Antigenic variability among two subtypes of human adenovirus serotype 7

Human adenovirus species B knob proteins as immunogens for inducing cross-neutralizing antibody responses

The re-emerging human adenovirus (HAdV) types 3, 7, 14, and 55 of species B have caused severe or even fatal acute respiratory disease. Therefore, the development of multivalent vaccines against HAdV types 3, 7, 14, and 55 remains an important goal. In our previous study, we identified a cross-neutralizing epitope that induced broadly reactive monoclonal neutralizing antibodies against the knob proteins of HAdV types 7, 11, 14, and 55. To study the immunogenicity of HAdV species B knob proteins, we evaluated humoral immune responses to the knob proteins in vivo and in vitro. We found that the knob proteins elicited robust binding and neutralizing antibody responses after three immunizations of mice. In addition, mouse antisera raised against the knob proteins exhibited cross-neutralizing activity against original species B members. Furthermore, immunization with a mix of HAdV-3, 7, and 55 knob proteins protected Chinese tree shrews against an experimental HAdV challenge. Our results provide insight into the immunogenicity of HAdV species B knob proteins.IMPORTANCEHuman adenovirus (HAdV) species B are common pathogens causing severe pneumonia in children, and there is currently no vaccine available. Because there are many HAdV species B types, developing broad-spectrum vaccines against HAdV species B is an important research goal. Our study revealed that immunization with recombinant HAdV species B knob proteins effectively elicited cross-neutralizing antibody responses against original species B members with protective immunity. This study provides a novel insight into the immunogenicity of HAdV species B knob proteins.

Seroprevalence of Neutralizing Antibodies against Six Human Adenovirus Types Indicates the Low Level of Herd Immunity in Young Children from Guangzhou, China

Human adenoviruses (HAdVs) commonly cause many diseases such as respiratory diseases, gastroenteritis, cystitis worldwide. HAdV-3, -7, -4 and emergent HAdV-55 and HAdV-14 are the most important types causing severe respiratory diseases. There is no effective drug available for clinical treatment, and no vaccine available for the general population. Therefore, it is important to investigate the seroprevalence against HAdV for developing novel vaccines and vectors. In this study, we investigated the seroprevalence and titer levels of neutralizing antibodies (NAb) against HAdV-3, -4, -7, -14, -55, and -11 in total 278 healthy populations between 0 months and 49 years of age (228 children and 50 adults) from Guangzhou. In children under the age of 18 years, the seropositive rates were significantly increased against HAdV-3 at 12.07%, 33.96%, and 64.29% and against HAdV-7 at 0%, 18.87%, and 19.05% in age groups of 1–2, 3–5, and 6–17 years, respectively. The seroprevalence was very low (0% ~ 8.1%) for all other four types. In adults aged between 18 and 49 years, HAdV-3, -4, and -7 (> 50.00%) were the most common types, followed by HAdV-14 (38.00%), -55 (34.00%), and -11 (24.00%). Adults tended to have high NAb titers against HAdV-4 and -55. HAdV-55-seropositive donors tended to be HAdV-11- and HAdV-14-seropositive. These results indicated the low level of herd immunity against all six HAdV types in young children, and HAdV-14, -55, -11 in adults from Guangzhou City. Our findings demonstrate the importance of monitoring HAdV types and developing vaccines against HAdV for children and adults.

