Biology Reference
In-Depth Information
The assay is highly reproducible and it allows a quantitative measurement of
the antibody concentration (Garaud et al., submitted). In its simple form, the
assay essentially detects IgG class antibodies but other immunoglobulin class-
es can be detected either by adding IgG molecules that recognize other human
immunoglobulin classes, such as IgM or IgA to insoluble protein A or protein
G or by using specific antibodies against anti-human classes or sub-classes
immunoglobulins covalently bound to agarose beads. The latter method allows
the determination of class and sub-class of anti-EPO antibodies.
Presence of anti-EPO antibodies
Ve r y few anti-EPO antibody cases have been reported in patients who have
never been treated with rHuEPO. Linardaki et al. have shown the presence of
anti-EPO antibodies in two patients with pure red cell aplasia as an initial man-
ifestation of systemic lupus erythematosus [13]. Peschle et al. [14] and
Casadevall et al. [8] reported the spontaneous appearance of anti-EPO anti-
bodies in three patients. One of these patients also harbored a thymoma, but no
pathologies were detectable in the other two patients. In each case, the anti-
bodies induced pure red cell aplasia. The antibodies have been extensively
characterized in the study of Casadevall et al. [8]. Their affinity was very high
(Kd of 430 pM), similar to the affinity of EPO for EPOR. The EPO binding
capacity of the patient serum was 2.7 U/mL serum. The high-affinity and the
high-binding capacity allowed the neutralization of all circulating EPO. The
antibodies were directed against a conformational epitope present in the pro-
tein part of the molecule.
The antibodies could not be thoroughly characterized in the study of
Peschle et al. due to the lack of available pure EPO at the time. Anti-EPO anti-
bodies disappared spontaneously [8] or as pure red cell aplasia resolved after
immunosuppressive treatment [14, 15]. Nevertheless, the spontaneous appear-
ance of such antibodies seems to be very rare and no other cases have been
documented to date. Since these antibodies induce severe pure red cell aplasia,
it is unlikely that other similar cases would have remained unrecognized. The
appearance of non-neutralizing anti-EPO antibodies cannot be ruled out (see
below), but seems impossible to be detected with current assays.
The induction of neutralizing anti-EPO antibodies in patients treated with
rHuEPO was very low up to 1998. Indeed, during the first 10 years of rHuEPO
use, only three cases of such antibodies were reported [12, 16, 17]. In each
case, these antibodies induced profound anemia. The three patients were treat-
ed with rHuEPO for anemia associated with renal failure. Thus,it can be con-
cluded that rHuEPO is extremely well tolerated and has induced only a very
few cases of neutralizing antibodies causing PRCA. Some reports, however,
suggest that rHuEPO could induce non-neutralizing anti-EPO antibodies with
a high frequency since such antibodies were detected in up to 67% of rHuEPO-
treated patients in one study. These antibodies have been detected by ELISA
