Development of radioimmunoassays for human erythropoietin using recombinant erythropoietin as tracer and immunogen

Erythropoietin: A Personal Alice in Wonderland Trip in the Shadow of the Giants

The identification of the hormone erythropoietin (EPO), which regulates red blood cell production, and its development into a pharmaceutical-grade product to treat anemia has been not only a herculean task but it has also been the first of its kind. As with all the successes, it had "winners" and "losers", but its history is mostly told by the winners who, over the years, have published excellent scientific and divulgate summaries on the subject, some of which are cited in this review. In addition, "success" is also due to the superb and dedicated work of numerous "crew" members, who often are under-represented and under-recognized when the story is told and often have several "dark sides" that are not told in the polished context of most reviews, but which raised the need for the development of the current legislation on biotherapeutics. Although I was marginally involved in the clinical development of erythropoietin, I have known on a personal basis most, if not all, the protagonists of the saga and had multiple opportunities to talk with them on the drive that supported their activities. Here, I will summarize the major steps in the development of erythropoietin as the first bioproduct to enter the clinic. Some of the "dark sides" will also be mentioned to emphasize what a beautiful achievement of humankind this process has been and how the various unforeseen challenges that emerged were progressively addressed in the interest of science and of the patient's wellbeing.

The Pharmacokinetics of Intraperitoneal Erythropoietin Administered Undiluted Or Diluted in Dialysate

+ Objective

To compare the bioavailability of intraperitoneal erythropoietin (EPO) administered undiluted versus diluted in 2 L of dialysis fluid.

+ Design

Group 1 patients received one dose of EPO, 400 Ulkg BW given with vehicle only. This dwelled for 8 hours after which 2 L of dialysate were infused. Group 2 patients received the same dose of EPO diluted in 2 L of dialysate which dwelled for 8 hours. Both groups resumed their CAPD regimen after the first 8 hours. Blood levels of EPO were measured for 24 hours in both groups.

+Setting

The Home Peritoneal Dialysis Unit, Toronto Hospital, Western Division.

+ Patients

The participants were on CAPD for at least three months, free of peritonitis, and had no abnormalities of peritoneal transport. Three patients took part in both arms of the study, and there were 6 patients altogether in each group.

+ Results

When EPO was administered undiluted, there was a greater than ninefold increase in bioavailability of the hormone as measured by the area under the curve (AUC), compared to when the same dose was diluted in 2 L of dialysis fluid.

+ Conclusions

The previous studies that reported low bioavailability of intraperitoneal EPO used the hormone diluted in dialysate. The current findings suggest that if EPO is given in the dry peritoneal cavity, the bioavailability is greatly improved and may be clinically effective. Intraperitoneal instillation may prove to be an alternative route for EPO in the peritoneal dialysis patient unable or unwilling to receive subcutaneous injections. We are currently studying the effectiveness of undiluted intraperitoneal EPO in CAPD patients.

Comparative Pharmacokinetics of Recombinant Erythropoietin Administered by the Intravenous, Subcutaneous, and Intraperitoneal Routes in Continuous Ambulatory Peritoneal Dialysis (CAPD) Patients

The single dose pharmacokinetics of recombinant human erythropoietin (r-HuEPO) were compared in six continuous ambulatory peritoneal dialysis (CAPD) patients after intravenous (i.v.), subcutaneous (s.c.), and intraperitoneal (i.p.) administration of 300 U/kg. Intravenous administration gave results close to those obtained in hemodialysis patients, with a half-life of 11.2 h and a volume of distribution of 5.0% of body weight. After subcutaneous administration, the serum concentration rose slowly to plateau between 24 and 36 h, the area under the serum concentration vs. time curve from 6 to 72 h being 18.2% of that after intravenous administration. After intraperitoneal administration, the serum concentration was even lower, the area under the curve from 0 to 24 h was between 2.5 and 3.6% of that after intravenous administration, and 80% of the administered dose was recovered in the first peritoneal effluent after a 4- h dwell time.

Pharmacokinetic and Pharmacodynamic Modeling of Recombinant Human Erythropoietin After Single and Multiple Doses in Healthy Volunteers

This study describes a pharmacokinetic (PK) model to account for serum recombinant human erythropoietin (rHuEpo) concentrations in healthy volunteers following intravenous (IV) and subcutaneous (SC) dosing; it also characterizes the pharmacodynamics (PD) of SC rHuEpo effects on reticulocytes, red blood cells (RBC), and hemoglobin (Hb) in blood. Data were obtained from 4 clinical studies carried out in healthy volunteers. Epoetin alfa (rHuEpo) was administered as 5 single IV doses ranging from 10 to 500 IU/kg, as 8 single SC doses ranging from 300 to 2400 IU/kg, and as 2 multiple SC dosage regimens (150 IU/kg/3 times a week [tiw] and 600 IU/kg/wk). A dual-absorption rate model (fast zero-order and slow first-order inputs) with nonlinear disposition characterized the PK of SC rHuEpo. A high K(m) value was obtained indicating that clearance was mildly nonlinear. Absorption was slow (t(max) approximately 24 hours), and the bioavailability of SC rHuEpo increased with dose (ranging from 46%-100%). A catenary cell production and loss model with a feedback down regulation component was used to fit the reticulocyte data yielding estimates of the stimulatory capacity (S(max)), sensitivity (SC(50)), and life span parameters. These parameters were used for simulations of RBC and Hb profiles. An SC(50) of 27 to 61 IU/L was estimated indicating that low physiological plasma rHuEpo concentrations were sufficient to produce pharmacological effects. No marked sex-dependent differences in clinical responses to rHuEpo therapy were found despite baseline differences. Realistic pharmacokinetic and physiological models accounted for clinical responses from a wide array of dosing conditions with rHuEpo. The rationale for greater efficacy of SC administration of rHuEpo compared to IV was ascertained.

Storage and preparation of samples for erythropoietin radioimmunoassay

The evaluation of a radioimmunoassay for erythropoietin developed using recombinant material as immunogen and radiotracer is presented. A series of serum samples prepared and stored under varying conditions showed that immunoreactive erythropoietin levels were stable at room temperature for at least 10 days and at -20 degrees C for 5 months. The optimum time for separating sera from samples was between 6 and 24 h after venepuncture. Serum EPO values were significantly higher than those measured in heparin or potassium EDTA plasma.

