Proceedings of the 14th European immunogenicity platform open symposium on immunogenicity of biopharmaceuticals.

Biologics have revolutionized disease management in many therapeutic areas by addressing unmet medical needs and overcoming resistance to standard-of-care treatment in numerous patients. However, the development of unwanted immune responses directed against these drugs, humoral and/or cellular, can hinder their efficacy and have safety consequences with various degrees of severity. Health authorities ask that a thorough immunogenicity risk assessment be conducted during drug development to incorporate an appropriate monitoring and mitigation plan in clinical studies. With the rapid diversification and complexification of biologics, which today include modalities such as multi-domain antibodies, cell-based products, AAV delivery vectors, and nucleic acids, developers are faced with the challenge of establishing a risk assessment strategy sometimes in the absence of specific regulatory guidelines. The European Immunogenicity Platform (EIP) Open Symposium on Immunogenicity of Biopharmaceuticals and its one-day training course gives experts and newcomers across academia, industry, and regulatory agencies an opportunity to share experience and knowledge to overcome these challenges. Here, we report the discussions that took place at the EIP's 14th Symposium, held in April 2023. The topics covered included immunogenicity monitoring and clinical relevance, non-clinical immunogenicity risk assessment, regulatory aspects of immunogenicity assessment and reporting, and the challenges associated with new modalities, which were discussed in a dedicated session.

Anti-drug Antibody Sample Testing and Reporting Harmonization.

A clear scientific and operational need exists for harmonized bioanalytical immunogenicity study reporting to facilitate communication of immunogenicity findings and expedient review by industry and health authorities. To address these key bioanalytical reporting gaps and provide a report structure for documenting immunogenicity results, this cross-industry group was formed to establish harmonized recommendations and a develop a submission template to facilitate agency filings. Provided here are recommendations for reporting clinical anti-drug antibody (ADA) assay results using ligand-binding assay technologies. This publication describes the essential bioanalytical report (BAR) elements such as the method, critical reagents and equipment, study samples, results, and data analysis, and provides a template for a suggested structure for the ADA BAR. This publication focuses on the content and presentation of the bioanalytical ADA sample analysis report. The interpretation of immunogenicity data, including the evaluation of the impact of ADA on safety, exposure, and efficacy, is out of scope of this publication.

When to Extend Monitoring of Anti-drug Antibodies for High-risk Biotherapeutics in Clinical Trials: an Opinion from the European Immunogenicity Platform.

The determination of a tailored anti-drug antibody (ADA) testing strategy is based on the immunogenicity risk assessment to allow a correlation of ADAs with changes to pharmacokinetics, efficacy, and safety. The clinical impact of ADA formation refines the immunogenicity risk assessment and defines appropriate risk mitigation strategies. Health agencies request for high-risk biotherapeutics to extend ADA monitoring for patients that developed an ADA response to the drug until ADAs return to baseline levels. However, there is no common understanding in which cases an extension of ADA follow-up sampling beyond the end of study (EOS) defined in the clinical study protocol is required. Here, the Immunogenicity Strategy Working Group of the European Immunogenicity Platform (EIP) provides recommendations on requirements for an extension of ADA follow-up sampling in clinical studies where there is a high risk of serious consequences from ADAs. The importance of ADA evaluation during a treatment-free period is recognized but the decision whether to extend ADA monitoring at a predefined EOS should be based on evaluation of ADA data in the context of corresponding clinical signals. If the clinical data set shows that safety consequences are minor, mitigated, or resolved, further ADA monitoring may not be required despite potentially detectable ADAs above baseline. Extended ADA monitoring should be centered on individual patient benefit.

Anti-drug Antibody Validation Testing and Reporting Harmonization.

Evolving immunogenicity assay performance expectations and a lack of harmonized anti-drug antibody validation testing and reporting tools have resulted in significant time spent by health authorities and sponsors on resolving filing queries. Following debate at the American Association of Pharmaceutical Sciences National Biotechnology Conference, a group was formed to address these gaps. Over the last 3 years, 44 members from 29 organizations (including 5 members from Europe and 10 members from FDA) discussed gaps in understanding immunogenicity assay requirements and have developed harmonization tools for use by industry scientists to facilitate filings to health authorities. Herein, this team provides testing and reporting strategies and tools for the following assessments: (1) pre-study validation cut point; (2) in-study cut points, including procedures for applying cut points to mixed populations; (3) system suitability control criteria for in-study plate acceptance; (4) assay sensitivity, including the selection of an appropriate low positive control; (5) specificity, including drug and target tolerance; (6) sample stability that reflects sample storage and handling conditions; (7) assay selectivity to matrix components, including hemolytic, lipemic, and disease state matrices; (8) domain specificity for multi-domain therapeutics; (9) and minimum required dilution and extraction-based sample processing for titer reporting.

