NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.

Cover of Molecular Imaging and Contrast Agent Database (MICAD)

Molecular Imaging and Contrast Agent Database (MICAD) [Internet].

Show details

Ultrasmall superparamagnetic iron oxide-anti-CD20 monoclonal antibody

USPIO-anti-CD20 MAb
, PhD
National Center for Biotechnology Information, NLM, NIH, Bethesda, MD, vog.hin.mln.ibcn@dacim

Created: ; Last Update: February 12, 2008.

Chemical name:Ultrasmall superparamagnetic iron oxide-anti-CD20 monoclonal antibody
Abbreviated name:USPIO-anti-CD20 MAb
Agent Category:Antibody
Target:CD20 antigen
Target Category:Antibody-antigen binding
Method of detection:Magnetic resonance imaging (MRI)
Source of signal /contrast:Ultrasmall superparamagnetic iron oxide (USPIO)
  • Checkbox In vitro
  • Checkbox Rodents

Click on protein, nucleotide (RefSeq), and gene for more information about CD20.



Ultrasmall superparamagnetic iron oxide-anti-CD20 monoclonal antibody (USPIO-anti-CD20 MAb) is a molecular imaging agent developed for magnetic resonance imaging (MRI) of CD20 antigen-positive B cell lymphomas (1). The in vitro magnetic properties of USPIO are reported to be a T1 relaxivity (r1) of 21.6 (mmol/liter·sec)−1 and a T2 relaxivity (r2) of 44.1 (mmol/liter·sec)−1 at 37ºC and 0.47 tesla (T), where mmol/liter is the concentration of iron oxide (2).

Conventional, water-soluble, paramagnetic contrast agents are generally metal chelates with unpaired electrons, and they work by shortening both T1 and T2 relaxation times of surrounding water protons to produce a signal-enhancing effect (3, 4). They distribute in the extracellular fluid and do not cross the intact blood–brain barrier (3-5). Another approach is the development of water-insoluble SPIO nanoparticles that comprise iron oxides such as magnetite (Fe3O4), maghemite (γFe2O3), or other ferrites (6, 7). Ferromagnetic crystals are composed of magnetized domains the size of a micron. Superparamagnetism occurs when the size of the crystals is smaller than the ferromagnetic domain (~30 nm). SPIO agents typically consist of an iron oxide core and a hydrophilic coating (8). They have very high relaxivities (R1 and R2), and the significant capacity of these particles to increase the susceptibility effect of the measured spin–spin relaxation time (T2*) is especially useful in MRI. This large T2* effect is the result of the non-homogeneous distribution of these superparamagnetic particles, which accelerates the loss of phase coherence of the spins contributing to the MRI signal. Clinically, SPIO are predominantly used for their negative enhancement effect on T2- and T2*-weighted sequences. This class of MRI agents includes large oral SPIO (300–3500 nm) agents, standard SPIO (60–150 nm) agents, USPIO (10–40 nm) agents, monocrystalline iron oxide (10–30 nm) nanoparticle (MION) agents, and cross-linked iron oxide (CLIO) agents (a form of MION with a cross-linked dextran coating) (9). Both the size and the surface properties of SPIO particles affect their pharmacokinetics, organ distribution, and intracellular uptake (10). Biologically, SPIO particles are usually taken up by the reticuloendothelial system and phagocytic cells. USPIO particles are less prone to liver uptake and are small enough to migrate across the capillary wall of tumors (11). They also represent a useful MRI label for developing molecular probes to target specific markers (1).

The CD20 antigen (B1) is a 35-kDa, cell-surface nonglycosylated, hydrophobic phosphoprotein expressed on normal and malignant B cells, and it does not shed, modulate, or internalize (12-14). B1 is present on ~9% of the peripheral blood mononuclear cell fraction and >90% of B cells from blood and lymphoid organs. Lymphoma cells from >90% of patients with B cell non-Hodgkin’s lymphoma (NHL) express this antigen. Despite the presence of CD20 on normal B cells, it is a good tumor target for molecular targeting with antibodies for the management of NHL. Baio et al. (1) demonstrated the successful use of a commercially available USPIO-anti-CD20 MAb conjugate for MRI imaging in a murine xenotransplant model.