Determination of KRN321 in rat serum by ELISA and correlation between ELISA and in vitro bioassay

KRN321, darbepoetin alfa, is a hyperglycosylated analog of recombinant human erythropoietin (rHuEPO, epoetin alfa). We carried out the validation study by using a commercially available ELISA assay kit to establish the ELISA quantitation method for KRN321 in rat serum for the implementation of the pharmacokinetic studies with a lower limit of quantitation at 100 pg/mL and quantitation range from 100 to 4,000 pg/mL. We also established the in vitro bioassay method as an index of biological activity using UT-7/Epo, derived from a human leukemia cell line with a lower limit of quantitation, at 10 ng/mL. Furthermore, good correlation was observed between the two methods; it indicated that KRN321 concentration determined by the ELISA maintained biological activity.

Erythropoietin-induced, antibody-mediated pure red cell aplasia

Pure red cell aplasia (PRCA) is a rare haematological condition that is characterized by severe aregenerative anaemia due to an almost complete cessation of red blood cell production. While antibody-mediated PRCA was extremely rare before 1998, the incidence of this disorder increased sharply after 1998 in patients receiving subcutaneous epoetin alfa produced by Ortho-Biotech and marketed outside the USA. The diagnosis of antibody-mediated PRCA relies mostly on the results of bone marrow biopsy or aspirate, which shows an absence of erythroid precursors and/or red cell maturation arrest while counts of white cell and platelet precursors are normal, and on the identification of circulating anti-erythropoietin antibodies. Retrospective analysis of PRCA cases has shown that immunosuppressive therapy can induce a disappearance of anti-erythropoietin antibodies in most patients. Eur J Clin Invest 2005; 35 (Suppl. 3): 95-99.

Erythropoietin Impairs Endothelial Vasodilatory Function in Patients with Renal Anemia and in Healthy Subjects

BACKGROUND/AIM

The mechanisms underlying the aggravation or development of hypertension frequently seen during treatment of renal anemia with epoetins are not fully elucidated. The aim of the present study was to investigate the effects of epoetin alfa on endothelial vasodilatory function in patients with renal anemia and in healthy subjects.

METHODS

Eighteen preuremic patients with anemia (GFR 23.4 +/- 11 SD ml/min, Hb 101 +/- 8 g/l) and 10 healthy subjects underwent evaluation of endothelium-dependent vasodilation (EDV) and endothelium-independent vasodilation (EIDV) by means of forearm blood flow (FBF) measurements with venous occlusion plethysmography during local intra-arterial infusions of methacholine (MCh, evaluating EDV) and sodium nitroprusside (SNP, evaluating EIDV). These investigations were performed before and 30 min after an intravenous injection of epoetin alfa (10,000 IU). Ten healthy subjects underwent the same procedure with the exception that saline were given instead of epoetin. The patients were treated with epoetin alfa subcutaneously for 12-19 weeks and reevaluated when Hb exceeded 120 g/l.

RESULTS

EDV was attenuated after the epoetin injection in both renal patients and healthy subjects. This impairment persisted after anemia had been treated. EDIV and blood pressure remained constant. Saline had no effect on the variables measured.

CONCLUSION

Our results indicate that epoetin alfa impairs endothelial function in renal patients and healthy subjects which may have an impact on vascular complications.

Control of rHuEPO biological activity: the role of carbohydrate

OBJECTIVE

Darbepoetin alfa, a novel erythropoiesis-stimulating protein, is a glycosylation analog of recombinant human erythropoietin (rHuEPO) with two additional N-linked carbohydrates. Used to treat anemia of cancer, chemotherapy, and kidney disease, it has a three-fold longer serum half-life and increased in vivo activity, but decreased receptor-binding activity. Glycosylation analogs with altered N-linked carbohydrate content were compared with rHuEPO to elucidate the relationship between carbohydrate content and activity.

METHODS

EPO glycosylation analogs and rHuEPO were expressed and, in some cases, purified from Chinese hamster ovary cells and carbohydrate characterized by Western blotting. Assays were performed to compare in vitro receptor binding and in vivo activity of rHuEPO, darbepoetin alfa, and analogs.

RESULTS

Reduced receptor binding of darbepoetin alfa could be accounted for entirely by increased sialic acid content and not by carbohydrate-related stearic hindrance or by amino acid differences. Shapes of dose-response curves, maximal responses in proliferation and colony assays, and magnitude and duration of downstream signaling events were comparable in vitro for rHuEPO and darbepoetin alfa. The in vivo response correlated with the number of N-linked carbohydrates. The number of carbohydrates was a more significant determinant for in vivo activity than position. The differences in in vivo erythropoietic activity among glycosylation analogs were more evident with increased time following administration in exhypoxic polycythemic mice.

CONCLUSION

Carbohydrate increases persistence of EPO, resulting in a prolonged and increased biological response in vivo, and overcoming reduced receptor-binding activity.

Endogenous and recombinant erythropoietin levels decline in human amniotic fluid and fetal plasma in vitro at 37 degrees C

OBJECTIVE

To determine the in vitro stability of endogenous and recombinant erythropoietin (EPO) incubated at 37 degrees C in amniotic fluid (AF) and fetal plasma.

STUDY DESIGN

Endogenous and recombinant EPO in AF, fetal plasma and phosphate buffer were incubated in vitro for 21 days at 37 degrees C. Serial aliquots were analyzed for EPO and the rates of EPO decline were compared within and between groups.

RESULTS

Endogenous and recombinant EPO declined significantly in plasma and AF at 37 degrees C. Endogenous EPO displayed a similar linear rate of decline in AF and plasma, with nearly 70% of the initial hormone concentration remaining at 21 days. Recombinant EPO incubated in buffer did not change.

CONCLUSIONS

Using the rate of decline in endogenous EPO we observed, EPO levels measured in AF or plasma within 21 days of fetal demise can be extrapolated back to the level likely present at fetal death.

