Physicochemical studies on the stability of influenza haemagglutinin in vaccine bulk material

Zinc Carnosine Metal-Organic Coordination Polymer as a Potent Broadly Active Influenza Vaccine Platform with In Vitro Shelf-Stability

Current seasonal influenza vaccines are limited in that they need to be reformulated every year in order to account for the constant mutation of the virus. Hemagglutinin (HA) immunogens have been developed using a computationally optimized broadly reactive antigen (COBRA) methodology, which are able to elicit an antibody response that neutralizes antigenically distinct influenza strains; however, subunit proteins are not immunogenic enough on their own to generate a substantial immune response. Due to this, different delivery strategies and adjuvants can be used to improve immunogenicity. Recently, we reported a new coordination polymer composed of the dipeptide carnosine and zinc (ZnCar) that is able to deliver protein antigens along with CpG to generate a potent immune response. In the present work, ZnCar was used to deliver the COBRA HA immunogen Y2 and the adjuvant CpG. We incorporated Y2 into ZnCar using two different methods to assess which would be the most immunogenic. Mice vaccinated with Y2 and CpG complexed with ZnCar showed an improved humoral and cellular response when compared to mice vaccinated with soluble Y2 and CpG. Further, we demonstrate in vitro that when Y2 and CpG are coordinated with ZnCar, they are protected from degradation at 40 °C for 3 months or 24 °C for 6 months. Overall, ZnCar shows promise as a delivery vehicle for subunit vaccines, given its superior immunogenicity and in vitro storage stability.

Analysis of Biologics Molecular Descriptors towards Predictive Modelling for Protein Drug Development Using Time-Gated Raman Spectroscopy

Pharmaceutical proteins, compared to small molecular weight drugs, are relatively fragile molecules, thus necessitating monitoring protein unfolding and aggregation during production and post-marketing. Currently, many analytical techniques take offline measurements, which cannot directly assess protein folding during production and unfolding during processing and storage. In addition, several orthogonal techniques are needed during production and market surveillance. In this study, we introduce the use of time-gated Raman spectroscopy to identify molecular descriptors of protein unfolding. Raman spectroscopy can measure the unfolding of proteins in-line and in real-time without labels. Using K-means clustering and PCA analysis, we could correlate local unfolding events with traditional analytical methods. This is the first step toward predictive modeling of unfolding events of proteins during production and storage.

Structural Stability and Antigenicity of Universal Equine H3N8 Hemagglutinin Trimer upon Release from Polyanhydride Nanoparticles and Pentablock Copolymer Hydrogels

Seasonal influenza A virus infections present substantial costs to both health and economic resources each year. Current seasonal influenza vaccines provide suboptimal protection and require annual reformulation to match circulating strains. In this work, a recombinant equine H3N8 hemagglutinin trimer (rH3₃) known to generate cross-protective antibodies and protect animals against sublethal, heterologous virus challenge was used as a candidate vaccine antigen. Nanoadjuvants such as polyanhydride nanoparticles and pentablock copolymer hydrogels have been shown to be effective adjuvants, inducing both rapid and long-lived protective immunity against influenza A virus. In this work, polyanhydride nanoparticles and pentablock copolymer hydrogels were used to provide sustained release of the novel rH3₃ while also facilitating the retention of its structure and antigenicity. These studies lay the groundwork for the development of a novel universal influenza A virus nanovaccine by combining the equine H3N8 rH3₃ and polymeric nanoadjuvant platforms.

Inactivated influenza vaccine stress can affect in vitro potency assay relationship to immunogenicity

Influenza vaccines are the most effective intervention to prevent the substantial public health burden of seasonal and pandemic influenza. The capability of hemagglutinin (HA), the main antigen in inactivated influenza vaccines (IIVs), to elicit functional neutralizing antibodies determines IIV effectiveness. When HA is subjected to environmental stress during manufacturing or while stored prior to administration, such as low pH and temperature excursions, the HA immunological activity can be affected. Single-radial immunodiffusion (SRID), the standard in vitro potency assay for IIVs, is believed to specifically detect immunologically active HA and has been applied to evaluate HA stability against stress. Here we report that transient low pH treatment and freeze/thaw cycles with HA in PBS abolish SRID-quantified in vitro potency for all HAs of multiple influenza strains. Raised temperature substantially decreases in vitro potency with more extensive HA structural changes. Chemical stress and mechanical stress moderately change SRID in vitro potency values in a strain-dependent manner. Trypsin digestion, which selectively degrades stressed HA, followed by RP-HPLC quantification as a candidate alternative in vitro potency assay yields results comparable to SRID. Mouse immunogenicity studies confirm that HA stressed by transient low pH treatment does not elicit functional antibodies in vivo, nor does it have a measureable SRID value. However, HA stressed by raised temperature elicits high titers of functional antibodies in vivo despite substantial loss of SRID in vitro potency. This discrepancy between SRID in vitro potency and vaccine immunogenicity suggests that SRID may not reliably indicate IIV potency under all conditions. Further efforts to develop alternate potency assays that can better predict in vivo immunogenicity should continue along with additional studies exploring HA conformation, SRID values and consequent immunogenicity.

