Detection of anti-erythropoietin antibodies in haemodialysis patients treated with recombinant human-erythropoietin

Parvovirus B19 (B19) and cytomegalovirus (CMV) infections and anti-erythropoietin (anti-EPO) antibodies in patients on dialysis hyporesponsive to erythropoietin therapy

BACKGROUND

Approximately 10% of patients receiving recombinant human erythropoietin (rHuEPO) do not respond to the treatment. We evaluated parvovirus B19 (B19) and cytomegalovirus (CMV) infections and antierythropoietin (anti-EPO) antibodies as potential causes of anemia in dialyzed patients, hyporesponsive to rHuEPO.

METHODS

Data from 120 dialyzed patients, receiving rHuEPO alfa, were collected: demographic characteristics, rHuEPO dose, duration of rHuEPO treatment and time on dialysis, etiology of chronic kidney disease and transfusion history. Serology and PCR were performed to address B19 and CMV infection status. An ELISA was developed to detect anti-EPO antibodies.

RESULTS

rHuEPO resistance correlated with high ferritin levels (p = 0.001) and short time on dialysis (p = 0.012). B19 DNA was found in 10 (8.3%) dialyzed patients and CMV DNA was detected in 33 (27.5%). There was no significant correlation between B19 infection and anemia,while a tendency of correlation between active CMV infection and hemoglobin levels or hematocrit value (p= 0.069 and p= 0.070, respectively) has been observed. Anti-EPO antibodies were not detected in any patient.

CONCLUSIONS

B19 infection is a rare complication in dialyzed patients and should be investigated after exclusion of other common causes, while CMV infection is rather common. The role of CMV infection in the hyporesponsiveness in dialyzed patients should be further evaluated in other studies. Our data suggest that anti-EPO antibodies are not involved in rHuEPO resistance in this population.

Development of a chemiluminescent imaging assay for the detection of anti-erythropoietin antibody in human sera

Measuring low amounts of anti-erythropoietin antibodies (anti-EPO Abs) is important to evaluate the therapeutic safety of recombinant human erythropoietin (rhEPO). In this work, a simple, sensitive and high-throughput chemiluminescent (CL) imaging assay was developed for the detection of anti-EPO Abs in human sera. The influence of several physicochemical parameters, such as coating conditions, incubation time, detergent concentration and exposure time, were investigated. A calibration curve was established and the range of quantitative detection was 0.12-13.91 ng/mL. The limit of detection (LOD, 3sigma) for the CL-imaging assay was 0.033 ng/mL. Compared to conventional colorimetric enzyme-linked immunosorbent assay (ELISA), the LOD of the CL-imaging assay is 50-fold lower. The recoveries of anti-EPO Abs in the fortified serum were in the range 87.1-116.9% using the present method, which highlighted the validity of the CL-imaging assay system to accurately determine the anti-EPO Abs in serum samples. CL-imaging assay was used to evaluate the presence of anti-EPO Abs in serum samples obtained from chronic renal failure (CRF) patients treated with rhEPO. Contrary to what was expected, the sera from CRF patients did not contain anti-EPO Abs.

Prevalence of Anti-Erythropoietin Antibodies in Hemodialysis Patients without Clinical Signs of Pure Red Cell Aplasia

BACKGROUND/AIMS

The prevalence of anti-erythropoietin antibodies in renal patients without clinical evidence of pure red cell aplasia (PRCA) who respond poorly to epoetin is unknown. This study tested for anti-erythropoietin antibodies in hemodialysis patients who were either hypo- or normoresponsive to epoetin treatment.

METHODS

Epoetin hyporesponsiveness (hemoglobin < or =10.5 g/dl and epoetin > or =9,000 IU/week) and normoresponsiveness (hemoglobin >10.5 g/dl and epoetin <7,000 IU/week) were arbitrarily defined. Prevalence of anti-erythropoietin antibodies in hemodialysis patients without symptoms of PRCA was determined by screening sera of 536 patients from 35 German KfH dialysis units, using enzyme-linked immunosorbent assay (ELISA). Positive results were verified by radioimmunoprecipitation assay (RIP) and neutralizing activity was determined by bioassay.