Structural requirements for additional N-linked carbohydrate on recombinant human erythropoietin

N-Linked glycosylation is a post-translational event whereby carbohydrates are added to secreted proteins at the consensus sequence Asn-Xaa-Ser/Thr, where Xaa is any amino acid except proline. Some consensus sequences in secreted proteins are not glycosylated, indicating that consensus sequences are necessary but not sufficient for glycosylation. In order to understand the structural rules for N-linked glycosylation, we introduced N-linked consensus sequences by site-directed mutagenesis into the polypeptide chain of the recombinant human erythropoietin molecule. Some regions of the polypeptide chain supported N-linked glycosylation more effectively than others. N-Linked glycosylation was inhibited by an adjacent proline suggesting that sequence context of a consensus sequence could affect glycosylation. One N-linked consensus sequence (Asn123-Thr125) introduced into a position close to the existing O-glycosylation site (Ser126) had an additional O-linked carbohydrate chain and not an additional N-linked carbohydrate chain suggesting that structural requirements in this region favored O-glycosylation over N-glycosylation. The presence of a consensus sequence on the protein surface of the folded molecule did not appear to be a prerequisite for oligosaccharide addition. However, it was noted that recombinant human erythropoietin analogs that were hyperglycosylated at sites that were normally buried had altered protein structures. This suggests that carbohydrate addition precedes polypeptide folding.

The detection of anti-erythropoietin antibodies in human serum and plasma

Rare cases of unexplained sudden severe anemia or red cell aplasia and resistance to recombinant human erythropoietin (rHuEPO) in patients with chronic renal failure (CRF) have been attributed to the development of anti-EPO antibodies. The development and validation of a radioimmunoprecipitation (RIP) assay to detect human anti-EPO antibodies in serum or plasma has been hampered by the lack of purified antibody to fully characterize and validate the assay. We have prepared an affinity-purified human antibody to EPO and used the antibody to characterize and validate a sensitive and reproducible RIP assay that can qualitatively measure anti-EPO antibody in serum or plasma samples. The lower limit of detection of the assay is 8 ng/ml of purified antibody. The threshold for detecting antibody is > or =0.9% cpm bound. The precision of the assay using purified antibody standards ranges from 5.8% to 15.3% and the precision of the assay using dilutions of the positive control ranges from 15.9% to 18.7%. EPO in the samples did not interfere with detection of the anti-EPO antibody except at high concentrations.

Darbepoetin alfa has a longer circulating half-life and greater in vivo potency than recombinant human erythropoietin

OBJECTIVE

Experiments on human erythropoietin (EPO) demonstrated that there is a direct relationship between the sialic acid-containing carbohydrate content of EPO, its circulating half-life, and in vivo bioactivity. This led to the hypothesis that an EPO analogue engineered to contain additional oligosaccharide chains would have enhanced biological activity. Darbepoetin alfa, a hyperglycosylated recombinant human EPO (rHuEPO) analogue with two extra carbohydrate chains, was designed and developed to test this hypothesis.

MATERIALS AND METHODS

Comparative pharmacokinetic and pharmacodynamic studies and biochemical analyses of darbepoetin alfa and rHuEPO were performed to define the consequences of the increased carbohydrate content.

RESULTS

Due to its increased sialic acid-containing carbohydrate content, darbepoetin alfa has a higher molecular weight, a greater negative charge, and a approximately fourfold lower EPO receptor binding activity than rHuEPO. It also has a threefold longer circulating half-life than rHuEPO in rats and dogs. In spite of its lower receptor binding, and perhaps counterintuitively, darbepoetin alfa is significantly more potent in vivo than rHuEPO. Due to the pharmacokinetic differences, the relative potency of the two molecules varies as a function of the dosing frequency. Darbepoetin alfa is 3.6-fold more potent than rHuEPO in increasing the hematocrit of normal mice when each is administered thrice weekly, but when the administration frequency is reduced to once weekly, darbepoetin alfa is approximately 13-fold to 14-fold more potent than rHuEPO.

CONCLUSIONS

Increasing the sialic acid-containing carbohydrate content beyond the maximum found in EPO leads to a molecule with a longer circulating half-life and thereby an increased in vivo potency that can be administered less frequently.

Erythropoietin in human milk: physiology and role in infant health

Human milk contains substantial concentrations of erythropoietin, a hormone best known for its role in the regulation of erythropoiesis. Recent studies show that erythropoietin receptors are widely distributed in human tissues, including the gastrointestinal tract, endothelial cells, spinal cord, and brain, suggesting that erythropoietin plays a wider role in infant development. Mammary epithelial cells contribute to the production of erythropoietin in human milk, and erythropoietin concentrations appear to rise slowly in human milk during the first few months of lactation. Current data suggest that erythropoietin in human milk may play a pleiomorphic role in erythropoiesis, neurodevelopment, maturation of the gut, apoptosis, and immunity in the infant.

Identification of Blood Erythroid Markers Useful in Revealing Erythropoietin Abuse in Athletes

Recombinant human erythropoietin (rEpo) is being used with increasing frequency by endurance athletes to improve aerobic potential. Although rEpo administration has been banned by the International Olympic Committee, no methods are available to unequivocally detect its abuse in sports. Prompted by these considerations, we evaluated the main hematological and biochemical modifications measured in the blood of 18 volunteers upon rEpo administration. Different rEpo regimens, iron, folic acid, and vitamin B12 administration did not significantly modify the percentage increase in hematocrit. However, a significant decrease in circulating ferritin (fr) and an increase in the soluble transferrin receptor (sTfr) were not found in athletes receiving low (30 IU/kg) doses of rEpo. Thus, an increase in the sTfr/fr ratio cannot be used as an indicator of rEpo abuse, at least when the hormone is administered at low concentrations. In contrast, the amounts of beta-globin mRNA detected by quantitative competitive (RT)-PCR in whole blood samples significantly increased above the threshold levels in all of the treatments investigated. Taken together, these data suggest that hematocrit value, reticulocyte count, soluble transferrin receptor content, and concentration of beta-globin mRNA, when included in a new multiparametric formula, can detect rEpo abuse in 57.5% of the samples examined with a confidence interval of 99.99%. Thus, the method reported in this paper could significantly improve the tests currently available, which in similar experiments allowed the detection of rEpo abuse in only 7.6% of the samples examined.

Erythropoietin

Maintenance of the red cell volume is a fundamental aspect of ensuring oxygen supply to the tissues. The balance between the very dynamic processes of erythropoiesis and erythrocyte loss is precarious and yet normal individuals experience a remarkably constant haematocrit. This is achieved by a very elegant and sensitive homeostatic mechanism which links tissue oxygen delivery to red cell production. The glycoprotein hormone erythropoietin (EPO) is the principle controller of this process. It is now clear that even minor underproduction of EPO will result in anaemia. The most widespread example of this is the anaemia of end-stage renal failure. The pharmacological use of recombinant human EPO (rHuEPO) in this setting is now well established and has had a dramatic impact on the quality of life of patients with renal disease. With the more widespread use of EPO in other clinical conditions and the advent of novel therapeutic approaches, this is an opportune moment to review the physiology and patho-physiology of this fascinating and essential hormone.