Development of a Freeze-Dried, Heat-Stable Influenza Subunit Vaccine Formulation

An influenza pandemic remains a major public health concern. A key strategy to prevent a pandemic is to stockpile and pre-position stable influenza vaccine to allow rapid deployment in response to an outbreak. However, most influenza vaccines today are formulated as liquids that are stable only within a temperature range of 2°C to 8°C and require use of a cold chain, making vaccine transportation, distribution, and storage complicated and expensive, particularly for developing countries. To support the National Strategy for Pandemic Influenza preparedness in the United States and internationally, we developed two lead dry formulations of stable H1N1 influenza subunit vaccines using freeze-drying technology. The stable formulations contain an excipient combination of a disaccharide, such as sucrose or trehalose, and glycine, in addition to a surfactant and phosphate buffer. The freeze-dried vaccines were shown to be safe and remained immunogenic in an in vivo study in mice. Moreover, the lead formulations demonstrated no significant loss of activity after 40 months at storage temperatures of 25°C and 37°C. This stability can be particularly attractive as it could eliminate the need to use a cold chain for vaccine deployment and facilitate integration of vaccine distribution with general drug distribution where appropriate. These freeze-dried thermostable influenza subunit vaccines could also reduce the frequency of vaccine stockpile turnover, offering a cost-effective option for pandemic preparedness.

Evaluating influenza vaccines: progress and perspectives

Severe influenza infections are responsible for 3–5 million cases worldwide and 250,000–500,000 deaths per year. Although vaccination is the primary and most effective means of inducing protection against influenza viruses, it also presents limitations. This review outlines the promising steps that have been taken toward the development of a broadly protective influenza virus vaccine through the use of new technologies. The future challenge is to develop a broadly protective vaccine that is able to induce long-term protection against antigenically variant influenza viruses, regardless of antigenic shift and drift, and thus to protect against seasonal and pandemic influenza viruses.

Evaluation of Epic® label-free technology to quantify functional recombinant hemagglutinin

Background

Alternative methods are being sought to measure the potency of influenza vaccines. Label-free technologies that do not require the use of hemagglutinin (HA)-specific antisera are particularly attractive as the preparation of antiserum delays availability of potency reagents. The objective of these experiments was to evaluate the use of a Corning Epic® label-free method to quantify functional influenza hemagglutinin in rHA preparations. The method was optimized to quantify recombinant HA (rHA) of B/Brisbane/60/2008 (B/BR/08). Fetuin was immobilized onto plates and the change in wavelength of refracted light measured using an Enspire (Perkin Elmer) instrument.

Results

The change in wavelength measured in response to addition of rHA of B/BR/08 was proportional to its concentration and was optimal in the presence of native rHA conformations. However, the assay was strain-dependent and did not correlate with HAU measured using turkey red blood cells.

Conclusions

The Corning Epic® label-free method is suitable for quantifying the native forms of rHA for B/BR/08 and A/Brisbane/59/2007 (H1N1) and A/Hangxhou/3/2013 (H7N9). This method is a useful tool for research purposes but further investigation is needed to identify suitable glycoproteins to use as ligands that allow quantification of HAs from a broader range of virus strains.

Electronic supplementary material

The online version of this article (doi:10.1186/s12575-015-0019-5) contains supplementary material, which is available to authorized users.

