Determination of Critical Quality Attributes for a Biotherapeutic in the QbD Paradigm: GCSF as a Case Study.

Estimating impact of the various product-related variants and impurities on a biotherapeutic's safety and efficacy is an essential requirement in the quality by design paradigm. In view of the limited role that clinical studies offer in this regard, we demonstrate a preclinical approach to achieve this for granulocyte colony-stimulating factor (GCSF). While our repeated-dose toxicity data suggest that these variants do not elicit any adverse effects or histopathological changes, aggregated GCSF impurity caused sluggishness in animal behavior manifested by a possible muscular injury. Cell assay data revealed that the cys-64-cys74 disulfide bond in reduced GCSF imparts stabilization in absence of the cys-36-cys42 bond. PK data demonstrate variability in half lives of different species when compared to the native GCSF. PD data along with differential expression of JAK-2 and STAT5a genes show that all the tested variants triggered the required signal transduction pathways for neutrophil proliferation and activation.

Comparison of biosimilar filgrastim, originator filgrastim, and lenograstim for autologous stem cell mobilization in patients with multiple myeloma.

BACKGROUND: Granulocyte-colony-stimulating factor (G-CSF) originators such as filgrastim (Neupogen) and lenograstim (Granocyte) are widely used for peripheral blood stem cell (PBSC) mobilization. In recent years, biosimilar agents have been approved for the same indications. The aim of this retrospective study was to compare the mobilization efficiency of the three G-CSF variants originator filgrastim, lenograstim, and the biosimilar Filgrastim Hexal in a homogeneous group of multiple myeloma (MM) patients in first-line therapy. STUDY DESIGN AND METHODS: Overall mobilization data of 250 patients with MM were included. Of these patients, 74 (30%), 131 (52%), and 45 (18%) were mobilized with originator filgrastim, biosimilar Filgrastim Hexal, or lenograstim, respectively, at a dose of 5 to 10 µg/kg body weight subcutaneously starting from Day 5 after chemomobilization with CAD (cyclophosphamide, doxorubicin, dexamethasone) until completion of PBSC collection. RESULTS: All but one patient reached the collection goal of a minimum of at least 2 × 106 CD34+ cells/kg body weight during a median of one (range, one to three) leukapheresis session. No significant differences in CD34+ mobilization and collection yields between the filgrastim-mobilized (median, 10.5; range, 2.7-40.4), Filgrastim Hexal-mobilized (median, 9.9; range, 0.2-26.0), and lenograstim-mobilized (median, 10.7; range, 3.1-27.9 CD34+ cells × 106 /kg body weight) patients were observed. CONCLUSION: Concerning the clinically relevant efficiencies of PBSC mobilization and in terms of reaching the individual collection target, this retrospective study did not detect any significant differences between the three G-CSF variants in the analyzed patient cohort.

Results of a prospective dose intensity and neutropenia prophylaxis evaluation programme (DIEPP) in cancer patients at risk of febrile neutropenia due to myelosuppressive chemotherapy.

OBJECTIVE: To describe the incidence of febrile neutropenia (FN) and use of pegfilgrastim in cancer patients with high overall risk of FN and to investigate the relationship between granulocyte-colony stimulating factor (G-CSF) guideline adherence and chemotherapy delivery in Central and Eastern Europe (CEE) and Austria. METHODS: Dose Intensity Evaluation Program and Prophylaxis (DIEPP) was a multicentre, prospective, and observational study of adult patients with breast cancer, lymphoma, lung cancer, gastric cancer, and ovarian cancer, who received chemotherapy with pegfilgrastim support and who had an overall risk of FN ≥ 20 %. Physicians assessed patient risk factors and reported their reasons for administering pegfilgrastim. RESULTS: Patients were enrolled from 113 centres in CEE and Austria between August 2010 and July 2013, and data were analysed from 1072 patients. The most common tumour types were breast cancer (50 %) and lymphoma (24 %). FN incidence was 5 % overall. FN occurred in 3 % of patients (28/875) who received pegfilgrastim as primary prophylaxis (PP) and 13 % of patients (19/142) who received it as secondary prophylaxis (SP); 79 % of FN events in SP patients occurred in the first cycle before pegfilgrastim was administered. The three most frequently chosen reasons for using pegfilgrastim were planned chemotherapy with high FN risk, female gender, and advanced disease. Overall, 40 % of patients received > 90 % of their planned chemotherapy dose within 3 days of the planned schedule. CONCLUSION: FN incidence was relatively low with pegfilgrastim PP in patients with a physician-assessed overall FN risk of ≥ 20 %. The most important reasons for pegfilgrastim use were consistent with the investigators' risk assessment and international guidelines.

