title: ¹¹¹In-anti-F4/80-A3-1 antibody: a novel tracer to image macrophages.
abstract: OBJECTIVE
  Here, the expression of F4/80 on the cell surface of murine macrophages was exploited to develop a novel imaging tracer that could visualize macrophages in vivo.
  
  
  METHODS
  The immunoreactive fraction and IC50 of anti-F4/80-A3-1, conjugated with diethylenetriaminepentaacetic acid (DTPA) and radiolabelled with (111)In, were determined in vitro using murine bone marrow-derived macrophages. In vivo biodistribution studies were performed with (111)In-anti-F4/80-A3-1 and isotype-matched control antibody (111)In-rat IgG2b at 24 and 72 h post-injection (p.i.) in SCID/Beige mice bearing orthotopic MDA-MB-231 xenografts. In some studies mice were also treated with liposomal clodronate. Macrophage content in tissues was determined immunohistochemically. Micro-single photon emission computed tomography (SPECT)/CT images were also acquired.
  
  
  RESULTS
  In vitro binding assays showed that (111)In-anti-F4/80-A3-1 specifically binds F4/80 receptor-positive macrophages. The immunoreactivity of anti-F4/80-A3-1 was 75 % and IC50 was 0.58 nM. In vivo, injection of 10 or 100 μg (111)In-anti-F4/80-A3-1 resulted in splenic uptake of 78 %ID/g and 31 %ID/g, respectively, and tumour uptake of 1.38 %ID/g and 4.08 %ID/g, respectively (72 h p.i.). Liposomal clodronate treatment reduced splenic uptake of 10 μg (111)In-anti-F4/80-A3-1 from 248 %ID/g to 114 %ID/g and reduced (111)In-anti-F4/80-A3-1 uptake in the liver and femur (24 h p.i.). Tracer retention in the blood and tumour uptake increased (24 h p.i.). Tumour uptake of (111)In-anti-F4/80-A3-1 was visualized by microSPECT/CT. Macrophage density in the spleen and liver decreased in mice treated with liposomal clodronate. Uptake of (111)In-rat IgG2b was lower in the spleen, liver and femur when compared to (111)In-anti-F4/80-A3-1.
  
  
  CONCLUSIONS
  Radiolabelled anti-F4/80-A3-1 antibodies specifically localize in tissues infiltrated by macrophages in mice and can be used to visualize tumours. The liver and spleen act as antigen sink organs for macrophage-specific tracers.
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, The Netherlands, samantha.terry@kcl.ac.uk.
authors.forename: Samantha Y A
authors.initials: SY
authors.lastname: Terry
authors.forename: Otto C
authors.initials: OC
authors.lastname: Boerman
authors.forename: Danny
authors.initials: D
authors.lastname: Gerrits
authors.forename: Gerben M
authors.initials: GM
authors.lastname: Franssen
authors.forename: Josbert M
authors.initials: JM
authors.lastname: Metselaar
authors.forename: Steffi
authors.initials: S
authors.lastname: Lehmann
authors.forename: Wim J G
authors.initials: WJ
authors.lastname: Oyen
authors.forename: Christian A
authors.initials: CA
authors.lastname: Gerdes
authors.forename: Keelara
authors.initials: K
authors.lastname: Abiraj
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000493:pharmacokinetics; D000943:Antigens, Differentiation / Q000276:immunology*; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007205:Indium Radioisotopes; D008264:Macrophages / Q000000981:diagnostic imaging*; D051379:Mice; D011849:Radioactive Tracers; D051381:Rats; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D000911:Antibodies, Monoclonal; D000943:Antigens, Differentiation; D007205:Indium Radioisotopes; D011849:Radioactive Tracers; C036763:monocyte-macrophage differentiation antigen