An innovative method for characterizing neutralizing antibodies against antibody-derived therapeutics.

Detection of anti-drug antibodies (ADA) that have a neutralizing capacity is an important aspect of immunogenicity evaluation during development of biotherapeutics, but developing and validating neutralizing antibody (NAb) assays that show direct interference of a biologic function is a challenging and resource-intensive activity. In particular, the need for adequate drug and target tolerance often requires extensive pre-treatment steps that limit assay sensitivity compared with a typical bridging-format assay used to detect binding ADA. Such limitations may complicate data interpretation as a positive ADA followed by a negative NAb result could be due to the presence of non-neutralizing antibodies or could be a false-negative for NAbs due to methodology differences. To address such issues, we developed a novel assay for Nanobodies® and other antibody-derived therapeutics that solely detects ADA directed against the complementarity-determining regions (CDRs) involved in drug-target interactions. This was achieved by creating a "null variant" of the therapeutic drug, which has mutated CDRs rendering it non-functional for target binding but is otherwise identical to the drug compound. Non-CDR-binding antibodies are pre-complexed with the null variant of the Nanobody leaving only CDR-binding ADA with neutralizing potential (ANP) to be detected in this assay, which is called a NAb Epitope Characterization Assay (NECA). Method qualification results confirmed highly comparable assay characteristics (sensitivity, drug tolerance, selectivity and precision) of both the NECA and a validated ADA assay for the same Nanobody. A panel of purified neutralizing and non-neutralizing antibodies as well as non-clinical and clinical samples were used to further substantiate the fit-for-purpose and advantages of this novel assay format to detect ANP. In the clinical case study, a 20 to 40-fold difference in assay sensitivity existed between the validated ADA assay and NAb assay, which complicated data interpretation. Implementation of the NECA allowed unambiguous comparison of the levels of binding ADA and ANP in study samples which enabled us to delineate the true neutralizing capacity of the responses. Depending on the risk of the therapeutic, this method could be a valuable alternative for NAb testing by enabling earlier detection of ADA with neutralizing potential and ensuring adequate immunogenicity risk assessment.

Transcytosis of F4 fimbriae by villous and dome epithelia in F4-receptor positive pigs supports importance of receptor-dependent endocytosis in oral immunization strategies.

Very few antigens have been described that induce an intestinal immunity when given orally. Our laboratory demonstrated that oral administration of isolated F4 (K88) fimbriae of Escherichia coli to F4-receptor positive (F4R(+)) pigs induces protective mucosal immunity against challenge infection. However, presence of F4-receptors (F4R) on villous enterocytes is a prerequisite for inducing the immune response, as no F4-specific antibody-secreting cells (ASC) can be induced in F4R(-) pigs. In this study, the in vivo binding of isolated F4 fimbriae (F4) to the gut epithelium was examined in F4R(+) and F4R(-) pigs. It was further investigated whether binding of F4 to the F4R results in endocytosis in and translocation across the gut epithelium using microscopy. F4 did not adhere to the intestinal epithelium of F4R(-) pigs, whereas it strongly adhered to the villous epithelium and the follicle-associated epithelium (FAE) of the jejunum and ileum of F4R(+) pigs. Following binding to F4R, F4 was endocytosed by villous enterocytes, follicle-associated enterocytes and M cells. Transcytosis of F4 across the epithelium resulted in the appearance of F4 in the lamina propria and dome region of the jejunal and ileal PP. This is the first study showing transcytosis of fimbriae across the gut epithelium. This receptor-dependent transcytosis can explain the success of F4 fimbriae as oral immunogen for inducing protective immunity in F4R(+) pigs strengthening the importance of receptor-dependent endocytosis and translocation in oral vaccine strategies. Further identification of the receptor responsible for this transport is in progress.

Induction of ovalbumin-specific tolerance by oral administration of Lactococcus lactis secreting ovalbumin.

