Dissecting the Impact of Environmental Oxygen Content on Natural Killer Cell Immunotherapy
Martin Felices PhD
University of Minnesota
Masonic Cancer center
Natural Killer (NK) cells are being studied in the clinic in a number of settings, including solid tumor immunotherapies. For these therapies to succeed, the NK cells need to enter the tumor microenvironment (TME) and retain functionality. While some studies have assessed the impact of checkpoint signals and immunosuppressive cells on NK cells, the role of oxygen content, usually low within the TME, has not been thoroughly evaluated. In order to study this question, oxygen content and pressure was manipulated using an advanced incubator system (AVATAR control system from xcellbio) to model the tumor microenvironment (1% O2 and 0.3 or 2 PSI), the blood environment (12% O2 and 2 PSI), and the bone marrow compartment (5% O2 and 0.6 PSI).
Our findings were controlled to a standard 5% CO2 incubator (20% oxygen). The effect of 24 hour, 3 day, and 7 day incubations in these conditions were then evaluated. While oxygen concentration did not seem to significantly impact NK cell survival, NK cell proliferation was markedly reduced at the 1% O2 (TME) and intermediately reduced at the 5% O2 (bone marrow) when compared to the 12% O2 (blood) and standard incubator conditions. NK cell mediated cytotoxicity against tumor targets was impacted negatively at low oxygen incubations. High-dimensional mass cytometry (CyTOF) analysis indicated that low oxygen resulted in disappearance of CD56bright NK cells, increased CD69 expressing cells, lack of proliferation (Ki67), decreased expression of NCRs (NKp44, NKp30, NKp46 and NKG2D), and low Perforin and Granzyme levels. These changes were accompanied by robust changes in gene expression as well as changes in NK cell metabolism.
Taken together, these results strongly support an important role for oxygen content in maintenance of NK cell cytolytic activity within the TME. We are currently in the process of drilling down on drivers for these changes in the hopes that they can be exploited for generation of NK cell products and treatments that will enhance solid tumor immunotherapy.