Comparison of two high-throughput assays for quantification of adenovirus type 5 neutralizing antibodies in a population of donors in China

High-Throughput Screening for the Prevalence of Neutralizing Antibodies against Human Adenovirus Serotype 5

Adenoviral vectors based on the human adenovirus species C serotype 5 (HAdV-C5) are commonly used for vector-based gene therapies and vaccines. In the preclinical stages of development, their safety and efficacy are often validated in suitable animal models. However, pre-existing neutralizing antibodies may severely influence study outcomes. Here, we generated a new HAdV-C5-based reporter vector and established a high-throughput screening assay for the multivalent detection of HAdV-C5-neutralizing antibodies in serum. We screened the sera of rhesus macaques at different primate centers, and of rabbits, horses, cats, and dogs, showing that HAdV-C5-neutralizing antibodies can be found in all species, albeit at different frequencies. Our results emphasize the need to prescreen model animals in HAdV-C5-based studies.

Seroprevalence of human adenovirus type 5 neutralizing antibodies in the Philippines

Human adenovirus (HAdV), particularly the HAdV type 5 (HAdV-5), has been extensively utilized in the development of vector vaccines due to its high immunogenicity, good safety profile, and ease of propagation. However, one of the main challenges in its use is the presence of pre-existing immunity among vaccine recipients. Pre-existing neutralizing antibodies (NAbs) can prevent the uptake of HAdV-5 vectors and reduce vaccine efficacy. Hence, this study investigated the seroprevalence of NAbs against HAdV-5 in urban and rural regions of the Philippines. Luciferase-based neutralization assay was performed on 391 plasma/serum samples. Out of these samples, 346 or 88.5% were positive for HAdV-5 NAbs, and the majority of them (56.8%) had high titers against the virus. Among the regions included in this study, Bicol (Region V) had the highest seroprevalence rate (94.1%). Our findings show that a significant number of adults in the Philippines have pre-existing immunity against HAdV-5. This supports the recommendation that vaccination programs in the country should consider implementing vaccination techniques, such as a prime-boost regimen or addition of booster doses, to address the potential negative effects of pre-existing HAdV-5 immunity in the efficacy of adenoviral vector-based vaccines.

A Sensitive and High-Throughput Flow Cytometry-Based Assay for Measuring Antibody Neutralization of Human Adenovirus Type 3

The assessment of neutralization activity is an important step in the evaluation of neutralizing antibodies (NAbs). The traditional methods for measuring the antibody neutralization of human adenovirus type 3 (HAdV-3) are the microneutralization (MN) assay, which has insufficient sensitivity, and the plaque reduction neutralization test (PRNT), which is not suitable for high-throughput screening. Herein, we describe the development of a flow cytometry-based neutralization (FCN) assay for measuring the neutralization of sera, cell culture supernatants, and chimeric antibodies against HAdV-3 on the basis of a recombinant HAdV-3 (rHAdV-3) construct expressing the enhanced green fluorescent protein (EGFP). For flow cytometry-based assays, the optimal cell confluence was determined as 90%, and the virus was titrated using the assay. The established FCN assay follows the percentage law and an optimal MOI of not less than 5 × 10^-4 was determined by using a purified chimeric antibody. In addition, comparison of the anti-HAdV-3 NAb titers of 72 human serum samples by the MN and FCN assays, showed that both assays correlated strongly with each other. Our FCN assay was an improvement over the MN assay because the observation period was reduced from 3 to 1 days and data analysis could be performed objectively and robotically. Importantly, the newly established FCN assay allows measurement of the neutralization activity of chimeric antibodies expressed in cell culture supernatants. Thus, this sensitive and high-throughput FCN assay is a useful alternative to the MN assay for measuring the antibody neutralization of HAdV-3 and for screening anti-HAdV-3 NAbs in cell culture supernatants.

