Recommendations for the Development of Cell-Based Anti-Viral Vector Neutralizing Antibody Assays

Unveiling the sex bias: higher preexisting and neutralizing titers against AAV in females and implications for gene therapy

Gene therapy with AAV vectors is a promising approach for treating numerous genetic disorders but is often hindered by preexisting antibodies that neutralize the vectors. Given that females may exhibit stronger immune responses than males, this study hypothesizes that females may have higher preexisting antibody titers against AAV. Serum samples from two U.S. cohorts were analyzed for antibody titers, antibody subtypes, and transduction inhibition activity against AAV serotypes AAV1, AAV2, AAV5, AAV8, and AAV9. We found that among seropositive samples, females had higher preexisting antibody levels and neutralizing activities against AAV9 and other serotypes. Immunoglobulin subclass analysis showed IgG1 dominance in both sexes, but females had higher IgA levels, whereas males had higher levels of IgG2. We further evaluated the cellular level of this differential immune response to AAV by stimulation of male and female human PBMCs. We observed dose-dependent increase in cytokines and chemokines in female PBMCs which suggests a differential inflammatory response. Altogether, our findings suggest that the enhanced immune response in females could lead to neutralization and faster clearance of AAV vectors with potential to impact the efficacy of gene therapy.

Global seroprevalence of neutralizing antibodies against adeno-associated virus serotypes used for human gene therapies

Adeno-associated virus (AAV) vectors are promising gene therapy candidates, but pre-existing anti-AAV neutralizing antibodies (NAbs) pose a significant challenge to successful gene delivery. Knowledge of NAb seroprevalence remains limited and inconsistent. We measured activity of NAbs against six clinically relevant AAV serotypes across 10 countries in adults (n = 502) and children (n = 50) using a highly sensitive transduction inhibition assay. NAb prevalence was generally highest for AAV1 and lowest for AAV5. There was considerable variability across countries and geographical regions. NAb prevalence increased with age and was higher in females, participants of Asian ethnicity, and participants in cancer trials. Co-prevalence was most frequently observed between AAV1 and AAV6 and less frequently between AAV5 and other AAVs. Machine learning analyses revealed a unique clustering of AAVs that differed from previous phylogenetic classifications. These results offer insights into the biological relationships between the immunogenicity of AAVs in humans beyond that observed previously using standard clades, which are based on linear capsid sequences. Our findings may inform improved vector design and facilitate the development of AAV vector-mediated clinical gene therapies.

Multicenter assessment and longitudinal study of the prevalence of antibodies and related adaptive immune responses to AAV in adult males with hemophilia

Adeno-associated virus (AAV) based gene therapy has demonstrated effective disease control in hemophilia. However, pre-existing immunity from wild-type AAV exposure impacts gene therapy eligibility. The aim of this multicenter epidemiologic study was to determine the prevalence and persistence of preexisting immunity against AAV2, AAV5, and AAV8, in adult participants with hemophilia A or B. Blood samples were collected at baseline and annually for ≤3 years at trial sites in Austria, France, Germany, Italy, Spain, and the United States. At baseline, AAV8, AAV2, and AAV5 neutralizing antibodies (NAbs) were present in 46.9%, 53.1%, and 53.4% of participants, respectively; these values remained stable at Years 1 and 2. Co-prevalence of NAbs to at least two serotypes and all three serotypes was present at baseline for ~40% and 38.2% of participants, respectively. For each serotype, ~10% of participants who tested negative for NAbs at baseline were seropositive at Year 1. At baseline, 38.3% of participants had detectable cell mediated immunity by ELISpot, although no correlations were observed with the humoral response. In conclusion, participants with hemophilia may have significant preexisting immunity to AAV capsids. Insights from this study may assist in understanding capsid-based immunity trends in participants considering AAV vector-based gene therapy.

2023 White Paper on Recent Issues in Bioanalysis: ISR for ADA Assays, the Rise of dPCR vs qPCR, International Reference Standards for Vaccine Assays, Anti-AAV TAb Post-Dose Assessment, NanoString Validation, ELISpot as Gold Standard (Part 3 - Recommendations on Gene Therapy, Cell Therapy, Vaccines Immunogenicity & Technologies; Biotherapeutics Immunogenicity & Risk Assessment; ADA/NAb Assay/Reporting Harmonization)

The 17th Workshop on Recent Issues in Bioanalysis (17th WRIB) took place in Orlando, FL, USA on June 19-23, 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 3) covers the recommendations on Gene Therapy, Cell therapy, Vaccines and Biotherapeutics Immunogenicity. Part 1A (Mass Spectrometry Assays and Regulated Bioanalysis/BMV), P1B (Regulatory Inputs) and Part 2 (Biomarkers, IVD/CDx, LBA and Cell-Based Assays) are published in volume 16 of Bioanalysis, issues 8 and 9 (2024), respectively.

