent, a cholesterol carrier. This study provides insights for developing chemically defined media to prepare clinical-grade NK cells efficiently.

The combination of oleic acid, linoleic acid, palmitoleic acid, and α-linolenic acid promoted the expansion of NK-92 cells in vitro

Cell culture medium is an important factor affecting the expansion of NK cells in vitro. As an important component of cell culture medium, lipids participate in various complex physiological activities of cells and significantly affect the expansion of cells. Using NK-92 cells as a model, the lipid metabolism of NK cells in vitro was analyzed, and combined with the kinetic relationship between lipid metabolism and NK cell expansion. Four fatty acids, oleic acid, linoleic acid, palmitoleic acid, and α-linolenic acid, were preliminatively identified as the key lipid combinations. The combination was preliminarily verified on the self-developed serum-free medium. It was found that when the key lipid combination was added according to the concentration in the serum, NK-92 cells expansion reached 188.03 ± 33.34-folds, which was significantly higher than 105.28 ± 13.23-folds in the basic medium. Additionally, NK-92 cells expanded by adding key lipid combinations could maintain cell killing function. Overall, this research provides technical support for the development of NK cell serum-free medium.

Optimizing glutamine concentration enhances ex vivo expansion of natural killer cells through improved redox status

Amino acids are vital components of the serum-free medium that influence the expansion and function of NK cells. This study aimed to clarify the relationship between amino acid metabolism and expansion and cytotoxicity of NK cells. Based on analyzing the mino acid metabolism of NK-92 cells and Design of Experiments (DOE), we optimized the combinations and concentrations of amino acids in NK-92 cells culture medium. The results demonstrated that NK-92 cells showed a pronounced demand for glutamine, serine, leucine, and arginine, in which glutamine played a central role. Significantly, at a glutamine concentration of 13 mM, NK-92 cells expansion reached 161.9 folds, which was significantly higher than 55.5 folds at 2.5 mM. Additionally, under higher glutamine concentrations, NK-92 cells expressed elevated levels of cytotoxic molecules, the level of cytotoxic molecules expressed by NK-92 cells was increased and the cytotoxic rate was 68.42%, significantly higher than that of 58.08% under low concentration. In view of the close relationship between glutamine metabolism and intracellular redox state, we investigated the redox status within the cells. This study demonstrated that intracellular ROS levels in higher glutamine concentrations were significantly lower than those under lower concentration cultures with decreased intracellular GSH/GSSG ratio, NADPH/NADP+ ratio, and apoptosis rate. These findings indicate that NK-92 cells exhibit improved redox status when cultured at higher glutamine concentrations. Overall, our research provides valuable insights into the development of serum-free culture medium for ex vivo expansion of NK-92 cells.

Advances in serum-free media for CHO cells: From traditional serum substitutes to microbial-derived substances

The Chinese hamster ovary (CHO) cell is an epithelial-like cell that produces proteins with post-translational modifications similar to human glycosylation. It is widely used in the production of recombinant therapeutic proteins and monoclonal antibodies. Culturing CHO cells typically requires the addition of a certain proportion of fetal bovine serum (FBS) to maintain cell proliferation and passaging. However, serum is characterized by its complex composition, batch-to-batch variability, high cost, and potential risk of exogenous contaminants such as mycoplasma and viruses, which impact the purity and safety of the synthesized proteins. Therefore, search for serum alternatives and development of serum-free media for CHO-based protein biomanufacturing are of great significance. This review systematically summarizes the application advantages of CHO cells and strategies for high-density expression. It highlights the developmental trends of serum substitutes from human platelet lysates to animal-free extracts and microbial-derived substances and elucidates the mechanisms by which these substitutes enhance CHO cell culture performance and recombinant protein production, aiming to provide theoretical guidance for exploring novel serum alternatives and developing serum-free media for CHO cells.