Pure red-cell aplasia and antierythropoietin antibodies in patients treated with recombinant erythropoietin

Recombinant human erythropoietin in oncology: current status and further developments

Anaemia effects up to 90% of cancer patients, with more than 60% requiring blood transfusion during or after treatment. With the advent of recombinant human erythropoietins (rHuEPO), an alternative to red blood cell transfusion has become available. So far, three drugs have been approved for the treatment of anaemia in patients with malignancies (epoetin alfa, epoetin beta and darbepoetin alfa). New concepts for the use of erythropoietin in cancer patients include 3- and 4-weekly dosing, as well as loading-dose concepts. Important factors helping to judge the impact of erythropoietin in cancer treatment include pharmacoeconomics and better predictive factors. Lately, the influence of erythropoietin therapy on survival in cancer patients has been discussed very intensively, because conflicting data have emerged. Studies aimed at correcting anaemia in cancer patients had indicated a possible survival advantage of those patients receiving erythropoietin. In contrast, two recent trials aimed at correction of haemoglobin levels beyond anaemia reported a poorer survival of patients receiving erythropoietin. This might grossly be attributed to a higher risk of thrombosis in these patients. The largest systematic review on the use of erythropoietin in cancer patients undergoing treatment indicates a suggestive but not significant survival advantage of erythropoietin-treated patients. In addition, very recent results of a Food and Drug Administration meeting on safety and survival of patients treated with erythropoietin are presented.

Development of a Transgenic Mouse Model Immune Tolerant for Human Interferon Beta

PURPOSE

Therapeutic proteins may induce antibodies that inhibit their efficacy or have other serious biological effects. There is a great need for strategies to predict whether a certain formulation will induce an immune response. In principle, conventional animals develop an immune response against all human proteins no matter how they are formulated, which restricts their use. The aim of this study was to develop a mouse model immune tolerant for human interferon beta (hIFNbeta).

METHODS

A transgenic mouse model immune tolerant for hIFNbeta was developed by making C57Bl/6 mice transgenic for the hIFNbeta gene. To evaluate the model, both wild-type and transgenic mice were immunized with recombinant human interferon beta 1a (rhIFNbeta-1a) and recombinant human interferon beta 1b (rhIFNbeta-1b). Serum antibodies against rhIFNbeta were detected by ELISA.

RESULTS

The genetically modified mice were shown to be immune tolerant for mammalian cell-derived rhIFNbeta-1a, which has a relative low immunogenicity in patients. However, Escherichia coli-derived rhIFNbeta-1b, known to have a relatively high immunogenicity in patients, was shown not only to be immunogenic in the wild-type mice but could also break the immune tolerance of the genetically modified mice.

CONCLUSIONS

This animal model offers the possibility to study the many factors influencing the immunogenicity of hIFNbeta and test new formulations before going into clinical trials. The model also provides the first evidence that the rhIFNbetas differ in the immunological mechanisms responsible for the development of antibodies.

Epoetin alfa for the treatment of combination therapy-induced hemolytic anemia in patients infected with hepatitis C virus

In the United States, about 2.7 million people are chronically infected with the hepatitis C virus, accounting for nearly 1.8% of the population. The current standard of therapy is a combination of pegylated interferon products and ribavirin. A common adverse effect associated with this therapy is anemia, which is frequently referred to as mixed anemia because of the synergistic contribution of the interferons and ribavirin. The effect of ribavirin on the development of anemia is considered greater than that of interferon. The current standard of practice for treating this adverse effect is reduction of the dosages of both drugs, at prespecified hemoglobin levels. However, recent findings underscore the importance of maintaining adequate dosages of interferon and ribavirin, which may be crucial in achieving an early virologic response and a sustained virologic response in treating patients with hepatitis C infection. Treatment with epoetin alfa for this mixed anemia significantly improved hemoglobin levels and quality of life, and enabled adequate dosages of ribavirin to be maintained. Future studies should address several issues: when to start epoetin alfa treatment, the duration of treatment, the drug's optimal dosage, its effects on end-of-treatment and sustained virologic response rates, and a cost analyses.

Antibody-mediated pure red cell aplasia due to epoetin alfa during antiviral therapy of chronic hepatitis C

Anemia frequently complicates the treatment of chronic hepatitis C with interferon and ribavirin (RVN), requiring dose reduction and jeopardizing sustained virologic response. Increasingly, epoetin alfa is used to prevent anemia in this setting. Below, we report the first case of pure red cell aplasia (PRCA) in a patient with chronic hepatitis C who received epoetin alfa (Procrit) to manage anti-viral treatment-induced anemia. Red blood cell transfusion-dependence developed 16 wk after the patient was started on peginterferon alfa-2b and RVN for chronic hepatitis C despite the simultaneous administration of epoetin alfa and subsequent discontinuation of the antiviral medications. Bone marrow biopsy was consistent with PRCA. High-titer erythropoietin antibodies, assayed by two methods, appeared shortly after epoetin alfa was administered, and were associated with a decline in serum erythropoietin to undetectable levels. Erythropoietin antibodies directed toward epoetin alfa were shown to cross react with darbepoetin alfa (Aranesp), and a neutralization assay confirmed that they inhibited cell growth in the presence of erythropoietin. Transfusion-dependence resolved approximately 16 wk after discontinuing epoetin alfa, and 6 wk after starting danazol. PRCA caused by the development of erythropoietin antibodies is a potentially life-threatening complication of administering epoetin alfa to prevent the anemia associated with antiviral therapy in patients with chronic hepatitis C.

Antibodies against Erythropoietin and Other Protein-Based Therapeutics: An Overview

Many factors influence the immunogenicity of protein-based therapeutics. At present, it is inconceivable to manufacture a biopharmaceutical without the risk of this adverse effect. Thus, the detection and characterization of antibodies against protein-based therapeutics is a significant task. Only clinical studies and careful monitoring of the market can be used to conclusively demonstrate rates of immunogenicity in humans for protein therapeutics. Fully validated, reliable, and robust in vitro assays, in combination with sensitive bioassays, should be used to address these topics.

Epoetin-Induced Autoimmune Pure Red Cell Aplasia

During the first 10 yr of therapy with recombinant human erythropoietin ([EPO]), only three cases of antibody-associated pure red cell aplasia have been described in patients who were treated with EPO, whereas several millions of patients have received this treatment. Thus, the possibility for epoetin to induce the formation of anti-EPO antibodies was considered extremely low. However, since 1998, a significant increase in the number of cases of EPO-induced pure red cell aplasia has been found in patients with chronic kidney disease with a peak in 2001 and 2002. The incidence rate seems now to be back to the baseline level. The change in formulation of epoetin a sold outside the United States seems to be the cause of these antibodies.