Genetic variability of human adenovirus type 7 circulating in mainland China

Human adenovirus (HAdV-7) is a highly contagious pathogen that causes severe respiratory illnesses. However, the epidemic patterns and genetic variability of HAdV-7 circulating in mainland China have not been well elucidated. In this study, we used Chinese HAdV sentinel surveillance data obtained from 2012-2015 to investigate the clinical features of 122 HAdV-7-positive cases and performed amplification and sequence determination of three capsid genes (penton base, hexon, and fiber) from 69 isolated viruses covering from seven provinces of China. Additionally, we compared with data from representative sequences of 21 strains covering seven more provinces in China and 32 international HAdV-7 strains obtained from GenBank database to determine the phylogenetic, sequence variations, and molecular evolution of HAdV-7. The results indicated that HAdV-7 infection occurred throughout the year, and a high proportion of severe cases (27 cases, 22.1%) exhibited infantile pneumonia. Moreover, phylogenetic analysis showed that all HAdV-7 strains could be divided into two major evolutionary branches, including subtype 1 and subtype 2, and subtype 3 was also formed according to analysis of the penton base gene. Subtypes 1 and 2 co-circulated in China before 2008, and HAdV-7 strains currently circulating in China belonged to subtype 2, which was also the predominant strain circulating worldwide in recent years. Further sequence variation analysis indicated that three genes of HAdV-7 were relatively stable across time and geographic space, particularly for viruses within subtypes, which shared almost the same variation sites. Owing to continuous outbreaks caused by HAdV-7, resulting in increased illness severity and fatality rates in China, the establishment of a national HAdV surveillance system is urgently needed for the development of effective preventive and infection-control interventions for adenovirus respiratory infections in China.

Development of two antigen-binding fragments to a conserved linear epitope of human adenovirus and their application in immunofluorescence

Detection of human adenoviruses (HAdVs) in nasopharyngeal swab samples by immunofluorescence assay (IFA) will be valuable for diagnosing HAdV infection, which is a leading cause of severe respiratory tract disease, and will help in curbing the spread of HAdV. Monoclonal antibodies employed in IFA for HAdV detection should ideally target highly conserved epitope types. Here, we describe the development of two antigen-binding fragments (Fabs) with specific reactivity to HAdV using phage antibody library technology. When tested with IFA, both Fabs recognized cells infected with several types of HAdV, some of which have been identified in epidemics globally, or associated with outbreaks of severe or fatal acute respiratory diseases. The specificity and cross-reactivity of both Fabs to HAdVs indicated that the generated Fabs could be applied in the development of IFAs to detect HAdVs. Both Fabs bound to the knob proteins, as shown by chemiluminescence enzyme immunoassay and western blot. In addition, epitope mapping showed that both Fabs recognized a conserved linear epitope among several types of HAdV. Two different Fabs recognized the same epitope, suggesting that the epitope triggered the production of at least two kinds of antibodies in the body. The generated Fabs exerted no neutralization against HAdVs. The results demonstrate that both Fabs bind to an epitope that plays no role in neutralization of HAdV.

Human adenovirus type 8: the major agent of epidemic keratoconjunctivitis (EKC)

Human adenovirus type 8 (HAdV-8) is the most common causative agent of a highly contagious eye disease known as epidemic keratoconjunctivitis (EKC). HAdV-8 strains have been classified into genome types HAdV-8A to 8K and HAdV/D1 to D12 according to restriction endonuclease analysis. This review focuses on the significance of HAdV-8 as an agent of EKC. Molecular analysis of HAdV-8 genome types HAdV-53 and HAdV-54 was performed to reveal potential genetic variation in the hexon and fiber, which might affect the antigenicity and tropism of the virus, respectively. On the basis of the published data, three patterns of HAdV-8 genome type distribution were observed worldwide: (1) genome types restricted to a microenvironment, (2) genome types distributed within a country, and (3) globally dispersed genome types. Simplot and zPicture showed that the HAdV-8 genome types were nearly identical to each other. HAdV-54 is very close to the HAdV-8P, B and E genomes, except in the hexon. In a restriction map, HAdV-8P, B, and E share a very high percentage of restriction sites with each other. Hypervariable regions (HVRs) of the hexon were conserved and were 100% identical among the genome types. The fiber knob of HAdV-8P, A, E, J and HAdV-53 were 100% identical. In phylogeny, HVRs of the hexon and fiber knob of the HAdV-8 genome types segregated into monophyletic clusters. Neutralizing antibodies against one genome type will provide protection against other genome types, and the selection of future vaccine strains would be simple due to the stable HVRs. Molecular analysis of whole genomes, particularly of the capsid proteins of the remaining genome types, would be useful to substantiate our observations.