title: In vivo, multimodal imaging of B cell distribution and response to antibody immunotherapy in mice.
abstract: BACKGROUND
  B cell depletion immunotherapy has been successfully employed to treat non-Hodgkin's lymphoma. In recent years, increasing attention has been directed towards also using B-cell depletion therapy as a treatment option in autoimmune disorders. However, it appears that the further development of these approaches will depend on a methodology to determine the relation of B-cell depletion to clinical response and how individual patients should be dosed. Thus far, patients have generally been followed by quantification of peripheral blood B cells, but it is not apparent that this measurement accurately reflects systemic B cell dynamics.
  
  
  RESULTS
  Cellular imaging of the targeted population in vivo may provide significant insight towards effective therapy and a greater understanding of underlying disease mechanics. Superparamagnetic iron oxide (SPIO) nanoparticles in concert with near infrared (NIR) fluorescent dyes were used to label and track primary C57BL/6 B cells. Following antibody mediated B cell depletion (anti-CD79), NIR-only labeled cells were expeditiously cleared from the circulation and spleen. Interestingly, B cells labeled with both SPIO and NIR were not depleted in the spleen.
  
  
  CONCLUSIONS
  Whole body fluorescent tracking of B cells enabled noninvasive, longitudinal imaging of both the distribution and subsequent depletion of B lymphocytes in the spleen. Quantification of depletion revealed a greater than 40% decrease in splenic fluorescent signal-to-background ratio in antibody treated versus control mice. These data suggest that in vivo imaging can be used to follow B cell dynamics, but that the labeling method will need to be carefully chosen. SPIO labeling for tracking purposes, generally thought to be benign, appears to interfere with B cell functions and requires further examination.
authors.affiliation: Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Daniel L J
authors.initials: DL
authors.lastname: Thorek
authors.forename: Patricia Y
authors.initials: PY
authors.lastname: Tsao
authors.forename: Vaishali
authors.initials: V
authors.lastname: Arora
authors.forename: Lanlan
authors.initials: L
authors.lastname: Zhou
authors.forename: Robert A
authors.initials: RA
authors.lastname: Eisenberg
authors.forename: Andrew
authors.initials: A
authors.lastname: Tsourkas
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D002478:Cells, Cultured; D005453:Fluorescence; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007167:Immunotherapy; D008212:Lymphocyte Depletion; D008279:Magnetic Resonance Imaging; D051379:Mice; D008810:Mice, Inbred C57BL; D009928:Organ Specificity; D013154:Spleen / Q000276:immunology / Q000473:pathology; D013194:Staining and Labeling; D051598:Whole Body Imaging
chemical_list: D000906:Antibodies