Kinetics of development and characteristics of antibodies induced in cancer patients against yeast expressed rDNA derived granulocyte macrophage colony stimulating factor (GM-CSF)

We have determined the presence and kinetics of granulocyte macrophage colony stimulating factor (GM-CSF) antibodies induced after repeated administration of a yeast expressed GM-CSF product in prostate cancer patients with minimal recurrent disease using a panel of assays for detection and characterization of antibodies. Results showed that all 15 prostate cancer patients treated with GM-CSF developed GM-CSF reactive antibodies during the course of therapy. Most patients (87%) developed GM-CSF reactive antibodies within 3 months while in other patients (13%), these antibodies were induced after additional cycles of GM-CSF treatment. For most patients, the timing of occurrence of these antibodies was the same regardless of whether the ELISA or surface plasmon resonance (SPR) assays were used for detection. However, in two patients, the recognition of GM-CSF reactive antibodies by SPR assays preceded their detection by ELISA. A significant number of patients (n=9, 60%) developed GM-CSF antibodies which neutralized the biological activity of GM-CSF in vitro in a cell-line based bioassay. These antibodies also recognized GM-CSF protein from different expression systems including the non-glycosylated protein from E. coli indicating that the antibody response is directed towards the amino acid backbone of the protein. A significant effect of GM-CSF antibodies on PSA modulation was not observed in this small cohort of patients despite an alteration in PSA levels in some treated patients. The study design used here did not allow conclusions regarding the relationship between neutralizing antibodies and the PSA levels which were used as a marker for clinical outcome. Implementation of a clinical strategy which permits monitoring for antibody development and for levels of a relevant pre-determined clinical marker at appropriate time-points is necessary for assessing the impact of antibody development on the therapeutic efficacy of the protein.

Antibody-mediated side effects of recombinant proteins

This brief review is focused on the unwanted clinical effects mediated by antibodies against genetechnologically produced drugs. While many antibodies binding biotech-drugs may not be harmful, others may have deleterious clinical effects exposing patients to high risks. These antibodies can cause either lack of efficacy or hypersensitivity reactions. Examples for antibody-mediated lack of efficacy are inhibitors in hemophiliacs treated with Factor VIII, evidence of decreasing therapeutic efficacy of beta-interferons in MS-patients and pure red cell aplasia (PRCA) in patients with chronic renal failure treated with erythropoietin. Antibody-mediated hypersensitivity reactions have to be expected with all recombinant proteins. The mechanisms and causes of antibody production against biotech-drugs in patients are discussed.

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

Neutralizing antibodies to erythropoietin (EPO) can cause a loss of response to recombinant human EPO (rHuEPO) and lead to rare cases of sudden, unexplained, severe anemia in chronic renal failure patients treated with rHuEPO. An assay for neutralizing anti-EPO antibodies has been validated that is based on the inhibition of proliferation of human UT-7/EPO cells, an immortalized cell line, by neutralizing antibodies in serum test samples using 3H-thymidine as a marker for proliferation. The dependence of the human cell line on EPO for growth and proliferation in a concentration-dependent manner enabled the validation of a rHuEPO standard curve for cell proliferation that can be used to determine the presence of neutralizing anti-EPO antibodies in serum samples. Proliferation of the cells increases with increasing concentrations of EPO, forming an S-shaped standard curve, which is fit with a 4-parameter logistic model, between 2.5 and 50 mU/mL rHuEPO, with a percent coefficient of variation (% CV) from 8.7% to 22.1% and a % accuracy of 103.5% to 109.5%. Anti-EPO antibodies and serum with anti-EPO antibodies neutralize UT-7/EPO proliferation by 10 mU/mL rHuEPO in a concentration- or dilution-dependent manner with < or = 25% CV. Percent neutralization is calculated by determining the amount of EPO recovered from the original 10 mU/mL added using the formula [((10-concentration recovered)/10)x100%]. Stem cell factor (SCF) stimulated cell proliferation, but not as effectively as rHuEPO. Antibodies to SCF were not able to inhibit the proliferative response induced by EPO and vice versa, confirming the specificity of the assay for antibodies to EPO. High EPO levels can impact both the radioimmunoprecipitation and neutralization assays to produce a false negative result. However, the impact can be mitigated by the large dilutions used in the neutralization assay.

Potential for protection and repair following injury to the developing brain: a role for erythropoietin?

Perinatal brain injury is a major contributor to perinatal morbidity and mortality, and a considerable number of these children will develop long term neurodevelopmental disabilities. Despite the severe clinical and socio-economic significance and the advances in neonatal care over the past twenty years, no therapy yet exists that effectively prevents or ameliorates detrimental neurodevelopmental effects in cases of perinatal/neonatal brain injury. Our objective is to review recent evidence in relation to the pervading hypothesis for targeting time-dependent molecular and cellular repair mechanisms in the developing brain. In addition we review several potential neuroprotective strategies specific to the developing nervous system, with a focus on erythropoietin (Epo) because of its potential role in protection as well as repair.

Rationally engineered therapeutic proteins with reduced immunogenicity

Chronic administration of protein therapeutics may elicit unacceptable immune responses to the specific protein. Our hypothesis is that the immunogenicity of protein drugs can be ascribed to a few immunodominant helper T lymphocyte (HTL) epitopes, and that reducing the MHC binding affinity of these HTL epitopes contained within these proteins can generate drugs with lower immunogenicity. To test this hypothesis, we studied the protein therapeutic erythropoietin (Epo). Two regions within Epo, designated Epo 91-120 and Epo 126-155, contained HTL epitopes that were recognized by individuals with numerous HLA-DR types, a property common to immunodominant HTL epitopes. We then engineered analog epitopes with reduced HLA binding affinity. These analog epitopes were associated with reduced in vitro immunogenicity. Two modified forms of Epo containing these substitutions were shown to be bioactive and nonimmunogenic in vitro. These findings support our hypothesis and demonstrate that immunogenicity of protein drugs can be reduced in a systematic and predictable manner.

Recombinant Human Erythropoietin and Overall Survival in Cancer Patients: Results of a Comprehensive Meta-analysis

BACKGROUND

Anemia associated with cancer and cancer therapy is an important clinical and economic factor in the treatment of malignant diseases.

