Until recently, the pathophysiological impact of natural killer (NK) lymphocytes has been largely elusive. Capitalizing on our previous discovery that NK cells mediate immunosurveillance against gastrointestinal stromal tumors (GISTs), we have now investigated the potential influence of immunostimulatory and immunosuppressive isoforms of the NK receptor NKp30 on the fate of infants with neuroblastoma. In three independent cohorts of high-risk neuroblastoma, we observed a similar prognostic impact of the ratio of immunostimulatory vs. immunosuppressive NKp30 isoforms. Patients with high-risk neuroblastoma that are in remission after induction chemotherapy have a higher risk of relapse if their circulating and bone marrow NK cells express the preponderantly immunosuppressive NKp30 C isoform, as determined by a robust RT-PCR-based assay. We also found that neuroblastoma cells express the NKp30 ligand B7-H6, which can be shed from the tumor cells. Elevated soluble B7-H6 levels contained in patient sera inhibited NK functions in vitro and correlated with downregulation of NK-p30 on NK cells, as well as with bone marrow metastasis and chemoresistance. Altogether, these results support the contention that NK cells play a decisive role in the immunosurveillance of neuroblastoma. In light of these results, efforts should be undertaken to investigate NK cell functions in all major cancer types, with the obvious expectation of identifying additional NK cell-related prognostic or predictive biomarkers and improving NK cell based immunotherapeutic strategies against cancer.
Keywords: NK cells; NKp30; immunosurveillance; neuroblastoma; pediatric cancer.