Imaging Lung Clearance of Radiolabeled Tumor Cells to Study Mice with Normal, Activated or Depleted Natural Killer (NK) Cells

Lung clearance of ⁵¹CR and ¹²⁵I iododeoxyuridine (IUDR) labeled cancer cells assess NK cell activity. It is desirable to develop noninvasive imaging technique to assess NK activity in mice. We labeled target YAC-1 tumor cells with ¹²⁵I, ¹¹¹In, ^99mTc, or ⁶⁷Ga and injected I.V. into three groups of BALB/c mice. Animals were treated with medium (group I), 300mg/kg cyclophosmamide (CY) to kill NK cell (group II), or anti-LY49C/1) (ab')₂ mAb to augment NK function (group III). Lungs were removed 15 min or 2 h later for tissue counting. Control and treated mice were imaged every 5 min with a scintillating camera for 1 h after 15 min of infusion of the ¹¹¹In labeled cells. Lung clearance increased after 15 min (lodging: 60-80%) and (2 h retention: 3-7%). Similar results were obtained with all the isotopes studied. Images distinguished the control and treated mice for lung activity. Cells labeled with ¹¹¹In, ^99mTc or ⁶⁷Ga are cleared similar to those labeled with ⁵¹Cr or ¹²⁵I. NK cell destruction of tumor cells may be assessed by noninvasive imaging method either by SPECT (^99mTc, ¹¹¹In, ⁶⁷Ga) or by PET (⁶⁸Ga).