METHODS

We conducted a systematic literature review to assess the efficacy of erythropoietin to prevent or treat anemia in cancer patients with regard to red blood cell transfusions, hematologic response, adverse events, and overall survival. We searched the Cochrane Library, Medline, EMBASE, and other databases for relevant articles published from January 1985 to December 2001. We included all randomized controlled trials that compared the use of recombinant human erythropoietin (plus transfusion, if needed) with no erythropoietin treatment (plus transfusion, if needed). Relative risks (RRs) and 95% confidence intervals (CIs) were calculated under a fixed-effects model. Clinical and statistical heterogeneity were examined with sensitivity analyses and meta-regression. Statistical tests for effect estimates were two-sided.

RESULTS

We identified 27 trials involving 3287 adult patients. Patients treated with erythropoietin had a lower relative risk of having a blood transfusion than untreated patients (RR = 0.67, 95% CI = 0.62 to 0.73). Erythropoietin-treated patients with baseline hemoglobin levels lower than 10 g/dL were more likely to have a hematologic response than untreated patients (RR = 3.60, 95% CI = 3.07 to 4.23). The relative risk for thromboembolic complications after erythropoietin treatment was not statistically significantly increased (RR = 1.58, 95% CI = 0.94 to 2.66) compared with that of untreated patients. There is suggestive but inconclusive evidence that erythropoietin may improve overall survival (adjusted data: hazard ratio [HR] = 0.81, 95% CI = 0.67 to 0.99; unadjusted data: HR = 0.84, 95% CI = 0.69 to 1.02).

CONCLUSIONS

Erythropoietin treatment may reduce the risk for blood transfusions and improve hematologic response in cancer patients. However, our favorable survival outcome is in contrast to two large (N = 351 and 939) recently published randomized controlled trials in which erythropoietin-treated patients had statistically significantly worse survival than untreated patients. Possible reasons for the disparity with our results include differences in study population and design, higher target hemoglobin levels and higher risk of thromboembolic complications, and concerns that erythropoietin may stimulate tumor growth.

Erythropoietin-resistant anaemia in a predialysis patient with Klinefelter syndrome. Case Report

A diabetic predialysis patient who had significantly reduced sensitivity to erythropoietin therapy was admitted to Tsukuba University Hospital. Many factors that might have been the cause of the erythropoietin resistance were examined, and a diagnosis of refractory anaemia was made based on a bone marrow aspiration biopsy. A cytogenetic abnormality (47, XXY) was also detected in the bone marrow biopsy specimen, and hence the patient was also diagnosed with Klinefelter syndrome. It was suspected that the sex chromosome abnormality influenced glucose intolerance, renal insufficiency, and erythropoietin resistance due to myelodysplastic changes in the bone marrow.

Protein drug stability: a formulation challenge

The increasing use of recombinantly expressed therapeutic proteins in the pharmaceutical industry has highlighted issues such as their stability during long-term storage and means of efficacious delivery that avoid adverse immunogenic side effects. Controlled chemical modifications, such as substitutions, acylation and PEGylation, have fulfilled some but not all of their promises, while hydrogels and lipid-based formulations could well be developed into generic delivery systems. Strategies to curb the aggregation and misfolding of proteins during storage are likely to benefit from the recent surge of interest in protein fibrillation. This might in turn lead to generally accepted guidelines and tests to avoid unforeseen adverse effects in drug delivery.

The new rHuEPO alpha (epotin) in the management of anemia of end-stage renal disease in patients on maintenance hemodialysis

Recombinant human erythropoietin has proved to be effective to treat anemia of end-stage renal disease (ESRD). The aim of this study was to assess the efficacy and safety profile of Epotin, a rHuEPO produced in the Middle East. One hundred thirty patients with Hct </= 27%; Hb </= 9 g/dL maintained on hemodialysis thrice weekly from 19centers in eight countries in the Middle East were recruited into this 13-week study. Depleted iron stores (TSTAT <20% and/or Serum ferritin < 100 microg/dL) were replenished prior to initiation of Epotin therapy, which was delivered intravenously in a dose of 150 U/kg body weight/week in three equal doses postdialysis and titrated according to hemoglobin (Hb) and hematocrit (Hct) response. Efficacy was assessed in terms of Hb/Hct response. Epotin raised the mean Hb level from 7.7 (+/- 1.2) g/dL to 12.0 (+/- 1.7) g/dL and Hct from 22.7 (+/- 4.1) % to 36.2 (+/- 5.7) % by week 13. The increase started to show significance at week 3. Targeting an absolute increase in Hb of 2.5 g/dL (Hct 7.5%) over a 13-week period, the success rate was of <85.71%. Segregating patients into subgroups of men and women and chronic ESRD versus recent ESRD failed to reveal a significant differences in either the severity of the anemia or the response to Epotin. Side effects were similar to other erythropoietins; no dropouts were reported. In conclusion, Epotin is effective to treat anemia in patients on maintenance hemodialysis with an acceptable safety profile. No difference in response was observed between men and women, nor between patients with different levels of chronicity of ESRD.

Characterizing biological products and assessing comparability following manufacturing changes

Changes in production methods of a biological product may necessitate an assessment of comparability to ensure that these manufacturing changes have not affected the safety, identity, purity, or efficacy of the product. Depending on the nature of the protein or the change, this assessment consists of a hierarchy of sequential tests in analytical testing, preclinical animal studies and clinical studies. Differences in analytical test results between pre- and post-change products may require functional testing to establish the biological or clinical significance of the observed difference. An underlying principle of comparability is that under certain conditions, protein products may be considered comparable on the basis of analytical testing results alone. However, the ability to compare biological materials is solely dependent on the tests used, since no single analytical method is able to compare every aspect of protein structure or function. The advantages and disadvantages of any given method depends on the protein property being characterized.

Pharmacotherapy of chemotherapy-induced anaemia

Anaemia in cancer patients is multifactorial. Anaemia of chronic disease due to the effects of cancer, as well as side effects of cancer treatment, are important factors. The impact of anaemia on the quality of life and social function of cancer patients has recently become more acknowledged. The traditional treatment for chemotherapy-induced anaemia (CIA) has been the use of red blood cell transfusions, with only short-lived effects and all their inherent risks. The finding of deficiency in erythropoietin, the endogenous hormone responsible for the production and maintenance of red blood cells in these patients, was the basis for the therapeutic development of erythropoietic proteins. With the introduction of epoetins (recombinant forms of human erythropoietin) in oncology and more recently, the novel long-acting darbepoetin alpha, physicians gained new pharmacotherapeutic approaches to treat CIA. Several forms of erythropoietic proteins are available in various regions of the world. Their characteristics, clinical evidence for use, guidelines for clinical administration and their safety are described in this review.

