Generating suppression-resistant natural killer cells as an enhanced immunotherapeutic for neuroblastoma

Abstract

Abstract Refractory neuroblastoma (NB) has a poor prognosis and there is a need to explore novel therapies. Natural killer (NK) cells serve as a promising immunotherapy for NB, however they are impaired by the immunosuppressive TGFb-rich NB tumor microenvironment. Critically, TGFβ impairs NK cell proliferation and cytolytic activity. To overcome these detrimental effects, we genetically modified NK cells to express a variant TGFβ receptor – composed of a truncated extracellular TGFbRII domain fused to a synthetic Notch-like receptor coupled to RELA – which may be able to associate with exogenous TGFβ and convert downstream signals to enhance NK cell function. NK cells were isolated from umbilical cord blood (CB; universal donor source) and expanded ex vivo. The modified TGFβ receptor was cloned into an SFG vector backbone. Expanded CB-derived NK cells were transduced with the modified TGFβ receptor (42.5±5.5%). Transduction did not negatively affect the endogenous expression of the activating receptors NKG2D, NKp44, or NKp30 (p>0.05) or NK cell proliferative capacity (p>0.05). Non-transduced (NT) NK cells were cytotoxic against K562 target cells in a dose-dependent manner (45.2±4.69% killing at 40:1), however NK cell cytolytic activity was impaired following exposure to TGFβ (p<0.05). In contrast, transduced-NK cells exhibited dose-dependent cytotoxicity (40.2±4.42% killing at 40:1), which was unaffected following exposure to TGFβ (p>0.05). Administration of transduced-NK cells in a xenograft model of human NB delayed tumor progression by >14 days and significantly prolonged survival compared to control NK cells (p=0.04). In summary, this novel immunotherapeutic may translate as a potent treatment modality for patients with NB.