Trailblazing precision medicine in Europe: A joint view by Genomic Medicine Sweden and the Centers for Personalized Medicine, ZPM, in Germany.

Over the last decades, rapid technological and scientific advances have led to a merge of molecular sciences and clinical medicine, resulting in a better understanding of disease mechanisms and the development of novel therapies that exploit specific molecular lesions or profiles driving disease. Precision oncology is here used as an example, illustrating the potential of precision/personalized medicine that also holds great promise in other medical fields. Real-world implementation can only be achieved by dedicated healthcare connected centers which amass and build up interdisciplinary expertise reflecting the complexity of precision medicine. Networks of such centers are ideally suited for a nation-wide outreach offering access to precision medicine to patients independent of their place of residence. Two of these multicentric initiatives, Genomic Medicine Sweden (GMS) and the Centers for Personalized Medicine (ZPM) initiative in Germany have teamed up to present and share their views on core concepts, potentials, challenges, and future developments in precision medicine. Together with other initiatives worldwide, GMS and ZPM aim at providing a robust and sustainable framework, covering all components from technology development to clinical trials, ethical and legal aspects as well as involvement of all relevant stakeholders, including patients and policymakers in the field.

Implementation of precision medicine in healthcare-A European perspective.

The technical development of high-throughput sequencing technologies and the parallel development of targeted therapies in the last decade have enabled a transition from traditional medicine to personalized treatment and care. In this way, by using comprehensive genomic testing, more effective treatments with fewer side effects are provided to each patient-that is, precision or personalized medicine (PM). In several European countries-such as in England, France, Denmark, and Spain-the governments have adopted national strategies and taken "top-down" decisions to invest in national infrastructure for PM. In other countries-such as Sweden, Germany, and Italy with regionally organized healthcare systems-the profession has instead taken "bottom-up" initiatives to build competence networks and infrastructure to enable equal access to PM. In this review, we summarize key learnings at the European level on the implementation process to establish sustainable governance and organization for PM at the regional, national, and EU/international levels. We also discuss critical ethical and legal aspects of implementing PM, and the importance of access to real-world data and performing clinical trials for evidence generation, as well as the need for improved reimbursement models, increased cross-disciplinary education and patient involvement. In summary, PM represents a paradigm shift, and modernization of healthcare and all relevant stakeholders-that is, healthcare, academia, policymakers, industry, and patients-must be involved in this system transformation to create a sustainable, non-siloed ecosystem for precision healthcare that benefits our patients and society at large.

Building a precision medicine infrastructure at a national level: The Swedish experience.

Precision medicine has the potential to transform healthcare by moving from one-size-fits-all to personalised treatment and care. This transition has been greatly facilitated through new high-throughput sequencing technologies that can provide the unique molecular profile of each individual patient, along with the rapid development of targeted therapies directed to the Achilles heels of each disease. To implement precision medicine approaches in healthcare, many countries have adopted national strategies and initiated genomic/precision medicine initiatives to provide equal access to all citizens. In other countries, such as Sweden, this has proven more difficult due to regionally organised healthcare. Using a bottom-up approach, key stakeholders from academia, healthcare, industry and patient organisations joined forces and formed Genomic Medicine Sweden (GMS), a national infrastructure for the implementation of precision medicine across the country. To achieve this, Genomic Medicine Centres have been established to provide regionally distributed genomic services, and a national informatics infrastructure has been built to allow secure data handling and sharing. GMS has a broad scope focusing on rare diseases, cancer, pharmacogenomics, infectious diseases and complex diseases, while also providing expertise in informatics, ethical and legal issues, health economy, industry collaboration and education. In this review, we summarise our experience in building a national infrastructure for precision medicine. We also provide key examples how precision medicine already has been successfully implemented within our focus areas. Finally, we bring up challenges and opportunities associated with precision medicine implementation, the importance of international collaboration, as well as the future perspective in the field of precision medicine.