Numerous chemical methods can be used to synthesize SPIO, and they are generally complex processes because of the colloidal nature of SPIO (6). The prototype of USPIO was developed by Weissleder et al. (2), and it was obtained through size fractionation of a heterogeneous iron oxide preparation with use of gel chromatography. Other processes have produced USPIO from solution, aerosol, or vapor (6, 15). After synthesis, a coating is required to prevent destabilization and agglomeration of the colloidal suspension. Many polymeric coating materials have been used, such as dextran, carboxymethylated dextran, carboxydetran, starch, polyethylene glycol, arabinogalactan, glycosaminoglycan, organic siloxane, and sulphonated syrenedivinylbenzene. The surface coating of USPIO allows chemical linkage of functional groups to couple macromolecules to nanoparticles. Oxidative and non-oxidative processes have been used to couple antibodies to USPIO (6). Baio et al. (1) used commercially available USPIO bound to an anti-CD20 MAb (IgG1-murine) stabilized with sodium citrate. The particles were composed of a biodegradable, nontoxic, ferromagnetic matrix (dextran). The overall mean particle diameter was ~30–50 nm. There were typically 10–200 antibody molecules/particle (30 nm in diameter). The in vitro R1 and R2 relaxivities measured at 37ºC and 1.5 T were 30 and 60 liter·s−1·mmol−1, respectively.

In Vitro Studies: Testing in Cells and Tissues


Baio et al. (1) studied the in vitro binding of USPIO-anti-CD20 MAb to human D430B cells (anaplastic large-cell lymphoma B cell line) and Raji Burkitt lymphoma cells. After incubation with the USPIO-MAb conjugates, unbound conjugates were removed and cells were included in a matrigel sponge for MRI imaging with a 1.5-T MRI system. Immunofluorescence analysis showed that USPIO-anti-CD20 MAb bound to the cell surface, and the D4308 cells expressed five times more CD20 molecules than the Raji Burkitt cells. USPIO-anti-CD20 MAb on D430B cells showed a decrease in signal intensity (SI) on T2*-weighted images and SI enhancement on T1-weighted images. In comparison, USPIO-anti-CD20 MAb on Raji Burkitt cells only showed a slight hypointensity on T2-weighted images and a non-homogeneous hyperintensity on T1-weighted images. Quantitative analysis showed that the changes in T1 SI (ΔSI = SInonlableled–SI USPIO-anti-CD20 MAb/noise) values from the three-dimensional fast-field echo sequences (3D-FFE) at 1.5 T for the USPIO-anti-CD20 MAb on D430B cells were −36.6, −12.4, and −6.2 for 0.03 μmol iron (Fe)/liter, 0.01 μmol Fe/liter, and 0.005 μmol Fe/liter USPIO-anti-CD20 MAb, respectively. The T2 ΔSI values were −73, −24, and −12 for 0.03 μmol Fe/liter, 0.01 μmol Fe/liter, and 0.005 μmol Fe/liter USPIO-anti-CD20 MAb, respectively. In comparison, the T1 ΔSI values of the USPIO-anti-CD20 MAb on Raji Burkitt cells were −25, −9, and −6 for 0.03 μmol Fe/liter, 0.01 μmol Fe/liter, and 0.005 μmol Fe/liter USPIO-anti-CD20 MAb, respectively. The T2 ΔSI values were −43, −17.7, and −12 for 0.03 μmol Fe/liter, 0.01 μmol Fe/liter, and 0.005 μmol Fe/liter USPIO-anti-CD20 MAb, respectively.

Animal Studies



MRI studies were performed in NOD-SCID mice bearing s.c. D430B or the Raji Burkitt tumors (0.5–1 cm2). Each mouse received an i.v. dose of 8 μmol Fe/kg 24 h before imaging with a 1.5 T-MRI system (1). The D430B tumors showed a non-homogeneous SI decrease on T2*-weighted images and a slight SI enhancement on T1-weighted images. In comparison, the Raji Burkitt tumors showed slight non-homogeneous hypointensity on T2*-weighted images and slight non-homogeneous hypertensity on T1-weighted images. Quantitative analysis studies were conducted with the region-of-interest technique to obtain the signal/noise (SNR) ratios. The T2*-weighted ΔSI value (SNRbefore/SNRafter) of the D403B tumor (n = 5) was 35 ± 7% (82 ± 9%/57 ± 11%), whereas the T2*-weighted ΔSI value of the Raji Burkitt tumor was 15 ± 8% (47 ± 10%/40 ± 13%). In comparison, tumors in mice injected with a nonspecific standard SPIO agent ferumoxide (17 μmol Fe/kg) showed a T2*-weighted ΔSI value of 5 ± 6% (1,392 ± 86%/1,322 ± 80%). The authors concluded that 1.5 T-MRI could detect USPIO-antibody conjugates that target a tumor-associated antigen in vivo.