BACKGROUND AND AIMS: Obtaining antigen-specific immune suppression is an important goal in developing treatments of autoimmune, inflammatory, and allergic gastrointestinal diseases. Oral tolerance is a powerful means for inducing tolerance to a particular antigen, but implementing this strategy in humans has been difficult. Active delivery of recombinant autoantigens or allergens at the intestinal mucosa by genetically modified Lactococcus lactis (L lactis) provides a novel therapeutic approach for inducing tolerance. METHODS: We engineered the food grade bacterium L lactis to secrete ovalbumin (OVA) and evaluated its ability to induce OVA-specific tolerance in OVA T-cell receptor (TCR) transgenic mice (DO11.10). Tolerance induction was assessed by analysis of delayed-type hypersensitivity responses, measurement of cytokines and OVA-specific proliferation, phenotypic analysis, and adoptive transfer experiments. RESULTS: Intragastric administration of OVA-secreting L lactis led to active delivery of OVA at the mucosa and suppression of local and systemic OVA-specific T-cell responses in DO11.10 mice. This suppression was mediated by induction of CD4(+)CD25(-) regulatory T cells that function through a transforming growth factor beta-dependent mechanism. Restimulation of splenocytes and gut-associated lymph node tissue from these mice resulted in a significant OVA-specific decrease in interferon gamma and a significant increase in interleukin-10 production. Furthermore, Foxp3 and CTLA-4 were significantly up-regulated in the CD4(+)CD25(-) population. CONCLUSIONS: Mucosal antigen delivery by oral administration of genetically engineered L lactis leads to antigen-specific tolerance. This approach can be used to develop effective therapeutics for systemic and intestinal immune-mediated inflammatory diseases.

The IgA system: a comparison of structure and function in different species.

The predominant immunoglobulin isotype on most mucosal surfaces is secretory immunoglobulin A (SIgA), a polypeptide complex comprising two IgA monomers, the connecting J chain, and the secretory component. The molecular stability and strong anti-inflammatory properties make SIgA particularly well suited to provide protective immunity to the vulnerable mucosal surfaces by preventing invasion of inhaled and ingested pathogens. In contrast to SIgA, IgA in serum functions as an inflammatory antibody through interaction with FcalphaR on immune effector cells. Although IgA appears to share common features and protective functions in different species, significant variations exist within the IgA systems of different species. This review will give an overview of the basic concepts underlying mucosal IgA defence which will focus on the variations present among species in structure, antibody repertoire development, pIgR-mediated transport, colostral IgA content, hepatobiliary transport, and function with particular emphasis on the IgA system of the pig and dog. These interspecies variations emphasise the importance of elucidating and analysing the IgA system within the immune system of the species of interest rather than inferring roles from conclusions made in human and mouse studies.

The role of enterocytes in the intestinal barrier function and antigen uptake.

The intestinal epithelium is a critical interface between the organism and its environment. The cell polarity and structural properties of the enterocytes, limiting the amount of antigen reaching the epithelial surface, form the basis of the integrity of the epithelium. However, apart from their participation in digestive processes, the enterocytes perform more than just a passive barrier function. The resistance of the tight junctions regulates the paracellular transport of antigens. Furthermore, the enterocytes take up and process antigens, involving two functional pathways. In the major pathway, enzymes in the lysosomes degrade the antigens. In the minor direct transcytotic pathway, the antigens are not degraded and are released into the interstitial space. Moreover, the enterocytes can present processed antigens directly to T cells and are often directly involved in immune processes. In inflammatory conditions, the properties of the epithelial barrier and the outcome of the immune response to luminal antigens can be changed.

Fimbrial subunit protein FaeG expressed in transgenic tobacco inhibits the binding of F4ac enterotoxigenic Escherichia coli to porcine enterocytes.

Plants offer a promising alternative for the production of foreign proteins for pharmaceutical purposes in tissues that are consumed as food and/or feed. Our long-term strategy is to develop edible vaccines against piglet diarrhoea caused by enterotoxigenic Escherichia coli (F4 ETEC) in feed plants. In this work, we isolated a gene, faeG, encoding for a major F4ac fimbrial subunit protein. Our goal was to test whether the FaeG protein, when isolated from its fimbrial background and produced in a plant cell, would retain the key properties of an oral vaccine, that is, stability in gastrointestinal conditions, binding to intestinal receptors and inhibition of the F4 ETEC attachment. For this purpose, tobacco was first transformed with a faeG construct that included a transit peptide encoding sequence to target the FaeG protein to the chloroplast. The best transgenic lines produced FaeG protein in amounts of 1% total soluble protein. The stability of the plant-produced FaeG was tested in fluids simulating piglet gastric (SGF) and intestinal (SIF) conditions. Plant-produced FaeG proved to be stable up to 2 h under these conditions. The binding and inhibition properties were tested with isolated piglet villi. These results showed that the plant-produced FaeG could bind to the receptors on the villi and subsequently inhibit F4 ETEC binding in a dose-dependent manner. Thus, the first two prerequisites for the development of an oral vaccine have been met.

Influence of porcine intestinal pH and gastric digestion on antigenicity of F4 fimbriae for oral immunisation.

