Survey Outcome on Immunogenicity Risk Assessment Tools for Biotherapeutics: an Insight into Consensus on Methods, Application, and Utility in Drug Development.

A survey conducted by the Therapeutic Product Immunogenicity (TPI) community within the American Association of Pharmaceutical Scientists (AAPS) posed questions to the participants on their immunogenicity risk assessment strategies prior to clinical development. The survey was conducted in 2 phases spanning 5 years, and queried information about in silico algorithms and in vitro assay formats for immunogenicity risk assessments and how the data were used to inform early developability effort in discovery, chemistry, manufacturing and control (CMC), and non-clinical stages of development. The key findings representing the trends from a majority of the participants included the use of high throughput in silico algorithms, human immune cell-based assays, and proteomics based outputs, as well as specialized assays when therapeutic mechanism of action could impact risk assessment. Additional insights into the CMC-related risks could also be gathered with the same tools to inform future process development and de-risk critical quality attributes with uncertain and unknown risks. The use of the outputs beyond supporting early development activities was also noted with participants utilizing the risk assessments to drive their clinical strategy and streamline bioanalysis.

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.

Use of In Vitro Assays to Assess Immunogenicity Risk of Antibody-Based Biotherapeutics.

An In Vitro Comparative Immunogenicity Assessment (IVCIA) assay was evaluated as a tool for predicting the potential relative immunogenicity of biotherapeutic attributes. Peripheral blood mononuclear cells from up to 50 healthy naïve human donors were monitored up to 8 days for T-cell proliferation, the number of IL-2 or IFN-γ secreting cells, and the concentration of a panel of secreted cytokines. The response in the assay to 10 monoclonal antibodies was found to be in agreement with the clinical immunogenicity, suggesting that the assay might be applied to immunogenicity risk assessment of antibody biotherapeutic attributes. However, the response in the assay is a measure of T-cell functional activity and the alignment with clinical immunogenicity depends on several other factors. The assay was sensitive to sequence variants and could differentiate single point mutations of the same biotherapeutic. Nine mAbs that were highly aggregated by stirring induced a higher response in the assay than the original mAbs before stirring stress, in a manner that did not match the relative T-cell response of the original mAbs. In contrast, mAbs that were glycated by different sugars (galactose, glucose, and mannose) showed little to no increase in response in the assay above the response to the original mAbs before glycation treatment. The assay was also used successfully to assess similarity between multiple lots of the same mAb, both from the same manufacturer and from different manufacturers (biosimilars). A strategy for using the IVCIA assay for immunogenicity risk assessment during the entire lifespan development of biopharmaceuticals is proposed.

Development of a human antibody tolerant mouse model to assess the immunogenicity risk due to aggregated biotherapeutics.

We describe a novel human immunoglobulin G2 (IgG2 )-tolerant and immune-competent heterozygous mouse model (Xeno-het) developed by crossbreeding a human Ig-tolerized XenoMouse® with a C57BL/6J wild-type mouse. The Xeno-het mouse expresses both mouse and human immunoglobulin G (IgG) genes, resulting in B-cells expressing human and mouse IgG, and secretion of human and mouse Ig into serum. This model was utilized to evaluate the immunogenicity risk of aggregated and chemically modified human antibodies. The mice were tested for their ability to break tolerance to self-tolerant monomeric antibodies. Aggregates made by mechanical stirring elicited an anti-drug antibody (ADA) response, but did not induce a robust and long-term memory B and T-cell response. Chemically modified antibodies made by oxidation were only weak and transient inducers of an immune response, as measured by a lack of both an ADA response and a B-cell antigen-specific response. Aggregate size was an important characteristic, as specific-sized protein-coated beads were able to elicit an immune response. We propose the use of this model to identify risk factors such as aggregation during manufacturing at early development for an increased potential immunogenicity risk.

A detailed examination of the antibody prevalence and characteristics of anti-ESA antibodies.

