It goes without saying that cellular immunotherapy is coming of age these days. There is the success of CAR-T cells as frontrunner in commercial application and curing patients. However, this comes also at the cost of serious side effects. Natural Killer (NK) cells and their derivatives are heavily being studied as a next generation cellular therapy and it is anticipated from the first clinical trials with these cell types that there are improvements in survival of patients with less side effects.

For NK cells to be effective, large numbers of cells are needed and many labs have established expansion protocols. Our lab also created a feeder cell line (K562) transduced with a lentivirus containing the genes for membrane-bound IL-21, 4-1BBL and GFP, as has also been published by others. We generated a clone that gave the highest expansion rate of NK cells. The clone was further expanded and prepared as a master cell bank under Good Manufacturing Practice in a B-grade clean room followed again by extensive Quality Control. Using this cell line, we further established a fast and effective NK cell expansion protocol ready for clinical manufacturing under GMP.

As usually irradiated feeder cells are used - a method that often has to be outsourced and makes production and regulatory protocols more complex. We developed an alternative method that can be performed inhouse and consists of preparing a hypotonic cell culture medium in combination with freeze/thaw cycles leading to mitotically suppressed feeder cells as is the case after irradiation. These feeder cells are equally effective in expanding NK cells and the NK cells demonstrate the same phenotype and function. Finally, these feeder cells are never present in the final product rendering the manufacturing method ready for clinical manufacturing.