Purification of adenovirus hexon protein by high-performance liquid chromatography

COVID-19 adenovirus vaccine triggers antibodies against PF4 complexes to activate complement and platelets

BACKGROUND

Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare coagulation disorder reported after administration of COVID-19 adenovirus-vectored vaccines. VITT is mediated by anti-platelet factor 4 (PF4) antibodies activating platelets through the Fcγ-receptor II (FcγRII), and it is associated with strong fibrin turnover. The complement system is involved in several other immunothrombotic entities, but its impact on VITT is not established.

OBJECTIVE

To assess antibodies in interaction with the activation of platelets and complement triggered by VITT.

METHODS

Antibodies against adenovirus type 2 hexon protein, ChAdOx1 adenoviral vector-specific IgG and PF4 were analyzed by enzyme immunoassays from VITT patients (n = 5). The EDTA plasma samples of the patients and controls were used to measure both terminal complement complexes (TCC) by ELISA and aggregation of healthy donor platelets. We studied the effects of human immunoglobulin (IVIG) and glycoprotein IIb/IIIa inhibitor (GPIIb/IIIa) on spontaneous and collagen-induced platelet aggregation supplemented with VITT plasma.

RESULTS

None of the patients had experienced a COVID-19 infection. Antibody analyses confirmed the immunogenicity of the adenovirus-vectored ChAdOx1 vaccine. Moreover, VITT plasma had anti-PF4 antibodies and elevated TCC levels as a sign of complement activation. In isolated healthy donor platelets, VITT patient plasma caused marked, spontaneous aggregation of platelets, which was abolished by eptifibatide and high-dose therapeutic IVIG.

CONCLUSIONS

Our findings suggest that VITT is triggered by antibodies against adenovirus vector and PF4-polyanion complexes which strongly co-activate complement and platelets. The spontaneous platelet aggregation was suppressed by IVIG or eptifibatide, indicating that besides FcγRII, also GPIIb/IIIa receptor exerts platelet procoagulant role in VITT.

Serological Array-in-Well Multiplex Assay Reveals a High Rate of Respiratory Virus Infections and Reinfections in Young Children

The multiplex immunoassay was successfully used to simultaneously detect antibodies against seven different viruses. The developed serological microarray is a new promising tool for diagnostic, epidemiological, and seroprevalence analyses of virus infections.

Serological assays are used to diagnose and characterize host immune responses against microbial pathogens. Microarray technologies facilitate high-throughput immunoassays of antibody detection against multiple pathogens simultaneously. To improve survey of influenza A virus (IAV), influenza B virus (IBV), respiratory syncytial virus (RSV), and adenovirus (AdV) antibody levels, we developed a microarray consisting of IAV H1N1, IAV H1N1pdm09 (vaccine), IAV H3N2, IBV Victoria, IBV Yamagata, RSV, AdV type 5 hexon protein, and control antigens printed on the bottom of a microtiter plate well. Bound IgG antibodies were detected with anti-human IgG-coated photon-upconverting nanoparticles and measured with a photoluminescence imager. The performance of the microarray immunoassay (MAIA) was evaluated with serum samples (n = 576) collected from children (n = 288) at 1 and 2 years of age and tested by standard enzyme immunoassays (EIAs) for antibodies to IAV vaccine and RSV. EIAs and MAIA showed substantial to almost perfect agreement (Cohen’s κ, 0.62 to 0.83). Applying MAIA, we found seroprevalences of 55% for IAV H1N1, 54% for IAV vaccine, 30% for IAV H3N2, 24% for IBV Victoria, 25% for IBV Yamagata, 38% for RSV, and 26% for AdV in 1-year-old children (n = 768). By the age of 2 years, IgG seropositivity rates (n = 714) increased to 74% for IAV H1N1, 71% for IAV vaccine, 49% for IAV H3N2, 47% for IBV Yamagata, 49% for IBV Victoria, 68% for RSV, and 58% for AdV. By analyzing increases in antibody levels not biased by vaccinations, we found a reinfection rate of 40% for RSV and 31% for AdV in children between 1 and 2 years of age.

IMPORTANCE The multiplex immunoassay was successfully used to simultaneously detect antibodies against seven different viruses. The developed serological microarray is a new promising tool for diagnostic, epidemiological, and seroprevalence analyses of virus infections.

