Chimeric antigen receptor (CAR) T cell therapy has emerged as a promising therapy against cancer in the last decade, showing great success in treating certain types of blood cancer. However, major limitations of CAR T cells include severe toxicities, tumor escape owing to antigen loss and failure of manufacturing the autologous product. Natural killer (NK) cells provide a promising alternative since these innate cytotoxic lymphocytes have shown no severe toxicities in clinical studies, maintain their innate activity against cancerous cells and can be manufactured for off-the-shelf use from healthy donors.

However, current CAR designs used in NK cells are based on findings achieved in T cells. Gaining more insights into CAR NK signaling is thus needed to tailor engineering strategies to NK cell biology, thereby favorably modulating their antitumor properties.

NK cell regulation is based on the integration of multiple signals. We have leveraged this concept for therapeutic purposes by co-expressing a CAR and a chimeric co-stimulation receptor (CCR) on NK cells, thereby introducing two different activation signals that act in synergy. We could show that the modified NK cells have increased antitumor activity against tumor cells expressing targets for the CAR and CCR. Moreover, these engineered CAR NK cells could kill tumor cells better in short term, but also during multiple tumor rechallenges. Furthermore, we have applied CRISPR/Cas9-mediated genome editing strategies including gene knock out and base editing to improve the functional persistence of CAR NK cells, resulting in improved antitumor efficacy.

In conclusion, NK cells hold great potential as an off-the shelf option for cellular therapy. By tailoring cell engineering approaches to the requirements of NK cells, CAR NK cells can improve cancer treatment outcomes in currently hard-to-treat malignancies.