Generation and evaluation of bispecific affibody molecules for simultaneous targeting of EGFR and HER2.

Coexpression of several ErbB receptors has been found in many cancers and has been linked with increased aggressiveness of tumors and a worse patient prognosis. This makes the simultaneous targeting of two surface receptors by using bispecific constructs an increasingly appreciated strategy. Here, we have generated six such bispecific targeting proteins, each comprising two monomeric affibody molecules with specific binding to either of the two human epidermal growth factor receptors, EGFR and HER2, respectively. The bispecific constructs were designed with (i) alternative positioning (N- or C-terminal) of the different affibody molecules, (ii) two alternative peptide linkers (Gly(4)Ser)(3) or (Ser(4)Gly)(3), and (iii) affibody molecules with different affinity (nanomolar or picomolar) for HER2. Using both Biacore technology and cell binding assays, it was demonstrated that all six constructs could bind simultaneously to both their target proteins. N-terminal positioning of the inherent monomeric affibody molecules was favorable to promote the binding to the respective target. Interestingly, bispecific constructs containing the novel (Ser(4)Gly)(3) linker displayed a higher affinity in cell binding, as compared to constructs containing the more conventional linker, (Gly(4)Ser)(3). It could further be concluded that bispecific constructs (but not the monomeric affibody molecules) induced dimer formation and phosphorylation of EGFR in SKBR3 cells, which express fairly high levels of both receptors. It was also investigated whether the bispecific binding would influence cell growth or sensitize cells for ionizing radiation, but no such effects were observed.

[Genomic Medicine Sweden - a national initiative for the broad introduction of precision medicine in Swedish healthcare]. / Genomic Medicine Sweden ­ initiativ för brett införande.

The Genomic Medicine Sweden (GMS) initiative aims to strengthen precision medicine across the country. This will be accomplished through the implementation of large-scale sequencing techniques in Swedish healthcare. With a patient-centered view, initial efforts will focus on rare diseases, cancer, pharmacogenomics, and infectious diseases, and subsequently extend to complex diseases. GMS is being implemented as a broad collaborative project involving healthcare, universities with medical faculty, SciLifeLab, industry and patient organizations. To deliver top tier diagnostics, regional genomic medicine centers (GMC) are currently under establishment together with a national informatics infrastructure for data sharing. GMS will also offer a unique resource for research that could pave the way for the development of novel drugs, and enhance collaboration with industry. In summary, GMS provides Sweden with an opportunity to take an international forefront position in the field of precision medicine.

Affibody molecules for epidermal growth factor receptor targeting in vivo: aspects of dimerization and labeling chemistry.

UNLABELLED: Noninvasive detection of epidermal growth factor receptor (EGFR) expression in malignant tumors by radionuclide molecular imaging may provide diagnostic information influencing patient management. The aim of this study was to evaluate a novel EGFR-targeting protein, the ZEGFR:1907 Affibody molecule, for radionuclide imaging of EGFR expression, to determine a suitable tracer format (dimer or monomer) and optimal label. METHODS: An EGFR-specific Affibody molecule, ZEGFR:1907, and its dimeric form, (ZEGFR:1907)2, were labeled with 111In using benzyl-diethylenetriaminepentaacetic acid and with 125I using p-iodobenzoate. Affinity and cellular retention of conjugates were evaluated in vitro. Biodistribution of radiolabeled Affibody molecules was compared in mice bearing EGFR-expressing A431 xenografts. Specificity of EGFR targeting was confirmed by comparison with biodistribution of non-EGFR-specific counterparts. RESULTS: Head-to-tail dimerization of the Affibody molecule improved the dissociation rate. In vitro, dimeric forms demonstrated superior cellular retention of radioactivity. For both molecular set-ups, retention was better for the 111In-labeled tracer than for the radioiodinated counterpart. In vivo, all conjugates accumulated specifically in xenografts and in EGFR-expressing tissues. The retention of radioactivity in tumors was better in vivo for dimeric forms; however, the absolute uptake values were higher for monomeric tracers. The best tracer, 111In-labeled ZEGFR:1907, provided a tumor-to-blood ratio of 100 (24 h after injection). CONCLUSION: The radiometal-labeled monomeric Affibody molecule ZEGFR:1907 has a potential for radionuclide molecular imaging of EGFR expression in malignant tumors.

