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Published on: February 22, 2020
In Vivo Imaging of Natural Killer Cell Trafficking in Tumors
Filippo Galli1, Anna Serafina Rapisarda2, Helena Stabile3
1Nuclear 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.
Unlabelled:
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.
Conclusion:
99mTc-anti-CD56 is a promising tool for in vivo imaging of TINK cell trafficking.
Insights
This study developed 99mTc-anti-CD56 for imaging natural killer (NK) cell trafficking. The radiolabeled antibody successfully targeted and visualized human NK cells in tumors within hours, showing promise for monitoring cancer immunotherapies.
Area of Science:
- Immunology
- Nuclear Medicine
- Oncology
Background:
- Natural killer (NK) cells are crucial for innate immunity and possess antitumor activity.
- Monitoring NK cell infiltration into tumors (TINKs) is vital for evaluating immunotherapies.
- Current methods for tracking NK cells in vivo are limited.
Purpose of the Study:
- To develop and evaluate 99mTc-labeled anti-CD56 antibody for targeting and imaging NK cells.
- To assess the feasibility of imaging human NK cell trafficking in a SCID mouse model with human cancer xenografts.
- To determine the potential of this imaging approach for monitoring TINKs.
Main Methods:
- Radiolabeling of anti-CD56 monoclonal antibody (mAb) with 99mTc.
- In vitro quality control of the radiolabeled mAb for purity, stability, and binding affinity.
- In vivo biodistribution studies in SCID mice.
- Targeting experiments in SCID mice with human NK cells and cancer cells (ARO).
Main Results:
- The 99mTc-anti-CD56 mAb demonstrated high radiochemical purity (>97%) and retained binding activity.
- In vivo studies showed specific targeting of CD56+ NK cells.
- Human NK cells were successfully imaged within tumors as early as 3 hours post-injection.
- Physiologic uptake was observed in the liver and kidneys.
Conclusions:
- 99mTc-anti-labeled anti-CD56 antibody is a viable tool for in vivo imaging of NK cell trafficking.
- This imaging technique shows potential for monitoring tumor-infiltrating NK (TINK) cells.
- It could aid in assessing the efficacy of NK cell-based cancer therapies.