Current status on the development of pseudoviruses for enveloped viruses

Emerging and reemerging infectious diseases have a strong negative impact on public health. However, because many of these pathogens must be handled in biosafety level, 3 or 4 containment laboratories, research and development of antivirals or vaccines against these diseases are often impeded. Alternative approaches to address this issue have been vigorously pursued, particularly the use of pseudoviruses in place of wild‐type viruses. As pseudoviruses have been deprived of certain gene sequences of the virulent virus, they can be handled in biosafety level 2 laboratories. Importantly, the envelopes of these viral particles may have similar conformational structures to those of the wild‐type viruses, making it feasible to conduct mechanistic investigation on viral entry and to evaluate potential neutralizing antibodies. However, a variety of challenging issues remain, including the production of a sufficient pseudovirus yield and the inability to produce an appropriate pseudotype of certain viruses. This review discusses current progress in the development of pseudoviruses and dissects the factors that contribute to low viral yields.

Neutralizing antibodies against adenovirus type 2 in normal and HIV-1-infected subjects: Implications for use of Ad2 vectors in vaccines

Pre-existing neutralizing antibodies (NAbs) directed against vaccine vectors have attracted considerable research attention. Therefore, our aim was to establish a high-throughput economical neutralization assay to investigate the epidemiology of adenovirus type 2 (Ad2)-specific immunity in China and developed countries, including in a Chinese Human immunodeficiency virus (HIV)-1-infected population, and to guide the application of Ad2-vectored vaccines. We established a FluoroSpot-based anti-Ad2-virus neutralization assay using a recombinant replication-deficient Ad2 that expresses enhanced green fluorescent protein and standardized the critical parameters, including the choice of cell line, cell concentration, viral infective dose, and incubation time. The sera of 561 healthy individuals from China and developed countries and from 230 HIV-1-infected Chinese individuals were screened with this assay for Nabs against Ad2. The prevalence of anti-Ad2 NAbs was high in both China (92.2%) and developed countries (86.9%). Of the Ad2-seropositive individuals, 64.6% in China and 77.4% in developed countries had high NAb titers (> 810). The frequency of anti-Ad2 NAbs was higher in Anhui (97.5%) than in Beijing (88.7%). Their prevalence differed significantly according to age in Beijing, but not in Anhui Province, but by sex in neither province. Ad2 seroprevalence was as high among HIV-1-infected individuals (88.7%) as among healthy individuals (92.2%) in China. In conclusion, a simple, intuitive, high-throughput, economical fluorescence-based neutralization assay was developed to determine anti-Ad2 NAbs titers. Ad2 exposure was high in both healthy and HIV-1-infected populations in China, so vectors based on Ad2 may be inappropriate for human vaccines.

The sero-prevalence of anti-adenovirus 5 neutralizing antibodies is independent of a chronic hepatitis B carrier state in China

We investigated the prevalence of neutralizing antibodies (NA) to human Adenovirus (Ad) 5 both in healthy subjects (HS) and Chronic Hepatitis B (CHB) patients in Shanghai. Detection of anti-Ad5 NA (percentage of detection and titers) was similar between HS and CHB patients. A high percentage of subjects harbored no detectable antibodies (32.2 %) while proportion of subjects displaying very high antibody titers was low (4 %). Neither demographic factors (gender, age, health) nor AST/ALT or HBV circulating DNA titers affected detection of Ad5-specific NA. These observations pave the ground for development of Ad5-based immunotherapeutics aiming at treating CHB patients in China.

A homogeneous chemiluminescent immunoassay method

A new homogeneous chemiluminescent immunoassay method featuring the use of specific binding members separately labeled with an acridan-based chemiluminescent compound and a peroxidase is reported. Formation of an immunocomplex brings the chemiluminescent compound and the peroxidase into close proximity. Without any separation steps, a chemiluminescent signal is generated upon addition of a trigger solution, and the intensity is directly correlated to the quantity of the analyte.