The effect of stable macromolecular complexes of ionic polyphosphazene on HIV Gag antigen and on activation of human dendritic cells and presentation to T-cells

Neonates and infants are susceptible to infection due to distinct immune responses in early life. Therefore, development of vaccine formulation and delivery systems capable of activating human newborn leukocytes is of global health importance. Poly[di(carboxylatophenoxy)phosphazene] (PCPP) belongs to a family of ionic synthetic polyphosphazene polyelectrolyte compounds that can form non-covalent interactions with protein antigens and demonstrate adjuvant activity in animals and in human clinical trials. However, little is known about their ability to activate human immune cells. In this study, we characterized the effects of PCPP alone or in combination with a model antigen (recombinant HIV-Gag (Gag)), on the maturation, activation and antigen presentation by human adult and newborn dendritic cells (DCs) in vitro. PCPP treatment induced DC activation as assessed by upregulation of co-stimulatory molecules and cytokine production. Studies benchmarking PCPP to Alum, the most commonly used vaccine adjuvant, demonstrated that both triggered cell death and release of danger signals in adult and newborn DCs. When complexed with Gag antigen, PCPP maintained its immunostimulatory characteristics while permitting internalization and presentation of Gag by DCs to HIV-Gag-specific CD4(+) T cell clones. The PCPP vaccine formulation outlined here has intrinsic adjuvant activity, can facilitate effective delivery of antigen to DCs, and may be advantageous for induction of beneficial T cell-mediated immunity. Moreover, polyphosphazenes can further reduce cost of vaccine production and distribution through their dose-sparing and antigen-stabilizing properties, thus potentially eliminating the need for cold chain distribution.

Novel antibody-independent receptor-binding SPR-based assay for rapid measurement of influenza vaccine potency

A WHO workshop organized following the 2009 H1N1 pandemic recommended development of alternative influenza vaccine potency assays as high priority that could expedite the release of vaccine lots in the face of future influenza pandemics. We have developed an antibody independent, simple, high throughput receptor-binding SPR-based potency assay, which does not require any reference antisera and could be used for rapid HA quantitation and vaccine release in pandemic scenarios. The assay utilizes synthetic glycans with sialic acid (SA) of either α-2,6 or α-2,3 linkage to galactose. Only functionally active forms of HA (trimers and oligomers) recognize the SA-glycans and are quantified in this receptor-binding SPR assay. The SA-glycan SPR assay demonstrated broad dynamic range for quantitation of HA content in influenza vaccines from different manufacturers for both seasonal (A/H1N1, A/H3N2, B lineages) and pandemic influenza (A/H5N1, A/H7N9) strains with high reproducibility and low variability across multiple assays. In addition, the SA-glycan SPR assay is indicative of active HA stability, and can accurately quantify HA content in alum and oil-in-water adjuvanted influenza vaccines. Importantly, there was a good agreement between HA content determined by the SPR-based potency assay and the traditional SRID assay.

Simplifying influenza vaccination during pandemics: sublingual priming and intramuscular boosting of immune responses with heterologous whole inactivated influenza vaccine

The best approach to control the spread of influenza virus during a pandemic is vaccination. Yet, an appropriate vaccine is not available early in the pandemic since vaccine production is time consuming. For influenza strains with a high pandemic potential like H5N1, stockpiling of vaccines has been considered but is hampered by rapid antigenic drift of the virus. It has, however, been shown that immunization with a given H5N1 strain can prime the immune system for a later booster with a drifted variant. Here, we investigated whether whole inactivated virus (WIV) vaccine can be processed to tablets suitable for sublingual (s.l.) use and whether s.l. vaccine administration can prime the immune system for a later intramuscular (i.m.) boost with a heterologous vaccine. In vitro results demonstrate that freeze-drying and tableting of WIV did not affect the integrity of the viral proteins or the hemagglutinating properties of the viral particles. Immunization experiments revealed that s.l. priming with WIV (prepared from the H5N1 vaccine strain NIBRG-14) 4 weeks prior to i.m. booster immunization with the same virus strongly enhanced hemagglutination-inhibition (HI) titers against NIBRG-14 and the drifted variant NIBRG-23. Moreover, s.l. (and i.m.) immunization with NIBRG-14 also primed for a subsequent heterologous i.m. booster immunization with NIBRG-23 vaccine. In addition to HI serum antibodies, s.l. priming enhanced lung and nose IgA responses, while i.m. priming enhanced lung IgA but not nose IgA levels. Our results identify s.l. vaccination as a user-friendly method to prime for influenza-specific immune responses toward homologous and drifted variants.

