Unique cell surface expression of receptor tyrosine kinase ROR1 in human B-cell chronic lymphocytic leukemia.
OBJECTIVE
Gene expression profiling identified receptor tyrosine kinase ROR1, an embryonic protein involved in organogenesis, as a signature gene in B-cell chronic lymphocytic leukemia (B-CLL). To assess the suitability of ROR1 as a cell surface antigen for targeted therapy of B-CLL, we carried out a comprehensive analysis of ROR1 protein expression.


METHODS
Peripheral blood mononuclear cells, sera, and other adult tissues from B-CLL patients and healthy donors were analyzed qualitatively and quantitatively for ROR1 protein expression by flow cytometry, cell surface biotinylation, Western blotting, and ELISA.


RESULTS
ROR1 protein is selectively expressed on the surface of B-CLL cells, whereas normal B cells, other normal blood cells, and normal adult tissues do not express cell surface ROR1. Moreover, cell surface expression of ROR1 is uniform and constitutive, i.e., independent of anatomic niches, independent of biological and clinical heterogeneity of B-CLL, independent of B-cell activation, and found at similar levels in all B-CLL samples tested. The antibody binding capacity of B-CLL cell surface ROR1 was determined to be in the range of 10(3) to 10(4) molecules per cell. A portion of B-CLL cell surface ROR1 was actively internalized upon antibody binding. Soluble ROR1 protein was detectable in sera of <25% of B-CLL patients and a similar fraction of healthy donors at concentrations below 200 ng/mL.


CONCLUSIONS
The restricted, uniform, and constitutive cell surface expression of ROR1 protein in B-CLL provides a strong incentive for the development of targeted therapeutics such as monoclonal antibodies.
Baskar
Sivasubramanian
S
Experimental Transplantation and Immunology Branch and Metabolism Branch, Center for Cancer Research, National Cancer Institute, and Hematology Branch, National Heart, Lung and Blood Institute, NIH, Bethesda, MD 20892-1203, USA.
Kwong
Ka Yin
KY
Hofer
Thomas
T
Levy
Jessica M
JM
Kennedy
Michael G
MG
Lee
Elinor
E
Staudt
Louis M
LM
Wilson
Wyndham H
WH
Wiestner
Adrian
A
Rader
Christoph
C
D001402:B-Lymphocytes / Q000201:enzymology; D014408:Biomarkers, Tumor; D001773:Blood Cells / Q000201:enzymology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000201:enzymology*; D007963:Leukocytes, Mononuclear / Q000201:enzymology; D020794:Receptor Protein-Tyrosine Kinases / Q000097:blood / Q000378:metabolism*; D057050:Receptor Tyrosine Kinase-like Orphan Receptors
D014408:Biomarkers, Tumor; C078716:ROR1 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D057050:Receptor Tyrosine Kinase-like Orphan Receptors