Abstract

These studies focused on a new radiolabeling technique with copper (64Cu) and zirconium (89Zr) for positron emission tomography (PET) imaging using a CD45 antibody. Synthesis of 64Cu-CD45 and 89Zr-CD45 immunoconjugates was performed and the evaluation of the potential toxicity of radiolabeling human peripheral blood stem cells (hPBSC) was assessed in vitro (viability, population doubling times, colony forming units). hPBSC viability was maintained as the dose of 64Cu-TETA-CD45 increased from 0 (92%) to 160 µCi/mL (76%, p>0.05). Radiolabeling efficiency was not significantly increased with concentrations of 64Cu-TETA-CD45 >20 µCi/mL (p>0.50). Toxicity affecting both growth and colony formation was observed with hPBSC radiolabeled with ≥40 µCi/mL (p<0.05). For 89Zr, there were no significant differences in viability (p>0.05), and a trend towards increased radiolabeling efficiency was noted as the dose of 89Zr-Df-CD45 increased, with a greater level of radiolabeling with 160 µCi/mL compared to 0–40 µCi/mL (p<0.05). A greater than 2,000 fold-increase in the level of 89Zr-Df-CD45 labeling efficiency was observed when compared to 64Cu-TETA-CD45. Similar to 64Cu-TETA-CD45, toxicity was noted when hPBSC were radiolabeled with ≥40 µCi/mL (p<0.05) (growth, colony formation). Taken together, 20 µCi/mL resulted in the highest level of radiolabeling efficiency without altering cell function. Young rhesus monkeys that had been transplanted prenatally with 25×106 hPBSC expressing firefly luciferase were assessed with bioluminescence imaging (BLI), then 0.3 mCi of 89Zr-Df-CD45, which showed the best radiolabeling efficiency, was injected intravenously for PET imaging. Results suggest that 89Zr-Df-CD45 was able to identify engrafted hPBSC in the same locations identified by BLI, although the background was high.

Highlights

  • In vivo imaging techniques with sufficient sensitivity to detect small quantities of cells are needed to determine the safety and efficiency of new stem/progenitor cell therapies for a spectrum of human diseases

  • 64Cu-CD45 and 89Zr-CD45 Immunoconjugates To investigate the feasibility of tracking cells after transplantation with positron emission tomography (PET), optimal conditions were explored using a humanspecific CD45 antibody and radiolabeling human peripheral blood stem cells (hPBSC) with either 64Cu-TETA-CD45 or 89Zr-Df-CD45

  • Results showed no significant differences in the percentage and mean fluorescence of hPBSC labeled with the immunoconjugates when compared to control cells

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Summary

Introduction

In vivo imaging techniques with sufficient sensitivity to detect small quantities of cells are needed to determine the safety and efficiency of new stem/progenitor cell therapies for a spectrum of human diseases. We adapted this method to radiolabel and track transplanted renal precursors differentiated from human embryonic stem cells in fetal rhesus monkeys in vivo [6]. These studies showed effective radiolabeling techniques for renal precursors without toxicity, and correlative imaging outcomes with PET, BLI, and at the tissue level

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