Role of kinesins in directed adenovirus transport and cytoplasmic exploration

Many viruses, including adenovirus, exhibit bidirectional transport along microtubules following cell entry. Cytoplasmic dynein is responsible for microtubule minus end transport of adenovirus capsids after endosomal escape. However, the identity and roles of the opposing plus end-directed motor(s) remain unknown. We performed an RNAi screen of 38 kinesins, which implicated Kif5B (kinesin-1 family) and additional minor kinesins in adenovirus 5 (Ad5) capsid translocation. Kif5B RNAi markedly increased centrosome accumulation of incoming Ad5 capsids in human A549 pulmonary epithelial cells within the first 30 min post infection, an effect dramatically enhanced by blocking Ad5 nuclear pore targeting using leptomycin B. The Kif5B RNAi phenotype was rescued by expression of RNAi-resistant Kif5A, B, or C, and Kif4A. Kif5B RNAi also inhibited a novel form of microtubule-based “assisted-diffusion” behavior which was apparent between 30 and 60 min p.i. We found the major capsid protein penton base (PB) to recruit kinesin-1, distinct from the hexon role we previously identified for cytoplasmic dynein binding. We propose that adenovirus uses independently recruited kinesin and dynein for directed transport and for a more random microtubule-based assisted diffusion behavior to fully explore the cytoplasm before docking at the nucleus, a mechanism of potential importance for physiological cargoes as well.

The role of plus-end directed microtubule motors in virus entry into host cells is a long-standing question. In this study, the authors identify the kinesins responsible for adenovirus plus end-directed transport along microtubules, the mechanism for kinesin recruitment, and both directed and motor-based exploratory movements involved in adenovirus’ search for the nucleus.

Conformational changes in the adenovirus hexon subunit responsible for regulating cytoplasmic dynein recruitment

Virus capsids provide genome protection from environmental challenges but are also poised to execute a program of compositional and conformational changes to facilitate virion entry and infection. The most abundant adenovirus serotype 5 (AdV5) capsid protein, hexon, directly recruits the motor protein cytoplasmic dynein following virion entry. Dynein recruitment is crucial for capsid transport to the nucleus and requires the transient exposure of AdV5 hexon to low pH, presumably mimicking passage through the endosomal compartment. These results suggest a pH-dependent capsid modification during early infection. The changes to hexon structure controlling this behavior have not been explored. We report that hexon remains trimeric at low pH but undergoes more subtle conformational changes. These changes are indicated by increased sensitivities to SDS-mediated dissociation and dispase proteolysis. Both effects are reversed at neutral pH, as is dynein binding by low-pH-treated hexon. Dispase cleavage, which we find maps to a specific site within hypervariable region 1 (HVR1) of AdV5 hexon, has no apparent effect on virion entry but completely inhibits its transport to the nucleus. In addition, an AdV5 mutant containing HVR1 of AdV48 is unable to bind dynein and is strongly inhibited in the postentry transport step. These results reveal that conformational changes involving hexon HVR1 are the basis for a novel viral mechanism controlling capsid transport to the nucleus.

IMPORTANCE

The adenovirus serotype 5 (AdV5) capsid protein hexon recruits the molecular motor protein cytoplasmic dynein in a pH-dependent manner, a function critical for efficient transport toward the nucleus and AdV5 infectivity. In this work, we describe how low-pH exposure induces reversible structural changes in AdV5 hexon and how these changes affect dynein binding. In addition, we identified a pH-sensitive dispase cleavage site in hexon HVR1, which depends on the same structural changes and furthermore regulates dynein recruitment and capsid redistribution in infected cells. These data provide the first evidence relating long-known but subtle pH-dependent structural changes in hexon to a more recently established essential but poorly understood role in virus transport. These results have broad implications for understanding virus infectivity in general, and our ability to block the recruitment mechanism has potential therapeutic implications as well.