Treatments for stroke

Stroke is the third leading cause of death and the leading cause of disability in developed countries, yet remains a poorly treated condition. Treatments for stroke can be aimed at acutely improving blood flow or protecting brain tissue against ischaemia, enhancing stroke recovery or reducing the risk of stroke recurrence. This paper reviews each of these approaches, particularly focusing on mechanisms for which there are agents in clinical trials. There are a number of appealing neuroprotective agents in Phase II and III clinical trials. However, the majority of acute treatments are likely to suffer from a narrow therapeutic time window and hence limited patient access. Combinations of acute approaches are likely to offer the greatest benefit, but present challenges in development. Promotion of recovery following stroke offers enormous potential for successful therapeutic intervention. Excitingly, new developments in preclinical research have identified possible ways in which this may be achieved.

The 'precautionary principle' as a guide for future drug development

During the last decade, the 'precautionary principle' health has gained importance. It is an approach to manage uncertain risks and to prevent any damage to the environment or human. A key element is to take action, even if some cause and effect relationships are not fully established scientifically. Although there are also critics of this principle, it is meanwhile, also increasingly implemented in medicine. An important subject is medicinal products of human or animal origin. Manifold official precaution-guided regulations have been stated to improve their safety, particularly to avoid any infection by viruses and pathogens causing transmissible spongiform encephalopathies. In addition to numerous regulations and decisions, it is generally recommended to substitute animal and human-derived products with adequate alternatives wherever possible. This is a great challenge for research and drug development. One option is recombinant proteins, which however, are not generally free of any risk of contamination. Therefore, the best strategy might be the development of synthetic, specifically acting drugs. The most widely used medicinal product of animal origin at present is heparin. Although there has been no indication of any viral contamination, many other reasons suggest its substitution by alternative antithrombotics. These actually promoted the research on new anticoagulants. With the approval of fondaparinux, the first synthetic, selective factor Xa, a first alternative to the porcine-derived heparin has become available. In addition, other synthetic antithrombotics are currently in clinical development. In principle, it is thus possible that the prophylaxis and therapy of thromboembolic diseases will become completely independent of animal-derived drugs, which would be in line with the precautionary principle.

Erythropoietin on a tightrope: balancing neuronal and vascular protection between intrinsic and extrinsic pathways

Enthusiasm for erythropoietin (EPO) as a broad cytoprotective agent continues to increase at an almost exponential rate. The premise that EPO was required only for erythropoiesis was eventually shed by recent work demonstrating the existence of EPO and its receptor in other organs and tissues outside of the liver and the kidney, such as the brain and heart. As a result, EPO has been identified as a possible candidate in the formulation of therapeutic strategies for both cardiac and nervous system diseases. EPO has been shown to mediate an array of vital cellular functions that involve progenitor stem cell development, cellular protection, angiogenesis, DNA repair, and cellular longevity. An important requirement to achieve the goal of preventing or even reducing cellular injury by any cytoprotective agent is the ability to uncover the cellular pathways that ultimately drive a cell to its demise. We present for consideration several critical cellular pathways modulated by EPO that involve Janus kinase 2 (Jak2), the serine-threonine kinase Akt, forkhead transcription factors, glycogen synthase kinase-3beta (GSK-3beta), cellular calcium, protein kinase C, caspases, as well as the control of inflammatory microglial activation. As we continue to gain new insight into these pathways, EPO should emerge as a critical agent for the development, maturation, and survival of cells throughout the body.

[Treatment of anemia and bone metastasis in metastatic non-small-cell lung cancer. A French survey]

Use of erythropoietin (EPO) for chemotherapy-induced anemia and biphosphonates (BP) for bone metastasis has increased steadily. However, there are no guidelines on their use in many situations such as non small cell lung carcinoma (NSCLC), which frequently alters quality of life markedly. Therefore, a multicentric survey was designed to assess the treatment of anemia and bone metastasis in chemotherapy-treated patients with non-small-cell lung carcinoma. Nine representative centers of the oncology working party of the French respiratory society (Groupe d'Oncologie de la Société de Pneumologie de Langue Française) participated. Inclusion criteria were stage IV NSCLC and at least one course of chemotherapy in the last 3 months. A total of 148 and 50 patients (pts) were included in the anemia and bone metastasis surveys, respectively. Anemia was present in 60.8% of patients, and was not treated in 75%; 15 patients received EPO (10.1%). Independent predictors of EPO use were presence of anemia-related symptoms, hemoglobin level, age and center: the rate of prescription in patients with anemia varied from 13 to 73% between centers. BP were administered in 38% of patients with bone metastasis. Independent predictors of BP use were calcium serum level, pain, and center with a rate of prescription ranging from 0 to 80% between centers. This study reveals that, in France, most patients with anemia are not treated, EPO being seldom prescribed. The use of both EPO and BP is highly variable between centers. Guidelines on the use of these supportive treatments could help improve the care for lung cancer patients receiving chemotherapy.

When biotech proteins go off-patent

The patents of the first generation of biopharmaceuticals derived from recombinant DNA such as interferons, growth hormone and epoietins are expiring, opening up the possibility for competitors to introduce biosimilar products. The concept of generics that applies to classical drugs and allows market admission on limited documentation cannot be extrapolated to these "off-patent biologics". Physicochemical characterization, bioassays and animals studies do not predict completely the efficacy and safety of therapeutic proteins. Clinical studies will nearly always be necessary to obtain marketing authorization for off-patent biologics. Immunogenicity is considered to be the main problem with therapeutic proteins. The recent upsurge of pure red cell aplasia (PRCA), a severe form of anemia associated with the use of epoietin-alpha, highlights both the unpredictability and the severe consequences of immunogenicity. A risk-based approach can be used to evaluate the potential induction of antibodies by off-patent biologics.

Expression, bioactivity, and clinical assessment of recombinant feline erythropoietin

OBJECTIVE

To determine the activity of recombinant feline erythropoietin (rfEPO) in murine bioassays and evaluate its efficacy and safety in cats with erythropoietin-dependent nonregenerative anemia.

ANIMALS

26 cats (group 1, 19 cats with anemia attributed to chronic kidney disease [CKD]; group 2, 7 cats with CKD and recombinant human erythropoietin [rhEPO]-induced red cell aplasia [RCA]).

PROCEDURE

The rfEPO was synthesized by use of Chinese hamster ovary (CHO) cells transfected with feline erythropoietin complementary DNA. Preclinical assessments of rfEPO included an erythroid cell proliferation assay and measurements of reticulocytosis in Balb/C mice. Clinical assessments of cats included hematologic, biochemical, and clinical examinations during 12 (group 1) or 6 (group 2) months of rfEPO treatment.