Austrian Arbeitsgemeinschaft für Gynäkologische Onkologie (AGO) guideline for prophylaxis with granulocyte colony-stimulating factors (G-CSF) in gynecologic malignancies, including breast cancer.

The current knowledge and recommendations on the clinical use of granulocyte colony-stimulating factors (G-CSF) in gynecologic cancers including breast cancer, along with the clinical experience of the members of the working group of the Austrian Arbeitsgemeinschaft für Gynäkologische Onkologie (AGO), have been summarized. G-CSF is either administered as primary or secondary prophylaxis of febrile neutropenia. The term "primary prophylaxis" denotes the prophylactic use of G-CSF as early as during the first cycle of a new chemotherapeutic regimen. Secondary prophylaxis, on the other hand, defines the use of G-CSF after development of grade 4 neutropenia or febrile neutropenia in a preceding cycle of a particular chemotherapeutic regimen. When chemotherapy regimens are associated with a > 20 % risk of febrile neutropenia such as TAC (docetaxel-doxorubicin-cyclophosphamide), primary prophylaxis with G-CSF is indicated. When chemotherapy regimens are associated with a 10-20 % risk of febrile neutropenia, the decision for primary prophylaxis with G-CSF is based upon patient-related risk factors such as age > 65 years, previous cytotoxic treatment(s) and/or radiation therapy, preexisting tumor-related neutropenia or bone marrow involvement, preexisting neutropenia, infections/open sores, reduced Karnofsky performance status/WHO performance status and reduced nutritional status, advanced malignant disease, history of prior febrile neutropenia, impaired kidney function, and hepatic failure particularly with hyperbilirubinaemia. The patient's individual overall febrile neutropenia risk should be assessed prior to each chemotherapy cycle.

Development and calibration of a standard for the protein content of granulocyte colony-stimulating factor products.

This collaborative study characterizes a homogeneous standard for the protein content determination of granulocyte colony-stimulating factor (G-CSF) products with traceability of the measurement. The Kjeldahl method was used to determine the average protein content of G-CSF bulk as 2.505 mg/ml (95% C.I: 2.467-2.543 mg/ml, GCV 4.0%). Using G-CSF bulk as a traceability benchmark, the protein content of the final freeze-dried standard using reverse phase HPLC (RP-HPLC) was 215.4 µg protein per ampoule (95% C.I: 212.407-218.486 µg/ampoule, GCV 3.4%). A comparative study showed that there was no difference between using Filgrastim CRS (European Pharmacopeia G-CSF reference standard) and freeze-dried homogeneous standard when quantifying G-CSF protein content by RP-HPLC (P > 0.05). However, there were significant differences in the G-CSF protein content obtained using a serum albumin standard by Lowry assay and a G-CSF standard with RP-HPLC. Therefore, use of RP-HPLC with a freeze-dried homogeneous standard would eliminate the systematic errors introduced when using a serum albumin standard because of the differences in protein composition between the standard and the sample. It would also be helpful to use this method to compare the quality of G-CSF biosimilar products in situations where the protein content has been calibrated using various standards.