The osmotic stress response of split influenza vaccine particles in an acidic environment

Oral influenza vaccine provides an efficient means of preventing seasonal and pandemic disease. In this work, the stability of envelope-type split influenza vaccine particles in acidic environments has been investigated. Owing to the fact that hyper-osmotic stress can significantly affect lipid assembly of vaccine, osmotic stress-induced morphological change of split vaccine particles, in conjunction with structural change of antigenic proteins, was investigated by the use of stopped-flow light scattering (SFLS), intrinsic fluorescence, transmission electron microscopy (TEM), and hemagglutination assay. Split vaccine particles were found to exhibit a step-wise morphological change in response to osmotic stress due to double-layered wall structure. The presence of hyper-osmotic stress in acidic medium (0.3 osmolarity, pH 2.0) induced a significant level of membrane perturbation as measured by SFLS and TEM, imposing more damage to antigenic proteins on vaccine envelope than can be caused by pH-induced conformational change at acidic iso-osmotic condition. Further supports were provided by the intrinsic fluorescence and hemagglutinin activity measurements. Thus, hyper-osmotic stress becomes an important factor for determining stability of split vaccine particles in acidic medium. These results are useful in better understanding the destabilizing mechanism of split influenza vaccine particles in gastric environment and in designing oral influenza vaccine formulations.

A novel synthetic receptor-based immunoassay for influenza vaccine quantification

Vaccination is the most effective prophylactic method for preventing influenza. Quantification of influenza vaccine antigens is critically important before the vaccine is used for human immunization. Currently the vaccine antigen quantification relies on hemagglutinin content quantification, the key antigenic component, by single radial immunodiffusion (SRID) assay. Due to the inherent disadvantages associated with the traditional SRID; i.e. low sensitivity, low throughput and need for annual reagents, several approaches have been proposed and investigated as alternatives. Yet, most alternative methods cannot distinguish native hemagglutinin from denatured form, making them less relevant to antigenic analyses. Here, we developed a quantitative immunoassay based on the sialic acid binding property of influenza vaccine antigens. Specifically, we chemically synthesized human and avian influenza virus receptors analogues, N-acetylneuraminic acid-2,6-lactose and N-acetylneuraminic acid-2,3-lactose derivatives with an azidopropyl aglycon, using α-2,6- and α-2,3-sialyltransferases, respectively. The azido group of the two sialyllactose-derivatives was reduced and conjugated to mouse serum albumin through a squarate linkage. We showed that the synthetic α-2,6- and α-2,3-receptors selectively bound to human and avian-derived hemagglutinins, respectively, forming the basis of a new, and robust assay for hemagglutinin quantification. Hemagglutinin treated at high temperature or low pH was measured differentially to untreated samples suggesting native conformation is dependent for optimal binding. Importantly, this receptor-based immunoassay showed excellent specificity and reproducibility, high precision, less turnaround time and significantly higher sensitivity and throughput compared with SRID in analyzing multiple influenza vaccines.

Modifying the thermostability of inactivated influenza vaccines

BACKGROUND

Respiratory infections caused by influenza viruses spread rapidly, resulting in significant annual morbidity and mortality worldwide. Currently, the most effective public health measure against infection is immunisation with an influenza vaccine matching the relevant circulating influenza strains. Although a number of developments in terms of influenza vaccine production, safety and immunogenicity have been reported, limitations in our understanding of vaccine stability still exist. In this report we seek to identify compounds that increase influenza vaccine thermostability.

METHODS

We use plaque inhibition on confluent MDCK cells to identify compounds which inhibit the entry of various seed strain viruses. The effect of these compounds on vaccine thermal lability is evaluated through SRID analysis. The significance of these results is tested by a two-way analysis of variance (ANOVA) method.

RESULTS

We identify two compounds which selectively inhibit entry of different group I or group II influenza strains through prevention of the neutral-pH to low-pH conformational change of hemagglutinin. Compounds which were able to inhibit virus entry were also able to limit thermally induced potency loss in matched influenza vaccines. Furthermore, we demonstrate that this effect is independent of product formulation or the presence of multiple HA types.

CONCLUSIONS

This work provides further evidence for a link between HA conformational stability in the virus and thermostability of the corresponding vaccine preparation. It also suggests straightforward approaches to improve the stability and predictability of influenza vaccine preparations.