Adenovirus recruits dynein by an evolutionary novel mechanism involving direct binding to pH-primed hexon

Following receptor-mediated uptake into endocytic vesicles and escape from the endosome, adenovirus is transported by cytoplasmic dynein along microtubules to the perinuclear region of the cell. How motor proteins are recruited to viruses for their own use has begun to be investigated only recently. We review here the evidence for a role for dynein and other motor proteins in adenovirus infectivity. We also discuss the implications of recent studies on the mechanism of dynein recruitment to adenovirus for understanding the relationship between pathogenic and physiological cargo recruitment and for the evolutionary origins of dynein-mediated adenovirus transport.

Adenovirus transport via direct interaction of cytoplasmic dynein with the viral capsid hexon subunit

Early in infection, adenovirus travels to the nucleus as a naked capsid using the microtubule motor cytoplasmic dynein. How the dynein complex is recruited to viral cargo remains unclear. We find that cytoplasmic dynein and its associated proteins dynactin and NudE/NudEL, but not LIS1 or ZW10, colocalized with incoming, postendosomal adenovirus particles. However, in contrast to physiological cargos, dynein binding to adenovirus was independent of these dynein-associated proteins. Dynein itself directly interacted through its intermediate and light intermediate chains with the adenovirus capsid subunit hexon in a pH-dependent manner. Expression of hexon or injection of anti-hexon antibody inhibited virus transport but not physiological dynein function. These results identify hexon as a direct receptor for cytoplasmic dynein and demonstrate that hexon recruits dynein for transport to the nucleus by a mechanism distinct from that for physiological dynein cargo.

A novel separation-free assay technique for serum antibodies using antibody bridging assay principle and two-photon excitation fluorometry

A new technique for separation-free detection of antigen-specific antibodies is presented. The new technique employs antibody bridging assay principle and the recently developed ArcDia TPX fluorescence detection technology. According to the assay scheme, antibody molecules from the sample bind with one arm to an antigen on polymer microspheres and with the other arm to a fluorescently labeled secondary antigen reagent. Consequently, fluorescent immunocomplexes are formed on the surface of microspheres in proportion to the concentration of the analyte in the sample. The fluorescence signal from individual microspheres is measured by means of two-photon excited fluorescence detection. In order to demonstrate the applicability of the new assay technique, an assay for anti-adenovirus antibodies was constructed. The function of the assay method was tested both with monoclonal anti-adenovirus antibody preparation (standard analyte), and with positive serum samples. Standard class-specific ELISA was used as a reference method. The new assay method provides comparable sensitivity and precision, and wider dynamic range for IgG antibodies than the ELISA method. The standard curve showed linear response (R(2)=0.999) with a dynamic range of three orders of magnitude, detection limit (mean+3S.D.) of 8 pM, and intra-assay signal precision of 5%. Applicability of the new method for clinical serodiagnostics is discussed.

Respiratory picornaviruses and respiratory syncytial virus as causative agents of acute expiratory wheezing in children

We studied the viral etiology of acute expiratory wheezing (bronchiolitis, acute asthma) in 293 hospitalized children in a 2-year prospective study in Finland. A potential causative viral agent was detected in 88% of the cases. Eleven different viruses were represented. Respiratory syncytial virus (RSV) (27%), enteroviruses (25%), rhinovirus (24%), and nontypable rhino/enterovirus (16%) were found most frequently. In infants, RSV was found in 54% and respiratory picornaviruses (rhinovirus and enteroviruses) in 42% of the cases. In older children, respiratory picornaviruses dominated (65% of children ages 1-2 years and 82% of children ages >3 years). Human metapneumovirus was detected in 4% of all children and in 11% of infants. To prevent and treat acute expiratory wheezing illnesses in children, efforts should be focused on RSV, enterovirus, and rhinovirus infections.

Switch from capsid protein import to adenovirus assembly by cleavage of nuclear transport signals

Replication and assembly of adenovirus occurs in the nucleus of infected cells, requiring the nuclear import of all viral structural proteins. In this report we show that nuclear import of the major capsid protein, hexon, is mediated by protein VI, a structural protein located underneath the 12 vertices of the adenoviral capsid. Our data indicate that protein VI shuttles between the nucleus and the cytoplasm and that it links hexon to the nuclear import machinery via an importin alpha/beta-dependent mechanism. Key nuclear import and export signals of protein VI are located in a short C-terminal segment, which is proteolytically removed during virus maturation. The removal of these C-terminal transport signals appears to trigger a functional transition in protein VI, from a role in supporting hexon nuclear import to a structural role in virus assembly.