Effect of subcutaneous recombinant human erythropoietin in cancer patients receiving radiotherapy: final report of a randomized, open-labelled, phase II trial

The purpose of this study was to determine the safety, efficacy and impact on quality of life of recombinant human erythropoietin (r-HuEPO) for cancer patients undergoing radiotherapy (RT). An open-labelled randomized design was used, with patients randomized to either treatment or control arms. Patients in the treatment arm received r-HuEPO given by subcutaneous injection at a dose of 200 units kg(-1) day(-1) plus oral iron supplements (ferrous sulphate 325 mg p.o. t.i.d.). Entry was restricted to patients with carcinoma of the lung, uterine cervix, prostate or breast who presented for RT with anaemia parameters reflective of 'the anaemia of chronic disease'. Radiotherapy policies (portals, doses, fraction size, etc.) were determined by the site and stage of disease. Complete blood counts (CBCs) were obtained weekly. The target level of haemoglobin was 15 g dl(-1) for men and 14 g dl(-1) for women. Quality of life (QOL) was assessed weekly by using an analogue scale to judge energy, activities of daily living and overall quality of life. Forty-eight patients were entered in the study, 24 in the treatment arm and 24 in the control arm. The prerandomization demographic characteristics and mean laboratory values were comparable in both arms. The mean haemoglobin at completion was 13.6 g dl(-1) for r-HuEPO-treated patients compared with 11.0 g dl(-1) for control subjects (P = 0.0012). Patients who received r-HuEPO demonstrated a mean weekly haemoglobin increase of 0.41 g dl(-1) compared with a decrease in mean haemoglobin level in controls for 6 of the 7 weeks of the study (mean weekly decrease of 0.073 g dl(-1)). Target levels of haemoglobin were achieved by 41.6% of r-HuEPO-treated patients compared with none of the control subjects. The mean platelet count declined in both arms of the study with RT but the decline from pretreatment was less rapid in r-HuEPO-treated patients (11.2% decrease) compared with controls (26.3% decrease) and was statistically significant during weeks 4-6. Toxicity was minor with only mild irritation at the injection site. Mean quality of life end points were superior in the treatment arm but not statistically significant. r-HuEPO had a beneficial effect on weekly haemoglobin levels in patients undergoing RT with response rates similar to other studies. There was also a less rapid decline in weekly platelet counts in r-HuEPO-treated patients compared with control subjects. Further studies are needed to address the optimum dose and scheduling as well as the impact of r-HuEPO on clinical outcomes.

The Physiologic Basis for the Pharmacologic Use of Recombinant Erythropoietin

While many growth factors influence erythroid progenitor cell proliferation, the hematopoietic growth factor erythropoietin has the most impact on the production of erythrocytes.

Chromatographic separation of recombinant human erythropoietin isoforms

Erythropoietin (EPO) is the main regulator of erythropoiesis. The human glycoprotein hormone is heterogeneous when analyzed by isoelectric focusing (IEF). We investigated the possibility of fractionating EPO isoforms using different chromatographic methods. A recombinant human EPO (rhEPO) was obtained from the culture supernatants of a human B-lymphoblastoid cell line transfected by the human EPO gene. Highly purified rhEPO preparations were obtained by immunoaffinity purification. More than fourteen isoforms were observed after IEF. Among the different methods developed for isoform fractionation, the most reproducible results were obtained by DEAE-Sephacel chromatography. Seven fractions of decreasing isoelectric point (pI) were obtained. The specific activity of these fractions measured by an immunoradiometric assay was not equally distributed.

A tracer interaction method for nonlinear pharmacokinetics analysis: application to evaluation of nonlinear elimination

A drug tracer is most commonly applied to get information about the pharmacokinetics (PK) of a drug that is not confounded by an endogenously produced drug or an unknown drug input. An equally important use of tracers that has not been fully recognized is their use in the study of nonlinear PK behavior. In the present study a system analysis is applied to examine the interaction between drug molecules characteristic and intrinsic to any nonlinear process which enables the nonlinearity to be identified and modeled using a drug tracer. The proposed Tracer Interaction Methodology (TIM) forms a general developmental framework for novel methods for examining nonlinear phenomena. Such methods are potentially much more sensitive and accurate than previous methods not exploiting the tracer principle. The methodology proposed is demonstrated in a simulation study and with real data in a specific implementation aimed at determining the Michaelis-Menten (MM) parameters of nonlinear drug elimination while accounting for drug distribution effects. The simulation study establishes that the TIM-based, MM parameter evaluation produces substantially more accurate parameter estimates than a nontracer (NT) conventional method. In test simulations the accuracy of the TIM was in many cases an order of magnitude better than the NT method without evidence of bias. The TIM-based, MM parameter estimation methodology proposed is ideally suitable for dynamic, non-steady-state conditions. Thus, it offers greater applicability and avoids the many problems specific to steady state evaluations previously proposed. TIM is demonstrated in an evaluation of the nonlinear elimination behavior of erythropoietin, a process that likely takes place via receptor-based endocytosis. Due to its high sensitivity, accuracy, and intrinsic nonlinearity the TIM may be suitable for in-vivo studies of receptor binding of the many biotechnology produced peptide drugs and endogenous compounds displaying receptor-mediated elimination.

Anemia associated with advanced prostatic adenocarcinoma: effects of recombinant human erythropoietin

BACKGROUND AND METHODS

Nine patients with hormone-refractory metastatic prostatic adenocarcinoma and anemia were treated with recombinant human erythropoietin (rHuEpo) at a median dose of 150 U/kg BW 3 times a week subcutaneously. Baseline hemoglobin (Hb) ranged from 70 to 116 g/L, and the study duration was 12 weeks (median patient participation period was 8 weeks).

RESULTS

Four patients demonstrated a median Hb increase of 20 g/L and were considered responders. Three patients showed a median increase of 17 g/L but required blood transfusion once, and were therefore considered as partial responders. Baseline erythropoietic status showed a significant correlation between serum Epo and Hb. Inadequate Epo production, evaluated by the observed/predicted log Epo ratio, was found in two patients. Defective bone marrow activity, demonstrated by low transferrin receptor (TfR), and hypoferremia in spite of abundant iron stores were also shown. Hemorheological investigations showed elevated plasma viscosity.