Other Non-Primate Mammals


No publication is currently available.

Non-Human Primates


No publication is currently available.

Human Studies


No publication is currently available.


Baio G., Fabbi M., de Totero D., Ferrini S., Cilli M., Derchi L.E., Neumaier C.E. Magnetic resonance imaging at 1.5 T with immunospecific contrast agent in vitro and in vivo in a xenotransplant model. Magma. 2006;19(6):313–20. [PubMed: 17160691]
Weissleder R., Elizondo G., Wittenberg J., Rabito C.A., Bengele H.H., Josephson L. Ultrasmall superparamagnetic iron oxide: characterization of a new class of contrast agents for MR imaging. Radiology. 1990;175(2):489–93. [PubMed: 2326474]
  • 3. Brasch, R.C., M.D. Ogan and B.L. Engelstad, Paramagnetic Contrast Agents and Their Application in NMR Imaging, in Contrast media; Biologic effects and clinical application, Z. Parvez, R., R. Monada and M. Sovak, Editor. 1987, CRC Press, Inc.: Boca Raton, Florida. p. 131-143.
  • 4. Saini, S., J.T. Ferrucci, Enhanced Agents for Magnetic Resonance Imaging: Clinical Applications, in Pharmaceuticals in Medical Imaging, D.P. Swanson, H.M. Chilton and J.H. Thrall, Editor. 1990, MacMillan Publishing Co., Inc.: New York. p. 662-681.
  • 5.
    Runge V.M., Kirsch J.E., Wells J.W., Awh M.H., Bittner D.F., Woolfolk C.E. Enhanced liver MR: Contrast agents and imaging strategy. Critical Reviews in Diagnostic Imaging. 1993;34(2):1–3. [PubMed: 8216813]
    Corot C., Robert P., Idee J.M., Port M. Recent advances in iron oxide nanocrystal technology for medical imaging. Adv Drug Deliv Rev. 2006;58(14):1471–504. [PubMed: 17116343]
    Bulte J.W., Kraitchman D.L. Iron oxide MR contrast agents for molecular and cellular imaging. NMR Biomed. 2004;17(7):484–99. [PubMed: 15526347]
    Thorek D.L., Chen A.K., Czupryna J., Tsourkas A. Superparamagnetic iron oxide nanoparticle probes for molecular imaging. Ann Biomed Eng. 2006;34(1):23–38. [PubMed: 16496086]
    Wang Y.X., Hussain S.M., Krestin G.P. Superparamagnetic iron oxide contrast agents: physicochemical characteristics and applications in MR imaging. Eur Radiol. 2001;11(11):2319–31. [PubMed: 11702180]
    Fleige G., Seeberger F., Laux D., Kresse M., Taupitz M., Pilgrimm H., Zimmer C. In vitro characterization of two different ultrasmall iron oxide particles for magnetic resonance cell tracking. Invest Radiol. 2002;37(9):482–8. [PubMed: 12218443]
    Sun R., Dittrich J., Le-Huu M., Mueller M.M., Bedke J., Kartenbeck J., Lehmann W.D., Krueger R., Bock M., Huss R., Seliger C., Grone H.J., Misselwitz B., Semmler W., Kiessling F. Physical and biological characterization of superparamagnetic iron oxide- and ultrasmall superparamagnetic iron oxide-labeled cells: a comparison. Invest Radiol. 2005;40(8):504–13. [PubMed: 16024988]
    Hainsworth J.D. Monoclonal antibody therapy in lymphoid malignancies. Oncologist. 2000;5(5):376–84. [PubMed: 11040273]
    Tobinai K. Rituximab and other emerging antibodies as molecular target-based therapy of lymphoma. Int J Clin Oncol. 2003;8(4):212–23. [PubMed: 12955576]
    Zelenetz A.D. A clinical and scientific overview of tositumomab and iodine I 131 tositumomab Semin Oncol 200330Suppl 42:22–30. [PubMed: 12728404]
    Gupta A.K., Gupta M. Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications. Biomaterials. 2005;26(18):3995–4021. [PubMed: 15626447]


    • PubReader
    • Print View
    • Cite this Page
    • PDF version of this page (586K)
    • MICAD Summary (CSV file)

    Search MICAD

    Limit my Search:

    Related information

    Similar articles in PubMed

    See reviews...See all...

    Recent Activity

    Your browsing activity is empty.

    Activity recording is turned off.

    Turn recording back on

    See more...