Protein Engineering and HDX Identify Structural Regions of G-CSF Critical to Its Stability and Aggregation.

The protein engineering and formulation of therapeutic proteins for prolonged shelf-life remain a major challenge in the biopharmaceutical industry. Understanding the influence of mutations and formulations on the protein structure and dynamics could lead to more predictive approaches to their improvement. Previous intrinsic fluorescence analysis of the chemically denatured granulocyte colony-stimulating factor (G-CSF) suggested that loop AB could subtly reorganize to form an aggregation-prone intermediate state. Hydrogen deuterium exchange mass spectrometry (HDX-MS) has also revealed that excipient binding increased the thermal unfolding transition midpoint (Tm) by stabilizing loop AB. Here, we have combined protein engineering with biophysical analyses and HDX-MS to reveal that increased exchange in a core region of the G-CSF comprising loop AB (ABI, a small helix, ABII) and loop CD packed onto helix B and the beginning of loop BC leads to a decrease in Tm and higher aggregation rates. Furthermore, some mutations can increase the population of the aggregation-prone conformation within the native ensemble, as measured by the greater local exchange within this core region.

WHO informal consultation on revision of guidelines on evaluation of similar biotherapeutic products, virtual meeting, 30 June - 2 July 2021.

The WHO informal consultation was held to promote the revision of WHO guidelines on evaluation of similar biotherapeutic products (SBPs) adopted by the Expert Committee on Biological Standardization (ECBS) in 2009. It was agreed in the past consultations that the evaluation principles in the guidelines are still valid, but a review was recommended to provide more clarity and case-by-case flexibility. The opportunity was therefore taken to review the experience and identify areas where the current guidance could be more permissive without compromising its basic principles, and where additional explanation could be provided regarding the possibility of reducing the amount of data needed for regulatory approval. The meeting participants applauded the leading role taken by the WHO in providing a much-needed streamlined approach for development and evaluation of SBPs which will provide efficient and cost-effective product development and increase patient access to treatments. It was recognized that the principles as currently described in the draft WHO guidelines are based on sound science and experience gained over the last fifteen years of biosimilar approvals. However, since these guidelines when finalised will constitute the global standard for biosimilar evaluation and assist national regulatory authorities in establishing revised guidance and regulatory practice in this complex area, it was felt that further revision and clarity on certain perspectives in specific areas was necessary to dispel uncertainties arising in the current revised version. This report describes the principles in the draft guidelines, including topics discussed and consensus reached.

The impact of thioredoxin reduction of allosteric disulfide bonds on the therapeutic potential of monoclonal antibodies.

Therapeutic mAbs are used to manage a wide range of cancers and autoimmune disorders. However, mAb-based treatments are not always successful, highlighting the need for a better understanding of the factors influencing mAb efficacy. Increased levels of oxidative stress associated with several diseases are counteracted by the activities of various oxidoreductase enzymes, such as thioredoxin (Trx), which also reduces allosteric disulfide bonds in proteins, including mAbs. Here, using an array of in vitro assays, we explored the functional effects of Trx-mediated reduction on the mechanisms of action of six therapeutic mAbs. We found that Trx reduces the interchain disulfide bonds of the mAbs, after which they remain intact but have altered function. In general, this reduction increased antigen-binding capacity, resulting in, for example, enhanced tumor necrosis factor (TNF) neutralization by two anti-TNF mAbs. Conversely, Trx reduction decreased the antiproliferative activity of an anti-tyrosine kinase-type cell-surface receptor HER2 mAb. In all of the mAbs, Fc receptor binding was abrogated by Trx activity, with significant loss in both complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC) activity of the mAbs tested. We also confirmed that without alkylation, Trx-reduced interchain disulfide bonds reoxidize, and ADCC activity is restored. In summary, Trx-mediated reduction has a substantial impact on the functional effects of an mAb, including variable effects on antigen binding and Fc function, with the potential to significantly impact mAb efficacy in vivo.

WHO implementation workshop on guidelines on procedures and data requirements for changes to approved biotherapeutic products, Seoul, Republic of Korea, 25-26 June 2019.