Regulatory requirements for therapeutic proteins: the relationship between the conformation and biological activity of filgrastim.

Higher order structure, including conformation, is considered a critical quality parameter of therapeutic proteins, and is mandatory information in development of first use and bio-similar therapeutic protein drugs, the assumption being that the biological activity of a protein is directly dependent on its adoption of a 'correct' conformation. Studies on the relationship between conformation and activity depend on the ability to induce conformational changes in proteins, and conventional approaches such as thermal or chemical denaturation are incompatible with bioactivity measurements. To explore the relationship between bio-activity and conformational studies, we have studied variants of the therapeutic protein filgrastim (rec met huGCSF) which have been mutated by the replacement of helical alanine residues with glycine, to destabilise the conformation of the molecule. In the GCSF A-G mutant series studied, single conformation-destabilising amino-acid substitutions significantly reduced the biological activity. These effects were not, however correlated with changes in secondary structure measurable by far-UV Circular Dichroism (CD) spectroscopy. Only the more extensively mutated double and triple substitutions showed measurable reductions in alpha-helical structure by CD. We conclude that in this system, GCSF does not readily adopt a reduced-activity altered conformational state which can be detected by low resolution techniques such as CD. In contrast, reductions in biological activity do reflect reductions in conformational stability, possibly caused by time-dependent degradation of the protein in the cell-proliferation bioassay. Although not a formal model of biosimilarity, we suggest that our results could inform the regulatory process in determining appropriate experimental approaches to meeting regulatory requirements for higher order structural analysis of therapeutic proteins.

The 2nd International Standard for human granulocyte colony stimulating factor.

Five candidate preparations of human sequence recombinant granulocyte-colony stimulating factor (G-CSF) were formulated and lyophilized at NIBSC prior to evaluation in a collaborative study for their suitability to serve as a replacement International Standard (IS). The preparations were tested by 13 laboratories using in vitro bioassays. The candidate preparation 09/136 was judged suitable to serve as a replacement international standard based on the data obtained for biological activity and stability. On the basis of the results reported here, the preparation coded 09/136 was established by the WHO Expert Committee on Biological Standardization (ECBS) as the 2nd IS for human G-CSF with an assigned value for G-CSF activity of 95,000 IU/ampoule. Calibration of the 2nd IS is primarily based on the bioassay in use in various laboratories and relies entirely on the estimates calculated relative to the WHO 1st IS for continuity of the IU.

Comparison of the physicochemical properties of a biosimilar filgrastim with those of reference filgrastim.

Recombinant human granulocyte-colony stimulating factor (filgrastim) is a therapeutic protein used primarily to reduce incidence and duration of severe neutropenia and its associated, and serious, complications. We have developed a biosimilar filgrastim (Hospira filgrastim; Nivestim) designed to be comparable to Amgen filgrastim (Neupogen). An extensive characterization study assessed the physiochemical similarity of Hospira filgrastim to Amgen filgrastim. Both drugs were supplied in 1 ml glass, single-use, prefilled syringes (five batches of each product at 480 microg/0.5 ml and one batch of each product at 300 microg/0.5 ml). Samples were evaluated using state-of-the-art analytical methods (validated in accordance with International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use or Pharmeuropa guidelines) to determine physicochemical properties, molecular characteristics, purity and biological activity. Samples were compared after long-term storage at 2-8 degrees C and storage at 40 degrees C (stress conditions) to evaluate their degradation impurity profiles. Hospira filgrastim and Amgen filgrastim were shown to have similar physicochemical properties, molecular characteristics, purity and biological activity. No significant differences in product-related impurities were recorded between Hospira filgrastim and Amgen filgrastim following storage for 12 weeks under stress conditions. These data show that the physicochemical profile of Hospira filgrastim is similar to that of Amgen filgrastim.

Chemotherapy for mobilisation of Ph-negative progenitor cells from patients with CML: impact of different mobilisation regimens.