CONCLUSIONS

Our results indicate that suppression of erythropoiesis can be mainly explained by the depressed marrow activity. The altered hemorheology might contribute to the anemia. This anemia could possibly be corrected with rHuEpo.

Assessment of erythropoiesis following renal transplantation

Ten patients, who received cadaveric kidneys, were followed for 24 wk with serial measurements of serum erythropoietin (S-Epo), transferrin receptor (S-TfR) and iron variables. The mean pretransplant creatinine clearance was 8.2 (range 0-22) ml/min and the mean haemoglobin (Hb) level was 99 +/- 18.6 (range 66-124) g/l. Nine patients demonstrated a gradual increase in S-Epo levels, which reached a peak, and was accompanied by a parallel increase in S-TfR levels with a median lag period of 3 wk between both peaks. Hb correction followed the S-TfR peak after a second lag period (median 7 wk). Elevated S-Epo and S-TfR did not result in correction of anaemia in 1 patient due to impaired graft function. Within 4 months, S-Epo levels reached the normal range while TfR levels were higher than normal. Follow-up of iron status demonstrated the development of iron deficiency in 5 patients, which was corrected spontaneously. Improvement in erythropoiesis after renal transplantation seems to occur by means of expansion of the erythroid marrow, as detected by increasing S-TfR levels, subsequent to a S-Epo peak. This expansion precedes Hb normalization. A nonuraemic environment is probably a prerequisite for the correction of anaemia but not for the increase in S-Epo or S-TfR levels. Iron deficiency may occur after transplantation due to an increase in iron utilization.

Anemia of cancer

Cancer patients frequently develop anemia, due either to the cancer itself or to the effects of cancer-related therapy. Recent years have brought insights into both the pathogenesis of the anemia of cancer and the extent to which erythropoietin regulation participates in this process. Although transfusion therapy was the mainstay of therapy for symptomatic anemia in the past, clinical trials have demonstrated that recombinant human erythropoietin can alleviate both anemia and transfusion requirements in many cancer patients and may prove to have an important role in the treatment of cancer-related anemia in the future.

Rise in erythropoietin concentrations in experimental Trypanosoma congolense infection of calves

A bioassay was used to measure erythropoietin (EPO) concentrations in calves with haemorrhagic anaemia due to blood loss and in calves with anaemia due to Trypanosoma congolense infection. The bioactivity of EPO was measured in the assay by its stimulatory effect on 125I-deoxyuridine incorporation in spleen cells from phenylhydrazine-treated mice. Erythropoietin concentrations in blood-volume-depleted calves were elevated 6 h after blood loss, maximal (1225 mU/ml) at 33 h and below detection limits at 72 h. Reticulocytes (0.05 +/- 0.1%) appeared in blood by 72 h, peaked at 120 h and disappeared from the circulation by 7 days after bleeding. The packed cell volume (PCV) started increasing at 120 h and reached near pre-bleeding values by 14 days. In T. congolense-infected calves, parasites were first detected in the peripheral blood 12 days post-infection (dpi). Parasitaemia peaked (5 x 10(5) trypanosomes/ml of blood) at 15-18 dpi and, thereafter, several waves of parasitaemia were observed, but the peaks gradually diminished. Undiluted plasma from T. congolense-infected calves suppressed 125I-deoxyuridine incorporation into spleen cells from 13 dpi onwards. The suppressive effect of plasma was partly negated by five-fold dilution, which made possible the detection of increased EPO concentrations during the acute and chronic stages of the anaemia. The highest EPO peaks, reaching 2300 mU/ml in one calf, were detected during the chronic stage of the infection. At 15-39 dpi, there was a transient bone-marrow erythropoietic response characterized by an increase in mean corpuscular volume and a decrease in mean corpuscular haemoglobin concentration but with few reticulocytes (0.4%). However, from 76 dpi onwards, this response waned despite low PCV and elevated EPO concentrations. These results suggest that there is an ineffective erythroid response in the face of elevated EPO concentrations during bovine trypanosomiasis. The negative effect of plasma and serum from trypanosome-infected calves on the in-vitro bioactivity of EPO suggests the presence of inhibitory factors.

Follow-up of very low birth weight infants after erythropoietin treatment to prevent anemia of prematurity

OBJECTIVE

Treatment with recombinant human erythropoietin (rHuEPO) stimulates erythropoiesis and reduces the need for transfusions in hospitalized preterm infants. The aim of our study was to follow very low birth weight infants after the initial 6 weeks of rHuEPO treatment.

DESIGN AND METHODS

We randomly assigned 97 very low birth weight infants with a gestational age of 31 weeks or less and birth weight of 1500 gm or less to receive rHuEPO, 300 units/kg per week (erythropoietin (EPO) 300, n = 33), rHuEPO, 750 units/kg per week (EPO 750; n = 28), or no treatment (control, n = 36). The rHuEPO was administered from the first week of life for 6 weeks. After EPO therapy was discontinued, 75 neonates were followed weekly until discharge and at 3, 6, and 12 months of age.

RESULTS

Mean numbers (+/- SD) of packed erythrocyte transfusions per patient from the time rHuEPO therapy was discontinued until discharge were 0.38 +/- 0.64 (EPO 300), 0.23 +/- 0.52 (EPO 750), 0.9 +/- 1.1 (control) (p < 0.05 in both EPO groups vs control). Mean reticulocyte counts at the sixth week were 6% +/- 2.2% (EPO 300), 6.9% +/- 2.2% (EPO 750), and 3.1% +/- 2.6% (control) in the three groups (p < 0.01 in both EPO groups vs control), and at the eighth week were 4.7% +/- 2.8% (EPO 300), 5.4% +/- 2.7% (EPO 750), and 2.6% +/- 2.2% (control) (p < 0.01 in both EPO groups vs control). Serum ferritin levels were significantly higher at the sixth week, and the percentage of hemoglobin F was significantly lower at 6, 8, and 10 weeks in the control group versus EPO groups. At 3, 6, and 12 months of age, there were no differences in reticulocytes, ferritin, HbF, and growth among groups.

CONCLUSION

Preterm infants who received rHuEPO had a normal pattern of erythropoiesis after the drug was discontinued. These data provide strong evidence that the anemia of prematurity is the result of a transient developmental abnormality in EPO production.