BACKGROUND: The antibody characteristics in erythropoiesis-stimulating agent (ESA)-treated patients who develop antibody-mediated pure red cell aplasia (PRCA; amPRCA) can be described as high-affinity, neutralizing anti-ESA antibodies with a mixed immunoglobulin G (IgG) subclass. The characteristics of an early-onset anti-ESA antibody response are not well documented, especially in the months prior to the development of amPRCA. Therefore, a detailed characterization of anti-ESA antibodies was performed in patients in both clinical studies and in a post-market setting. Both baseline and post-dose samples were tested and antibody-positive samples were characterized. Antibody characteristics such as concentration, isotype and specificity were evaluated in subjects with non-neutralizing anti-ESA antibodies and subjects that developed neutralizing anti-ESA antibodies associated with amPRCA. METHODS: Serum samples were analyzed for the presence of anti-ESA antibodies, using a validated surface plasmon resonance (SPR)-based immunoassay or SPRIA. RESULTS: Among the clinical studies, pre-existing non-neutralizing anti-ESA antibodies were found in 6% of the subjects from clinical studies in nephrology, oncology and congestive heart failure (CHF). After ESA treatment, 2.3% of the subjects developed binding, non-neutralizing antibodies with 0.1% confirmed as having an IgG isotype and were specific to the ESA protein. IgM antibodies were detected at baseline and post-ESA treatment and reported to be specific to the glycosylation of the ESA. No clinical study subjects progressed to amPRCA. In contrast, anti-ESA antibody-positive subjects from the post-market setting with a confirmed IgG subclass were specific to the ESA protein. Subjects that had progressed to amPRCA were noted to have high antibody concentrations with neutralizing activity and a diverse IgG subtype. CONCLUSIONS: A low prevalence of non-neutralizing anti-ESA IgM specific to glycosylation on the ESA and IgG1 antibodies specific to the ESA protein was detected across all clinical patient populations. Patients with amPRCA were noted to have high IgG antibody concentrations, neutralizing antibodies and the presence of anti-ESA IgG4 antibodies.

The future of protein particle characterization and understanding its potential to diminish the immunogenicity of biopharmaceuticals: a shared perspective.

Biopharmaceuticals represent an important and growing class of medicines. Immunogenic responses to biopharmaceuticals in patients can sometimes result in reduced safety and efficacy. Although multiple factors are known to influence immunogenicity, our understanding of the complex underlying mechanisms remains imperfect. In particular, the potential impact of protein aggregates (particulates) on immunogenicity is currently not well understood. This commentary discusses emerging technologies for particle assessment, what is known about the link between particulates and product safety and efficacy, and current regulatory guidances and perspectives. We consider approaches that in the future may permit specific particle attributes to be correlated with relative immunogenic risk, including the value of data derived from clinical and postmarketing surveillance. Finally, we identify some key remaining questions, which, when answered, may guide future strategies for decreasing the immunogenicity of biopharmaceuticals.

Highly aggregated antibody therapeutics can enhance the in vitro innate and late-stage T-cell immune responses.

Aggregation of biotherapeutics has the potential to induce an immunogenic response. Here, we show that aggregated therapeutic antibodies, previously generated and determined to contain a variety of attributes (Joubert, M. K., Luo, Q., Nashed-Samuel, Y., Wypych, J., and Narhi, L. O. (2011) J. Biol. Chem. 286, 25118-25133), can enhance the in vitro innate immune response of a population of naive human peripheral blood mononuclear cells. This response depended on the aggregate type, inherent immunogenicity of the monomer, and donor responsiveness, and required a high number of particles, well above that detected in marketed drug products, at least in this in vitro system. We propose a cytokine signature as a potential biomarker of the in vitro peripheral blood mononuclear cell response to aggregates. The cytokines include IL-1ß, IL-6, IL-10, MCP-1, MIP-1α, MIP-1ß, MMP-2, and TNF-α. IL-6 and IL-10 might have an immunosuppressive effect on the long term immune response. Aggregates made by stirring induced the highest response compared with aggregates made by other methods. Particle size in the 2-10 µm range and the retention of some folded structure were associated with an increased response. The mechanism of aggregate activation at the innate phase was found to occur through specific cell surface receptors (the toll-like receptors TLR-2 and TLR-4, FcγRs, and the complement system). The innate signal was shown to progress to an adaptive T-cell response characterized by T-cell proliferation and secretion of T-cell cytokines. Investigating the ability of aggregates to induce cytokine signatures as biomarkers of immune responses is essential for determining their risk of immunogenicity.