Novel assay format for total anti-adeno-associated virus antibody detection with low capsid consumption and built-in specificity control

Aim: To develop an assay format for detection of total anti-adeno-associated virus 2 (AAV2) antibodies with low capsid material consumption. Methods: An immune complex (IC) assay format was developed. The format is based on the formation of ICs in solution and their subsequent detection using an anti-AAV2 antibody for capture and an antibody against the study species IgG for detection. Results: The feasibility of the IC assay for detection of preexisting and treatment-emergent anti-AAV2 antibodies was demonstrated in cynomolgus monkey and human serum samples, including samples from a preclinical study with AAV2-based therapies. Conclusion: The presented IC assay is an easy-to-perform total anti-AAV2 antibody assay that requires a small amount of unlabeled capsid material and provides an intrinsic specificity control.

Preexisting antibody assays for gene therapy: Considerations on patient selection cutoffs and companion diagnostic requirements

Recombinant adeno-associated virus (AAV) vectors are the leading delivery vehicle used for in vivo gene therapies. Anti-AAV antibodies (AAV Abs) can interact with the viral capsid component of an AAV-based gene therapy (GT). Therefore, patients with preexisting AAV Abs (seropositive patients) are often excluded from GT trials to prevent treatment of patients who are unlikely to benefit1 or may have a higher risk for adverse events outweighing treatment benefits. On the contrary, unnecessary exclusion of patients with high unmet medical need should be avoided. Instead, a risk-benefit assessment that weighs the potential risks due to seropositivity vs. severity of disease and available treatment options, should drive the decision if patient selection is required. Assays for patient selection must be validated according to their intended use following national regulations/standards for diagnostic assays in appropriate laboratories. In this review, we summarize the current process of patient selection, including assay cutoff criteria and related assay validation approaches. We further provide considerations on regulatory requirements for the development of in vitro diagnostic tests supporting market authorization of a corresponding GT.

Prednisolone and rapamycin reduce the plasma cell gene signature and may improve AAV gene therapy in cynomolgus macaques

Adeno-associated virus (AAV) vector gene therapy is a promising approach to treat rare genetic diseases; however, an ongoing challenge is how to best modulate host immunity to improve transduction efficiency and therapeutic outcomes. This report presents two studies characterizing multiple prophylactic immunosuppression regimens in male cynomolgus macaques receiving an AAVrh10 gene therapy vector expressing human coagulation factor VIII (hFVIII). In study 1, no immunosuppression was compared with prednisolone, rapamycin (or sirolimus), rapamycin and cyclosporin A in combination, and cyclosporin A and azathioprine in combination. Prednisolone alone demonstrated higher mean peripheral blood hFVIII expression; however, this was not sustained upon taper. Anti-capsid and anti-hFVIII antibody responses were robust, and vector genomes and transgene mRNA levels were similar to no immunosuppression at necropsy. Study 2 compared no immunosuppression with prednisolone alone or in combination with rapamycin or methotrexate. The prednisolone/rapamycin group demonstrated an increase in mean hFVIII expression and a mean delay in anti-capsid IgG development until after rapamycin taper. Additionally, a significant reduction in the plasma cell gene signature was observed with prednisolone/rapamycin, suggesting that rapamycin's tolerogenic effects may include plasma cell differentiation blockade. Immunosuppression with prednisolone and rapamycin in combination could improve therapeutic outcomes in AAV vector gene therapy.

Prevalence of Adeno-Associated Virus-9-Neutralizing Antibody in Chinese Patients with Duchenne Muscular Dystrophy

The delivery of a mini-dystrophin gene to skeletal muscles using recombinant adeno-associated virus serotype (AAV) holds great potential as a gene therapy for Duchenne muscular dystrophy (DMD). However, the presence of anti-AAV-neutralizing antibodies (NAbs) may impede the effectiveness of gene transduction. This study aimed to evaluate the prevalence of anti-AAV9 NAbs in Chinese patients with DMD, and to characterize the target population for an AAV gene therapy. A total of one hundred male patients with DMD were included in this study, and demographic and clinical data were collected. A blood specimen was obtained from each participant for the purpose of evaluating the existence of anti-AAV9 NAbs through a cell-based functional assay conducted at a central laboratory. A NAb titer exceeding 1:4 was considered positive. The positivity rates of anti-AAV9 NAb were compared among different subgroups. The median age of this DMD cohort was 8 years old, ranging from 3 to 15 years of age. Forty-two percent of patients tested positive for anti-AAV9 NAb. Notably, all samples from patients under 4 years of age tested negative, and the positivity rates of anti-AAV9 NAb differed significantly across the three age subgroups (<4 years old, ≥4 years old and <12 years old, and ≥12 years old, χ2 = 7.221, p = 0.023). Further investigation into the living environment revealed a higher positivity rate of anti-AAV9 NAb in rural patients compared with urban patients (χ2 = 3.923, p = 0.048). Moreover, the prevalence in patients from different cities/provinces varied greatly (χ2 = 16.550, p = 0.003). There was no statistically significant difference in the positivity rate of NAb among subgroups of patients with different motor functions (ambulatory or nonambulatory) and different treatment strategies (taking or not taking glucocorticoid). In Chinese DMD patients, the prevalence of anti-AAV9 NAb was found to reach 42%. Moreover, the antibody-positive rate in children <4 years of age was low and revealed notable regional discrepancies.