RESULTS

Biological activity of rfEPO was broadly equivalent to rhEPO in preclinical murine bioassays. Median Hct and absolute reticulocyte count in cats increased significantly during the first 3 weeks of rfEPO treatment, and median Hct generally could be maintained within a target range of 30% to 40% with periodic adjustments of rfEPO doses. Unexpectedly, 5 cats in group 1 and 3 cats in group 2 that initially responded to rfEPO treatment again developed anemia that was refractory to additional rfEPO treatments, even at higher doses.

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment with rfEPO can reestablish active erythropoiesis in most cats with CKD, even those with anemia attributable to rhEPO-induced RCA. Unfortunately, development of RCA during treatment with CHO cell-derived recombinant erythropoietin proteins was not eliminated as a serious safety concern, even for this feline-specific preparation.

Projecting future drug expenditures—2005

PURPOSE

Drug expenditure trends in 2003 and 2004 and projected drug expenditures for 2005 are discussed.

SUMMARY

Various factors are likely to affect drug costs, including drug prices, drugs in development, and generic drugs. In 2003 there was a continued moderation of the increase in drug expenditures. Drug expenditures increased by 11.4% from 2002 to 2003. Through the first nine months of 2004, expenditures increased by only 8.7% compared with 2003. This moderation can be attributed to many factors, particularly patent expirations, prescription-to-nonprescription conversions and a continued slowdown in new drug approvals. Higher cost sharing for consumers and continued weaknesses in several sectors of the U.S. economy affecting employment levels and insurance coverage also contributed to this smaller increase in drug utilization. It is expected that 2005 drug expenditure growth will out-pace the growth in overall health care expenditures and growth in the economy.

CONCLUSION

In 2005, there should be a 10-12% increase in drug expenditures in outpatient settings, a 12-15% increase in clinics, and a 6-9% increase in hospitals.

Both proteasomes and lysosomes degrade the activated erythropoietin receptor

Activation of the erythropoietin receptor (EpoR) after Epo binding is very transient because of the rapid activation of strong down-regulation mechanisms that quickly decrease Epo sensitivity of the cells. Among these down-regulation mechanisms, receptor internalization and degradation are probably the most efficient. Here, we show that the Epo receptor was rapidly ubiquitinated after ligand stimulation and that the C-terminal part of the Epo receptor was degraded by the proteasomes. Both ubiquitination and receptor degradation by the proteasomes occurred at the cell surface and required Janus kinase 2 (Jak2) activation. Moreover, Epo-EpoR complexes were rapidly internalized and targeted to the lysosomes for degradation. Neither Jak2 nor proteasome activities were required for internalization. In contrast, Jak2 activation was necessary for lysosome targeting of the Epo-EpoR complexes. Blocking Jak2 with the tyrphostin AG490 led to some recycling of internalized Epo-Epo receptor complexes to the cell surface. Thus, activated Epo receptors appear to be quickly degraded after ubiquitination by 2 proteolytic systems that proceed successively: the proteasomes remove part of the intracellular domain at the cell surface, and the lysosomes degrade the remaining part of the receptor-hormone complex. The efficiency of these processes probably explains the short duration of intracellular signaling activated by Epo.

A cross-sectional immunosurveillance study of anti-EPO antibody levels in CRF patients receiving epoetin alfa in 5 Ontario Renal Centers

BACKGROUND

Epoetin alfa (Eprex*; Johnson & Johnson, Manati, PR) has been used successfully to correct the anemia of chronic renal failure for more than 12 years. Anti-erythropoietin (anti-EPO) antibodies have been reported in a small number of patients, resulting in a blood disorder, pure red cell aplasia (PRCA). To evaluate the utility of a large-scale anti-EPO antibody screening program in patients with chronic kidney disease (CKD) administered epoetin alfa, a study involving 5 large renal centers in southern Ontario, Canada, was conducted.

METHODS

More than 1,500 hemodialysis, peritoneal dialysis, and predialysis patients were screened for the prevalence of anti-EPO antibodies by means of a radioimmunoprecipitation (RIP) assay. Serum samples were drawn and shipped to PPD Development (Richmond, VA) for the immunoprecipitation assay. Serum EPO levels also were measured. All samples that tested positive or borderline for antibodies were sent to MDS Pharma Services (Montreal, Canada) for the neutralization assay.

RESULTS

Of 1,531 samples tested, 1 patient tested low-positive and 3 borderline results were detected by means of RIP. PRCA previously was diagnosed in the patient with the low-positive antibody level; the patient was treated with cyclosporine and currently is being administered epoetin alfa with good response. The 3 patients with borderline antibody results manifested no clinical signs of PRCA. Neutralization assays performed on all 4 serum samples were negative for anti-EPO antibodies.

CONCLUSION

Results from this surveillance study show that the prevalence of antibody to EPO in patients with CKD administered epoetin alfa in 5 Canadian renal centers is low, and the value of a large-scale antibody screening program for PRCA cannot be justified.

Recommendations on haematological criteria for the diagnosis of epoetin-induced pure red cell aplasia

Pure red cell aplasia (PRCA) is a rare condition characterised by an arrest in red blood cell production, which may be congenital or acquired. Recombinant human erythropoietin (epoetin) was introduced in 1989 for the treatment of anaemia of chronic kidney disease patients and has maintained an excellent therapeutic and safety record while treating hundreds of thousands of patients. A very rare, but serious adverse event associated with epoetin administration is a condition in which patients develop neutralising anti-erythropoietin antibodies and, consequently, PRCA. This condition is referred to as epoetin-induced PRCA (epo-PRCA). Since it is a rare condition, many haematologists and nephrologists around the world see the condition infrequently and may be uncertain about the diagnosis. For this reason, an ad hoc international working group of expert haematologists and nephrologists met together to derive new recommendations for the haematological diagnosis of epo-PRCA. These recommendations, which represent the consensus opinions of the working group, address haematological approaches to monitor and investigate suspected epo-PRCA and should help physicians differentiate between PRCA and other bone marrow diseases, as well as, between PRCA and epo-PRCA.

Pure red-cell aplasia caused by the antibody to recombinant erythropoietin, epoetin-beta, in a Japanese patient with chronic renal failure

A 68-year-old male with chronic renal failure and anemia received recombinant human erythropoietin (rHuEPO), epoetin beta, for approximately 1 year. Although the agent was initially effective for improving anemia, anemia refractory to EPO administration appeared and then worsened later, and pure red-cell aplasia (PRCA) was diagnosed. Anti-EPO antibody was detected by radioimmunoprecipitation (RIP) assay in the patient's serum. The antibody inhibited the proliferation of EPO-dependent cell line in a dose-dependent manner neutralizing EPO activity. The antibody also reacted with the other epoetin alfa products. The antibody did not recognize the carbohydrate moieties or denatured epoetin beta. The result suggested that the antibody recognized the conformational epitope of epoetin beta peptide molecule. Withdrawal of EPO and administration of cyclosporine decreased the titers of antibody; however, erythroid progenitor has not yet regenerated although the requirement for red blood cell transfusion is decreasing.