Considerations for optimization and validation of an in vitro PBMC derived T cell assay for immunogenicity prediction of biotherapeutics.

An immune response to a biotherapeutic can be induced when the therapeutic is processed and presented by antigen presenting cell to T helper cells. This study evaluates the performance of an in vitro assay that can elicit antigen specific effector T cell responses. Two biotherapeutics with known clinical immunogenicity [FPX1 and FPX2] were assessed for their ability to induce antigen-specific IFN-γ secreting T cells in peripheral blood mononuclear cells (PBMC). The 24 amino acid peptide component of FPX1 elicited an antigen-specific response in 16/34 (47%) individual naïve healthy donors. This in vitro effect was consistent with high rate of immunogenicity which was observed when this drug was administered in clinical trials. FPX2 did not induce antigen-specific T cells in vitro, which correlates with the low rate of development of anti-drug antibody responses to this molecule in the clinic. The assay has the potential to predict immunogenicity and help in the selection of biotherapeutics at the early development stage of a clinical candidate.

Intradermal vaccination of MUC1 transgenic mice with MUC1/IL-18 plasmid DNA suppresses experimental pulmonary metastases.

MUC1 (mucin 1) is a transmembrane glycoprotein normally expressed on epithelia of the pancreas, breast, prostate, colon, and lung. However, this self-antigen is over-expressed and aberrantly glycosylated in adenocarcinomas, thereby making it a potential target for immunotherapy. Toward this goal, DNA plasmids encoding human MUC1 (pMUC1) and mouse interleukin-18 (pmuIL-18) were developed, and previous work demonstrated pMUC1/pmuIL18 vaccination protected MUC1 transgenic mice (MUC1.Tg) from subcutaneous tumor challenge. This report shows that pMUC1/pmuIL-18 is effective in preventing and treating pulmonary metastases in MUC1.Tg mice. Vaccination with pMUC1 or pmuIL-18 alone was insufficient to elicit measurable anti-tumor effects. However, co-administration of pMUC1 with pmuIL-18 reduced the incidence of lung tumors and prolonged survival. Furthermore, pMUC1/pmuIL-18 immunization protected mice from challenge with MUC1+ tumors, but not from MUC1- tumors, indicating that the anti-tumor effect is antigen-specific. More importantly, pMUC1/pmuIL-18 was effective in treating established tumors. Finally, in vivo antibody-mediated lymphocyte depletion and neutralization of interferon gamma (IFNgamma) revealed that CD8+ T cells and IFNgamma mediate the anti-tumor immunity. Collectively, these results demonstrate that pMUC1/pmuIL-18 breaks tolerance to MUC1, and induces antigen-specific immunity with protective and therapeutic benefit. This suggests that pMUC1/pmuIL-18 DNA vaccination may provide clinical benefit for patients with MUC1+ tumors.

Engineering human IL-18 with increased bioactivity and bioavailability.

Cytokines in plasmid form can act as potent adjuvants when co-administered with DNA vaccines, resulting in an enhanced immune response to the DNA-encoded antigen. This is true of interleukin-18 (IL-18), which has been shown to serve as an adjuvant in conjunction with certain DNA vaccines. To determine if the properties of IL-18 could be optimized for use as a DNA vaccine adjuvant, a model of IL-18/IL-18R binding was developed to identify variants of human IL-18 that were predicted to improve receptor interactions and potentially bioactivity. The linkage of mature IL-18 to a secretion signal sequence provided improved protein expression from mammalian cells and signal peptidase cleavage of this protein produced the authentic N-terminus. The IL-18 variant proteins secreted this way were bioactive, as demonstrated by their ability to induce interferon gamma (IFNgamma) expression by human peripheral blood mononuclear cells (PBMCs) and to bind to IL-18R, as demonstrated by BIAcore analysis. The IL-18 variants were inhibited by IL-18 binding protein (IL-18BP), the soluble inhibitor of IL-18, as measured by neutralization of the IFNgamma response in PBMCs. One variant, V11I/T63A, demonstrated increases both in bioactivity and mammalian cell expression as compared to native IL-18, indicating that this molecule may be particularly well suited for use as a DNA-encoded vaccine adjuvant.