A sensitive AAV transduction inhibition assay assists evaluation of critical factors for detection and concordance of pre-existing antibodies

Pre-existing antibodies to viral capsids may have a negative impact on the efficacy and safety of adeno-associated virus (AAV)-based gene therapies. Total antibody (TAb) and/or cell-based transduction inhibition (TI) assays have been used to exclude seropositive individuals in clinical studies. Published AAV seroprevalence and patient enrollment criteria regarding antibody status lack comparability between assay formats, hindering a direct cross-study comparison. To identify critical factors impacting TI assay detection of AAV neutralizing antibodies (NAbs), we created a reporter construct expressing NanoLuc® luciferase (Nluc) that enabled a more sensitive and robust detection of AAV6 NAbs than using firefly luciferase. Assessment of additional factors including multiplicity of infection, cell lines, viral production, and capsid purity revealed the reporter is the major determinant of assay sensitivity impacting NAb detection. The Nluc reporter was further used to assess seroprevalence to AAV5, 8, and 9. Last, we compared AAV6 Nluc TI with two TAb assay formats. A higher correlation of Nluc TI was observed with direct binding (90%) than with the more sensitive bridging TAb assay (65%), suggesting both assay sensitivity and TAb formats contribute to AAV seropositivity concordance. Our results support a need to standardize assay formats to ensure proper assessment of pre-existing AAV immunity.

Validation of Anti-Adeno Associated Virus Serotype rh10 (AAVrh.10) Total and Neutralizing Antibody Immunogenicity Assays

Immunogenicity assessment of Adeno-Associated Virus (AAV) vectors is a critical part of gene therapy drug development. Whether the assays are used for inclusion/exclusion criteria or to monitor the safety and efficacy of the gene therapy, they are critical bioanalytical assessments. While total anti-AAV assays are perceived as easier to develop and implement than neutralizing anti-AAV assays, the gene therapy field is still nascent, and it is not yet clear which of the assays should be implemented at what stage of drug development. Recently AAVrh.10 has gained interest for use in gene therapies targeting cardiac, neurological, and other diseases due to its enhanced transduction efficiency. There is limited information on anti-AAVrh.10 antibodies and their clinical impact; thus, the information presented herein documents the validation of both a total antibody assay (TAb) and a neutralizing antibody (NAb) assay for anti-AAVrh.10 antibodies. In this manuscript, the validation was performed in accordance with the 2019 FDA immunogenicity guidance with additional evaluations to comply with CLIA where applicable. The AAVrh.10 TAb and NAb assays were compared in terms of sensitivity, drug tolerance, and precision, along with a concordance analysis using the same individual serum samples. This comparison gave insight into the utility of each format as a screening assay for inclusion into clinical studies.

An Integrated Research-Clinical BSL-2 Platform for a Live SARS-CoV-2 Neutralization Assay

A reliable and efficient serological test is crucial for monitoring neutralizing antibodies against SARS-CoV-2 and its variants of concern (VOCs). Here, we present an integrated research-clinical platform for a live SARS-CoV-2 neutralization assay, utilizing highly attenuated SARS-CoV-2 (Δ3678_WA1-spike). This strain contains mutations in viral transcription regulation sequences and deletion in the open-reading-frames 3, 6, 7, and 8, allowing for safe handling in biosafety level 2 (BSL-2) laboratories. Building on this backbone, we constructed a genetically stable reporter virus (mGFP Δ3678_WA1-spike) by incorporating a modified green fluorescent protein sequence (mGFP). We also constructed mGFP Δ3678_BA.5-spike and mGFP Δ3678_XBB.1.5-spike by substituting the WA1 spike with variants BA.5 and XBB.1.5 spike, respectively. All three viruses exhibit robust fluorescent signals in infected cells and neutralization titers in an optimized fluorescence reduction neutralization assay that highly correlates with a conventional plaque reduction assay. Furthermore, we established that a streamlined robot-aided Bench-to-Clinics COVID-19 Neutralization Test workflow demonstrated remarkably sensitive, specific, reproducible, and accurate characteristics, allowing the assessment of neutralization titers against SARS-CoV-2 variants within 24 h after sample receiving. Overall, our innovative approach provides a valuable avenue for large-scale testing of clinical samples against SARS-CoV-2 and VOCs at BSL-2, supporting pandemic preparedness and response strategies.