RESULTS

Anti-erythropoietin antibodies were detected in 3 hyporesponsive and 3 normoresponsive patients using ELISA. One patient per group was verified as borderline by RIP testing; the other 4 were negative. The bioassay was negative for 1 patient; the other died unrelated to PRCA before testing. Follow-up with RIP testing after 15 months under continuous epoetin treatment was negative (4 patients, 2 deceased).

CONCLUSION

This survey did not identify anti-erythropoietin antibodies in hemodialysis patient's hyporesponsive to epoetin and does not support presumptive antibody screening as a routine work-up in these patients.

Blood doping: present procedures and detection techniques

Blood doping represents a serious risk in endurance athletes. Blood transfusion practices (either autologous or homologous) have been used since 1960 and, despite the significant improvement in the laboratory methods, only homologous blood transfusion can be detected currently, while for autologous blood transfusion, no validated methods exist. In the last 15 years, a number of drugs have been developed to treat anemic patients. From recombinant erythropoietin to synthetic hemoglobin, all the developed tools are potentially useful to increase the oxygen transport to peripheral tissues in endurance athletes. Thus, the availability of doping-detection methods can only be sustained by the knowledge of any novel therapeutic approach in this field. The identification of the doping molecule is the gold standard of any antidoping campaign; despite this, indirect methods based on the detection of the effects induced by the doping procedure will be a very powerful tool in the near future. Nevertheless, while direct methods are only affected by the sensitivity and the specificity of the method itself (deterministic methods), indirect approaches are affected by the statistic weight of the results (probabilistic methods). Thus, blood doping will be better controlled by the combination of the two approaches.

Clinical experience with therapeutic AIDS vaccines

Recently, there has been a renewed interest in therapeutic vaccination as an adjunct or alternative to current treatment options for HIV. The first immunotherapeutic trial relevant to this topic was published in 1983. Since then, several dozen therapeutic vaccine trials have been carried out. The results have consistently shown that although in vitro-measured HIV-specific immune responses were evident as a result of vaccination, clinical improvement has been seldom observed. The instances of apparent clinical benefit however, were invariably associated with the usage of vaccines that acted in accord with the principles of allo- or autoimmunization. The majority of these vaccines were derived from the blood of HIV carriers or a cell culture and therefore inherently contained host-cell antigens unrelated to HIV. These observations raise the issue of whether this clinically successful approach has been unduly neglected. Most commercial vaccines on the market today are made the old-fashioned way, but very little support or attention has been given to the development of such vaccines for AIDS therapy. The current strategy, biased toward vaccines which have shown little evidence of clinical efficacy, is shortsighted and needs to be revised.

Incidence of recombinant erythropoietin (EPO) hyporesponse, EPO-associated antibodies, and pure red cell aplasia in dialysis patients

BACKGROUND

Since 1998, an increase of anti-erythropoietin (anti-EPO) antibody-induced pure red cell aplasia (PRCA) has been reported. As data up to now consisted mostly of spontaneously reported cases the question arose about the frequency of this increase in EPO-induced PRCA. The objectives of this study were to determine the incidence and causes of recombinant EPO hyporesponse, of antibodies to EPO in patients on dialysis, and to relate the detection of anti-EPO antibodies to the presence of PRCA.

METHOD

This multicenter cohort study used existing patient data and serum samples collected at 6-month intervals from 1677 patients with incident end-stage renal disease (ESRD) participating in The Netherlands Cooperative Study on the Adequacy of Dialysis-2 (NECOSAD-2).

RESULTS

Fifty-seven patients had an inadequate EPO response, which resulted in an incidence of 16.7 per 1000 patient-years on EPO while on dialysis. All available sera specimens (N = 232) of these patients were screened for anti-EPO antibodies. The sera specimens of two of these 57 patients tested positive. Of the 57 patients with inadequate EPO response, one had clinical PRCA (incidence 0.29 per 1000 patient-years on EPO and on dialysis). Of the 1346 patients without symptoms of inadequate EPO response, one patient tested borderline positive for anti-EPO antibodies. In total, three patients developed EPO antibodies during follow-up, leading to an estimated incidence of 1.27/1000 (95% CI 0.3 to 3.7/1000) patient-years since the start of dialysis.

