Role of natural killer cells in hormone-independent rapid tumor formation and spontaneous metastasis of breast cancer cells in vivo

Natural killer activity of peripheral-blood mononuclear cells in breast cancer patients

Natural killer (NK) activity of immune cells plays a central role in host defense against cancer and virus-infected cells. Natural cytotoxic activity of peripheral-blood mononuclear cells was assessed by a Calcein-AM release assay in 89 subjects. In the present study, we here demonstrated that NK activities of peripheral-blood mononuclear cells (PBMCs) from breast cancer patients were significantly lower as compared with that of healthy individuals. There were significant differences in the NK activities of PBMCs from HER2-negative breast cancer patients as compared with HER2-positive patients. Our results suggest that NK activity of PBMCs is lower in breast cancer indicating a role for immunological natural host defense mechanisms against cancer.

Tracking of [18F]FDG-labeled natural killer cells to HER2/neu-positive tumors

INTRODUCTION

The objective of this study was to label the human natural killer (NK) cell line NK-92 with [(18)F]fluoro-deoxy-glucose (FDG) for subsequent in vivo tracking to HER2/neu-positive tumors.

METHODS

NK-92 cells were genetically modified to NK-92-scFv(FRP5)-zeta cells, which express a chimeric antigen receptor that is specific to the tumor-associated ErbB2 (HER2/neu) antigen. NK-92 and NK-92-scFv(FRP5)-zeta cells were labeled with [(18)F]FDG by simple incubation at different settings. Labeling efficiency was evaluated by a gamma counter. Subsequently, [(18)F]FDG-labeled parental NK-92 or NK-92-scFv(FRP5)-zeta cells were intravenously injected into mice with implanted HER2/neu-positive NIH/3T3 tumors. Radioactivity in tumors was quantified by digital autoradiography and correlated with histopathology.

RESULTS

The NK-92 and NK-92-scFv(FRP5)-zeta cells could be efficiently labeled with [(18)F]FDG by simple incubation. Optimal labeling efficiencies (80%) were achieved using an incubation period of 60 min and additional insulin (10 IU/ml). After injection of 5x10(6) [(18)F]FDG-labeled NK-92-scFv(FRP5)-zeta cells into tumor-bearing mice, digital autoradiography showed an increased uptake of radioactivity in HER2/neu-positive tumors at 60 min postinjection. Conversely, injection of 5x10(6) NK-92 cells not directed against HER2/neu receptors did not result in increased uptake of radioactivity in the tumors. Histopathology confirmed an accumulation of the NK-92-scFv(FRP5)-zeta cells, but not the parental NK cells, in tumor tissues.

CONCLUSION

The human NK cell line NK-92 can be directed against HER2/neu antigens by genetic modification. The genetically modified NK cells can be efficiently labeled with [(18)F]FDG, and the accumulation of these labeled NK cells in HER2/neu-positive tumors can be monitored with autoradiography.