Goats with low levels of AAV antibody may serve as candidates for large animal gene therapy

AAV vector-mediated gene therapy has been proposed as a feasible strategy for several eye diseases. However, AAV antibodies in the serum prior to treatment hinder the transduction efficiency and thus the therapeutic effect. Therefore, it is necessary to evaluate AAV antibodies in the serum before gene therapy. As large animals, goats are more closely related to humans than rodents and more economically available than nonhuman primates. Here, we first evaluated the AAV2 antibody serum level in rhesus monkeys before AAV injection. Then, we optimized a cell-based neutralizing antibody assay for detecting AAV antibodies in the serum of Saanen goats and evaluated the consistency of the cell-based neutralizing antibody assay and ELISA for goat serum antibody evaluation. The cell-based neutralizing antibody assay showed that the percentage of macaques with low antibody levels was 42.86%; however, there were no macaques with low antibody levels when the serum was evaluated by ELISA. The proportion of goats with low antibody levels was 56.67% according to the neutralizing antibody assay and 33. 33% according to the ELISA, and McNemar's test showed that the results of the two assays were not significantly different (P = 0.754), but that their consistency is poor (Kappa = 0.286, P = 0.114). Moreover, longitudinal evaluation of serum antibodies before and after intravitreal injection of AAV2 in goats revealed that the level of AAV antibodies increased and transduction inhibition subsequently increased, as reported in humans, indicating that transduction inhibition should be taken into account at different stages of gene therapy. In summary, starting with an evaluation of monkey serum antibodies, we optimized a detection method of goat serum antibodies, providing an alternative large animal model for gene therapy, and our serum antibody measurement method may be applied to other large animals.

Preclinical evaluation of ADVM-062, a novel intravitreal gene therapy vector for the treatment of blue cone monochromacy

Blue cone monochromacy (BCM) is a rare X-linked retinal disease characterized by the absence of L- and M-opsin in cone photoreceptors, considered a potential gene therapy candidate. However, most experimental ocular gene therapies utilize subretinal vector injection which would pose a risk to the fragile central retinal structure of BCM patients. Here we describe the use of ADVM-062, a vector optimized for cone-specific expression of human L-opsin and administered using a single intravitreal (IVT) injection. Pharmacological activity of ADVM-062 was established in gerbils, whose cone-rich retina naturally lacks L-opsin. A single IVT administration dose of ADVM-062 effectively transduced gerbil cone photoreceptors and produced a de novo response to long-wavelength stimuli. To identify potential first-in-human doses we evaluated ADVM-062 in non-human primates. Cone-specific expression of ADVM-062 in primates was confirmed using ADVM-062.myc, a vector engineered with the same regulatory elements as ADVM-062. Enumeration of human OPN1LW.myc-positive cones demonstrated that doses ≥3 × 1010 vg/eye resulted in transduction of 18%-85% of foveal cones. A Good Laboratory Practice (GLP) toxicology study established that IVT administration of ADVM-062 was well tolerated at doses that could potentially achieve clinically meaningful effect, thus supporting the potential of ADVM-062 as a one-time IVT gene therapy for BCM.

Low cross reactivity between wild type and deamidated AAV can lead to false negative results in immune monitoring T-cell assays

During gene therapy trials, immune responses against adeno-associated virus (AAV) vectors are monitored by antibody assays that detect the humoral and T-cell mediated cellular responses to AAV vectors. T cell assays commonly utilize the collection of patients' peripheral blood mononuclear cells (PBMCs) and stimulation with AAV-derived overlapping peptides. We recently described that spontaneous deamidation coincides with T cell epitopes in AAV capsids and that spontaneous deamidation may enhance or decrease immunogenicity in some individuals. This raised the concern for false negative results of antibody detection and PBMC immune monitoring assays because these assays use wild-type (WT) AAV or WT peptides for T cell re-stimulation and these peptides may not re-activate T cells that were stimulated with deamidated AAV capsid. To investigate this concern, we modeled the scenario by expanding T cells with deamidated peptides and evaluated the cross-reactivity of expanded T cells to WT peptides. In the majority of samples, cells that were expanded with deamidated peptides and restimulated with WT peptide had significantly lowered IL-2 and IFN-γ production. Spiking the four deamidated peptides to the WT peptide pool used for re-stimulation, restored the signal and corrected the performance of the assay. We also evaluated the impact of deamidation on anti AAV binding antibodies and did not observe a major impact on seroprevalence detection of AAV9. These data indicate that a high level of deamidation in AAV therapy may result in underestimation or even failure to detect immune responses against WT peptides during cellular immune monitoring.

