I have been trying to expand NK cells isolated from Healthy Donors in CTS NK Xpander Medium from Thermofisher with IL2 at 500U/mL conc. being provided. Alongside, I am pre-activating NK cells with IL12/15/18 as well and trying to proliferate them with IL15 (50ng/mL-100ng/mL). I have been trying several permutation-combination but facing difficulty in stimulating the expansion of the NK cells. Can anyone provide me any kind of technical and scientific solution to this?