Armed oncolytic adenovirus elicits a "self-feeder" effect to supercharge NK cells for solid tumor control.

BACKGROUND

Natural killer (NK) cells are pivotal effectors in innate anti-tumor immunity, but their efficacy against solid tumors is constrained by inadequate tumor infiltration and functional suppression within the tumor microenvironment (TME). Although ex vivo expansion increases NK cell numbers, poor tumor homing and transient post-infusion activity persist as major limitations. This work aims to develop a combinatorial approach integrating ex vivo NK cell expansion with localized immunomodulation via engineered oncolytic adenoviruses (oAds) to address these challenges.

METHODS

K562 feeder cells were engineered to stably express IL-2, membrane-bound IL-21 (mbIL-21), and 4-1BBL to activate and expand NK cells ex vivo. Following irradiation, these cells were used to expand NK cells ex vivo. Armed oAds (oAd-IL-2/mbIL-21/4-1BBL) were designed to express IL-2, mbIL-21, and 4-1BBL. In vitro assays were used to evaluate the impact of oAd-IL-2/mbIL-21/4-1BBL on tumor cell lysis, as well as NK cell proliferation, activation, and migration. A HCT116 subcutaneous tumor-bearing mouse model was used to assess the combined anti-tumor effects of ex vivo-expanded NK cells and oAd-IL-2/mbIL-21/4-1BBL, focusing on tumor growth inhibition and NK cell infiltration in tumor lesions.

RESULTS

We firstly constructed K562 feeder cells stably co-express IL-2, mbIL-21, and 4-1BBL, enabling 100-fold NK cell expansion (>85% purity) within 14 days. Concurrently, armed oAds were engineered to deliver these immunomodulators. oAd-IL-2/mbIL-21/4-1BBL enhanced NK cell proliferation, activation, migration, and tumor cell lysis in vitro. In HCT116 colorectal xenograft models, combing ex vivo-expanded NK cells with oAd-IL-2/mbIL-21/4-1BBL synergistically suppressed tumor growth and increased tumor-infiltrating NK cells. Mechanistically, oAds elicited a "self-feeder" effect through localized immunomodulator production, sustaining NK cell activity within the TME.

CONCLUSIONS

These findings define a dual-phase strategy that integrate scalable ex vivo expansion with in situ activation to overcome key barriers in NK cell therapy for solid tumors.