Immunogenicity of Recombinant Adeno-Associated Virus (AAV) Vectors for Gene Transfer

Recombinant adeno-associated viruses (AAVs) have emerged as promising gene delivery vehicles resulting in three US Food and Drug Administration (FDA) and one European Medicines Agency (EMA)-approved AAV-based gene therapies. Despite being a leading platform for therapeutic gene transfer in several clinical trials, host immune responses against the AAV vector and transgene have hampered their widespread application. Multiple factors, including vector design, dose, and route of administration, contribute to the overall immunogenicity of AAVs. The immune responses against the AAV capsid and transgene involve an initial innate sensing. The innate immune response subsequently triggers an adaptive immune response to elicit a robust and specific response against the AAV vector. AAV gene therapy clinical trials and preclinical studies provide important information about the immune-mediated toxicities associated with AAV, yet studies suggest preclinical models fail to precisely predict the outcome of gene delivery in humans. This review discusses the contribution of the innate and adaptive immune response against AAVs, highlighting the challenges and potential strategies to mitigate these responses, thereby enhancing the therapeutic potential of AAV gene therapy.

Comparison of Pre-existing Anti-AAV8 Total Antibody Screening and Confirmatory Assays with a Cell-Based Neutralizing Assay in Normal Human Serum

Pre-existing adeno-associated viruses (AAV) neutralizing antibodies (NAb) can prevent AAV vectors from transducing target tissues. The immune responses can include binding/total antibodies (TAb) and neutralizing antibodies (NAb). This study is aimed at comparing total antibody assay (TAb) and cell-based NAb assay against AAV8 to help inform the best assay format for patient exclusion criteria. We developed a chemiluminescence-based enzyme-linked immunosorbent assay to analyze AAV8 TAb in human serum. The specificity of AAV8 TAb was determined using a confirmatory assay. A COS-7-based assay was used to analyze anti-AAV8 NAbs. The TAb screening cut point factor was determined to be 2.65, and the confirmatory cut point (CCP) was 57.1%. The prevalence of AAV8 TAb in 84 normal subjects was 40%, of which 24% were NAb positive and 16% were NAb negative. All NAb-positive subjects were confirmed to be TAb-positive and also passed the CCP-positive criteria. All 16 NAb-negative subjects did not pass the CCP criterion for the positive specificity test. There was a high concordance between AAV8 TAb confirmatory assay and NAb assay. The confirmatory assay improved the specificity of the TAb screening test and confirmed neutralizing activity. We proposed a tiered assay approach, in which an anti-AAV8 screening assay should be followed by a confirmatory assay during pre-enrollment for patient exclusions for AAV8 gene therapy. This approach can be used in lieu of developing a NAb assay and can be also implemented as a companion diagnostic assay for post-marketing seroreactivity assessments due to ease of development and use.

Binding and neutralizing anti-AAV antibodies: Detection and implications for rAAV-mediated gene therapy

Assessment of anti-adeno-associated virus (AAV) antibodies in patients prior to systemic gene therapy administration is an important consideration regarding efficacy and safety of the therapy. Approximately 30%-60% of individuals have pre-existing anti-AAV antibodies. Seroprevalence is impacted by multiple factors, including geography, age, capsid serotype, and assay type. Anti-AAV antibody assays typically measure (1) transduction inhibition by detecting the neutralizing capacity of antibodies and non-antibody neutralizing factors, or (2) total anti-capsid binding antibodies, regardless of neutralizing activity. Presently, there is a paucity of head-to-head data and standardized approaches associating assay results with clinical outcomes. In addition, establishing clinically relevant screening titer cutoffs is complex. Thus, meaningful comparisons across assays are nearly impossible. Although complex, establishing screening assays in routine clinical practice to identify patients with antibody levels that may impact favorable treatment outcomes is achievable for both transduction inhibition and total antibody assays. Formal regulatory approval of such assays as companion diagnostic tests will confirm their suitability for specific recombinant AAV gene therapies. This review covers current approaches to measure anti-AAV antibodies in patient plasma or serum, their potential impact on therapeutic safety and efficacy, and investigative strategies to mitigate the effects of pre-existing anti-AAV antibodies in patients.

