Development of a CD19 PET tracer for detecting B cells in a mouse model of multiple sclerosis

Abstract

Background: B cells play a central role in multiple sclerosis (MS) through production of injurious antibodies, secretion of pro-inflammatory cytokines, and antigen presentation. The therapeutic success of monoclonal antibodies (mAbs) targeting B cells in some but not all individuals suffering from MS highlights the need for a method to stratify patients and monitor response to treatments in real time. Herein, we describe the development of the first CD19 positron emission tomography (PET) tracer and its evaluation in a rodent model of MS, experimental autoimmune encephalomyelitis (EAE).Methods: Female C57BL/6J mice were induced with EAE through immunisation with myelin oligodendrocyte glycoprotein (MOG1–125). PET imaging of naïve and EAE mice was performed 19 h after administration of [64Cu]CD19-mAb. Thereafter, radioactivity in organs of interest was determined by gamma counting, followed by ex vivo autoradiography of central nervous system (CNS) tissues. Anti-CD45R (B220) immunostaining of brain tissue from EAE and naïve mice was also conducted.Results: Radiolabelling of DOTA-conjugated CD19-mAb with 64Cu was achieved with a radiochemical purity of 99% and molar activity of 2 GBq/mol. Quantitation of CD19 PET images revealed significantly higher tracer binding in whole brain of EAE compared to naïve mice (2.02±0.092 vs. 1.68±0.06 percentage of injected dose per gram, %ID/g, p=0.0173). PET findings were confirmed by ex vivo gamma counting of perfused brain tissue (0.22±0.020 vs. 0.12±0.003 %ID/g, p=0.0010). Moreover, ex vivo autoradiography of brain sections corresponded with PET imaging results and the spatial distribution of B cells observed in B220 immunohistochemistry – providing further evidence that [64Cu]CD19-mAb enables visualisation of B cell infiltration into the CNS of EAE mice. Conclusion: CD19-PET imaging can be used to detect elevated levels of B cells in the CNS of EAE mice, and has the potential to impact the way we study, monitor, and treat clinical MS.

Current State of Targeted Radiometal-Based Constructs for the Detection and Treatment of Disease in the Brain

“…What has been shown is that things that were previously thought to be impractical for use within the brain have shown some of the best promise. Two particularly noteworthy examples are 89 Zr-bevacizumab for imaging GBM and 64 Cu-CD19-mAb for imaging MS. 27,80 Despite being large antibody constructs, these two agents have shown uptake through an intact BBB. In the case of 89 Zr-bevacizumab, intraarterial administration significantly improves BBB penetration compared to intravenous injection, but the reason for this is yet to be clarified.…”

“…In a study by Stevens et al, EAE was induced in female C57BL/6 J mice with myelin oligodendrocyte glycoprotein (MOG 1−125 ). 80 This is a standard method of inducing EAE. 81 DOTA-NHS was conjugated to CD19-mAb and radiolabeled with 64 Cu.…”

“…This construct positively imaged the increase in B cell infiltration in EAE mice compared to naive mice. 80 This work demonstrated evidence toward the development of CD19 based tracers for MS, as well as other neuromuscular and neurological illnesses such as stroke, myasthenia gravis, and neuromyelitis optica. 64 Cu-CD19-mAb also appears to cross the BBB, with intravenous administration leading to suitable brain uptake with no indication of artificial BBB opening.…”

Opportunities for Molecular Imaging in Multiple Sclerosis Management: Linking Probe to Treatment

“…Recently, 64 Cu-labeled anti-CD19 monoclonal antibodies were used to visualize B-cell trafficking in EAE mice (93).…”

Clinical and neuroimaging findings in MOGAD–MRI and OCT

“…Proton emission tomography (PET)‐MRI research has allowed for more in‐vivo molecular imaging, where radionuclide tracers can be used to calculate myelin kinetics, concentrations of neuroinflammatory molecules and help to investigate pathophysiology [ 119 ]. PET tracers rely upon the radiolabelling of antibodies or chemical chelates that bind to specific targets of interest [ 120 ]. However, to detect the radioactive decay signals, X‐ray computed tomography (CT) imaging is traditionally applied to first create an image for quantification of the signal [ 121 ], and currently very few PET‐MRI systems are available globally.…”