Engineering TGF-ß-resistant NK cells for cancer immunotherapy.

TGF-ß is a suppressive factor curtailing the effectiveness of NK cell adoptive transfer for cancer treatment. Inspired by data of SMAD4 haploinsufficient NK cells, we explored the possibility of knocking out SMAD4 by CRISPR/Cas9 in human NK cells as a novel strategy for circumventing TGF-ß suppression. Human SMAD4KO NK cells were resistant to TGF-ß inhibition, retaining their anti-tumor function and their proliferation in response to IL-2/IL-15. In addition, SMAD4KO NK cells exposed to TGF-ß showed improved tumor-penetration, associated to changes in adhesion molecules and chemokine receptors. Indeed, the cytotoxic activity of SMAD4KO NK cells surpassed that of control NK cells treated with a TGF-ß inhibitor, indirectly evidencing the advantage of maintaining SMAD4-independent TGF-ß-signaling. Furthermore, SMAD4KO NK cells were also resistant to Activin A inhibition. Overall, disrupting TGF-ß/activin A signaling by inactivating SMAD4 represents a promising strategy for simultaneously enhancing the homing and function of NK cell products for cancer immunotherapy.