A MUC1/IL-18 DNA vaccine induces anti-tumor immunity and increased survival in MUC1 transgenic mice.

MUC1 (mucin 1) is a tumor-associated antigen that is overexpressed in many adenocarcinomas. Active immunotherapy targeting tumors expressing MUC1 could have great treatment value. MUC1 DNA vaccines were evaluated in MUC1 transgenic (MUC1.Tg) mice challenged with MC38/MUC1+ tumor cells. Vaccination with MUC1 plasmid DNA (pMUC1) alone was insufficient to induce tumor protection. However, co-administration of pMUC1 with a plasmid encoding murine interleukin-18 (pmuIL-18) resulted in significant tumor protection and survival after tumor challenge. Protection was durable in the absence of additional vaccination, as demonstrated by continued protection of vaccinated mice following tumor rechallenge. Mice surviving challenges with MC38/MUC1+ cells showed significant protection after challenge with MUC1(-) MC38 tumor cells, suggesting that these mice had developed immune responses to epitopes shared between the tumor cell lines. Antibody-mediated depletion of lymphocyte subsets demonstrated that protection was due largely to CD4+ T cells. This work demonstrates that a naked DNA vaccine can break tolerance to MUC1 and induce an immune response capable of mediating both significant protection from tumor challenge and increased survival.

Induction of dendritic cell maturation by IL-18.

IL-18 is a pluripotent proinflammatory cytokine produced primarily by antigen presenting cells involved in numerous aspects of immune regulation most notably on lymphoid cells. The effect of IL-18 stimulation on cells in the myeloid compartment, however, has been poorly studied. Human monocytes did not respond to IL-18. However, the human myelomonocytic cell line KG-1 and monocyte-derived dendritic cells (generated by GM-CSF+IL-4) showed a marked increase in CD83, HLA-DR, and several costimulatory molecules upon stimulation with IL-18. Furthermore, IL-18 decreased pinocytosis of these cells and increased their ability to stimulate alloreactive T cell proliferation, all characteristics of mature dendritic cells. These results suggest that IL-18 is involved in the maturation of myeloid DCs, but not differentiation of monocytes into DCs. The finding that IL-18 is involved in the maturation of dendritic cells is both novel and unexpected and indicates another important role for IL-18 as a key regulator of immune responses.

Pilot trial of tumor-specific peptide vaccination and continuous infusion interleukin-2 in patients with recurrent Ewing sarcoma and alveolar rhabdomyosarcoma: an inter-institute NIH study.

BACKGROUND: Patients with recurrent Ewing sarcoma and alveolar rhabdomyosarcoma have poor prognoses and limited therapeutic options. We have investigated the use of peptide pulsed vaccination in an attempt to immunologically target the breakpoint region of tumor specific fusion proteins expressed in these tumors. PROCEDURE: Sixteen patients with recurrent, translocation positive, Ewing sarcoma, and alveolar rhabdomyosarcoma underwent apheresis for collection of peripheral blood mononuclear cells. Following countercurrent centrifugal elutriation, an apheresis product comprised predominantly of monocytes but containing small numbers of circulating immature dendritic cells was pulsed with peptides derived from the breakpoint region of the fusion proteins. Vaccines were administered intravenously concomitant with continuous intravenous rhIL-2 at 9 x 10(6) IU/m(2)/day. RESULTS: Toxicity was limited to IL-2 related effects and was generally mild. Following vaccination, all patients showed progressive disease, most in a rapid fashion following the first vaccine. One patient showed evidence of an immunologic response and another showed a mixed clinical response. Patients enrolled on this tumor vaccine trial showed significant immunosuppression and large bulky tumors. CONCLUSIONS: Peptide vaccination as administered in this trial did not alter the dismal clinical outcome for patients with recurrent pediatric sarcomas. Future trials of tumor vaccines in this population should target patient populations with improved immune competence and smaller tumor burdens. Furthermore, optimization of the antigen presenting cell populations may be important for inducing immune responses to peptide antigens.