Stability of seasonal influenza vaccines investigated by spectroscopy and microscopy methods

The stability of different seasonal influenza vaccines was investigated by spectroscopy and microscopy methods before and after the following stress-conditions: (i) 2 and 4 weeks storage at 25°C, (ii) 1 day storage at 37°C and (iii) one freeze-thaw cycle. The subunit vaccine Influvac (Solvay Pharma) and the split vaccine Mutagrip (Sanofi Pasteur) were affected by all stresses. The split vaccine Fluarix (GlaxoSmithKline) was affected only by storage at 25°C. The virosomal vaccine Inflexal V (Berna Biotech) was stable after the temperature stresses but aggregated after one freeze-thaw cycle. This study provides new insights into commercial vaccines of low antigen concentration and highlights the importance of using multiple techniques to assess vaccine stability.

Confronting the next pandemic--workshop on lessons learned from potency testing of pandemic (H1N1) 2009 influenza vaccines and considerations for future potency tests, Ottawa, Canada, July 27-29, 2010

Please cite this paper as: Hardy et al. (2011) Confronting the next pandemic—Workshop on lessons learned from potency testing of pandemic (H1N1) 2009 influenza vaccines and considerations for future potency tests, Ottawa, Canada, July 27–29, 2010. Influenza and Other Respiratory Viruses 5(6), 438–442.

Dry powder vaccines for mucosal administration: critical factors in manufacture and delivery

Dry powder vaccine formulations have proved effective for induction of systemic and mucosal immune responses. Here we review the use of dry vaccines for immunization in the respiratory tract. We discuss techniques for powder formulation, manufacture, characterization and delivery in addition to methods used for evaluation of stability and safety. We review the immunogenicity and protective efficacy of dry powder vaccines as compared to liquid vaccines delivered by mucosal or parenteral routes. Included is information on mucosal adjuvants and mucoadhesives that can be used to enhance nasal or pulmonary dry vaccines. Mucosal immunization with dry powder vaccines offers the potential to provide a needle-free and cold chain-independent vaccination strategy for the induction of protective immunity against either systemic or mucosal pathogens.

PCPP-formulated H5N1 influenza vaccine displays improved stability and dose-sparing effect in lethal challenge studies

The potential impact of an influenza pandemic can be mitigated through the realization of a successful vaccination program. The implementation of antigen stabilization and dose-sparing technologies is an important step in improving availability of vaccines at the time of a pandemic outbreak. We investigated poly[di(carboxylatophenoxy)phosphazene] (PCPP) as a potential stabilizing and immunostimulating agent for H5N1 influenza vaccine. Physicochemical characterization of PCPP-formulated H5N1 influenza vaccine revealed macromolecular complexation in the system, whereas single radial immunodiffusion assay verified antigenicity of the formulation in vitro. PCPP-enhanced formulation displayed a fourfold increase in the half-life at 40°C compared with a nonadjuvanted vaccine. Lethal challenge studies in ferrets demonstrated 100% protection for low-antigen dose PCPP-adjuvanted formulations (1 μg of hemagglutinin) and at least a 10-fold antigen-sparing effect. Therefore, PCPP demonstrated an ability to improve thermal stability of H5N1 influenza vaccine in solutions and provide for a substantial dose-sparing effect in vivo.

Stability of protein pharmaceuticals: an update

In 1989, Manning, Patel, and Borchardt wrote a review of protein stability (Manning et al., Pharm. Res. 6:903-918, 1989), which has been widely referenced ever since. At the time, recombinant protein therapy was still in its infancy. This review summarizes the advances that have been made since then regarding protein stabilization and formulation. In addition to a discussion of the current understanding of chemical and physical instability, sections are included on stabilization in aqueous solution and the dried state, the use of chemical modification and mutagenesis to improve stability, and the interrelationship between chemical and physical instability.

Development of stable influenza vaccine powder formulations: challenges and possibilities

Influenza vaccination represents the cornerstone of influenza prevention. However, today all influenza vaccines are formulated as liquids that are unstable at ambient temperatures and have to be stored and distributed under refrigeration. In order to stabilize influenza vaccines, they can be brought into the dry state using suitable excipients, stabilizers and drying processes. The resulting stable influenza vaccine powder is independent of cold-chain facilities. This can be attractive for the integration of the vaccine logistics with general drug distribution in Western as well as developing countries. In addition, a stockpile of stable vaccine formulations of potential vaccines against pandemic viruses can provide an immediate availability and simple distribution of vaccine in a pandemic outbreak. Finally, in the development of new needle-free dosage forms, dry and stable influenza vaccine powder formulations can facilitate new or improved targeting strategies for the vaccine compound. This review represents the current status of dry stable inactivated influenza vaccine development. Attention is given to the different influenza vaccine types (i.e. whole inactivated virus, split, subunit or virosomal vaccine), the rationale and need for stabilized influenza vaccines, drying methods by which influenza vaccines can be stabilized (i.e. lyophilization, spray drying, spray-freeze drying, vacuum drying or supercritical fluid drying), the current status of dry influenza vaccine development and the challenges for ultimate market introduction of a stable and effective dry-powder influenza vaccine.

