In Vivo Imaging of Natural Killer Cell Trafficking in Tumors.
Natural killer cells (NKs) are important effectors of the innate immune system, with marked antitumor activity. Imaging NK trafficking in vivo may be relevant to following up the efficacy of new therapeutic approaches aiming at increasing tumor-infiltrating NKs (TINKs). The specific aims of present study were to efficiently target NKs using a 99mTc-anti-CD56 and to image human NK trafficking in SCID mice bearing human cancer.


METHODS
The anti-CD56 monoclonal antibody (mAb) was radiolabeled with 99mTc, and in vitro quality controls were performed to test labeling efficiency, stability, and binding affinity to CD56. In vivo biodistribution was determined by injecting 5.5 MBq (104 ng) of radiolabeled antibody in the tail vein of SCID mice, which were then sacrificed at 1, 3, 6, and 24 h after injection. Targeting experiments were performed on 2 groups of SCID mice inoculated subcutaneously with increasing numbers of human NKs in the right thigh (from 2.5×10(6) to 40×10(6)) and human granulocytes (CD56-) or anaplastic thyroid cancer (ARO) cells in the contralateral thigh as control. TINK trafficking imaging was achieved by injecting 5.5 MBq of 99mTc-anti-CD56 mAb in SCID mice bearing ARO tumor xenografts in the right thigh, 24 h after being reconstituted with 10(5), 10(6), or 10(7) human NKs.


RESULTS
Anti-CD56 mAb was radiolabeled, achieving a radiochemical purity of more than 97% and a specific activity of 3,700 MBq/mg and retaining biochemical integrity and binding activity. In vivo studies revealed physiologic uptake in the liver and kidneys. Targeting experiments confirmed the specificity of labeled antibody to CD56+ cells. Human NK cells injected in CD1 nude mice accumulated in the ARO tumors within 24 h and were imaged as early as 3 h after intravenous administration of (99m)Tc-anti-CD56.


CONCLUSIONS
99mTc-anti-CD56 is a promising tool for in vivo imaging of TINK cell trafficking.
Nuclear Medicine Unit, Faculty of Medicine and Psychology, Department of Medical-Surgical Sciences and of Translational Medicine, "Sapienza" University, Rome, Italy Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
Filippo
F
Galli
Nuclear Medicine Unit, Faculty of Medicine and Psychology, Department of Medical-Surgical Sciences and of Translational Medicine, "Sapienza" University, Rome, Italy.
Anna Serafina
AS
Rapisarda
Department of Molecular Medicine, "Sapienza" University, Rome, Italy.
Helena
H
Stabile
Nuclear Medicine Unit, Faculty of Medicine and Psychology, Department of Medical-Surgical Sciences and of Translational Medicine, "Sapienza" University, Rome, Italy Nuclear Medicine Unit, CRUK Beatson Institute, Glasgow, Scotland.
Gaurav
G
Malviya
Molecular Oncogenesis Laboratory, Experimental Oncology Department, Regina Elena National Cancer Institute, Rome, Italy; and.
Isabella
I
Manni
Department of Biomedicine and Prevention, "Tor Vergata" University, Rome, Italy.
Elena
E
Bonanno
Molecular Oncogenesis Laboratory, Experimental Oncology Department, Regina Elena National Cancer Institute, Rome, Italy; and.
Giulia
G
Piaggio
Department of Molecular Medicine, "Sapienza" University, Rome, Italy.
Angela
A
Gismondi
Department of Molecular Medicine, "Sapienza" University, Rome, Italy.
Angela
A
Santoni
Nuclear Medicine Unit, Faculty of Medicine and Psychology, Department of Medical-Surgical Sciences and of Translational Medicine, "Sapienza" University, Rome, Italy Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands alberto.signore@uniroma1.it.
Alberto
A
Signore
D000818:Animals; D000911:Antibodies, Monoclonal; D019002:CD56 Antigen; D045744:Cell Line, Tumor; D006801:Humans; D007694:Killer Cells, Natural / Q000000981:diagnostic imaging*; D051379:Mice; D008819:Mice, Nude; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000276:immunology*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D013667:Technetium / Q000493:pharmacokinetics*; D014018:Tissue Distribution
D000911:Antibodies, Monoclonal; D019002:CD56 Antigen; D019275:Radiopharmaceuticals; D013667:Technetium
NK cells; TINKs; anti-CD56; imaging; nuclear medicine