Engineered affinity proteins for tumour-targeting applications.

Targeting of tumour-associated antigens is an expanding treatment modality in clinical oncology as an alternative to, or in combination with, conventional treatments, such as chemotherapy, external-radiation therapy and surgery. Targeting of antigens that are unique or more highly expressed in tumours than in normal tissues can be used to increase the specificity and reduce the cytotoxic effect on normal tissues. Several targeting agents have been studied for clinical use, where monoclonal antibodies have been the ones most widely used. More than 20 monoclonal antibodies are approved for therapy today and the largest field is oncology. Advances in genetic engineering and in vitro selection technology has enabled the feasible high-throughput generation of monoclonal antibodies, antibody derivatives [e.g. scFvs, Fab molecules, dAbs (single-domain antibodies), diabodies and minibodies] and more recently also non-immunoglobulin scaffold proteins. Several of these affinity proteins have been investigated for both in vivo diagnostics and therapy. Affinity proteins in tumour-targeted therapy can affect tumour progression by altering signal transduction or by delivering a payload of toxin, drug or radionuclide. The ErbB receptor family has been extensively studied as biomarkers in tumour targeting, primarily for therapy using monoclonal antibodies. Two receptors in the ErbB family, EGFR (epidermal growth factor receptor) and HER2 (epidermal growth factor receptor 2), are overexpressed in various malignancies and associated with poor patient prognosis and are therefore interesting targets for solid tumours. In the present review, strategies are described for tumour targeting of solid tumours using affinity proteins to deliver radionuclides, either for molecular imaging or radiotherapy. Antibodies, antibody derivatives and non-immunoglobulin scaffold proteins are discussed with a certain focus on the affibody (Affibody) molecule.

Engineering and characterization of a bispecific HER2 x EGFR-binding affibody molecule.

HER2 (human epidermal-growth-factor receptor-2; ErbB2) and EGFR (epidermal-growth-factor receptor) are overexpressed in various forms of cancer, and the co-expression of both HER2 and EGFR has been reported in a number of studies. The simultaneous targeting of HER2 and EGFR has been discussed as a strategy with which to potentially increase efficiency and selectivity in molecular imaging and therapy of certain cancers. In an effort to generate a molecule capable of bispecifically targeting HER2 and EGFR, a gene fragment encoding a bivalent HER2-binding affibody molecule was genetically fused in-frame with a bivalent EGFR-binding affibody molecule via a (G4S)3 [(Gly4-Ser)3]-encoding gene fragment. The encoded 30 kDa affibody construct (ZHER2)2-(G4S)3-(ZEGFR)2, with potential for bs (bispecific) binding to HER2 and EGFR, was expressed in Escherichia coli and characterized in terms of its binding capabilities. The retained ability to bind HER2 and EGFR separately was demonstrated using both biosensor technology and flow-cytometric analysis, the latter using HER2- and EGFR-overexpressing cells. Furthermore, simultaneous binding to HER2 and EGFR was demonstrated in: (i) a sandwich format employing real-time biospecific interaction analysis where the bs affibody molecule bound immobilized EGFR and soluble HER2; (ii) immunofluorescence microscopy, where the bs affibody molecule bound EGFR-overexpressing cells and soluble HER2; and (iii) a cell-cell interaction analysis where the bs affibody molecule bound HER2-overexpressing SKBR-3 cells and EGFR-overexpressing A-431 cells. This is, to our knowledge, the first reported bs affinity protein with potential ability for the simultaneous targeting of HER2 and EGFR. The potential future use of this and similar constructs, capable of bs targeting of receptors to increase the efficacy and selectivity in imaging and therapy, is discussed.