The first global workshop on implementation of the WHO guidelines on procedures and data requirements for changes to approved biotherapeutic products adopted by the WHO Expert Committee in 2018 was held in June 2019. The workshop participants recognized that the principles based on sound science and the potential for risk, as described in the WHO Guidelines on post-approval changes, which constitute the global standard for product life-cycle management are providing clarity and helping national regulatory authorities in establishing guidance while improving time-lines for an efficient regulation of products. Consequently, the regulatory situation for post-approval changes and guideline implementation is changing but there is a disparity between different countries. While the guidelines are gradually being implemented in some countries and also being considered in other countries, the need for regional workshops and further training on post-approval changes was a common theme reiterated by many participants. Given the complexities relating to post-approval changes in different regions/countries, there was a clear understanding among all participants that an efficient approach for product life-cycle management at a national level is needed to ensure faster availability of high standard, safe and efficacious medicines to patients as per the World Health Assembly Resolution 67.21.

Reprint of "Anti-therapeutic antibodies and their clinical impact in patients treated with the TNF antagonist adalimumab".

Patients treated with the TNF antagonist adalimumab develop anti-therapeutic antibodies (ATA), the prevalence of which varies depending on the assay used. Most assays are compromised due to the presence of adalimumab in the clinical samples. Our objective was to develop an antibody assay, applicable for clinical testing, which overcomes the limitation of therapeutic interference and to further determine the relationship between ATA development, adalimumab levels and disease activity in patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA) or ankylosing spondylitis (AS). Use of an electrochemiluminescence platform permitted development of fit-for-purpose immunoassays. Serum samples from patients, taken prior to and at 12 and 24 weeks of treatment, were retrospectively analysed for levels of adalimumab and ATA. Overall, the antibody prevalence was 43.6% at 12 weeks and 41% at 24 weeks of treatment. Disruption of immune complexes by acid dissociation, a strategy often adopted for this purpose, only marginally increased the antibody prevalence to 48.7% and 46% at 12 and 24 weeks respectively. We found that antibody formation was associated with decreasing levels of circulating adalimumab, but no direct effect on disease activity was evident as assessed using DAS28 for RA patients and BASDAI for PsA and AS patients. However, a negative correlation of free adalimumab trough levels with disease activity scores was observed. Data showed that adalimumab levels can serve as an indicator of ATA development which can then be confirmed by ATA testing. Monitoring of both therapeutic and antibodies should be considered during adalimumab therapy to allow clinicians to personalise treatments for maximal therapeutic outcomes.

WHO informal consultation on development of guidelines on procedures and data requirements for changes to approved biotherapeutic products, Seoul, Republic of Korea, 27-28 April 2017.

In April 2017, WHO convened an informal consultation to develop WHO guidelines on procedures and data requirements for changes to approved biotherapeutic products. The objective of the meeting was to review the draft of WHO guidelines and the comments received from the public consultation. The guidelines were recognized by the participants as a tool for regulatory convergence and harmonization. Regulation of changes to approved biotherapeutic products is a key in ensuring that products of consistent quality, safety and efficacy are distributed after they receive authorization or licensure. Participants agreed that the guidelines would contribute to assuring the continued quality, safety and efficacy throughout the life-cycle of biotherapeutics as well as continuity in supply and access. In the meeting, participants further requested WHO should assist national regulatory authorities in improving technical expertise in the evaluation of biotherapeutics and their post-approval changes by organizing implementation workshops and developing case studies and e-training modules on various technical topics. At its meeting in October 2017, the WHO Expert Committee on Biological Standardization formally adopted the WHO guidelines on procedures and data requirements for changes to approved biotherapeutic products.

Influence of Escherichia coli chaperone DnaK on protein immunogenicity.

