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Neuroblastoma (NB) is the most common malignant extracranial solid tumor in children. Despite significant survival improvements in multiple pediatric malignancies, children with relapsed neuroblastoma (NB) have dismal outcomes. ROR1 is highly expressed on the majority of NB (Rebagay/Yan Front Oncol , 2012). Our group has successfully expanded functional and active peripheral blood NK cells (exPBNK) with irradiated feeder cells and electroporated CAR mRNA to exPBNK (Chu/Cairo, et al, Can Imm Res 2015). N-803 (ALT-803) is a novel IL15 superagonist complex where mutant IL-15N72D is bound to an IL-15RαSu-Fc fusion protein with higher potency and longer half-life compared to IL-15 (Han/Wong, Cytokine , 2011). To determine if anti-ROR1 CAR engineered NK cells can efficiently target ROR1+ NB and if the cytotoxicity can be further enhanced in combination with N-803. ExPBNK cells were expanded with lethally irradiated K562-mbIL21cells (Denman/Lee Plos One , 2012) and isolated as previously described (Chu/Cairo, Can Imm Res , 2015). ExPBNK cells were electroporated with anti-ROR1-CAR mRNA (ROR1-CAR was generously provided by Riddell S) using maxcyte electroporator. ALT-803 was generously provided by Altor BioScience. CHLA-255 and CHLA-136 were generously provided by Seeger R. In vitro cytotoxicity of anti-ROR1 CAR NK against NB cell lines were examined at different E:T ratios. Granzyme B, Perforin and IFN-γ levels were evaluated by ELISA assays. High dimentionsal CyTOF analysis was performed to character the immunophenotying of anti-ROR1-CAR-NK. NB xenografted NSG mice were generated and tumor burden was monitored as we previously described (Chu/Cairo, Oncoimmunology 2017). Anti-ROR1-CAR was efficiently expressed on exPBNK after CAR mRNA-electroporation at 24 hrs. Anti-ROR1-CAR-NK were effective in killing NB cells even at very low E:T ratio compared to mock NK with enhanced granzyme B, perforin and interferon- release (p<0.001). Addition of ALT-803 even further improved the cytotoxicity of anti-ROR1-CAR-NK cells at 24 hours and significantly enhanced granzyme B, perforin and interferon-γ secretion (p<0.05) from anti-ROR1-CAR-NK cells in killing NB cells compared to other controls. CyTOF analysis showed the phosphorylated STAT5 level was enhanced in expanded NK and CAR NK by ALT803 with/without NB tumor cells (Fig.1). Further more, anti-ROR-1 CAR NK cells decreased tumor burden and significantly extended mice survival in human NB xenografted NSG mice (p<0.01) (Fig.2). The addition of ALT-803 to anti-ROR1 CAR NK cells significantly decreased tumor burden (p<0.05). anti-ROR1-CAR NK had significantly enhanced cytotoxicity against ROR1+ NB cells in vitro and in vivo using human NB xenografted NSG mice compared to controls. ALT-803 further enhanced the anti-tumor effect of anti-ROR1 CAR NK (supported by W81XWH-17-1-0420). [ABSTRACT FROM AUTHOR]