Newly weaned piglets can be orally immunised against F4+ enterotoxigenic Escherichia coli (ETEC) infection with F4 fimbriae. However, to efficiently develop a vaccine against ETEC induced postweaning diarrhoea, knowledge of the stability of the F4 fimbriae to different pH and gastric digestion is needed. The gastrointestinal pH in suckling and recently weaned piglets was measured and the stability of F4 fimbriae to different pH and to pepsin was assessed in vitro. In the stomach the lowest pH was found in the fundus gland region. Gastric pH values below 2.5 were not found in suckling piglets or at the day of weaning, in contrast to piglets 1 and 2 weeks postweaning. Along the first half of the small intestine and in the caecum, a negative correlation was found between pH and age. The F4 fimbriae were stable to pH 1.5 and 2 for 2 h, whereas longer incubation periods resulted in conversion of the multimeric forms into monomers. The F4 fimbriae were partially degraded by incubation for 15-30 min in simulated gastric fluid at pH 1.5 and 2, and completely digested from 3 h onwards. At pH 3, the fimbriae maintained their antigenicity for at least 4h. The results demonstrate that gastric digestion will only have a limited impact on oral immunisation since liquid passes through the stomach relatively quickly (50% within 2 h). However, we previously demonstrated that the transit times are prolonged shortly after weaning. Shortly after weaning it could be necessary to protect the F4 fimbriae against gastric digestion to obtain efficient oral immunisation of the piglets.

Biological containment of genetically modified Lactococcus lactis for intestinal delivery of human interleukin 10.

Genetically modified Lactococcus lactis secreting interleukin 10 provides a therapeutic approach for inflammatory bowel disease. However, the release of such genetically modified organisms through clinical use raises safety concerns. In an effort to address this problem, we replaced the thymidylate synthase gene thyA of L. lactis with a synthetic human IL10 gene. This thyA- hIL10+ L. lactis strain produced human IL-10 (hIL-10), and when deprived of thymidine or thymine, its viability dropped by several orders of magnitude, essentially preventing its accumulation in the environment. The biological containment system and the bacterium's capacity to secrete hIL-10 were validated in vivo in pigs. Our approach is a promising one for transgene containment because, in the unlikely event that the engineered L. lactis strain acquired an intact thyA gene from a donor such as L. lactis subsp. cremoris, the transgene would be eliminated from the genome.

Mucosal immune responses following oral immunisation of pigs with fimbrial antigens of enterotoxigenic E. coli.

The intestinal mucosal immune system can discriminate actively between harmful pathogens and harmless food antigens resulting in different immune responses namely IgA production and oral tolerance, respectively. Whereas particulate antigen (microorganisms) can induce an IgA response, soluble antigen often leads to tolerance. Recently, it has been demonstrated that F4 fimbrial antigens of enterotoxigenic E. coli (F4 ETEC) can be used to immunise piglets. Oral administration of soluble F4 to F4R+ piglets (pigs with a receptor for these fimbriae (F4R+) on their small intestinal villous enterocytes) results in an intestinal mucosal immune response that completely protects the piglets against a challenge infection. In F4R- pigs, such an intestinal mucosal immune response does not occur. However, a priming of the systemic immune system can be seen similar to the priming in pigs fed with the same dose of a food antigen, suggesting that F4 in F4R- pigs behaves as a food antigen. These results indicate that a receptor-mediated mechanism is involved in the induction of a protective intestinal mucosal immune response using soluble antigen. However, oral administration of soluble F18 fimbriae of verotoxigenic E. coli to F18R+ piglets could not induce a similar protective immune response. So the type of the receptor and/or the nature of the antigen seem to be important to obtain an intestinal IgA response.

Oral immunisation of pigs with fimbrial antigens of enterotoxigenic E. coli: an interesting model to study mucosal immune mechanisms.

The intestinal mucosal immune system can discriminate actively between harmful pathogenic agents and harmless food antigens resulting in different immune responses namely IgA production and oral tolerance, respectively. Recently, a pig model has been developed for studying intestinal mucosal immune responses in which F4 fimbrial antigens of enterotoxigenic Escherichia coli (F4 ETEC) are used as oral antigens. A unique feature of this model is that soluble F4 antigens can be administered to pigs which have a receptor for this fimbriae (F4R(+)) on their small intestinal villous enterocytes and pigs which do not have this receptor (F4R(-)). Oral administration of F4 to the F4R(+) pigs results in an intestinal mucosal immune response that completely protects the pigs against a challenge infection. In F4R(-) pigs such an intestinal mucosal immune response does not occur. However, a priming of the systemic immune system can be seen similar to the priming in pigs fed with the same dose of a food antigen, suggesting that F4 in F4R(-) pigs behaves as a food antigen. The fact that different mucosal immune responses can be induced with soluble F4, makes it an interesting model to study mucosal immune mechanisms in the pig.