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.