PD‑L1 deficient exosomes derived from lung cancer cell line enhances NK cell‑mediated anti‑tumor immunity against lung cancer

As innate immune cells, natural killer (NK) cells play a vital role in combating tumors and infections, making them a promising tool for cancer immunotherapy. Although NK cell has achieved impressive results in treating of hematologic malignancies, the therapeutic efficiency of NK cells on solid tumors remains unsatisfactory. By enhancing the sensitivity of NK cells to specific target cells, it is possible to boost their cytotoxicity and therapeutic effect against solid tumors. Tumor derived exosomes (TEXs) have immunostimulatory effects on NK cells, however, the TEXs carried immune checkpoints ligand also impair NK cells activity. In the present study, PD-L1 was knocked out from lung cancer cell line A549, and the exosomes derived from wild-type A549 cells (WT-EXO) and PD-L1 knocked-out A549 cell (KO-EXO) were used to pre-immunize NK cells. Results showed that, PD-L1 knocking out can reduce the inhibitory effect of WT-EXO on NK cells viability. Meanwhile, A549 cells derived exosomes (WT-EXO and KO-EXO) both boost the cytotoxicity of NK cells, with KO-EXO exhibited better stimulated effect than the other one. The enhanced killing rates of NK cells can be partially attributed to increased IFN-γ secretion following exosomes pre-immunization. Western blot results indicated that the signaling proteins pSTAT1, along with their associated pathways, play important roles in exosomes-induced enhancement of NK cell cytotoxicity. Simultaneously, it was observed that exosomes-preimmunized NK cells exhibited an upregulation of immunological memory markers CD25 and CD159c. Moreover, KO-EXO pre-immunized NK cells showed better infiltration and anti-tumor effects compared to the untreated NK cells in A549 cell bearing mice model. These results highlight the therapeutic potential of engineered TEXs in boosting NK cell based anti-lung cancer immunotherapy.