Non-viral technologies can pave the way for CAR-NK cell therapy.

Natural killer (NK) cells are a promising platform for cancer immunotherapy. NK cells have high intrinsic killing capability, and the insertion of a chimeric antigen receptor (CAR) can further enhance their anti-tumor potential. In first human trials, CAR-NK cells demonstrated strong clinical activity without therapy-induced side effects. The applicability of NK cells as an "off-the-shelf" product makes them highly attractive for gene-engineered cell-therapies. Traditionally, viral transduction has been used for gene-editing; however, the use of viral vectors remains a safety concern and is associated with high costs and regulatory requirements. Here, we review the current landscape of non-viral approaches for CAR-NK cell generation, which include transfection of vector particles and electroporation of mRNA and DNA vectors resulting in transient gene-modification and CAR expression. In addition, using non-viral transposon technologies, NK cells can be stably modified ensuring long-lasting CAR expression. Finally, we discuss CRISPR/Cas9 tools to edit key genes for NK cell functionality.