The production of anti-drug antibodies can impact significantly upon the safety and efficacy of biotherapeutics. It is known that various factors, including aggregation and the presence of process-related impurities, can modify and augment the immunogenic potential of proteins. The purpose of the investigations reported here was to characterize in mice the influence of aggregation and host cell protein impurities on the immunogenicity of a humanized single-chain antibody variable fragment (scFv), and mouse albumin. Host cell protein impurities within an scFv preparation purified from Escherichia coli displayed adjuvant-like activity for responses to the scFv in BALB/c strain mice. The 70 000 MW E. coli chaperone protein DnaK was identified as a key contaminant of scFv by mass spectrometric analysis. Preparations of scFv lacking detectable DnaK were spiked with recombinant E. coli DnaK to mimic the process-related impurity. Mice were immunized with monomeric and aggregated preparations, with and without 0·1% DnaK by mass. Aggregation alone enhanced IgM and IgG2a antibody responses, but had no significant effect on total IgG or IgG1 responses. The addition of DnaK further enhanced IgG and IgG2a antibody responses, but only in the presence of aggregated protein. DnaK was shown to be associated with the aggregated scFv by Western blot analysis. Experiments with mouse albumin showed an overall increase in immunogenicity with protein aggregation alone, and the presence of DnaK increased the vigour of the IgG2a antibody response further. Collectively these data reveal that DnaK has the potential to modify and enhance immunogenicity when associated with aggregated protein.

Anti-therapeutic antibodies and their clinical impact in patients treated with the TNF antagonist adalimumab.

Patients treated with the TNF antagonist adalimumab develop anti-therapeutic antibodies (ATA), the prevalence of which varies depending on the assay used. Most assays are compromised due to the presence of adalimumab in the clinical samples. Our objective was to develop an antibody assay, applicable for clinical testing, which overcomes the limitation of therapeutic interference and to further determine the relationship between ATA development, adalimumab levels and disease activity in patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA) or ankylosing spondylitis (AS). Use of an electrochemiluminescence platform permitted development of fit-for-purpose immunoassays. Serum samples from patients, taken prior to and at 12 and 24weeks of treatment, were retrospectively analysed for levels of adalimumab and ATA. Overall, the antibody prevalence was 43.6% at 12weeks and 41% at 24weeks of treatment. Disruption of immune complexes by acid dissociation, a strategy often adopted for this purpose, only marginally increased the antibody prevalence to 48.7% and 46% at 12 and 24weeks respectively. We found that antibody formation was associated with decreasing levels of circulating adalimumab, but no direct effect on disease activity was evident as assessed using DAS28 for RA patients and BASDAI for PsA and AS patients. However, a negative correlation of free adalimumab trough levels with disease activity scores was observed. Data showed that adalimumab levels can serve as an indicator of ATA development which can then be confirmed by ATA testing. Monitoring of both therapeutic and antibodies should be considered during adalimumab therapy to allow clinicians to personalise treatments for maximal therapeutic outcomes.

Immunogenicity assessment of biotherapeutic products: An overview of assays and their utility.

Biotherapeutic products (BTPs) are the fastest growing medicines in the pharmaceutical market. Despite their clinical success, the immunogenicity of BTPs continues to be a major concern. Assessment of immunogenicity as well as appropriate interpretation of immunogenicity data is therefore, of critical importance for defining safety profile of these products for the purpose of their licensure and use. In the past decade, much progress has been made towards how immunogenicity should be studied. This article reflects the content of the brief presentation on principles of methods used for immunogenicity assessment and their merits and limitations given at the first World Health Organization (WHO) implementation workshop on rDNA derived biotherapeutic products held in the Republic of Korea in May 2014 to support the case studies on immunogenicity presented and discussed during the workshop. The purpose of this article is to provide an overview of the methods used for assessing immunogenicity of biotherapeutic products (BTPs) and the most important considerations in interpreting results in the context of regulatory overview of these products.

Biosimilars: what clinicians should know.

Biosimilar medicinal products (biosimilars) have become a reality in the European Union and will soon be available in the United States. Despite an established legal pathway for biosimilars in the European Union since 2005 and increasing and detailed regulatory guidance on data requirements for their development and licensing, many clinicians, particularly oncologists, are reluctant to consider biosimilars as a treatment option for their patients. Major concerns voiced about biosimilars relate to their pharmaceutical quality, safety (especially immunogenicity), efficacy (particularly in extrapolated indications), and interchangeability with the originator product. In this article, the members and experts of the Working Party on Similar Biologic Medicinal Products of the European Medicines Agency (EMA) address these issues. A clear understanding of the scientific principles of the biosimilar concept and access to unbiased information on licensed biosimilars are important for physicians to make informed and appropriate treatment choices for their patients. This will become even more important with the advent of biosimilar monoclonal antibodies. The issues also highlight the need for improved communication between physicians, learned societies, and regulators.

