In Vivo PET Imaging of 89Zr-Labeled Natural Killer Cells and the Modulating Effects of a Therapeutic Antibody

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Introduction: Natural Killer (NK) cells can kill cancer cells via antibody-dependent cell-mediated cytotoxicity (ADCC): a tumor-associated IgG antibody binds to the Fcγ Receptor CD16 on NK cells via the antibody Fc region and activates NK cell cytotoxic functions. Here, we employed PET imaging to assess NK cell migration to HER2-positive HCC1954 breast tumors, examining the influence of HER2-targeted trastuzumab antibody treatment on NK cell tumor accumulation.

Methods: Human NK cells from healthy donors were expanded ex vivo and labeled with [89Zr]89Zr-Oxine. In vitro experiments compared the phenotypic markers, viability, proliferation, migration, degranulation, and ADCC behaviors of both labeled (89Zr-) and unlabeled NK cells. Female NSG mice bearing orthotopic human breast HCC1954 tumors were administered 89Zr-NK cells alongside trastuzumab treatment or a sham treatment, then scanned using PET/CT imaging over 7 days. Flow cytometry and gamma-counting were used to analyze the presence of 89Zr-NK cells in liver and spleen tissues.

Results: 89Zr cell radiolabeling yields measured 42.2 ± 8.0%. At an average specific activity of 16.7 ± 4.7 kBq/106 cells, 89Zr-NK cells retained phenotypic and functional characteristics including CD56 and CD16 expression, viability, migration, degranulation and ADCC capabilities. In vivo PET/CT studies indicated predominant accumulation of 89Zr-NK cells in the liver and spleen. Ex vivo analyses of liver and spleen tissues indicated that the administered human 89Zr-NK cells retain their radioactivity in vivo and that 89Zr does not transfer to cells of murine soft tissues, thus validating this 89Zr PET method for NK cell tracking. Notably, 89Zr-NK cells migrated to HER2-positive tumors, both with and without trastuzumab treatment. Trastuzumab treatment was associated with increased 89Zr-NK cell signal at days 1 and 3 PI.

Conclusions: In vitro, 89Zr-NK cells maintained key cellular and cytotoxic functions. In vivo, 89Zr-NK cells trafficked to HER2-postive tumors, with trastuzumab treatment correlating with enhanced 89Zr-NK infiltration. This study demonstrates the feasibility of using PET to image 89Zr-NK cell infiltration to solid tumors.
Original languageEnglish
JournalJournal of Nuclear Medicine
Publication statusPublished - 2024


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