Safety and Feasibility of Infusing Ex Vivo Expanded Allogeneic Canine Natural Killer Cells for the Treatment of Metastatic Solid Tumours.

Companion canines need advances in therapeutic options for solid tumour malignancies. Natural killer (NK) cell infusions offer a promising treatment modality in canines with solid tumours. Autologous natural killer products are limited by dysfunctional immunity and a manufacturing process that delays care whereas allogeneic NK cells offer the possibility of 'off-the-shelf' therapy to be administered from healthy donors. Peripheral blood mononuclear cells (PBMCs) were isolated from healthy canine donors via density gradient separation. NK cells were expanded with recombinant human IL-2 and canine IL-21 with the addition of K562 feeder cells transfected with CD137 ligand and membrane bound human IL-15. Additional experiments included IL-12 during expansion. In vitro potency was assessed via co-culture with the D17-mKate2 canine osteosarcoma cell line. Three canines were enrolled in a phase 1 trial infusing ex vivo expanded allogeneic NK cells after lymphodepletion. Flow cytometric analysis confirmed successful expansion of canine NK cells with up to 50% of cells demonstrating NKp46+ after 14 days. Residual T cell numbers varied based on donor. The addition of IL-12 led to increased NK cell expansion. Incucyte demonstrated potency with increasing osteosarcoma cell death at higher effector to target ratios. Three canines with metastatic/refractory solid tumours were successfully lymphodepleted and infused with allogeneic NK cell products. The canines tolerated the infusions well. Canine allogeneic NK cells were successfully expanded and activated ex vivo, demonstrated potency in vitro and safety in vivo. Further studies will optimise the NK cell product and escalate dosing to reach the maximal tolerable dose.