CONCLUSION

The incidence of inadequate EPO response in our population of dialysis patients is in concordance with tentative calculations found in the literature. Furthermore, we found the incidence of EPO-induced PRCA and EPO antibodies to be low.

Darbepoetin alfa (Aranesp) in children with chronic renal failure

BACKGROUND

Darbepoetin alfa use has been reported in 7 children with chronic renal failure (CRF). Our objective was to evaluate the efficacy and safety of darbepoetin and determine a therapeutic dose in a larger sample of children with CRF.

METHODS

Twenty-six children with chronic renal insufficiency (CRI) GFR <30 mL/min/1.73 m(2), on peritoneal dialysis (PD) or hemodialysis (HD) entered a prospective, open-label study of darbepoetin. Seven ineligible children who underwent the same evaluation were analyzed retrospectively. The starting dose was 0.45 microg/kg/week. IRB/REB approval and informed consent were obtained. The primary outcome measure was hemoglobin (Hb) response within a target range of 10.0 to 12.5 g/dL between 8 and 12 and 20 and 28 weeks.

RESULTS

Thirty-three children (15 CRI, 9 HD, 9 PD; aged 1-17 years) were enrolled in the study. Ten patients dropped out (3 before 12 weeks and 7 before 28 weeks), none due to darbepoetin. Mean Hbs were 11.8 and 11.4 between weeks 8 and 12 and 20 and 28, respectively; the proportion of patients with Hb values >10.0 g/dL was 97% and 91% in the same intervals. No effect of grouping patients into CRI, HD, or PD or prospective versus retrospective was observed. One of 13 serious adverse events (hypertension) was possibly related to darbepoetin; 8/14 children reported injection-site pain. At 12 and 28 weeks, respectively, 73% and 87% were receiving darbepoetin less than once weekly.

CONCLUSION

A dose approximating 0.5 microg/kg/week of darbepoetin effectively treats anemia in children with chronic renal failure; for many, this may be proportionately increased and injected less than once weekly.

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.

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.

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.

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.

A single monoclonal antibody as probe to detect the entire set of native and partially unfolded rhEPO glycoforms

Human erythropoietin (hEPO) is a highly heterogeneous glycosylated protein that requires well-characterised immunochemical reagents to evaluate the glycoform profile along its biotechnological production as a recombinant hormone. These reagents should be suitable for several assay conditions (like those used for immunoblotting analysis, liquid or solid-phase quantitative assays, immunoaffinity purification) with no glycoform selectivity. Five anti-recombinant hEPO monoclonal antibodies (mAbs) were characterised with the aim of selecting the appropriate reagent. These antibodies mapped two spatially distinct epitopes and neutralised the in vitro biological activity of the cytokine. All of them were able to bind to both, the partially denatured and the native form of the protein. Isoelectric focusing analysis followed by immunoblotting confirmed that all the mAbs, herein described, were able to bind to each glycoform, recognising amino acid sequences of the hEPO. Nevertheless, only mAb 2B2 preserved the ability to bind to soluble recombinant human erythropoietin (rhEPO) when it was coated to polystyrene plates or immobilised on CNBr-activated Sepharose matrix. Besides, mAb 2B2 was able to bind to the complete set of soluble rhEPO glycoforms, showing the same affinity for the glycosylated and deglycosylated cytokine. Thus, mAb 2B2 was useful as a capture antibody to develop a sandwich enzyme-linked immunosorbent assay (ELISA), performing a simple, specific and fast assay to quantify rhEPO with a detection limit of 7 ng ml(-1). mAb 2B2 was also satisfactorily employed as affinity ligand to purify rhEPO. Our work led us to find a suitable and single reagent to perform a variety of immunochemical approaches, where the binding of each glycoform in the native or partially unfolded form of rhEPO is required.

Combined use of erythropoietin and granulocyte colony-stimulating factor does not decrease blood transfusion requirements during induction therapy for high-risk neuroblastoma: a randomized controlled trial

PURPOSE

To evaluate the efficacy of recombinant erythropoietin (EPO) and granulocyte colony-stimulating factor (G-CSF) in reducing blood transfusion requirements and stimulating hematopoiesis in children with high-risk neuroblastoma.

