Detection limit of 89Zr-labeled T cells for cellular tracking: an in vitro imaging approach using clinical PET/CT and PET/MRI

Abstract

Purpose: Tracking cells in vivo using imaging can provide non-invasive information to understand the pharmacology, efficacy, and safety of novel cell therapies. Zirconium-89 (t 1/2 = 78.4 h) has recently been used to synthesize [ 89 Zr]Zr(oxinate) 4 for cell tracking using positron emission tomography (PET). This work presents an in vitro approach to estimate the detection limit for in vivo PET imaging of Jurkat T cells directly labeled with [ 89 Zr]Zr(oxinate) 4 utilizing clinical PET/CT and PET/MRI. Methods: Jurkat T cells were labeled with varying concentrations of [ 89 Zr]Zr(oxinate) 4 to generate different cell-specific activities (0.43-31.91 kBq/10 6 cells). Different concentrations of labeled cell suspensions (10 4 , 10 5 , and 10 6 cells) were seeded on 6-well plates and into a 3 × 3 cubic-well plate with 1 cm 3 cubic wells as a gel matrix. Plates were imaged on clinical PET/ CT and PET/MRI scanners for 30 min. The total activity in each well was determined by drawing volumes of interest over each well on PET images. The total cell-associated activity was measured using a well counter and correlated with imaging data. Simulations for non-specific signal were performed to model the effect of non-specific radioactivity on detection. Results: Using this in vitro model, the lowest cell number that could be visualized on 6-well plate images was 6.8 × 10 4 , when the specific activity was 27.8 kBq/10 6 cells. For the 3 × 3 cubic-well, a plate of 3.3 × 10 4 cells could be detected on images with a specific activity of 15.4 kBq/10 6 cells. Conclusion: The results show the feasibility of detecting [ 89 Zr]Zr(oxinate) 4-labeled Jurkat T cells on clinical PET systems. The results provide a best-case scenario, as in vivo detection using PET/CT or PET/MRI will be affected by cell number, specific activity per cell, the density of cells within the target volume, and non-specific signal. This work has important implications for cell labeling studies in patients, particularly when using radiosensitive cells (e.g., T cells), which require detection of low cell numbers while minimizing radiation dose per cell.

Whole-Body Imaging to Assess Cell-Based Immunotherapy: Preclinical Studies with an Update on Clinical Translation

“…as approximately 55 kBq/kg dose of 89 Zr-oxine-labeled cells (approximately 3 × 10 6 cells/kg dose with cells labeled at 18.5 kBq/10 6 cells) could be imaged with high quality and have their migration quantitated [29]. Also using clinical PET/CT and PET/MRI scanners, 3.3 × 10 4 /cm 3 Jurkat cells labeled with 89 Zr-oxine at 15.4 kBq/10 6 cells were detected [68].…”

“…Cell surface molecule-based human reporter gene systems include NIS that is compatible with multiple SPECT tracers (e.g., 99m Tc-pertechnetate, 123 I) and PET tracers (e.g., 124 I, 18 F-tetrafluoroborate), SSTR2 with 68 Ga-DOTA-D-Phe 1 -Tyr 3 -octreotate ( 68 Ga-DOTATATE, DOTA:…”

“…1,4,7,10-tetraazacyclododecane-N,N′,N″,N′-tetra-acetic acid) and 68 Ga-DOTA-D-Phe 1 -Tyr 3 -octreotide ( 68 Ga-DOTATOC) for PET, norepinephrine transporter (NET, SLC6A2) with 124 I-metaiodobenzylguanidine ( 124 I-MIBG) for SPECT and 18 F-meta-fluorobenzylguanidine ( 18 F-MFBG) for PET, and PSMA with 2-(3-{1-carboxy-5-[(6-[ 18 F]fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid ( 18 F-DCFpyI, Fig. 1b).…”

“…These tracers have been used in the clinic, some for a long time, for detecting endogenous lesions (e.g., 68 Ga-DOTATATE and 68 Ga-DOTATOC to detect neuroendocrine tumors [73]). 68 Ga-DOTATOC has been approved by the US Food and Drug Administration in 2019 and 18 F-DCFpyl followed in 2021. 18 F-tetrafluoroborate for NIS has been evaluated in healthy human volunteers [74] and thyroid cancer patients [75].…”

In Vivo Cell Tracking Using PET: Opportunities and Challenges for Clinical Translation in Oncology

“…This approach allows the imaging of labelled cells for at least 7 days post-injection due to the longer radioactive decay. The in vitro detection limit of [ 89 Zr]Zr-oxine labelled T-cells has been found to be on the order of 10 4 cells, with cellular activities as low as 15 kBq/10 6 cells, on both clinical PET/CT and PET/MRI [37]. The clinical application of this approach is planned.…”