Mobilised peripheral blood stem cells are widely used for autografting in patients with chronic myeloid leukaemia (CML) and it is generally thought that a high proportion of Ph-negative progenitor cells in the graft is desirable. We report here the results of 91 stem cell mobilisations performed with various chemotherapy regimens followed by G-CSF. We show that mobilisation of Ph-negative cells is possible after diagnosis as well as in advanced stages of the disease. The yield of Ph-negative cells is highly dependent on the chemotherapy regimen: while the combination of idarubicin and cytarabin for 3-5 days (IC3-5) mobilised Ph-negative cells in most patients, high-dose cyclophosphamide was ineffective. Mobilisation of Ph-negative progenitor cells after IC3 was at least as effective as after IC5; however, less apheresis sessions were required, and toxicity was much reduced after IC3. Compared to historical controls, IC was equally effective as the widely used ICE/miniICE (idarubicin, cytarabin, etoposide) protocol. No correlation was found between graft quality and the cytogenetic response to subsequent treatment with interferon-alpha. We conclude that IC3 is an effective and well-tolerated regimen for mobilising Ph-negative cells that compares well with more aggressive approaches such as IC5 and ICE/miniICE.

Glycosylated vs non-glycosylated granulocyte colony-stimulating factor (G-CSF)--results of a prospective randomised monocentre study.

The discovery of the haematopoietic growth factor granulocyte colony-stimulating factor (G-CSF) has reduced infection-related morbidity in cancer patients by alleviating post-chemotherapy neutropenia. Two formulations of recombinant human (rh) G-CSF, one glycosylated and one non-glycosylated, are available. The glycosylated form, lenograstim, possesses at least 25% greater bioactivity in vitro. Some comparative studies into the preparation's potential to mobilise haematopoietic stem cells suggest a similar advantage. In the light of the great clinical importance of G-CSF, we have performed the first prospective, randomised, crossover study on children with chemotherapy-induced neutropenia. G-CSF (250 microg/m(2)) was started 1 day after the chemotherapy block, and was administered until a WBC >1500/microl was achieved on 3 successive days. Thirty-three G-CSF cycles from 11 patients (16 lenograstim, 17 filgrastim) were studied. They were investigated for duration of very severe (WBC <500/microl, 9 vs 9.5 days, lenograstim vs filgrastim, median) and severe leukopenia (WBC <1000/microl, 11 vs 11 days), infections (CRP >5 mg/dl, 5 vs 5.5 days), infection-related hospital stay (11 vs 9 days) and antibiotic treatment (9 vs 9 days). Statistical evaluation by paired analysis could not detect any difference between treatment groups; the median difference for all end-points was zero. In summary, at least at 250 microg/m(2), in terms of their clinical effect on neutropenia, the two G-CSF preparations appear to have identical activity.

Ifosamide, epirubicin and granulocyte colony-stimulating factor: a regimen for successful mobilization of peripheral blood progenitor cells in patients with multiple myeloma.

In general, the mobilization of peripheral blood progenitor cells (PBPC) in multiple myeloma (MM) patients is poor and is achieved in most cases by combined cyclophosphamide and G-CSF. This study was performed to examine the efficacy of combined ifosfamide/epirubicine and G-CSF for PBPC mobilization and purging. Sixteen patients suffering from multiple myeloma in stage II/A and III/A according to Durie and Salmon underwent chemotherapy consisting of a total of three cycles of ifosfamide (3 g/m(2) on days 1 and 2 and epirubicine 80 mg/m(2) on day 1) and G-CSF (10 or 20 microg/kg body weight (BW) daily until harvesting). PBPC harvesting was performed after the first and third cycle of chemotherapy. The median number of PBPC after the first cycle of chemotherapy was 7.79 x 10(6) CD34+ cells/kg BW (ranging from 0.94-26.36 x 10(6)) and 6.38 x 10(6) CD34+ cells/kg BW (ranging from 0.79-29.31 x 10(6)) after the third cycle of chemotherapy. Clinical re-evaluation after three cycles of chemotherapy showed 13 (81 per cent) patients in partial remission (PR), two (12 per cent) in complete remission (CR) and one (6.25 per cent) in stable disease (SD). No major side-effects were observed, six patients developed hematological toxicity stage IV WHO for a median of 3.9 days but no serious infection episodes occurred. Combined ifosfamide/epirubicin and standard G-CSF is able to mobilize sufficient PBPC without serious side-effects for patients with MM and for purging procedures resulting in a high proportion of complete remissions after tandem high-dose melphalan chemotherapy.