Multiplexing AAV Serotype-Specific Neutralizing Antibodies in Preclinical Animal Models and Humans

The accurate assessment of AAV-specific pre-existing humoral immunity due to natural viral infection is critical for the efficient use of clinical gene therapy. The method described in the present study applies equivalent infection conditions to each AAV serotype (AAV1, AAV2, AAV3, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10, and AAVAnc80L65). In the current study, we validated the assay by assessing AAV-neutralizing antibody titers in a limited cohort of random human donors and well-established preclinical large animal models, including dogs and non-human primates (NHPs). We achieved a rapid and accurate evaluation of neutralizing titers for each individual subject that can be used for clinical enrollment based on specific AAV serotypes and individualized selection of the most suitable AAV serotype for each specific patient.

Immunogenicity assessment of AAV-based gene therapies: An IQ consortium industry white paper

Immunogenicity has imposed a challenge to efficacy and safety evaluation of adeno-associated virus (AAV) vector-based gene therapies. Mild to severe adverse events observed in clinical development have been implicated with host immune responses against AAV gene therapies, resulting in comprehensive evaluation of immunogenicity during nonclinical and clinical studies mandated by health authorities. Immunogenicity of AAV gene therapies is complex due to the number of risk factors associated with product components and pre-existing immunity in human subjects. Different clinical mitigation strategies have been employed to alleviate treatment-induced or -boosted immunogenicity in order to achieve desired efficacy, reduce toxicity, or treat more patients who are seropositive to AAV vectors. In this review, the immunogenicity risk assessment, manifestation of immunogenicity and its impact in nonclinical and clinical studies, and various clinical mitigation strategies are summarized. Last, we present bioanalytical strategies, methodologies, and assay validation applied to appropriately monitor immunogenicity in AAV gene therapy-treated subjects.

Current Status, Issues and Future Prospects of Personalized Medicine for Each Disease

In recent years, with the advancement of next-generation sequencing (NGS) technology, gene panel tests have been approved in the field of cancer diseases, and approaches to prescribe optimal molecular target drugs to patients are being developed. In the field of rare diseases, whole-genome and whole-exome analysis has been used to identify the causative genes of undiagnosed diseases and to diagnose patients’ diseases, and further progress in personalized medicine is expected. In order to promote personalized medicine in the future, we investigated the current status and progress of personalized medicine in disease areas other than cancer and rare diseases, where personalized medicine is most advanced. We selected rheumatoid arthritis and psoriasis as the inflammatory disease, in addition to Alzheimer’s disease. These diseases have high unmet needs for personalized medicine from the viewpoints of disease mechanisms, diagnostic biomarkers, therapeutic drugs with diagnostic markers and treatment satisfaction. In rheumatoid arthritis and psoriasis, there are many therapeutic options; however, diagnostic methods have not been developed to select the best treatment for each patient. In addition, there are few effective therapeutic agents in Alzheimer’s disease, although clinical trials of many candidate drugs have been conducted. In rheumatoid arthritis and psoriasis, further elucidation of the disease mechanism is desired to enable the selection of appropriate therapeutic agents according to the patient profile. In the case of Alzheimer’s disease, progress in preventive medicine is desired through the establishment of an early diagnosis method as well as the research and development of innovative therapeutic agents. To this end, we hope for further research and development of diagnostic markers and new drugs through progress in comprehensive data analysis such as comprehensive genomic and transcriptomic information. Furthermore, new types of markers such as miRNAs and the gut microbiome are desired to be utilized in clinical diagnostics.

Confirmatory detection of neutralizing antibodies to AAV gene therapy using a cell-based transduction inhibition assay

Successful treatment with adeno-associated virus (AAV)-based gene therapies can be limited by pre-existing anti-AAV antibodies. Cell-based transduction inhibition (TI) assays are useful to characterize the neutralizing potential of anti-AAV antibodies in patient samples. While these assays are commonly used, they are not specific for neutralizing antibodies (NAbs) against AAV, also detecting non-antibody-based factors that inhibit AAV transduction in vitro but may not substantially decrease efficacy in vivo. This paper describes the development and bioanalytical validation of a confirmatory assay to improve the specificity of detecting anti-AAV5 NAbs in cell-based TI assays. Samples that screen positive for transduction inhibitors are subsequently depleted of all classes of immunoglobulins using agarose resins conjugated with protein A, G, and L (AGL), which restores AAV5 transduction for NAb-containing samples. Unconjugated agarose resin serves as a mock control for non-specific depletion effects and facilitates normalization of the transduction efficiencies between an AGL- and mock-treated sample; the normalized value is termed the AGL/mock ratio. During validation, a confirmatory cut point for the AGL/mock ratio was derived; sensitivity, precision, selectivity, and matrix interference were also assessed. This confirmatory TI assay facilitates a characterization of humoral immunity to AAV gene therapy by reliably distinguishing NAbs from non-antibody-based neutralizing factors.

