Purpose Adoptive transfer of natural killer (NK) cells combined with tumor-specific monoclonal antibodies (mAbs) has therapeutic potential for malignancies. We determined if large numbers of activated NK (aNK) cells can be grown ex vivo from peripheral blood mononuclear cells (PBMC) of children with high-risk neuroblastoma using artificial antigen-presenting cells (aAPC). Experimental Design Irradiated K562-derived Clone 9.mbIL21 aAPC were co-cultured with PBMC, and propagated NK cells were characterized with flow cytometry, cytotoxicity assays, Luminex® multi-cytokine assays, and a NOD/SCID mouse model of disseminated neuroblastoma. Results Co-culturing patient PBMC with aAPC for 14 days induced 2,363±443-fold expansion of CD56+CD3−CD14− NK cells with 83±4% purity (n=10). Results were similar with PBMC from normal donors (n=5). Expression of DNAM-1, NKG2D, FcγRIII/CD16 and CD56 increased 6±3, 10±2, 21±20, and 18±3-fold respectively on day 14 compared to day 0, demonstrating activation of NK cells. In vitro, aNK cells were highly cytotoxic against neuroblastoma cell lines, and killing was enhanced with GD2-specific monoclonal antibody ch14.18. When mediating cytotoxicity with ch14.18, release of TNFα, GM-CSF, IFNγ, sCD40L, CCL2/MCP-1, CXCL9/MIG, and CXCL11/I-TAC by aNK cells increased 4-, 5- 6-, 15-, 265-, 917- and 363-fold (151 to 9,121 pg/mL), respectively, compared to aNK cells alone. Survival of NOD/SCID mice bearing disseminated neuroblastoma improved when treated with thawed and immediately intravenously infused cryopreserved aNK cells compared to un-treated mice and was further improved when ch14.18 was added. Conclusion Propagation of large numbers of aNK cells that maintain potent anti-neuroblastoma activities when cryopreserved supports clinical testing of adoptive cell therapy with ch14.18.

Neuroblastoma cells have been reported to be resistant to death induced by soluble, recombinant forms of TRAIL (CD253/TNFSF10) due to low or absent expression of caspase-8 and/or TRAIL-receptor 2 (TRAIL-R2/DR5/CD262/TNFRSF10b). However, their sensitivity to membrane-bound TRAIL on natural killer (NK) cells is not known. Comparing microarray gene expression and response to NK cell-mediated cytotoxicity, we observed a correlation between TRAIL-R2 expression and the sensitivity of fourteen neuroblastoma cell lines to the cytotoxicity of NK cells activated with IL-2 plus IL-15. Even though most NK cytotoxicity was dependent upon perforin, the cytotoxicity was supplemented by TRAIL in fourteen of seventeen (82%) neuroblastoma cell lines as demonstrated using an anti-TRAIL neutralizing antibody. Similarly, a recently developed NK cell expansion system employing IL-2 plus lethally irradiated K562 feeder cells constitutively expressing membrane-bound IL-21 (K562 clone 9.mbIL21) resulted in activated NK cells derived from normal healthy donors and neuroblastoma patients that also utilized TRAIL to supplement cytotoxicity. Exogenous IFNγ up-regulated expression of caspase-8 in three of four neuroblastoma cell lines and increased the contribution of TRAIL to NK cytotoxicity against two of the three lines; however, relatively little inhibition of cytotoxicity was observed when activated NK cells were treated with an anti-IFNγ neutralizing antibody. Constraining the binding of anti-TRAIL neutralizing antibody to membrane-bound TRAIL but not soluble TRAIL indicated that membrane-bound TRAIL alone was responsible for essentially all of the supplemental cytotoxicity. Together, these findings support a role for membrane-bound TRAIL in the cytotoxicity of NK cells against neuroblastoma cells.