Cellular studies of binding, internalization and retention of a radiolabeled EGFR-binding affibody molecule.

INTRODUCTION: The cellular binding and processing of an epidermal growth factor receptor (EGFR) targeting affibody molecule, (Z(EGFR:955))(2), was studied. This new and small molecule is aimed for applications in nuclear medicine. The natural ligand epidermal growth factor (EGF) and the antibody cetuximab were studied for comparison. METHODS: All experiments were made with cultured A431 squamous carcinoma cells. Receptor specificity, binding time patterns, retention and preliminary receptor binding site localization studies were all made after (125)I labeling. Internalization was studied using Oregon Green 488, Alexa Fluor 488 and CypHer5E markers. RESULTS: [(125)I](Z(EGFR:955))(2) and [(125)I]cetuximab gave a maximum cellular uptake of (125)I within 4 to 8 h of incubation, while [(125)I]EGF gave a maximum uptake already after 2 h. The retention studies showed that the cell-associated fraction of (125)I after 48 h of incubation was approximately 20% when delivered as [(125)I](Z(EGFR:955))(2) and approximately 25% when delivered as [(125)I]cetuximab. [(125)I]EGF-mediated delivery gave a faster (125)I release, where almost all cell-associated radioactivity had disappeared within 24 h. All three substances were internalized as demonstrated with confocal microscopy. Competitive binding studies showed that both EGF and cetuximab inhibited binding of (Z(EGFR:955))(2) and indicated that the three substances competed for an overlapping binding site. CONCLUSION: The results gave information on cellular processing of radionuclides when delivered with (Z(EGFR:955))(2) in comparison to delivery with EGF and cetuximab. Competition assays suggested that [(125)I](Z(EGFR:955))(2) bind to Domain III of EGFR. The affibody molecule (Z(EGFR:955))(2) can be a candidate for EGFR imaging applications in nuclear medicine.

Immunisation of mice against neosporosis with recombinant NcSRS2 iscoms.

The coccidian parasite Neospora caninum is an intracellular protozoan, causing abortion in cattle in many countries around the world. In this study, the protective potential of the major N. caninum surface antigen NcSRS2, expressed in Escherichia coli and formulated into immunostimulating complexes (iscoms), was investigated in an experimental mouse model. The recombinant protein was specially designed for binding to iscoms via biotin-streptavidin interaction. Two groups of 10 BALB/c mice were immunised twice, on days 0 and 28 with iscoms containing either the recombinant NcSRS2 (NcSRS2 iscoms) or similar iscoms with NcSRS2 substituted by an unrelated recombinant malaria peptide (M5) as a control (M5 iscoms). A third group of 10 age-matched BALB/c mice served as an uninfected control group. Immunisation with recombinant NcSRS2 iscoms resulted in production of substantial antibody titres against N. caninum antigen, while the mice immunised with M5 iscoms produced only very low levels of antibodies reacting with N. caninum antigen. After challenge infection with N. caninum tachyzoites on day 69, mice immunised with NcSRS2 iscoms showed only mild and transient symptoms, whereas the group immunised with M5 iscoms showed clinical symptoms until the end of the experiment at 31 days post inoculation. A competitive PCR assay detecting Nc5-repeats was applied to evaluate the level of parasite DNA in the brain. The amount of Nc5-repeats in the group vaccinated with NcSRS2 iscoms was significantly lower than in the control group given M5 iscoms. In conclusion, it was found that the recombinant NcSRS2 iscoms induced specific antibodies to native NcSRS2 and immunity sufficient to reduce the proliferation of N. caninum in the brains of immunised mice.

Elevated Serum GAD65 and GAD65-GADA Immune Complexes in Stiff Person Syndrome.