Prevalence of pre-existing neutralizing antibodies against AAV serotypes 1, 2, 5, 6, 8, and 9 in sera of different pig strains

Pre-existing neutralizing antibodies (NAb) to adeno-associated virus (AAV) may diminish the efficacy of AAV-based therapies depending on the titer. To support gene therapy studies in pigs, the seroprevalence of NAb to AAV 1, 2, 5, 6, 8, and 9 serotypes were assessed in the sera of 3 different strains of pigs consisting of 60 Norsvin Topigs-20 strain, 22 Gottingen minipigs, and 40 Yucatan minipigs. Cell-based NAb assays were developed for various AAV serotypes. The sera were tested for NAb in a Lec-2 cell line for AAV9 vector and in a COS-7 cell line for the other AAV serotypes. In the 60 Topigs-20 strain aged 2 to 4 years old, 100% were positive for AAV2 NAb, 45 % positive for AAV6 NAb, and ~20% positive for each of AAV1, 5, 8, and 9 NAb. These data showed that approximately 80% of Norsvin Topigs-20 pigs evaluated were seronegative for pre-existing NAb to the AAV1, 5, 8, and 9 serotypes, respectively. In 22 Gottingen minipigs at 5-6 months of age, serum AAV-serotype specific NAb co-existed with that of various other AAV serotypes at 32 to 46 % between two serotypes. These results suggested that coexisting NAb resulted either from multiple AAV serotype co-infection or from one (or more) serotypes that can cross-react with other AAV serotypes in some minipigs. Among the 40 Yucatan minipigs, 20 of the minipigs were less than 3 months old and were all negative for NAb against AAV5, 8 and 9, and only one of these 20 pigs was positive to AAV1 and 6. We further determined the titers in those positive pigs and found most Gottingen minipigs had low titer at 1:20, whereas some of Topigs-20 pigs had titers between 1:80 to 1: 320, and some of Yucatan pigs had titers between 1: 160 to 1: 640. These results suggested that the majority of the pigs in the three strains would be amenable to gene therapy study using AAV1, AAV5, AAV8, and AAV9 and that prescreening on circulating AAV antibodies could be helpful before inclusion of pigs into studies.

Adeno-Associated Viruses (AAV) and Host Immunity - A Race Between the Hare and the Hedgehog

Adeno-associated viruses (AAV) have emerged as the lead vector in clinical trials and form the basis for several approved gene therapies for human diseases, mainly owing to their ability to sustain robust and long-term in vivo transgene expression, their amenability to genetic engineering of cargo and capsid, as well as their moderate toxicity and immunogenicity. Still, recent reports of fatalities in a clinical trial for a neuromuscular disease, although linked to an exceptionally high vector dose, have raised new caution about the safety of recombinant AAVs. Moreover, concerns linger about the presence of pre-existing anti-AAV antibodies in the human population, which precludes a significant percentage of patients from receiving, and benefitting from, AAV gene therapies. These concerns are exacerbated by observations of cellular immune responses and other adverse events, including detrimental off-target transgene expression in dorsal root ganglia. Here, we provide an update on our knowledge of the immunological and molecular race between AAV (the “hedgehog”) and its human host (the “hare”), together with a compendium of state-of-the-art technologies which provide an advantage to AAV and which, thus, promise safer and more broadly applicable AAV gene therapies in the future.

Evaluation of the Humoral Response to Adeno-Associated Virus-Based Gene Therapy Modalities Using Total Antibody Assays

The number of viral vector-based gene therapies (GTx) continues to grow with two products (Zolgensma® and Luxturna®) approved in the USA as of March 2021. To date, the most commonly used vectors are adeno-associated virus-based (AAV). The pre-existing humoral immunity against AAV (anti-AAV antibodies) has been well described and is expected as a consequence of prior AAV exposure. Anti-AAV antibodies may present an immune barrier to successful AAV transduction and hence negatively impact clinical efficacy and may also result in adverse events (AEs) due to the formation of large immune complexes. Patients may be screened for the presence of anti-AAV antibodies, including neutralizing (NAb) and total binding antibodies (TAb) prior to treatment with the GTx. Recommendations for the development and validation of anti-AAV NAb detection methods have been presented elsewhere. This manuscript covers considerations related to anti-AAV TAb-detecting protocols, including the advantages of the use of TAb methods, selection of assay controls and reagents, and parameters critical to monitoring assay performance. This manuscript was authored by a group of scientists involved in GTx development representing eleven organizations. It is our intent to provide recommendations and guidance to industry sponsors, academic laboratories, and regulatory agencies working on AAV-based GTx viral vector modalities with the goal of achieving a more consistent approach to anti-AAV TAb assessment.