Serum immunoreactive erythropoietin in health and disease

Erythropoietin, the glycoprotein which regulates erythropoiesis is unique amongst the hematopoietic growth factors since it is the only one which behaves like a hormone. Produced primarily in the kidneys in adults, erythropoietin interacts with erythroid precursors in the marrow to increase red cell production. Because erythropoietin behaves like a hormone, measurements of erythropoietin in the serum have proved useful in determining when production of this hormone is inadequate. Tissue hypoxia is the only physiologic stimulus for erythropoietin production and thus, with anemia, serum erythropoietin levels should be increased. Assuming normal marrow function and adequate nutrient supplies, when anemia is associated with a low serum erythropoietin level, it can be concluded that the anemia is in part due to erythropoietin lack and should be correctable by administration of erythropoietin. As a corollary, a high serum erythropoietin level (greater than 500 mU/ml) in the presence of anemia suggests that there is end organ failure, and erythropoietin therapy is not likely to be useful.

The effect of cytokines on the in-vitro erythropoietin bioassay

The effects of various concentrations of granulocyte macrophage colony stimulating factor (GM-CSF), gamma interferon (gamma IFN) and interleukins 1 alpha (IL-1 alpha), 1 beta (IL-1 beta) and 3 (IL-3) on the anaemic mouse spleen cell bioassay for erythropoietin (EPO) were investigated. Addition of IL-3 and GM-CSF at various concentrations had no effect on EPO stimulated 3H thymidine incorporation. However the addition of IL-1 alpha, IL1-beta and gamma IFN (3.3 x 10(-8) gl-1) caused a significant (P < 0.01) inhibition of EPO stimulated thymidine incorporation. This suggests that the EPO bioassay may be influenced by variable levels of some inflammatory cytokines in serum. Previous studies have shown that the bioassay is influenced by serum transferrin levels and thus serum immunoassays remain the technique of choice for specific estimates of EPO. Since EPO bioassays are not specific, they should be reserved for situations in which an estimate of the total erythropoietic activity of serum is required.

Erythropoietin response to anaemia is not altered by surgery or recombinant human erythropoietin therapy

Recombinant human erythropoietin (EPO) therapy has been shown to increase red blood cell (RBC) production and facilitate autologous blood donation before elective surgery. However, recent reports have suggested that surgery and/or EPO therapy may suppress endogenous erythropoietin secretion in response to anaemia. We therefore analysed the haemoglobin/erythropoietin relationship preoperatively and postoperatively in 71 autologous blood donors subjected to aggressive phlebotomy and six treatments with either EPO (150 U/kg, n = 16, 300 U/kg, n = 18, or 600 U/kg, n = 19) or placebo (n = 18). Using data from the three preoperative study visits, the linear relationship between log erythropoietin and haemoglobin was determined for each of the 18 placebo patients. We found no significant differences in the slopes of the relationships in this group during aggressive phlebotomy. Furthermore, there was no evidence of a significant difference in the erythropoietin level recorded postoperatively for each patient to that predicted from the patient's postoperative haemoglobin level, based on the haemoglobin/log erythropoietin relationship preoperatively. Similarly, for each of the EPO-treated groups, there was no evidence of a significant difference when comparing the recorded erythropoietin level to that predicted from each patient's postoperative haemoglobin level, based on the haemoglobin/log erythropoietin relationship preoperatively. We conclude that preoperative recombinant human erythropoietin therapy and/or surgery do not adversely affect the postoperative erythropoietin response to anaemia.

Reticulocyte measurements as a bioassay for erythropoietin

The possibility of using reticulocyte counts in peripheral blood to assay erythropoietic activity of recombinant human erythropoietin (r-HuEPO) was evaluated in normal mice. Mice were injected subcutaneously with r-HuEPO on days 0, 1 and 2 and bled on day 4 for reticulocyte count determinations, using an automated counting system with thiazole orange fluorescent staining and flow cytometric analysis. Reticulocyte counts increased in a dose-dependent fashion upon administration of r-HuEPO. The reticulocyte count was unaffected by asialylated EPO as well as other substances tested (interleukin-1, interleukin-3, dexamethasone, human chorionic gonadotropin). These data demonstrate the usefulness of employing reticulocyte counts as a rapid, specific and reproducible assay for in vivo erythropoietic activity of r-HuEPO.

Serum erythropoietin concentrations measured by radioimmunoassay in normal, polycythemic, and anemic dogs and cats

Serum erythropoietin (Epo) concentrations were measured by radioimmunoassay (RIA) in normal, polycythemic, and anemic dogs and cats. The serum Epo concentration in normal dogs (n = 25) ranged from 7 to 37 mU/mL (median, 20 mU/mL); and in normal cats (n = 11) ranged from 9 to 38 mU/mL (median, 18 mU/mL). Polycythemic animals (PCV > 55% in dogs, > 45% in cats) were classified as those with primary (polycythemia vera), secondary, or polycythemia of uncertain etiology. Dogs with polycythemia vera (PV, n = 8) had a median serum Epo concentration in the normal range (17 mU/mL); cats with PV (n = 7) also had a median serum Epo concentration that was within the normal range (10 mU/mL). In the category of secondary polycythemias, dogs (n = 7) (median, 30.7 mU/mL) and cats (n = 2) had normal Epo concentrations. The median serum Epo concentration was significantly decreased (P < .05) in dogs with PV compared with dogs with secondary polycythemias. The median serum Epo concentrations in dogs (n = 13) and cats (n = 5) with anemias not due to chronic renal disease were significantly increased (P < .05) compared with normal dogs and cats. In cats with anemias due to chronic renal disease (n = 5) the median serum Epo concentration was not significantly different from normal cats. The measurement of the serum EPO concentration may be useful in assessment of anemia or polycythemia but the overlap of values with the normal range in all groups evaluated limit its diagnostic use.

Immunocytochemical demonstration of erythropoietin in hypoxic human hepatoma cultures

The possibility of demonstrating erythropoietin at the light microscopic level was examined in homogenous cultures of the erythropoietin-producing human hepatoma cell lines HepG2 and Hep3B. Immunoperoxidase staining was applied in combination with several mono- and polyclonal antibodies. Sufficiently strong colour responses were obtained with all three polyclonal antibodies and with one of three monoclonal antibodies raised against recombinant human erythropoietin. The staining intensity was increased in hypoxic versus nonhypoxic hepatoma cultures. Intracellular erythropoietin immunoreactivity was confirmed by Western blot analysis of HepG2 extracts. The effect of oxygen supply on erythropoietin gene expression was confirmed by competitive polymerase chain reaction of erythropoietin mRNA and by radioimmunoassay of secreted erythropoietin.