Phase II study of a high-dose ifosfamide-based chemotherapy regimen with growth factor rescue in recurrent aggressive NHL. High response rates and limited toxicity, but limited impact on long-term survival.

The purpose of the study was to evaluate in patients with recurrent intermediate-grade NHL, the tolerance to and efficacy of an intensive salvage regimen consisting of high doses of ifosfamide, etoposide and mitoxantrone with G-CSF support, followed by autologous stem cell transplantation and to identify prognostic factors for survival in patients with recurrent aggressive lymphoma. Patients with recurrent intermediate-grade NHL under the age of 60 years were eligible. Induction consisted of ifosfamide 10 g/m(2) and etoposide 900 mg/m(2) with G-CSF 5 microg/kg twice a day. Upon recovery, patients underwent stem cell apheresis. Patients achieving complete remission (CR) underwent autologous stem cell transplantation using BEAM conditioning. Those with partial remission (PR) received treatment with ifosfamide 10 g/m(2), mitoxantrone 20 mg/m(2) and G-CSF 5 microg/kg. Those with CR received BEAM, those with PR received cyclophosphamide 4.5 g/m(2), etoposide 1200 mg/m(2) and cisplatin 135 mg/m(2) with stem cell rescue followed by BEAM. Antibiotic prophylaxis was given with all treatment cycles. The results were compared with those obtained in a prior study that used MINE-ESHAP salvage. Forty-four patients with recurrent intermediate-grade NHL were enrolled between March 1994 and September 1996. Median age was 50 years (24-61). Eleven patients had transformed lymphoma and seven had a T cell phenotype. Response rate to the high-dose ifosfamide regimen was 77% +/- 12% after two cycles and the complete response rate was 41% +/- 14%. Myelosuppression was profound but short. Median nadir ANC was 0 and the median duration of ANC <0.5 x 10(9)/l was 6 days (range 3-12). No severe infections occurred; 55% of the patients required blood transfusion and 42% required platelet transfusions. Myelosuppression and transfusion requirements were similar after the first and second cycles. Thirty-five of the 44 patients proceeded to autologous stem cell transplantation and one transplant-related death occurred. With a median follow-up of 52 months, progression-free survival at 2 years is 38% +/- 14% and survival is 52% +/- 15%. Data from these 44 patients were pooled with data on 53 patients who had received salvage treatment with MINE-ESHAP, for a multivariate analysis of prognostic factors. In multivariate analysis, serum LDH was strongly associated with survival. The use of a more intensive salvage regimen, did not result in a significant increase in long-term outcome, despite a high response rate. In conclusion, duration of treatment, response rates, treatment-related mortality and survival compare favorably with previous salvage regimens, but recurrence remains a major problem. Long-term survival in recurrent large cell lymphoma is influenced more by disease characteristics than by the type of salvage regimen used.

Recombinant human granulocyte colony-stimulating factor therapy for patients with neutropenia and/or neutrophil dysfunction secondary to glycogen storage disease type 1b.