A sensitive and reproducible cell-based assay via secNanoLuc to detect neutralizing antibody against adeno-associated virus vector capsid

Most gene therapy clinical trials that systemically administered adeno-associated virus (AAV) vector enrolled only patients without anti-AAV-neutralizing antibodies. However, laboratory tests to measure neutralizing antibodies varied among clinical trials and have not been standardized. In this study, we attempted to improve the sensitivity and reproducibility of a cell-based assay to detect neutralizing antibodies and to determine the detection threshold to predict treatment efficacy. Application of the secreted type of NanoLuc and AAV receptor-expressing cells reduced the multiplicity of infection (MOI) for AAV transduction and improved the sensitivity to detect neutralizing antibodies with a low coefficient of variation, whereas the detection threshold could not be improved by the reduction of MOI to <100. After human immunoglobulin administration into mice at various doses, treatment with high-dose AAV8 vector enabled evasion of the inhibitory effect of neutralizing antibodies. Conversely, gene transduction was slightly influenced in the mice treated with low-dose AAV8 vector, even when neutralizing antibodies were determined to be negative in the assay. In conclusion, we developed a reliable and sensitive cell-based assay to measure neutralizing antibodies against AAV and found that the appropriate MOI to detect marginal neutralizing antibodies was 100. Other factors, including noninhibitory antibodies, marginally influence in vivo transduction at low vector doses.

Efficacy and Safety of Adalimumab Biosimilars: Current Critical Clinical Data in Rheumatoid Arthritis

Adalimumab, as a TNF inhibitor biologic for the treatment of rheumatoid arthritis, is one of the top-selling drugs worldwide. As its various patents have gradually expired, experiments on its biosimilars are constantly being implemented. In this review, we summarized clinical trials of seven biosimilars currently approved by the FDA and/or EMA for the treatment of rheumatoid arthritis, namely: ABP 501 (Amjevita/Amgevita/Solymbic), BI 695501 (Cyltezo), SB5 (Imraldi/Hadlima), GP2017 (Hyrimoz/Hefiya/Halimatoz), MSB11022 (Idacio), FKB327 (Hulio), and PF-06410293 (Abrilada). Overall, these biosimilars showed similar efficacy, safety, and immunogenicity to adalimumab. All biosimilar switching trials indicated that switching from adalimumab to a biosimilar does not have a significant impact on efficacy, safety, and immunogenicity.

2020 White Paper on Recent Issues in Bioanalysis: Vaccine Assay Validation, qPCR Assay Validation, QC for CAR-T Flow Cytometry, NAb Assay Harmonization and ELISpot Validation (Part 3 - Recommendations on Immunogenicity Assay Strategies, NAb Assays, Biosimilars and FDA/EMA Immunogenicity Guidance/Guideline, Gene & Cell Therapy and Vaccine Assays)

The 14^th edition of the Workshop on Recent Issues in Bioanalysis (14^th WRIB) was held virtually on June 15-29, 2020 with an attendance of over 1000 representatives from pharmaceutical/biopharmaceutical companies, biotechnology companies, contract research organizations, and regulatory agencies worldwide. The 14^th WRIB included three Main Workshops, seven Specialized Workshops that together spanned 11 days in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy and vaccine. Moreover, a comprehensive vaccine assays track; an enhanced cytometry track and updated Industry/Regulators consensus on BMV of biotherapeutics by LCMS were special features in 2020. As in previous years, this year's WRIB continued to gather a wide diversity of international industry opinion leaders and regulatory authority experts working on both small and large molecules to facilitate sharing and discussions focused on improving quality, increasing regulatory compliance and achieving scientific excellence on bioanalytical issues. This 2020 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop and is aimed to provide the Global 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 2020 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 3) covers the recommendations on Vaccine, Gene/Cell Therapy, NAb Harmonization and Immunogenicity). Part 1 (Innovation in Small Molecules, Hybrid LBA/LCMS & Regulated Bioanalysis), Part 2A (BAV, PK LBA, Flow Cytometry Validation and Cytometry Innovation) and Part 2B (Regulatory Input) are published in volume 13 of Bioanalysis, issues 4 and 5 (2020), respectively.

Modifiers of Adeno-Associated Virus-Mediated Gene Expression in Implication for Serotype-Universal Neutralizing Antibody Assay

Adeno-associated virus (AAV)-based gene therapy is undergoing major expansion into clinical practice, with two treatments currently being granted Food and Drug Administration (FDA) approval. However, the presence of pre-existing neutralizing antibodies (NAB) is one of the significant hurdles for the clinical application of AAV vectors that significantly limits the patient population, which benefits from the treatment. A reliable diagnostic to evaluate the patient's seropositivity is required to ensure the effectiveness of the AAV-mediated therapeutic. Here, we describe a simple method for the determination of AAV NAB activity based on our finding that Compound C makes HEK293 cell highly permissive for infection by 10 commonly used AAV serotypes.