Darbepoetin alpha for the treatment of anaemia in low-intermediate risk myelodysplastic syndromes

Thirty-seven anaemic subjects with low-to-intermediate risk myelodysplastic syndrome (MDS) received the highly glycosylated, long-acting erythropoiesis-stimulating molecule darbepoetin-alpha (DPO) at the single, weekly dose of 150 microg s.c. for at least 12 weeks. Fifteen patients (40.5%) achieved an erythroid response (13 major and two minor improvements, respectively, according to International Working Group criteria). Such results are currently maintained after 7-22 months in 13 of the responders, one of whom required iron substitutive therapy during the treatment. One patient relapsed after 4 months. Another responder died after 5 months because of causes unrelated to the treatment. No relevant side-effects were recorded. At multivariate analysis, significant predictive factors of response were baseline serum levels of endogenous erythropoietin <100 IU/l, absent or limited transfusional needs, no excess of blasts and hypoplastic bone marrow. This study suggests that DPO, at the dose and schedule used, can be safely given in low-intermediate risk MDS and may be effective in a significant proportion of these patients.

Interleukin-7 improves reconstitution of antiviral CD4 T cells

We evaluated whether long-term (2 months) administration of interleukin-7 (IL7) hastens immune recovery in baboons rendered severely lymphopenic by total body irradiation and antithymocyte globulin (ATG). Four baboons were treated with recombinant baboon IL7 and three baboons with placebo. Median CD4 T cell count at the end of IL7/placebo treatment was higher in the IL7-treated animals (2262 vs. 618/microl, P = 0.03). This appeared to be a result of peripheral expansion rather than de novo generation. Median cytomegalovirus (CMV)-specific IFNgamma-producing CD4 T cell count at the end of IL7/placebo treatment was higher in the IL7-treated animals (122 vs. 1/microl, P = 0.03). All animals were pretransplant cytomegalovirus-seropositive. One animal died at the end of IL7 treatment; necropsy showed extensive T cell infiltration of kidneys and lungs. In conclusion, IL7 stimulates the expansion of CD4 T cells, including functional antiviral cells. Clinical risk-benefit ratio needs to be evaluated.

Preclinical safety testing of biotechnology-derived pharmaceuticals: understanding the issues and addressing the challenges

The unique and complex nature of biotechnology-derived pharmaceuticals has meant that it is often not possible to follow the conventional safety testing programs used for chemicals, and hence they are evaluated on a case-by-case basis. Nonclinical safety testing programs must be rationally designed with a strong scientific understanding of the product, including its method of manufacture, purity, sequence, structure, species specificity, pharmacological and immunological effects, and intended clinical use. This knowledge, coupled with a firm understanding of the regulatory requirements for particular product types, will ensure that the most sensitive and regulatory-compliant test systems are used to optimize the chances of gaining regulatory approval for clinical testing or marketing authorization in the shortest possible time frame.

Development and validation of a cell-based bioassay for the detection of neutralizing antibodies against recombinant human erythropoietin in clinical studies

An in vitro cell-based bioassay capable of detecting neutralizing antibodies (NAb) to recombinant human erythropoietin (rHuEPO) in clinical samples was developed and validated. The bioassay uses the IL-3-dependent murine 32D cell line transfected with human EPO receptors (EPOR). This cell line responds to rHuEPO with proliferation measurable by [methyl-3H] thymidine incorporation into the cellular DNA. The reduction of rHuEPO-induced cell proliferation response indicates the possible presence of anti-rHuEPO NAb. In addition, a specificity assay using murine IL-3 (mIL-3) induced proliferation of the same cell line was developed and validated. The specificity assay allowed testing of samples that inhibited the biologic activity of rHuEPO to evaluate whether the inhibition was specific and not attributable to cytotoxicity of the serum sample. Both assays are conducted in a 5% human serum matrix in 96-well microtiter plates. The Guidelines of the International Conference on Harmonization (ICH) were followed for the validation of different assay parameters including analytical recovery, precision, sensitivity, specificity, selectivity, and robustness. The anti-rHuEPO NAb assay is capable of detecting concentrations of NAb equivalent to 500 ng/ml of the positive control antibody in undiluted human serum. The anti-rHuEPO NAb assay yielded consistent results with cells cultured for up to 30 days. The positive control antibody maintained its ability to inhibit the biologic activity of rHuEPO upon freezing and thawing. The presence of free rHuEPO in serum samples interfered with the detection of the antibody. The validated assay was sensitive, specific and robust and was successfully used to monitor NAb development in patients.

2004 Japanese Society for Dialysis Therapy Guidelines for Renal Anemia in Chronic Hemodialysis Patients

The guideline committee of Japanese Society for Dialysis Therapy (JSDT), chaired by Professor F. Gejyo of Niigata University, now publishes an original Japanese guideline entitled 'Guidelines for Renal Anemia in Chronic Hemodialysis Patients'. It includes the re-evaluation of the usage of recombinant human erythropoietin (rHuEPO) with the medical and economical arguments regarding the prognosis and the quality of life of Japanese hemodialysis patients. This guideline consists of 7 sections. The first section comprises the general definition and the differential diagnosis of anemia. The hemoglobin (Hb) level of the Japanese population seemed to be low when compared with that of the European and American populations. The second section describes the target Hb level in hemodialysis patients. Multivariate analysis of the data that were collected from dialysis institutions throughout the country showed that an Hb level of 10-11 g/dL (Ht level 30-33%) at the first dialysis session in a week is the ideal range for chronic hemodialysis patients in terms of the 3-5 year survival rate. The supine position at blood sampling and the sampling timing at the first dialysis session in a week might affect the lower setting of target Hb hematocrit (Ht), compared to that of European and American guidelines. However, we particularly recommended that an Hb level of 11-12 g/dL (Ht level from 33 to 36%) at the first dialysis session in a week is desirable in relatively young patients. In the third section, the markers of iron deficiency are discussed. The Transferin saturation test (TSAT) and serum ferritin were emphasized as the standard markers. The routes of administration of rHuEPO and its dosages are written in the fourth section. The subcutaneous route was associated with the occurrence of secondary red cell aplasia due to anti-rHuEPO antibodies; however, secondary red cell aplasia was seldom observed in the venous injection. From this fact we recommend venous injection for chronic hemodialysis patients. We advocate an initial dosage of 1500 U three times per week. The fifth section deals with the factors refractory to treatment with rHuEPO. If the patient shows an inadequate response to the usage of 9000 U per week, this condition defines the inadequate response to rHuEPO in Japan. Blood transfusion must be avoided where possible. The reasons for this and the adverse effects are interpreted in section six. In the final section, the adverse effects of rHuEPO are listed. Among them, hypertension, thrombotic events and secondary red cell aplasia were emphasized as the major complications.