2023 White Paper on Recent Issues in Bioanalysis: EU IVDR 2017/746 Implementation/Impact, IVD/CDx/CLIA Approved Assays, High Dimensional Cytometry, Multiplexing Technologies, LBA Tissue Analysis, Vaccine Study Endpoints, Cell-Based Assays for Biomarkers, Cell Therapy and Vaccines (PART 2 - Recommendations on Development & Validation of Biomarkers, IVD, CDx, Cell-Based, Flow Cytometry, Ligand-Binding and Enzyme Assays; Advanced Critical Reagents Strategies).

The 17th Workshop on Recent Issues in Bioanalysis (17th WRIB) took place in Orlando, FL, USA on 19-23 June 2023. Over 1000 professionals representing pharma/biotech companies, CROs, and multiple regulatory agencies convened to actively discuss the most current topics of interest in bioanalysis. The 17th WRIB included 3 Main Workshops and 7 Specialized Workshops that together spanned 1 week to allow an exhaustive and thorough coverage of all major issues in bioanalysis of biomarkers, immunogenicity, gene therapy, cell therapy and vaccines.Moreover, in-depth workshops on "EU IVDR 2017/746 Implementation and impact for the Global Biomarker Community: How to Comply with these NEW Regulations" and on "US FDA/OSIS Remote Regulatory Assessments (RRAs)" were the special features of the 17th edition.As in previous years, WRIB continued to gather a wide diversity of international, industry opinion leaders and regulatory authority experts working on both small and large molecules as well as gene, cell therapies and vaccines to facilitate sharing and discussions focused on improving quality, increasing regulatory compliance, and achieving scientific excellence on bioanalytical issues.This 2023 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2023 edition of this comprehensive White Paper has been divided into three parts for editorial reasons.This publication (Part 2) covers the recommendations on Biomarkers, IVD/CDx, LBA and Cell-Based Assays. Part 1A (Mass Spectrometry Assays and Regulated Bioanalysis/BMV), P1B (Regulatory Inputs) and Part 3 (Gene Therapy, Cell therapy, Vaccines and Biotherapeutics Immunogenicity) are published in volume 16 of Bioanalysis, issues 9 and 7 (2024), respectively.

Immunoglobulin G1 and immunoglobulin G4 antibodies in multiple sclerosis patients treated with IFNß interact with the endogenous cytokine and activate complement.

A subset of patients with relapsing-remitting multiple sclerosis (RRMS) on therapy with interferon beta (IFNß) develop neutralising anti-drug antibodies (ADA) resulting in reduced, or loss of, therapeutic efficacy. The aims were to characterise the relative contributions of anti-IFNß antibody isotypes to drug neutralising activity, ability of these antibodies to cross-react with endogenous IFNß, to form immune complexes and activate complement. IFNß-specific ADA were measured in plasma from RRMS patients treated with IFNß1a (Rebif(®)). Neutralisation of endogenous and therapeutic IFNß by ADA was determined by IFNß bioassay. IFNß-ADA profile was predominantly comprised of IgG1 and IgG4 antibody isotypes. The contribution of IgG4-ADA towards neutralising activity was found to be minimal. Neutralising IFNß-ADA blocks endogenous IFNß activity. ADA interaction with therapeutic IFNß results in immune complex formation and complement activation. In summary, IgG1 and IgG4 IFNß-ADA have the ability to neutralise therapeutic and endogenous protein and to activate complement.

Severity of the TGN1412 trial disaster cytokine storm correlated with IL-2 release.