Glutamic acid decarboxylase 65 (GAD65) and autoantibodies specific for GAD65 (GADA) are associated with autoimmune diseases including Stiff Person Syndrome (SPS) and Type 1 diabetes (T1D). GADA is recognized as a biomarker of value for clinical diagnosis and prognostication in these diseases. Nonetheless, it remains medically interesting to develop sensitive and specific assays to detect GAD65 preceding GADA emergence, and to monitor GADA-GAD65 immune complexes in blood samples. In the present study, we developed a highly sensitive proximity ligation assay to measure serum GAD65. This novel assay allowed detection of as little as 0.65 pg/ml GAD65. We were also able to detect immune complexes involving GAD65 and GADA. Both free GAD65 and GAD65-GADA levels were significantly higher in serum samples from SPS patients compared to healthy controls. The proximity ligation assays applied for detection of GAD65 and its immune complexes may thus enable improved diagnosis and better understanding of SPS.

Protein tag-mediated conjugation of oligonucleotides to recombinant affinity binders for proximity ligation.

While antibodies currently play a dominant role as affinity reagents in biological research and for diagnostics, a broad range of recombinant proteins are emerging as promising alternative affinity reagents in detection assays and quantification. DNA-mediated affinity-based assays, such as immuno-PCR and proximity ligation assays (PLA), use oligonucleotides attached to affinity reagents as reporter molecules. Conjugation of oligonucleotides to affinity reagents generally employs chemistries that target primary amines or cysteines. Because of the random nature of these processes neither the number of oligonucleotides conjugated per molecule nor their sites of attachment can be accurately controlled for affinity reagents with several available amines and cysteines. Here, we present a straightforward and convenient approach to functionalize recombinant affinity reagents for PLA by expressing the reagents as fusion partners with SNAP protein tags. This allowed us to conjugate oligonucleotides in a site-specific fashion, yielding precisely one oligonucleotide per affinity reagent. We demonstrate this method using designed ankyrin repeat proteins (DARPins) recognizing the tumor antigen HER2 and we apply the conjugates in different assay formats. We also show that SNAP or CLIP tags, expressed as fusion partners of transfected genes, allow oligonucleotide conjugations to be performed in fixed cells, with no need for specific affinity reagents. The approach is used to demonstrate induced interactions between the fusion proteins FKBP and FRB by allowing the in situ conjugated oligonucleotides to direct the production of templates for localized rolling circle amplification reactions.

Affibody-mediated retention of the epidermal growth factor receptor in the secretory compartments leads to inhibition of phosphorylation in the kinase domain.

Abnormal activity of the epidermal growth factor receptor (EGFR) is associated with various cancer-related processes and motivates the search for strategies that can selectively block EGFR signalling. In this study, functional knockdown of EGFR was achieved through expression of an affibody construct, (ZEGFR:1907)(2-)KDEL, with high affinity for EGFR and extended with the amino acids KDEL to make it resident in the secretory compartments. Expression of (ZEGFR:1907)(2-)KDEL resulted in 80% reduction ofthe cell surface level of EGFR, and fluorescent staining for EGFR and the (ZEGFR:1907)(2-)KDEL construct showed overlapping intracellular localisation. Immunocapture of EGFR from cell lysates showed that an intracellular complex between EGFR and the affibody construct had been formed, further indicating aspecific interaction between the affibody construct and EGFR. Surface depletion of EGFR led to a dramatic decrease in the amount of kinase domain phosphorylated EGFR, coincident with a significant decrease in the proliferation rate.

Directed evolution to low nanomolar affinity of a tumor-targeting epidermal growth factor receptor-binding affibody molecule.