[Erythropoietin treatment in critically ill children]

OBJECTIVE

To analyze whether erythropoietin treatment increases hemoglobin and decreases transfusion requirements in critically ill children.

PATIENTS AND METHODS

We performed an observational, prospective study of 23 critically ill children aged between 1 month and 6 years. Recombinant human eritropoietin (rHuEPO) was administered at a dosage of 150-750 U/kg/week over 3 days. Hemogram, reticulocyte, iron metabolism, serum ferritin and transferrin were measured before treatment started and weekly thereafter.

RESULTS

After erythropoietin treatment, hematocrit, hemoglobin and red blood cells progressively increased, with a maximal response in the sixth week. At the end of treatment, hemoglobin increased 1.68 g/dl, hematocrit by 5 % and erythrocytes 600,000/ml/mm3. Transfusion requirements decreased from 59 transfusions at baseline to 12 in the first week of treatment and none from the sixth week. No treatment-related adverse effects were observed.

CONCLUSION

Erythropoietin can be an effective treatment for anemia in some critically ill children, decreasing the number of transfusions and increasing hemoglobin.

Prolonged course of pure red cell aplasia after erythropoietin therapy

Pure red cell aplasia (PRCA) caused by neutralising anti-erythropoietin antibodies is a very rare disease. Since 1998, an increased incidence of PRCA in patients with kidney failure following treatment with recombinant human erythropoietin (rhEpo) has been reported, mostly in Europe. In most cases, PRCA was cured by immunosuppressive therapy, immunoglobulins, plasmapheresis or renal transplantation. We report an exceptionally prolonged course of PRCA over 68 months despite renal transplantation and different immunosuppressive regimens.

Neurodevelopmental outcome and growth at 18 to 22 months' corrected age in extremely low birth weight infants treated with early erythropoietin and iron

BACKGROUND

Clinical trials evaluating the use of erythropoietin (Epo) have demonstrated a limited reduction in transfusions; however, long-term developmental follow-up data are scarce.

OBJECTIVE

We compared anthropometric measurements, postdischarge events, need for transfusions, and developmental outcomes at 18 to 22 months' corrected age in extremely low birth weight (ELBW) infants treated with early Epo and supplemental iron therapy with that of placebo/control infants treated with supplemental iron alone.

METHODS

The National Institute of Child Health and Human Development Neonatal Research Network completed a randomized, controlled trial of early Epo and iron therapy in preterm infants < or =1250 g. A total of 172 ELBW (< or =1000-g birth weight) infants were enrolled (87 Epo and 85 placebo/control). Of the 72 Epo-treated and 70 placebo/control ELBW infants surviving to discharge, follow-up data (growth, development, rehospitalization, transfusions) at 18 to 22 months' corrected age were collected on 51 of 72 Epo-treated infants (71%) and 51 of 70 placebo/controls (73%) by certified examiners masked to the treatment group. Statistical significance was determined using chi2 analysis.

RESULTS

There were no significant differences between treatment groups in weight or length or in the percentage of infants weighing <10th percentile either at the time of discharge or at follow-up, and no difference was found in the mean head circumference between groups. A similar percentage of infants in each group was rehospitalized (38% Epo and 35% placebo/control) for similar reasons. There were no differences between groups with respect to the percentage of infants with Bayley-II Mental Developmental Index <70 (34% Epo and 36% placebo/control), blindness (0% Epo and 2% placebo/control), deafness or hearing loss requiring amplification (2% Epo and 2% placebo/control), moderate to severe cerebral palsy (16% Epo and 18% placebo/control) or the percentage of infants with any of the above-described neurodevelopmental impairments (42% Epo and 44% placebo/control).

CONCLUSIONS

Treatment of ELBW infants with early Epo and iron does not significantly influence anthropometric measurements, need for rehospitalization, transfusions after discharge, or developmental outcome at 18 to 22 months' corrected age.

Development and evaluation of a new ELISA for the detection and quantification of antierythropoietin antibodies in human sera

Assays for the analysis of antierythropoietin antibodies (anti-EPO Abs) currently suffer from a high degree of nonspecificity or are cumbersome and time consuming to perform. They are therefore not well suited for the analysis of large numbers of human sera samples, a task that has become increasingly important due to an increase in the number of patients developing anti-EPO Abs. The objective of this study was to develop and validate a sensitive and specific ELISA for the determination of anti-EPO Abs that would suit these purposes. In this new double antigen bridging ELISA, anti-EPO Abs bind via one site to recombinant human erythropoietin (rhEPO)-biotin immobilized to streptavidin-coated microtiter plates (MTPs) and by a second site to rhEPO labelled with digoxigenin (DIG). The amount of bound antibody is determined using an anti-DIG antibody coupled to peroxidase. A rabbit polyclonal anti-EPO Ab purified by immunoadsorption is used as reference antibody preparation. The dynamic range of this ELISA was 1-75 ng/ml per assay calibrated with the reference antibody preparation. The assay was specific for anti-EPO Abs and did not react with other immunoglobulins (Ig) present in human serum. The lower limit of detection (LLD) of the assay was 0.5 ng/ml, and the lower limit of quantitation (LLQ) was 1.0 ng/ml. Anti-EPO Abs could be detected in the sera of pure red cell aplasia (PRCA) patients. In contrast to previous reports, no anti-EPO Abs could be detected in the sera of patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Sjogren's syndrome (SS), or in the sera of dialysis patients.

Treating anemia early in renal failure patients slows the decline of renal function: a randomized controlled trial

BACKGROUND

Erythropoietin is known to improve outcomes in patients with anemia from chronic renal disease. However, there is uncertainty about the optimal timing of initiation of erythropoietin treatment in predialysis patients with non-severe anemia.

METHODS

We conducted a randomized controlled trial of early versus deferred initiation of erythropoietin in nondiabetic predialysis patients with serum creatinine 2 to 6 mg/dL and hemoglobin 9 to 11.6 g/dL. The early treatment arm was immediately started on 50 U/kg/wk of erythropoietin alpha with appropriate titration aiming for hemoglobin of > or =13 g/dL. The deferred treatment arm would start erythropoietin only when hemoglobin decreased to <9 g/dL. The primary end point was a composite of doubling of creatinine, renal replacement, or death.

