Introduction: Invasive aspergillosis (IA) is a major opportunistic fungal infection afflicting patients with compromised immune systems. High morbidity, mortality and limited options in current anti-fungal treatment call for research into adjunctive therapeutic options such as immunotherapy. While natural killer (NK) cells are known to possess potent, direct and indirect cytotoxic activity against microbes, there is limited data regarding in vitro mechanism and in vivo antifungal activity of NK cells in murine models.
Methodology: Human NK cell were expanded by using K562 cells as feeders, which were genetically modified to express 4-1BB ligand and membrane-bound interleukin-15 (K562-41BBL-mbIL-15). Expanded NK cells were seeded (effector-to-target ratio of 2:1) on the plate containing Aspergillus fumigatus maintained at 3 stages of fungal growth i.e. hyphae, germinating conidia and resting conidia. Resazurin based in vitro toxicology assay (XTT) was performed after incubating for 18-24 hours. Cytokine production was assessed by Enzyme linked immunosorbent assay (ELISA) of supernatants collected at 18-24 hours. Involvement of Dectin-1 was elucidated by inhibition assay, using laminarin. In vivo antifungal activity of expanded NK cells was assessed by using immunosuppressed, pulmonary aspergillosis BALB/c mice model.
Results: Expanded NK cells were found to possess morphotypal-dependent killing activity. Fungicidal activity against germinating conidia and resting conidia was significantly higher (by ~20%) than against hyphae (p <0.05). Aspergillus hyphae suppressed IFNγ mediated killing activity and perforin production of NK cells. Blocking with laminarin reduced the fungicidal effect of NK cells, implicating the role of Dectin-1. In murine Aspergillosis model, NK treated mice had lower fungal load in the lungs than untreated control group.
Conclusion: Expanded human NK cells have a potential role in immunotherapy against invasive aspergillosis (IA). Further explorations and elucidation of anti-fungal mechanisms are needed to understand the interplay between NK cells and Aspergillus in order to strengthen antifungal armamentarium in immunocompromised hosts.