AIM: To determine if cytokine release with a solid phase assay is predictive of adverse responses for a range of therapeutic mAbs. METHODS: Cytokine ELISAs and a multi-array system were used to compare responses generated by different therapeutic mAbs using a solid phase assay. Flow cytometry was employed to determine the cellular source of those cytokines. RESULTS: Only TGN1412 and muromonab-CD3 stimulated CD4+ T-cell mediated cytokine release characterized by significant (all P < 0.0001) IFNγ, TNFα, IL-2, IL-4, IL-5, IL-10, IL-12, IL-13, IL-17 and IL-22 release, comparable with T-cell mitogen. Significantly greater (P < 0.0001) IL-2 release with TGN1412 (2894-6051 pg ml⁻¹) compared with muromonab-CD3 (62-262 pg ml⁻¹) differentiated otherwise comparable cytokine responses. Likewise, TGN1412 stimulated significantly more (P = 0.0001) IL-2 producing CD4+ T-cells than muromonab-CD3 and induced Th1, Th2, Th17 and Th22 subsets that co-release this cytokine. Significant TNFα release was observed with bevacizumab (P = 0.0001), trastuzumab (P = 0.0031) and alemtuzumab (P = 0.0177), but no significant IL-2 release. TGN1412 and muromonab-CD3 caused pro-inflammatory cytokine release despite significantly (both P < 0.0001) increasing numbers of T-cells with a regulatory phenotype. CONCLUSIONS: The severity of the adverse response to TGN1412 compared with muromonab-CD3 and other therapeutic mAbs correlates with the level of IL-2 release.

WHO guidelines on biosimilars: Toward improved access to safe and effective products.

The World Health Assembly resolution on access to biotherapeutics in 2014 urges WHO and Member States to facilitate access to biotherapeutics while ensuring their quality, safety, and efficacy. While efforts to date have contributed to increased availability and better access to biotherapeutics, including biosimilars, huge gaps still remain, with lack of product access identified as a problem in many countries. A thorough review of the WHO guidelines on biosimilars issued in 2009 in view of technical developments, accumulated and emerging scientific evidence as well as experience in biosimilar evaluation since the release of the guidelines provided an opportunity to introduce greater flexibility and to reduce regulatory requirements in biosimilar development where possible. Based on the identification, draft revisions of the WHO guidelines were prepared with input from extensive consultation with various stakeholders and the broader public. The move toward a greater emphasis on quality and functional in vitro assessment enables the reduction of cost and timelines of development and supports streamlined regulatory approval as a first critical step toward product availability. This article includes the key updates that have been incorporated in the revised guidelines but are not restricted to these alone and should be read in conjunction with the guidelines.

Freeze drying formulation using microscale and design of experiment approaches: a case study using granulocyte colony-stimulating factor.

The lyophilization of proteins in microplates, to assess and optimise formulations rapidly, has been applied for the first time to a therapeutic protein and, in particular, one that requires a cell-based biological assay, in order to demonstrate the broader usefulness of the approach. Factorial design of experiment methods were combined with lyophilization in microplates to identify optimum formulations that stabilised granulocyte colony-stimulating factor during freeze drying. An initial screen rapidly identified key excipients and potential interactions, which was then followed by a central composite face designed optimisation experiment. Human serum albumin and Tween 20 had significant effects on maintaining protein stability. As previously, the optimum formulation was then freeze-dried in stoppered vials to verify that the microscale data is relevant to pilot scales. However, to validate the approach further, the selected formulation was also assessed for solid-state shelf-life through the use of accelerated stability studies. This approach allows for a high-throughput assessment of excipient options early on in product development, while also reducing costs in terms of time and quantity of materials required.

Impact of Formulation Choices on the Freeze-Drying of an Interleukin-6 Reference Material.

Formulation is critical to successful delivery of lyophilized biologics. We have compared the impact of buffer choice and the addition of sodium chloride (a formulant often viewed as unfavorable for freeze-drying applications) on the outcome of trial lyophilization of an interleukin-6 reference material. While phosphate buffer was a preferred choice and yielded well-formed cakes associated with fair recovery of biological activity, the resultant residual moisture content was high (2-4% w/w). By inclusion of isotonic levels of NaCl, the freeze-dried appearance and process were not impaired, but the residual moisture delivered was considerably reduced to levels <1% w/w. We postulate that this is due to the presence of a more open-cake structure and support this with evidence from thermal analysis and scanning electron microscopy. This work illustrates the importance of wide ranging empirical investigation of formulation options in order to optimize freeze-drying outcomes for biologics.

