Anti-erythropoietin receptor (EPO-R) monoclonal antibodies inhibit
erythropoietin binding and neutralize bioactivity
AD D'Andrea, BJ Rup, MJ Fisher and S Jones
Division of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard
Medical School, Boston, MA 02115.
We have generated six high affinity monoclonal antibodies (MoAbs) to the
human erythropoietin receptor (hEPO-R) polypeptide. All six MoAbs bind to
the extracytoplasmic domain of the hEPO-R, and all immunoprecipitate
35S-labeled hEPO-R from metabolically labeled Ba/F3- hEPO-R cells. Four of
the MoAbs neutralize the EPO-dependent growth of Ba/F3-hEPO-R cells,
whereas two MoAbs are non-neutralizing. None of the MoAbs inhibit the
EPO-dependent growth of Ba/F3 cells expressing the murine EPO-R (mEPO-R),
even though the hEPO-R and mEPO-R share 82% amino acid identity. All six of
the anti-EPO-R MoAbs bind to the cell surface human EPO-R but none bind to
the cell surface murine EPO-R. Of the four neutralizing MoAbs, the one-half
maximal inhibition occurs at MoAb concentrations ranging from 1 nmol/L to
50 nmol/L. These MoAbs also compete with radiolabeled EPO for hEPO-R
binding. The two non- neutralizing MoAbs fail to inhibit EPO-dependent
growth or compete with EPO-binding, even at antibody concentrations as high
as 500 nmol/L. The four neutralizing MoAbs, designated group I, compete
with each other for an epitope of the hEPO-R polypeptide required for
EPO-binding. The two non-neutralizing MoAbs recognize discrete epitopes,
and are designated group II and group III MoAbs. In conclusion, this is the
first description of MoAbs specific for the hEPO-R. The MoAbs, which
recognize three discrete epitopes, may be useful in characterizing the
spectrum of cells that display the hEPO-R and in further defining the role
of EPO in hematopoiesis.
Volume 82,
Issue 1,
pp. 46-52,
07/01/1993
Copyright © 1993 by The American Society of Hematology
