To investigate subcutaneous (s.c.) and intravenous (i.v.) administration of a novel zirconium-89 (⁸⁹Zr)-labeled-anti-CD20-antibody (Ab), and compare the PET-CT imaging and biodistribution in control (sham-injected) and experimental autoimmune encephalomyelitis (EAE) mice.

B-cell directed immunotherapies using monoclonal antibodies are emerging targets in the treatment of multiple sclerosis. In an earlier study, ⁸⁹Zr-labeled-anti-CD20-Ab administered as s.c. versus i.v. injection to healthy mice demonstrated effective absorption from the injection site and subsequent biodistribution preferentially to the lymph nodes, blood, and the spleen to a lesser extent.

C57BL/6J mice (12-15 weeks old; n=39) were EAE-induced using rhMOG. At peak of the disease (14 days after EAE induction; mean clinical score 2.5±0.6), ⁸⁹Zr-labeled-anti-CD20-Ab was injected in control and EAE mice in the tail vein (i.v.) or right lower flank (s.c.). Region-of-interest analysis of PET-CT images and ex vivo biodistribution studies were performed on Days 1, 3 and 7 for quantifying ⁸⁹Zr-labeled-anti-CD20-Ab accumulation in different organs.

Correlation between in vivo PET-CT data and ex vivo biodistribution studies confirmed sensitivity and specificity for in vivo CD20 targeting. ⁸⁹Zr-labeled-anti-CD20-Ab was effectively absorbed from s.c. versus i.v. injection site and successfully distributed to all major organs (lymph nodes, blood, and spleen) in the EAE and control mice. Across all disease states in EAE mice, a significant correlation was observed for ⁸⁹Zr-labeled-anti-CD20-Ab uptake within the spinal cord and central nervous system (CNS) following s.c. and i.v. administration.

⁸⁹Zr-labeled-anti-CD20-Ab administered s.c. or i.v. demonstrated effective absorption from the injection site, and biodistribution to the major organs in the EAE and control mice. PET-CT imaging confirmed rapid and specific localization of ⁸⁹Zr-labeled-anti-CD20-Ab to the B-cell compartment. Biodistribution studies revealed that CNS infiltration of B cells in the spinal cord and brain of EAE-induced mice can be detected using ⁸⁹Zr-labeled-anti-CD20-Ab, establishing this as a potential imaging biomarker for target antigen expression.