2021 White Paper on Recent Issues in Bioanalysis: ISR for Biomarkers, Liquid Biopsies, Spectral Cytometry, Inhalation/Oral & Multispecific Biotherapeutics, Accuracy/LLOQ for Flow Cytometry (Part 2 - Recommendations on Biomarkers/CDx Assays Development & Validation, Cytometry Validation & Innovation, Biotherapeutics PK LBA Regulated Bioanalysis, Critical Reagents & Positive Controls Generation).

The 15th edition of the Workshop on Recent Issues in Bioanalysis (15th WRIB) was held on 27 September to 1 October 2021. Even with a last-minute move from in-person to virtual, an overwhelmingly high number of nearly 900 professionals representing pharma and biotech companies, contract research organizations (CROs), and multiple regulatory agencies still eagerly convened to actively discuss the most current topics of interest in bioanalysis. The 15th WRIB included three Main Workshops and seven Specialized Workshops that together spanned 1 week in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy, cell therapy and vaccines. Moreover, in-depth workshops on biomarker assay development and validation (BAV) (focused on clarifying the confusion created by the increased use of the term "context of use" [COU]); mass spectrometry of proteins (therapeutic, biomarker and transgene); state-of-the-art cytometry innovation and validation; and critical reagent and positive control generation were the special features of the 15th edition. This 2021 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop, and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2021 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 2) covers the recommendations on ISR for Biomarkers, Liquid Biopsies, Spectral Cytometry, Inhalation/Oral & Multispecific Biotherapeutics, Accuracy/LLOQ for Flow Cytometry. Part 1A (Endogenous Compounds, Small Molecules, Complex Methods, Regulated Mass Spec of Large Molecules, Small Molecule, PoC), Part 1B (Regulatory Agencies' Inputs on Bioanalysis, Biomarkers, Immunogenicity, Gene & Cell Therapy and Vaccine) and Part 3 (TAb/NAb, Viral Vector CDx, Shedding Assays; CRISPR/Cas9 & CAR-T Immunogenicity; PCR & Vaccine Assay Performance; ADA Assay Comparability & Cut Point Appropriateness) are published in volume 14 of Bioanalysis, issues 9 and 11 (2022), respectively.

Endothelial cells co-stimulate peripheral blood mononuclear cell responses to monoclonal antibody TGN1412 in culture.

The failure of preclinical testing to predict the severity of the cytokine storm experienced by the recipients of the superagonistic anti-CD28 monoclonal antibody (mAb) TGN1412 during its Phase 1 clinical trial prompted the development of new in vitro experimental approaches for mimicking in vivo cytokine release and lymphoproliferation. Peripheral blood mononuclear cells (PBMC) presented to TGN1412 immobilised on plastic has previously been shown to stimulate a pro-inflammatory cytokine response. The aim of the present study was to investigate a 'co-culture' model for the detection of TGN1412-like immunomodulatory activity in which TGN1412 was presented to PBMC in the presence of monolayers of endothelium-derived cells and other cell types, followed by measurement of cytokine levels in the culture supernatants and proliferation of PBMC. Culturing PBMC with TGN1412 over primary human umbilical vein endothelial cells (HUVEC) and HUVEC-derived cell lines retaining classic endothelial markers, but not cell lines of non-endothelial origin, mediated the specific release of IL-6, IL-8 and TNFα, and proliferation of PBMC. Low levels of IL-2 and IFNγ were also detected in supernatants with most donors of PBMC. An anti-CD28 mAb agonist, i.e., not a superagonist like TGN1412, did not stimulate cytokine release or proliferation of PBMC in co-cultures. In conclusion, co-culture experiments for TGN1412-specific cytokine release required cells of endothelial origin. However, the profile of released cytokines in co-cultures did not mirror that in the clinical trial participants or the responses from PBMC exposed to TGN1412 immobilised on plastic, suggesting that TGN1412 stimulation of PBMC can occur through more than one mechanism.

Intended use of reference products & WHO International Standards/Reference Reagents in the development of similar biological products (biosimilars).

Reference Products and WHO International Standards/Reference Reagents have roles to play in the development and characterization of similar biological products (SBPs). However, these roles are distinct and non-interchangeable. The uses of these materials and their limitations are considered in this paper.