PATIENTS AND METHODS

Thirty-eight patients given six cycles of intensive induction chemotherapy for high-risk neuroblastoma were randomized to receive G-CSF (n = 20) or G-CSF + EPO (n = 18). Cytokines were given subcutaneously each day, starting 24 hours after each chemotherapy cycle and continuing until 48 hours before the start of the next cycle. The primary end point was the effect of EPO on total red cell transfusion requirements during induction therapy.

RESULTS

Patients who received G-CSF + EPO had a higher red cell transfusion requirement (median, 161.0 mL/kg) than did those who received G-CSF alone (median, 106.6 mL/kg; P =.005). In addition, among patients given transfusions for hemoglobin < or = 8 g/dL, those in the G-CSF + EPO group received more red cell transfusions than did those given G-CSF alone (median per patient, 10 v 8, respectively; P =.044). The two treatment groups had similar cumulative durations of neutropenia, incidences of febrile neutropenia, platelet transfusion requirements, and numbers of platelet transfusions; they also received induction chemotherapy for similar durations and had similar probabilities of progression-free survival and overall survival.

CONCLUSION

The addition of EPO to the G-CSF regimen provides no benefit for patients receiving intensive induction chemotherapy for high-risk neuroblastoma.

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.

Safety of donating multiple products in a single apheresis collection: Are we expecting too much?

Modern blood separators rapidly process many liters of donor blood and efficiently collect vast quantities of blood components from donors, who may be stimulated with potent recombinant hematopoietic growth factors or cytokines. Accordingly, the potential risks of modern multiple product/unit apheresis donations and recombinant growth factors is analyzed in this report. As is true for all medical procedures, risks are associated with apheresis donations. Risks of a "standard" apheresis donation, in which one unit of PLTs or plasma is collected, are comparable to the risks of whole blood donation. Risks of multiple unit apheresis donations, in which either vast quantities of a single blood component or multiple units of various components are collected, are incompletely understood, particularly, when donors are stimulated with recombinant hematopoietic growth factors to increase component yields. To minimize donor risks and to increase knowledge of multiple component apheresis donations, both short-term problems (e.g., donor reactions accompanying apheresis procedures and pre- vs. post-procedure changes in results of donor laboratory studies) and long-term problems (e.g., medical diagnoses/problems and abnormalities of donor blood counts and laboratory test results) should be monitored, ideally, by a repeat donor registry. When recombinant hematopoietic growth factors are prescribed, donors should give informed consent, and blood center professionals must be aware of 1) the effects of these drugs given at pharmacologic, rather than physiologic, doses; 2) the differences between the molecular structure of recombinant vs. natural/endogenous growth factors; 3) the fact that recombinant growth factors have both narrow/focused and broad biological activities; and 4) the probability that results of studies in sick/immunosuppressed patients may not be applicable to healthy/immunocompetent donors.

Indirect evidence of hormone abuse. Proof of doping?

Besides anabolic steroids, the most common performance-enhancing hormones are erythropoietin (EPO), insulin, GH, and gonadotropins, mostly indistinguishable from endogenous hormones and with very short half-life. This makes virtually impossible to demonstrate their use by measuring their concentration in the blood or urine. A possible approach to the problem may lie in in-direct demonstration through detection of the biological effects of these substances. The finding of an increased hematocrit level is suspicious but not clearly demonstrative of EPO abuse. Very high levels of circulating EPO could be associated with a strong suspicion of doping, when associated to other abnormal parameters, such as Ht, sTFRr, EPO, RDW. The presence of antibodies against the polysaccharide fraction of lateral chains of EPO has been observed only in patients treated with rhEPO. Owing to the pulsatile pattern of GH, particularly during physical exercise, pathologically high values may be found in normal subjects. Therefore, as in the case of EPO, evidence of GH abuse can be gathered only indirectly by detecting the biological effects of its administration. In training subjects GH treatment increased GH, IGF-I, IGFBP-3 and ALS, and decreased IGBP-2. After cessation of treatment IGF-I, IGFBP-3 and ALS approached basal values between 49 and 96 h. Also the bone parameters PICP ICIP, PIUP and osteocalcin increased significantly. Four days after cessation of treatment, levels of PIIIP and ICTP were still abnormally elevated. In conclusion, increases in IGF-I, IGFBP-3, ALS, PIIIP and ICTP are all indicative of recent GH abuse or of acromegaly.