The epidermal growth factor receptor 1 (EGFR) is overexpressed in various malignancies and is associated with a poor patient prognosis. A small, receptor-specific, high-affinity imaging agent would be a useful tool in diagnosing malignant tumors and in deciding upon treatment and assessing the response to treatment. We describe here the affinity maturation procedure for the generation of Affibody molecules binding with high affinity and specificity to EGFR. A library for affinity maturation was constructed by rerandomization of selected positions after the alignment of first-generation binding variants. New binders were selected with phage display technology, using a single oligonucleotide in a single-library effort, and the best second-generation binders had an approximately 30-fold improvement in affinity (K(d)=5-10 nM) for the soluble extracellular domain of EGFR in biospecific interaction analysis using Biacore. The dissociation equilibrium constant, K(d), was also determined for the Affibody with highest affinity using EGFR-expressing A431 cells in flow cytometric analysis (K(d)=2.8 nM). A retained high specificity for EGFR was verified by a dot blot assay showing staining only of EGFR proteins among a panel of serum proteins and other EGFR family member proteins (HER2, HER3, and HER4). The EGFR-binding Affibody molecules were radiolabeled with indium-111, showing specific binding to EGFR-expressing A431 cells and successful targeting of the A431 tumor xenografts with 4-6% injected activity per gram accumulated in the tumor 4 h postinjection.

Immunogenicity and protective effect against murine cerebral neosporosis of recombinant NcSRS2 in different iscom formulations.

Recombinant NcSRS2, a major immunodominant surface antigen of the intracellular protozoan parasite Neospora caninum, was used as a model antigen to compare the immunogenicity of iscoms prepared according to three different methods. Two NcSRS2 fusion proteins were used, one that was biotinylated upon expression in Escherichia coli and linked to Ni2+-loaded iscom matrix (iscom without any protein) via a hexahistidyl (His6)-tagged streptavidin fusion protein, and another that contained both a His6-tag and streptavidin (His6-SA-SRS2') and was coupled to either Ni2+-loaded or biotinylated matrix. While all three iscom preparations induced N. caninum specific antibodies at similar levels, His6-SA-SRS2' coupled to biotinylated matrix generated the strongest cellular responses measured as in vitro proliferation and production of interferon-gamma and interleukin-4 after antigen stimulation of spleen cells. However, the relationship between the levels of these cytokines as well as between IgG1 and IgG2a titres in serum induced by the three iscom preparations were similar, indicating that the balance between Th1 and Th2 responses did not differ. After challenge infection, mice immunised with His6-SA-SRS2' coupled to biotinylated matrix had significantly lower amounts of parasite DNA in their brains compared to the other immunised groups. Possible reasons for the performance of the different iscom formulations are discussed.

Selection and characterization of an HIV-1 gp120-binding affibody ligand.

To evaluate the possibility of generating novel proteins binding to highly glycosylated viral proteins, affibody ligands were selected by bacteriophage display technology to the HIV-1 envelope glycoprotein gp120 (glycoprotein 120), from a combinatorial protein library based on the 58-amino-acid-residue staphylococcal Protein A domain. The predominant variant from the bacteriophage selection was produced in Escherichia coli and characterized by biosensor analyses. Both univalent and bivalent affibody molecules were shown to bind selectively to the gp120 target molecule in a biosensor analysis. The dissociation equilibrium constants (KD) were determined to be approx. 100 nM for the univalent affibody and 10 nM for the bivalent affibody, confirming the stronger gp120 binding of the bivalent affibody ligand. The affibody constructs were further introduced into the Ad5 (adenovirus type 5) fibre gene, and the recombinant fibres were shown to bind selectively to gp120 in a biosensor analysis and to gp160 transiently expressed in African-green-monkey (Cercopithecus aethiops) kidney cells. Neither the affibody ligand nor the Ad5 fibres showed any virus neutralization activity, suggesting that the affibody bound to a non-neutralizing site on gp120. To investigate the binding site for the affibody ligand on gp120, CD4 (cluster of differentiation 4) and a panel of mAbs (monoclonal antibodies) known to bind to gp120 were allowed to compete with the affibody ligand in a biosensor study. Two mAbs, 670-30D and 697-30D, were found to compete with gp120 for overlapping binding sites. Although neutralization effects were not achieved in this initial investigation, the successful selection of a gp120-binding affibody ligand indicates that future affibody-based strategies might evolve to complement antibody-based efforts for HIV-1 therapy. Strategies for directed selection of affibody ligands binding to neutralizing epitopes and the potential of using adenovirus for gene-therapy-mediated efforts are discussed.