Effect of recombinant human erythropoietin after allogenic bone marrow transplantation

The hematologic effects of recombinant human erythropoietin after allogeneic bone marrow transplantation (BMT) were studied. Nineteen patients received 150 U/kg/day of C127 mouse-cell-derived recombinant human erythropoietin (rHu EPO) as a daily continuous intravenous infusion until hematocrit exceeded 35%. These data were compared with a treatment-matched historical control group of 43 patients. RHu EPO-treated patients recovered erythropoiesis more rapidly and became independent from erythrocyte transfusions after a median of 17 days, which was 7 days earlier than the control patients.

Erythropoietin in cardiac surgery

Erythropoietin is the primary growth factor for red blood cells. A glycoprotein hormone synthesized by the kidneys, erythropoietin serves to increase red blood cell production in response to tissue hypoxia. It exerts its effect by increasing the numbers of erythroid progenitor cells in the bone marrow, and by increasing the rate at which their development is accomplished. With the introduction of recombinant erythropoietin in 1987, an important pharmacological agent became available for the manipulation of erythropoiesis. While used primarily for the treatment of the anemia of renal failure, recombinant erythropoietin has also shown usefulness in treating other types of anemias in which the endogenous erythropoietin response is insufficient. Perioperative use of the drug grew as a natural extension of this, and erythropoietin has been applied to correct preoperative anemia, augment autologous blood donation, and improve postoperative red cell recovery. Analysis of these perioperative clinical studies reveals success in these areas, but it also reveals that closer attention to the physiology of the natural response, and to the pharmacology of the recombinant product, might significantly improve results. Such an improvement in efficacy is both desirable and necessary when use of the drug is viewed in the setting of today's changing health care environment. By optimizing dosing schedules and targeting the drug to those most at risk for red cell transfusion, recombinant erythropoietin will likely become an important tool in efforts to achieve the elusive goal of bloodless cardiac surgery.

Treatment of orthostatic hypotension with erythropoietin

BACKGROUND AND METHODS

Patients with orthostatic hypotension caused by autonomic neuropathy frequently have a decreased red-cell mass. This would be expected to compromise their effective circulating blood volume and aggravate the orthostatic hypotension. We studied the effect of increasing the red-cell mass with erythropoietin, given subcutaneously in a dose of 50 U per kilogram of body weight three times a week for 6 to 10 weeks to eight patients with orthostatic hypotension--four men, one teenage boy, and three women (age range, 17 to 68 years). Four patients had type I diabetes mellitus and autonomic neuropathy, three patients had pure autonomic failure, and one patient had sympathotonic orthostatic hypotension. Seven patients received fludrocortisone (0.1 or 0.2 mg per day) before, during, and after the trial of erythropoietin. The red-cell volume, plasma volume, and hemodynamic response to orthostatic stress were measured before and after therapy.

RESULTS

Erythropoietin increased the mean (+/- SD) hematocrit from 0.34 +/- 0.04 to 0.45 +/- 0.04 (P < 0.005) and increased the red-cell volume from 16.8 +/- 3.9 to 25.3 +/- 3.1 ml per kilogram (P < 0.005), but had no effect on plasma volume. The systolic blood pressure increased from 81 +/- 11 to 100 +/- 24 mm Hg (P < 0.01) and the diastolic blood pressure increased from 46 +/- 10 to 63 +/- 18 mm Hg (P < 0.01) while the patients were standing. The average systolic and diastolic blood pressure while the patients were supine did not increase significantly, although hypertension in the supine position developed in three patients. Orthostatic dizziness improved during treatment in six of the eight patients.

CONCLUSIONS

In patients with orthostatic hypotension, increasing the red-cell volume with erythropoietin elevates blood pressure while standing. Possible long-term adverse effects are not known.

Unreliability in immunoassays of erythropoietin: anomalous estimates with an assay kit

We report the finding of inappropriately high estimates of erythropoietin (Epo) in 11% of serum samples tested by one commercial assay kit. These estimates were not confirmed when the same samples were tested independently in four other systems for the immunoassay of Epo. As yet no explanation has been found to account for the anomalously high estimates.

Reduced erythropoietin secretion in senile anemia

To investigate the etiology of the age-related decrease in hemoglobin (Hb) concentration, we measured serum erythropoietin (EPO), serum iron, total iron binding capacity, and serum ferritin levels in 247 elderly subjects aged 60-99 years. EPO levels were determined by radioimmunoassay. An age-related increase in the serum EPO concentration (r = 0.220; P < 0.01) and a significant inverse relationship between EPO and Hb concentrations were found in normal elderly subjects without anemia (r = -0.302; P < 0.001), but not in 111 younger controls. Serum EPO levels were slightly higher in elderly subjects with pre-anemic iron deficiency than in the normal elderly subjects (P < 0.05). These results suggest that the EPO secretion is accelerated in the elderly even though the Hb remains above 12.0 g/dl, probably as a compensatory mechanism for peripheral tissue hypoxia. An inverse relationship between the EPO and Hb concentrations was found in the elderly subjects with iron deficiency anemia, but not in those with unexplained senile anemia. The changes of EPO levels were also assessed in 20 elderly subjects who had developed anemia when reviewed after 12 months. Serum EPO levels increased in relation to the decrease in Hb concentration in those with iron deficiency anemia, but not in those with unexplained senile anemia. Reduced EPO secretion thus seems to play a role in the progression of unexplained senile anemia, and recombinant human EPO may possibly be effective for treating this type of anemia by mobilizing excess iron.

Simple in vivo bioassay without radioisotopes for recombinant human erythropoietins

A simple in vivo bioassay suitable for routine testing of quality control of recombinant human erythropoietin (rHuEPO) analogues was developed. The assay took four days, normal mice were used and radioactive compounds were not needed. EPO activity was measured by the increased number of some part of reticulocytes which increased specifically and dose-dependently by the injection of rHuEPO. They were considered to be mostly immature reticulocytes and were counted as the residual particles from blood cells after treatment with a hemolysing reagent. These particles could be counted by conventional automated microcell counters. The assay procedure was simple and easy. The sensitivity, reliability and reproducibility of this method were acceptable for routine in vivo bioassay of rHuEPOs. This method was economical, and can be used instead of the existing bioassays for rHuEPOs.