RESULTS

Eighty-eight patients were randomized (early treatment N= 45, deferred treatment N= 43) and followed for a median of 22.5 months. During follow-up, 13 versus 23 patients reached the primary end point in the two arms, respectively (log-rank P= 0.0078). The relative hazard for reaching an end point was 0.42 (P= 0.012). Adjusting for baseline serum creatinine, the adjusted relative hazard was 0.37 (P= 0.004), while the risk increased 2.23-fold (P < 0.001) per 1 mg/dL higher creatinine at baseline. The benefit was similar regardless of the baseline hemoglobin and proteinuria. No patients had any severe adverse events.

CONCLUSION

Early initiation of erythropoietin in predialysis patients with non-severe anemia significantly slows the progression of renal disease and delays the initiation of renal replacement therapy.

Interpretation of erythropoietin levels in patients with various degrees of renal insufficiency and anemia

BACKGROUND

Chronic renal failure leads to hyporegenerative anemia due to erythropoietin deficiency. The creatinine clearance and hemoglobin levels, at which anemia treatment with recombinant erythropoietin should be started, are unclear. Interpretation of serum erythropoietin levels in the context of renal insufficiency remains controversial and was addressed in this study.

METHODS

Three hundred and ninety-five patients were randomly chosen out of over 5000 consecutive patients investigated by coronary angiography at a single center between 1997 and 2001. Laboratory values and clinical information were prospectively collected in a central registry. Serum samples were frozen before angiography and now used to measure serum erythropoietin levels and evaluate the relationship between erythropoietin and hemoglobin levels in the context of various degrees of renal insufficiency.

RESULTS

The patients with the lowest renal function (creatinine clearance <20 mL/min) had significantly lower hemoglobin levels than the group with normal renal function. However, erythropoietin levels were identical indicating a lower set point for erythropoietin regulation. Above a creatinine clearance of 40 mL/min a significant inverse correlation between erythropoietin and hemoglobin levels was observed and described with the formula erythropoietin [U/L]= 2.5 x (140 - hemoglobin [g/L]) or alternatively Deltaerythropoietin (U/L) =-2.5 xDeltahemoglobin (g/L). Below 40 mL/min no significant correlation was found.

CONCLUSION

A cut-off level for an altered set point of erythropoietin regulation was determined at 40 mL/min creatinine clearance. Above this cut-off hemoglobin negatively regulates erythropoietin. Below the cut-off erythropoietin levels remain stable. Pathophysiologic concepts for this finding and clinical implications in patients with moderate renal failure are discussed.

High levels of neutralizing IL-6 autoantibodies in 0.1% of apparently healthy blood donors

IL-6-specific autoantibodies (aAb-IL-6) have been reported in diseased and healthy individuals. We recently established a model for aAb-IL-6 in different mouse strains, based on vaccination with immunogenic IL-6 analogues, in which titers of aAb-IL-6 above 1,000 resulted in an in vivo IL-6 deficiency. Here, we examined aAb-IL-6 in 4,230 blood donors. Stable low titers of aAb-IL-6 were found in 9% of the donors, while 1% had titers ranging from 64 to greater than 10,000. Such aAb-IL-6-positive donors appeared normal with no overt signs of pathology. Natural and recombinant forms of IL-6 bound avidly to their IgG, and their plasma strongly neutralized IL-6 in vitro. Slightly elevated concentrations of IL-6 exclusively in the form of IL-6-IgG complexes were present in their circulation. The complexes did not contain soluble IL-6 receptors. Titers of 0.1% of the blood donors were as positive as the vaccination-induced IL-6-deficient mice. Such donors might be IL-6 deficient, and if so, IL-6 seems be dispensable for several months in otherwise healthy individuals. Such highly positive donors also explain why normal human IgG for pharmaceutical use may contain high anti-IL-6 activity. Finally, transfusion of plasma with a high titer of aAb-IL-6 might, temporally, render a recipient IL-6 deficient.

[Possible complications of erythropoietin therapy in patients with chronic renal failure]

INTRODUCTION

There have been many publications in the past 20 years about positive effects of human recombinant erythropoietin, which is used in treatment of anemia, especially in patients on dialysis.

COMPLICATIONS

The most important complications in patients treated with erythropoietin include: hypertensive reactions; thrombosis of AV fistula in patients on hemodialysis and appearance of severe anemia as a part of Pure Red Cell Aplasia (PRCA). The first two complications were managed quite easily with adequate erythropoietin dosage, and slower establishment of normal hemoglobin kevel, hematocrit level and red blood cell count, (our "target" Hb varied between 100 and 110 g/dl). PURE RED CELL APLASIA (PRCA): Pure Red Cell Aplasia is a progressive, marked anemia with sudden appearance of significant loss or complete absence of erythrocyte precursor cells in normal bone marrow. In patients with end stage renal disease treated with erythropoietin PRCA appears in acute form as a consequence of production of neutralizing antibodies to erythropoietin. Time period between the beginning of erythropoietin therapy and appearance of PRCA is from 3 weeks to approximately 9 months.

SYMPTOMS AND SIGNS

PRCA is characterized by sudden appearance of anemia in patients who had a satisfactory response to erythropoietin therapy till that moment. In PRCA, anemia is normocytic, normochromic with normal survival of red blood cells, without deficit in components such as iron, folic acid or vitamin B12, low reticulocyte count, decrease in Hg and normal platelet count.

DIAGNOSIS

Diagnosis is based on clinical data (marked anemia), bone marrow biopsy, which shows a lower number of precursor red blood cells and presence of antibodies against erythropoietin. Before PRCA is diagnosed, all other causes for erythropoietin resistance must be excluded.

THERAPY

Therapy of PRCA is based on cessation of erythropoietin therapy (all kinds), and correction of anemia with blood transfusions.

INCIDENCE

PRCA is very rare and occurs in less than 1:10.000 patient-years in patients treated with erythropoietin, not lethal by itself and generally reversible. Till December 31, 2002. PRCA has been diagnosed in 142 patients world wide. In Serbia and Montenegro till this moment there hasn't been a single case of this syndrome.

PREVENTIVE MEASURES

Continuous follow-up of reticulocyte count is the first step. Although this is a very rare disease, most of European Societies of Nephrology made protocols that recommend only intravenous application of -epoetin. Considering this new situation, Nephrology Society of Serbia and Montenegro recommends that -epoetin should be given to patients on hemodialysis only intravenously, while subcutaneous application of -epoetin is recommended in patients before beginning the dialysis treatment and in patients on hemodialysis, or who had undergone kidney transplantation.