The purpose of this study was to evaluate the efficacy and toxicity of recombinant human granulocyte colony-stimulating factor (rhG-CSF) therapy in patients with neutropenia and/or neutrophil dysfunction secondary to glycogen storage disease (GSD) type 1b. Thirteen patients with neutropenia and/or neutrophil dysfunction secondary to GSD type 1b were treated with rhG-CSF. The effects of therapy on neutrophil numbers and in vitro neutrophil function and on bone marrow cellularity and morphology were studied. The clinical status of the patients and the occurrence of adverse events associated with rhG-CSF use were monitored. Use of rhG-CSF therapy was associated with a significant increase in circulating neutrophil numbers (P <. 01) and an improvement in neutrophil function as assessed in vitro. In addition, rhG-CSF therapy produced a significant increase in marrow cellularity and an increase in myeloid:erythroid (M:E) ratio, indicating stimulation of granulopoeisis. No adverse effects on marrow function were noted; in particular, no myelodysplasia or marrow exhaustion was seen. Use of rhG-CSF therapy was associated with objective and subjective improvements in infection-related morbidity. The therapy was well tolerated, although all patients developed splenomegaly, and 5 patients developed mild hypersplenism that did not require any specific treatment. rhG-CSF therapy is efficacious in the management of neutropenia and neutrophil dysfunction associated with GSD type 1b. Patients on this therapy need to be monitored for hypersplenism. Continued follow-up will be necessary to confirm long-term safety; however, no significant short-term toxicity was noted.

Use of concurrent G-CSF + GM-CSF vs G-CSF alone for mobilization of peripheral blood stem cells in children with malignant disease.

There is limited experience in the mobilization of peripheral blood progenitor cells (PBPC) in children and the optimal method for PBPC mobilization is unknown. The present study was conducted to ascertain whether mobilization with G-CSF + GM-CSF (group I) provides some advantage over G-CSF alone (group II) in terms of collected CD34+ cells and hematopoietic recovery following myeloablative conditioning in children with malignancies. An economic analysis was also performed. Each group comprised 21 consecutive patients. The mean number of aphereses was 1.5+/-0.5 in group I and 1.2+/-0.46 in group II (NS). The mean number of CD34+ cells was 3.8 x 106+/-4.03/kg in group I and 4.2+/-5.4 in group II (NS). The mean number of total blood volumes (TBV) processed was 4.4+/-1.5 in group I and 4.3+/-1.5 in group II (NS). The mean duration of the procedure was 276+/-74.1 min in group I and 286.7+/-75.9 min in group II (NS), and the inlet flow was 45.1+/-12 ml/min in group I and 39.5+/-15.1 ml/min in group II (NS). No significant differences in the neutrophil and platelet engraftment probability were observed between the two groups. The mean overall cost of group II was not statistically significant from that of group I (US$ 9521+/-330 vs US$ 10201+/-1028, P = NS). The cost of mobilization was significantly higher in group I than in group II, conditioning regimen costs were similar in both groups and the costs related to the post-transplant period were similar in both groups. We conclude that PBPC mobilization with G-CSF + GM-CSF in children does not enhance hematological recovery in comparison with mobilization using G-CSF alone. However, the combination of G-CSF + GM-CSF does not significantly increase the overall cost of transplantation.

Granulocyte colony-stimulating factor versus granulocyte-macrophage colony-stimulating factor for collection of peripheral blood progenitor cells from healthy donors.

The harvesting of peripheral blood progenitor cells (PBPCs) after granulocyte colony-stimulating factor or granulocyte-macrophage colony-stimulating factor stimulation instead of bone marrow in healthy donors has become increasingly popular. Donors, given the choice between bone marrow and PBPC donation, often prefer cytapheresis because of the easier access, no necessity for general anesthesia, and no multiple bone marrow punctures. In addition, accelerated engraftment and immunomodulation by granulocyte colony-stimulating factor-mobilized PBPCs are advantageous for the recipient. However, because of donor inconvenience and poor mobilization, there is a need to develop improved procedures. Aspects such as durability of hematopoietic engraftment, characterization of the earliest stem cell, and composition of PBPCs are not yet well defined, and international donor registration and follow-up must be considered when evaluating long-term safety profiles in healthy donors. This review concentrates on the most significant developments on mobilization of PBPCs published during the past year.