Achieving directed immunostimulating complexes incorporation.

In recent years, several studies have been reported with the common aim of generating general expression systems for straightforward production and subsequent coupling of expressed antigens to an adjuvant system. Here, we describe a series of such efforts with a common theme of using gene fusion technology for association of recombinant antigens to immunostimulating complexes (iscoms). In the early stages of vaccine development, uniform antigen preparations are crucial to allow the comparison of immune responses to different antigens, or even subdomains thereof, and we believe that the described systems constitute an important development in this context.

Applying biotin-streptavidin binding for iscom (immunostimulating complex) association of recombinant immunogens.

We have previously reported strategies for Escherichia coli production of recombinant immunogens fused to hydrophobic peptide or lipid tags to improve their capacity to be incorporated into an adjuvant formulation. In the present study, we have explored the strong interaction between biotin and SA (streptavidin) (K(D) approximately 10(-15) M) to couple recombinant immunogens to iscoms (immunostimulating complexes). Two different concepts were evaluated. In the first concept, a His(6)-tagged SA fusion protein (His(6)-SA) was bound to Ni(2+)-loaded iscom matrix (iscom without associated protein), and biotinylated immunogens were thereafter associated with the SA-coated iscoms. The immunogens were either biotinylated in vivo on E. coli expression or double biotinylated in vivo and in vitro. In the second concept, the recombinant immunogens were expressed as SA fusion proteins, which were directly bound to a biotinylated iscom matrix. A 53-amino-acid malaria peptide (M5), derived from the central repeat region of the Plasmodium falciparum blood-stage antigen Pf155/RESA, and a 232-amino-acid segment (SRS2') from the central region (from Pro-97 to Lys-328) of the major surface antigen NcSRS2 of the protozoan parasite Neospora caninum, served as model immunogens in the present study. All fusion proteins generated were found to be efficiently expressed and could be recovered to high purity using affinity chromatography. The association between the different immunogen-containing fusion proteins and the corresponding iscom matrix was demonstrated by analytical ultracentrifugation in a sucrose density gradient. However, some fusion proteins were, to a certain extent, also found to associate unspecifically with a regular iscom matrix. Furthermore, selected iscom fractions were demonstrated to induce high-titre antigen-specific antibody responses on immunization of mice. For the particular target immunogen SRS2', the induced antibodies demonstrated reactivity to the native antigen NcSRS2. We believe that the presented concepts offer convenient methods to achieve efficient adjuvant association of recombinant immunogens, and the advantages and disadvantages of the two concepts are discussed.

General strategies for efficient adjuvant incorporation of recombinant subunit immunogens.

We have previously reported strategies for Escherichia coli production of recombinant immunogens fused to hydrophobic peptides or lipid tags to improve their capacity to be incorporated into an adjuvant formulation, e.g., immunostimulating complexes (iscoms). Recently, we also explored the strong interaction between biotin and streptavidin to achieve iscom association of recombinant immunogens. Plasmodium falciparum,Toxoplasma gondii and Neospora caninum antigens have served as model immunogens in the different studies. Generated fusion proteins have been found to be successfully incorporated into iscoms and high-titer antigen-specific antibody responses have been obtained upon immunization of mice. We believe that the different concepts presented, utilizing either hydrophobic peptide or lipid tags, or the recently explored biotin-streptavidin principle, offer convenient methods to achieve efficient adjuvant incorporation of recombinant immunogens.