Immuno-PET imaging of tumor-infiltrating lymphocytes using zirconium-89 radiolabeled anti-CD3 antibody in immune-competent mice bearing syngeneic tumors

Abstract

The ability to non-invasively monitor tumor-infiltrating T cells in vivo could provide a powerful tool to visualize and quantify tumor immune infiltrates. For non-invasive evaluations in vivo, an anti-CD3 mAb was modified with desferrioxamine (DFO) and radiolabeled with zirconium-89 (Zr-89 or 89Zr). Radiolabeled 89Zr-DFO-anti-CD3 was tested for T cell detection using positron emission tomography (PET) in both healthy mice and mice bearing syngeneic bladder cancer BBN975. In vivo PET/CT and ex vivo biodistribution demonstrated preferential accumulation and visualization of tracer in the spleen, thymus, lymph nodes, and bone marrow. In tumor bearing mice, 89Zr-DFO-anti-CD3 demonstrated an 11.5-fold increase in tumor-to-blood signal compared to isotype control. Immunological profiling demonstrated no significant change to total T cell count, but observed CD4+ T cell depletion and CD8+ T cell expansion to the central and effector memory. This was very encouraging since a high CD8+ to CD4+ T cell ratio has already been associated with better patient prognosis. Ultimately, this anti-CD3 mAb allowed for in vivo imaging of homeostatic T cell distribution, and more specifically tumor-infiltrating T cells. Future applications of this radiolabeled mAb against CD3 could include prediction and monitoring of patient response to immunotherapy.

Multi-Modal PET and MR Imaging in the Hen’s Egg Test-Chorioallantoic Membrane (HET-CAM) Model for Initial In Vivo Testing of Target-Specific Radioligands

“…The development of target-specific radiolabeled probes like on the basis of small molecules, peptides, antibodies, or nanoparticles, always requires information on biodistribution and in particular on the level of specific binding of the novel probe to the target in the in vivo situation, which means specific radiotracer accumulation in the target-expressing region of interest [1][2][3][4][5]. Up to now, animal experiments are necessary to obtain this information mostly using mice with xenografts expressing the specific target and often also target-negative xenografts as controls.…”

Role of noninvasive molecular imaging in determining response

“…Preclinical models of 89 Zr-DFO-anti-CD3 immuno-PET have demonstrated the ability to visualize homeostatic T-cell populations in healthy mice as well as TIL in tumor-bearing counterparts. 60 These investigations demonstrated an 11.5-fold increase in tumor-to-blood signal relative to control and no change in the absolute CD3+ count, which allays concerns about potential lymphodepletion. However, DFO-anti-CD3 did skew the T-cell population toward a CD8+ T-cell central/effector memory phenotype with a relative decrease in CD4+ T-cells.…”

Cell Tracking in Cancer Immunotherapy

“…Ideally, this antigen should be exclusively expressed on target cells, but most of the time other tissue also express it. For T lymphocytes, many targets have been tested, e.g., CD3, CD8, CD2, and CD7 (56)(57)(58).…”

“…Whole antibodies, labeled with zirconium-89 afford similar results (56). Many target antigens have been tested in animal models (56,58) and CD7 seems so far to be the best candidate to target T lymphocytes, with the lowest toxicity (56).…”

“…For example, 64 Cu-labeled diabody specific for CD8 was used to assess CD8 T cell density in tumors in mice and treatment related changes (92). Whole antibodies, labeled with zirconium-89 afford similar results (56). Many target antigens have been tested in animal models (56,58) and CD7 seems so far to be the best candidate to target T lymphocytes, with the lowest toxicity (56).…”