Transcutaneous delivery and thermostability of a dry trivalent inactivated influenza vaccine patch

A patch containing a trivalent inactivated influenza vaccine (TIV) was prepared in a dried, stabilized formulation for transcutaneous delivery. When used in a guinea pig immunogenicity model, the dry patch was as effective as a wet TIV patch in inducing serum anti-influenza IgG antibodies. When the dry TIV patch was administered with LT as an adjuvant, a robust immune response was obtained that was comparable with or better than an injected TIV vaccine. When stored sealed in a nitrogen-purged foil, the dry TIV patch was stable for 12 months, as measured by HA content, under both refrigerated and room temperature conditions. Moreover, the immunological potency of the vaccine product was not affected by long-term storage. The dry TIV patch was also thermostable against three cycles of alternating low-to-high temperatures of -20/25 and -20/40 degrees C, and under short-term temperature stress conditions. These studies indicate that the dry TIV patch product can tolerate unexpected environmental stresses that may be encountered during shipping and distribution. Because of its effectiveness in vaccine delivery and its superior thermostable characteristics, the dry TIV patch represents a major advance for needle-free influenza vaccination.

Rational design of an influenza subunit vaccine powder with sugar glass technology: Preventing conformational changes of haemagglutinin during freezing and freeze-drying

The development of a stable influenza subunit vaccine in the dry state was investigated. The influence of various carbohydrates, buffer types and freezing rates on the integrity of haemagglutinin after freeze-thawing or freeze-drying was investigated with a range of analytical and immunological methods. The use of fast freezing, Hepes buffer and carbohydrates (trehalose, inulin or dextran) as cryo- and lyoprotectants resulted in a significant reduction or even absence of conformational changes of HA as revealed by the used methods. The subunit vaccine in the powder was shown to remain immunogenic in an in vivo study in mice, using reconstituted powder. Moreover, the HA potency of the influenza subunit vaccine powder was stable for at least 26 weeks at room temperature.

HPLC and tandem detection to monitor conformational properties of biopharmaceuticals

High-performance liquid chromatography (HPLC) with UV, circular dichroism (CD) and intrinsic fluorescence detection was applied to monitor conformational properties of recombinant human interferon alpha2b when performing size exclusion chromatography (SEC) and reversed-phase HPLC (RP-HPLC). In this way native conditions during SEC and structural changes of the protein during RP-HPLC were demonstrated. These results were confirmed by stand-alone fluorescence and CD measurements. With respect to HPLC tandem detection, the fluorescence detector compared favourably to the UV and CD detector regarding linearity, sensitivity and selectivity. SEC combined with intrinsic fluorescence scanning detection permits conformational analysis of small amounts of aggregates in the presence of excess native monomeric protein. In conclusion, HPLC with on-line UV and intrinsic fluorescence detection provides a promising concept for analysing the amount and conformational properties of a biopharmaceutical and its impurities.

High-performance anion-exchange chromatography combined with intrinsic fluorescence detection to determine erythropoietin in pharmaceutical products

A high-performance anion-exchange chromatography (HPAEC) method was developed for determination of recombinant human erythropoietin (EPO) in pharmaceutical products. A fluorescence detector was added to the HPLC system as intrinsic fluorescence detection compared favourably to UV detection regarding sensitivity and selectivity. The HPLC method has been successfully applied to analyse erythropoietin products even in the presence of albumin as excipient. The intrinsic fluorescence chromatograms of both proteins revealed various peaks attributed to either micro-heterogeneous erythropoietin or albumin variants. The intrinsic fluorescence signal was linear over the range 10-200 microg/ml erythropoietin corresponding to pharmaceutically relevant concentrations. The HPLC method appeared to be a suitable method for differentation between recombinant human erythropoietin epoetin-alpha and -beta as they revealed different intrinsic fluorescence elution profiles. In conclusion, this study contributes to the development of a straightforward physicochemical method for specific quantification of recombinant human erythropoietin in pharmaceutical preparations.