title: Fluorine-18 labeled mouse bone marrow-derived dendritic cells can be detected in vivo by high resolution projection imaging.
abstract: Immunization with ex vivo generated dendritic cells has become a focus for many clinical applications. The optimal site of injection and the migration pattern of these cells remain to be elucidated. We therefore developed a novel method for labeling mouse bone marrow-derived dendritic cells (BMDC) with the positron emitting radioisotope F-18 using N-succinimidyl-4-[F-18]fluorobenzoate, which covalently binds to the lysine residues of cell surface proteins. When we determined the stability of F-18 labeled BMDC, we found that at 4 h only 44+/-10% of the initial cell-bound activity was retained at 37 degrees C, whereas considerably more (91+/-3%) was retained at 4 degrees C. Labeled cells did not exhibit any significant alteration in cell viability or phenotype as determined by trypan blue exclusion and FACS analysis 24 h after radiolabeling. Furthermore, F-18-labeled BMDC stimulated allogeneic T cells in a mixed leukocyte reaction as potently as did sham-treated BMDC and migrated towards secondary lymphoid tissue chemokine (SLC) in a chemotaxis assay in vitro with the same efficiency as sham-treated BMDC. Migration of F-18-labeled BMDC was studied after footpad injection by (1) ex vivo counting of dissected tissues using a gamma counter and (2) in vivo by imaging mice with PiPET, a 2-mm resolution positron projection imager. After 4 h, the ratio between measured activity in draining vs. contralateral (D/C) lymph nodes (LN) was 166+/-96 (n=7) in the case of live cell injections, whereas if we injected heat-killed F-18-labeled BMDC or F-18-labeled macrophages the D/C ratios were 17+/-2 (n=2) and 14+/-4 (n=2), respectively. Injection of cell-free activity in the form of F-18-labeled 4-fluorobenzoic acid resulted in a D/C ratio of 7+/-2 (n=3), suggesting that the activity measured in the draining lymph node was associated with migrated F-18-labeled BMDC. When F-18-labeled live cells were injected into the footpad, 0.18+/-0.04% (n=7) of footpad activity was found in the draining LN within 4 h, whereas none was found in the contralateral LN. Quantitative assessment of cell migration by PET projection imaging of mice confirmed the ex-vivo counting results. These studies indicate that PET imaging offers a new approach for in vivo studies of dendritic cell biodistribution and migration.
authors.affiliation: Dermatology Branch, National Cancer Institute, National Institutes of Health, Bldg. 10, Room 12N238, 10 Center Drive, MSC 1908, Bethesda, MD 20892-1908, USA.
authors.forename: Edit B
authors.initials: EB
authors.lastname: Olasz
authors.forename: Lixin
authors.initials: L
authors.lastname: Lang
authors.forename: Jurgen
authors.initials: J
authors.lastname: Seidel
authors.forename: Michael V
authors.initials: MV
authors.lastname: Green
authors.forename: William C
authors.initials: WC
authors.lastname: Eckelman
authors.forename: Stephen I
authors.initials: SI
authors.lastname: Katz
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology*; D003713:Dendritic Cells / Q000166:cytology* / Q000276:immunology; D005456:Fluorescent Dyes; D005462:Fluorine Radioisotopes; D007091:Image Processing, Computer-Assisted; D051379:Mice; D008807:Mice, Inbred BALB C; D013194:Staining and Labeling / Q000379:methods*
chemical_list: D005456:Fluorescent Dyes; D005462:Fluorine Radioisotopes