Development of an animal–human antibody complex for use as a control in ELISA

In order to provide the equivalent of a human anti-human protein antibody as positive control in ELISAs, a goat-human antibody complex was created using chemical cross-linking. The resulting hybrid complex had a larger molecular size on HPLC and SDS-PAGE. In ELISA, the goat-human complex bound to human antigen and was detectable by a secondary anti-human conjugate. The method to make the hybrid complex is simple, cost-effective and can be used to make human-like antibodies to many human proteins.

Investigation for the presence of anti-erythropoietin antibodies in patients with myelodysplastic syndromes

OBJECTIVES

Recombinant human erythropoietin (rHuEpo) improves anemia in 25% of patients with myelodysplastic syndromes (MDS). The variable and sometimes low response rate to rHuEpo treatment raises the question whether the existence of autoantibodies against erythropoietin (epo) is partially responsible. In the present study we investigated the presence of anti-epo autoantibodies in MDS patients.

METHODS

Forty-three patients with MDS were studied. Sixteen patients had refractory anemia (RA), 13 had RA with ringed sideroblasts, 3 had RA with excess of blasts (RAEB), 9 had RAEB in transformation and 2 patients had chronic myelomonocytic leukemia. They were divided in 3 groups according to rHuEpo treatment. Group A consisted of 10 patients who did not receive rHuEpo treatment. Group B included 13 patients who were on rHuEpo treatment (150 IU/kg subcutaneously, 3 times weekly) showing an increase of hemoglobin (Hb) values or reduction of transfusion requirements and Group C consisted of 20 patients who did not respond or stopped responding to rHuEpo treatment. Laboratory studies consisted of a complete blood cell count, measurement of serum epo and determination of anti-epo antibodies using ELISA.

RESULTS

There were no significant differences with regard to age and sex among the three groups. No autoantibodies against epo were found in the examined sera, apart from a female patient from group A who showed a low positive titer.

CONCLUSION

We suggest that anti-epo autoantibodies do not contribute to the development of MDS-related anemia and are not responsible for the modest response to rHuEpo treatment. Further investigation is needed to identify possible reasons for the low response rate to rHuEpo treatment.

Prolonged neutropenia in a novel mouse granulocyte colony-stimulating factor neutralizing auto-immunoglobulin G mouse model

Therapeutic use of recombinant human cytokines in humans can result in the generation of drug-specific antibodies. To predetermine the maximum potential effects of a granulocyte colony-stimulating factor (G-CSF) neutralizing auto-immunoglobulin G (auto-IgG) response during recombinant human G-CSF therapy, we developed a mouse model of mouse G-CSF (mG-CSF) neutralizing auto-IgG response. Mice were immunized and boosted with mG-CSF chemically conjugated to either keyhole limpet hemocyanin or ovalbumin on an alternating schedule. Sera were analyzed for mG-CSF-specific titers and full blood counts were performed on a Technicon H-1E. On day 252, tissues were collected for histology. IgG was protein A affinity purified from pooled mG-CSF autoimmune sera. Mice immunized with mG-CSF conjugates produced mG-CSF-specific auto-IgG responses that lasted for the length of the study. Significant neutropenia (p(max) < 0.004) was concurrent with the rise in mG-CSF-specific IgG titers. However, neutrophil counts remained at approximately 20% of preimmunization levels through day 252. Endogenous mG-CSF neutralizing auto-IgG had no significant effect on hemoglobin, erythrocyte, lymphocyte, eosinophil, basophil, and platelet counts, and had minor, transient, or no effects on monocyte counts. Bone marrow colony assays from mG-CSF autoimmune mice demonstrated no significant effect of G-CSF neutralization on the numbers or proliferative capacity of preneutrophil lineage progenitors. Purified IgG from mG-CSF autoimmune mice neutralized mG-CSF in vitro. High-titer G-CSF neutralizing auto-IgG in adult mice partially inhibited steady-state granulopoiesis and had little or no effect on steady-state levels of other hematopoietic cells.