Efficacy of a new formulation of lenograstim (recombinant glycosylated human granulocyte colony-stimulating factor) containing gelatin for the treatment of neutropenia after consolidation chemotherapy in patients with acute myeloid leukemia.

The efficacy and safety of a new formulation of lenograstim (recombinant glycosylated granulocyte colony-stimulating factor) prepared by switching the stabilizer from human serum albumin (HSA) to gelatin was investigated for the treatment of neutropenia after consolidation chemotherapy in patients with acute myeloid leukemia (AML). The results obtained in the study using the gelatin-containing formulation (gelatin-lenograstim) were retrospectively compared to those obtained from a placebo-controlled double-blind randomized study (AML-DBT) using the HSA-containing formulation (HSA-lenograstim). The median time of neutrophil recovery to > or = 1000/mm3 was significantly shorter in the gelatin-lenograstim group (14 days) than in the placebo group (21 days, P = .0001), and there was no significant difference between the gelatin-lenograstim group and the HSA-lenograstim group (14.5 days of AML-DBT, P = .5462). The incidences of febrile neutropenia were significantly reduced in the gelatin-lenograstim group (24/43, 55.8%) compared to the placebo group (58/64, 90.6%, P < .0001). The incidence of fever and antibiotic use was also significantly lower in the gelatin-lenograstim group (69.8% and 83.7%, respectively) than in the placebo group (92.2%, P = .0034, and 96.9%, P = .0285, respectively). However, between the 2 groups there were no differences in the number of patients who had infectious episodes. No serious adverse drug reactions ascribed to gelatin-lenograstim were encountered. These results demonstrate that gelatin-lenograstim exerted beneficial effects in the acceleration of neutrophil recovery and in the reduction of fever, febrile neutropenia, and antibiotic use, and its efficacy was equivalent to HSA-lenograstim. Therefore, we concluded that the gelatin-lenograstim formulation, which offers no risk of virus contamination and can be stored at room temperature, is more beneficial than the HSA-lenograstim formulation.

Cytokine and growth factor standardization: the need for research to answer modern issues.

New and novel cytokines are being discovered, cloned and entered into clinical trials at such a rate that often the biological activities of these proteins are poorly understood during their development as therapeutic agents. When estimating the biological activity of different preparations with different specific activities by bioassay, mass units cannot be used. Biological activity is therefore expressed as "biological potency units". Due to the pleiotropic nature of cytokine activity, the biological unit requires definition by a standard that is assay-independent. The need to investigate the biological activity of any proposed standard material in a variety of assays, with statistically valid numbers of participants and with appropriate scientific rationale, has led to the design of international collaborative studies that have provided extremely useful data about the biological activity of cytokines. Such information has had a great impact on the choice of material to serve as a standard and has prevented the establishment of inappropriate preparations. Over the years, WHO international standards have been used to reduce the variation in estimates of cytokine preparations within and between laboratories for both immunoassays and bioassays.

Recombinant human albumin as a stabilizer for biological materials and for the preparation of international reference reagents.

Recombinant human albumin expressed in Saccharomyces cerevisiae was compared with native human serum albumin in its physicochemical properties and in its use as a stabilizer in lyophilized preparations of thyroid-stimulating hormone (TSH), interleukin 15 (IL-15) and granulocyte colony-stimulating factor (G-CSF). Advantages of recombinant albumin include its lack of potential human contaminants and infectious agents. When used at concentrations of 0.1-0.2% (w/v), recombinant albumin was equivalent to native serum albumin in its capacity to protect immunological, biological and biochemical properties of TSH, IL-15 and G-CSF. Physicochemical characteristics of the two forms of albumin including their binding to fatty acids were also similar. The recombinant form of albumin used in this study should be considered as a suitable stabilizer in the preparation of lyophilized products and reference reagents.