Serum immunoreactive erythropoietin in patients with idiopathic aplastic and Fanconi's anaemias

In patients with idiopathic aplastic anaemia (n = 34) and Fanconi's anaemia (n = 8), sampled once or on several occasions, serum erythropoietin (Epo) increased with increasing severity of anaemia with apparently similar rates of increase in each group. However, after adjustment for Hb, log Epo values for the Fanconi's anaemics tended to be greater than those for the idiopathic aplastic anaemics (P < 0.01). Erythropoietin concentrations in serum samples from patients with Fanconi's and idiopathic aplastic anaemias tended to be greater than in samples from patients with anaemias from protein energy malnutrition, myelodysplasia and iron deficiency. The results suggest that there is no deficiency of erythropoietin in Fanconi's and idiopathic aplastic anaemias and that if exogenous erythropoietin is of any benefit it would need to be administered in doses large enough to induce a significant increase in log Epo. Results of the study illustrate the need to take account of the assumptions which underlie interpretation of the statistical analysis. Use of erythropoietin values in place of log Epo gives misleading conclusions demonstrable as invalid as the conditions for normality of distribution of the data and homogeneity of variances were not satisfied.

Regulation of iron absorption in iron loaded subjects with end stage renal disease: effects of treatment with recombinant human erythropoietin and reduction of iron stores

The effects on iron absorption of variation in erythroid activity, haemoglobin and iron stores were studied in six anaemic dialysis-dependent subjects in whom iron stores were increased from previous red cell transfusions. Gastrointestinal mucosal uptake and whole body retention of oral iron were measured at the beginning of the study, after starting treatment with recombinant erythropoietin (but before significant increase in haemoglobin), after partial correction of anaemia, after further reduction of iron stores by repeated phlebotomy, and when erythropoiesis decreased from the discontinuation of treatment with erythropoietin. Between successive measurements, valid comparisons were made in five subjects. Correction of anaemia decreased whole body retention of iron through decreased mucosal uptake (P = 0.032). Further reduction in iron stores through repeated phlebotomy whilst the increase in haemoglobin was maintained by treatment with erythropoietin, tended to increase whole body retention of iron through an increase in mucosal transfer (P = 0.010). With initial enhancement of erythropoiesis in anaemic iron-loaded subjects there was no change in any measured component of iron absorption. However, after correction of anaemia and reduction of iron stores, a decrease in erythropoiesis was associated with decreased whole body iron retention in all subjects through decreased mucosal transfer (P = 0.028). The data suggest that anaemia upregulates mucosal iron uptake, and that erythroid activity upregulates mucosal transfer but that this latter effect may be counter-balanced by iron overload which downregulates mucosal transfer.

Recombinant human erythropoietin in the treatment of infants with anaemia of prematurity

Recombinant human erythropoietin (rHuEPO) was administered subcutaneously three times a week to 18 infants with the anaemia of prematurity at doses of 75, 150, 300, or 600 units/kg per week for 4 weeks, starting at 3-4 weeks of postnatal age. A significant and dose-dependent increase in reticulocyte count was observed from a mean baseline value of 71 x 10(9)/l to 200 x 10(9)/l after 3 weeks of therapy, compared with a change from 69 to 97 x 10(9)/l in 66 historical controls. The haematocrit value remained unchanged during rHuEPO treatment, whereas it steadily declined until 9 weeks of postnatal age in the controls. These effects were accompanied by a marked reduction in serum iron concentration and transferrin saturation in patients receiving standard-dose iron supplements, but not in those given larger doses. Only 3 of 18 patients required a red blood cell transfusion. These infants were among the most anaemic at entry into the study and 2 of them were unable to complete rHuEPO therapy, while the third developed iron deficiency anaemia. These data indicate that rHuEPO with appropriate iron supplementation may accelerate the recovery from anaemia of prematurity. Larger scale placebo-controlled studies are now needed to confirm these findings and verify their impact on transfusion requirements of premature infants.

A comparison of the responses to recombinant human erythropoietin in normal and uremic subjects

The erythropoietic response to graded doses of recombinant human erythropoietin (epoetin alfa) was assessed in 24 hemodialysis patients by quantitative ferrokinetic studies, and measurement of the reticulocyte count and plasma levels of transferrin receptor protein. These responses were compared to those of 22 normal subjects. Epoetin alfa was given intravenously at 15, 50 or 150 U/kg every other day for four injections. Three patients with chronic renal failure were restudied after renal function was restored following renal transplantation. The results of these three different measurements of erythroid function showed that the acute response to recombinant human erythropoietin was similar in normal subjects and patients with renal failure. We conclude that chronic uremia does not alter the responsiveness to erythropoietin in vivo.

Serum erythropoietin levels in gynecologic cancer patients during cisplatin combination chemotherapy

To investigate the participation of erythropoietin (Epo) in anemias induced by cisplatin combined chemotherapy, serum Epo levels were measured by radioimmunoassay on a serial basis in eight patients with gynecologic cancer undergoing this chemotherapy. The data demonstrated that serum Epo levels, the mean level before chemotherapy being 20.1 +/- 6.6 mU/ml, were significantly elevated after the first course of the chemotherapy (52.1 +/- 32.2 mU/ml; P less than 0.05) when anemia was not evident. The serum Epo level continued to increase as the course of chemotherapy advanced, and furthermore, patients with normocytic anemia after a multiple course of this chemotherapy still showed high Epo levels (115.2 +/- 53.5 mU/ml) that were appropriate for given degrees of anemia. It is suggested that cisplatin combined chemotherapy caused the elevated serum Epo levels through an unknown mechanism other than anemia, and that in anemias induced by cisplatin, Epo deficiency is not evident.

Recombinant human erythropoietin is effective in correcting erythropoietin-deficient anaemia after allogeneic bone marrow transplantation

Two children affected by severe aplastic anaemia (SAA) underwent allogeneic bone marrow transplantation (BMT) using partially matched family donors. In both cases there was a successful engraftment of donor haemopoietic stem cells. However, after an initial erythropoietic recovery, 5 months following BMT both children became severely anaemic. Although multiple factors were responsible for anaemia, in both cases there was a markedly impaired erythropoietin response to anaemia, as indicated by the inappropriately low levels of serum erythropoietin (EPO). Treatment with recombinant human erythropoietin (rHuEPO) induced a sustained erythropoietic response with complete correction of anaemia. This pilot study suggests that rHuEPO can be effective in correcting long-lasting anaemia after marrow transplantation, characterized by inadequate erythropoietin production.