Nuclear import of adenovirus DNA in vitro involves the nuclear protein import pathway and hsc70

Adenovirus, a respiratory virus with a double-stranded DNA genome, replicates in the nuclei of mammalian cells. We have developed a cytosol-dependent in vitro assay utilizing adenovirus nucleocapsids to examine the requirements for adenovirus docking to the nuclear pore complex and for DNA import into the nucleus. Our assay reveals that adenovirus DNA import is blocked by a competitive excess of classical protein nuclear localization sequences and other inhibitors of nuclear protein import and indicates that this process is dependent on hsc70. Previous work revealed that the hexon (coat) protein of adenovirus is the only major protein on the surface of the adenovirus nucleocapsid that docks at the nuclear pore complex. This, together with our finding that in vitro nuclear import of hexon is inhibited by an excess of classical nuclear localization sequences, suggests a role for the hexon protein in adenovirus DNA import. However, recombinant transport factors that are sufficient for hexon import in permeabilized cells do not support DNA import, indicating that there are other as yet unidentified factors required for this process.

Comparison of enterovirus-specific cellular immunity in two populations of young children vaccinated with inactivated or live poliovirus vaccines

Enterovirus-specific cellular immunity was studied in Estonian and in Finnish children at the age of 9 months. The aim was to evaluate the level of responsiveness in two neighbouring countries with different poliovirus immunization practices and striking differences in the incidence of insulin-dependent diabetes mellitus (IDDM), a disease in which early enterovirus infections are an aetiological risk factor. The Estonian children immunized with live attenuated polio vaccine had stronger T cell responses to coxsackievirus B4 and poliovirus type 1 when compared with Finnish children immunized with inactivated polio vaccine (median stimulation indices 10.4 and 6.3 in Estonian children and 1.9 and 2.9 in Finnish children, respectively; P < 0.05). Lymphocytes stimulated by poliovirus type 1 antigen expressed interferon-gamma (IFN-gamma) mRNAs, which strongly correlated with the level of proliferation responses. Lymphocytes of Estonian children had a tendency towards stronger expression of IFN-gamma upon poliovirus challenge when compared with Finnish children. The number of children who had experienced coxsackievirus B infections, as determined by the presence of neutralizing antibodies, did not differ between Estonian and Finnish children. The results show that Finnish children have weaker cellular immunity against enteroviruses at the age of 9 months compared with Estonian children at the same age. This is most probably due to the difference in polio vaccination schedules; in Estonia live poliovirus vaccine is used and given at earlier ages than the inactivated vaccines in Finland. This leads to stronger T cell immunity which cross-reacts with other enterovirus serotypes. This may explain the lower incidence of IDDM in Estonia by providing effective protection against diabetogenic enterovirus strains in Estonian children.

T cell responses to enterovirus antigens and to beta-cell autoantigens in unaffected children positive for IDDM-associated autoantibodies

Enterovirus infections have been implicated in the pathogenesis of IDDM in a number of studies. The aim of the present study was to evaluate whether the cellular immune response to enterovirus antigens is abnormal in children who test positive for IDDM-associated autoantibodies. Lymphocyte proliferation responses were analysed to enterovirus antigens and to a panel of beta-cell autoantigen preparations in 31 non-diabetic ICA and/or GAD65 antibody-positive children and in 19 ICA/GAD65-negative control children. The responses to highly purified enteroviruses did not differ between autoantibody (AA)-positive and -negative subjects. However, proliferation responses to coxsackievirus-infected cell lysate, which also included non-structural proteins of the virus, were higher in AA-positive than in AA-negative subjects (P<0.05). This difference was most marked in children carrying the HLA-DQB1*02 allele (P=0.01). AA-positive subjects also had higher responses to one of the three GAD65 antigen preparations compared to AA-negative subjects (P<0.05). Proliferation responses to the adenovirus hexon protein did not differ between the groups. These results show that the increased responses to virus infected cell lysates are associated with early phases of beta-cell autoimmunity.

Enterovirus infections and enterovirus specific T-cell responses in infancy

The development of enterovirus specific T-cell and antibody responses were examined in a cohort of 60 healthy infants at the ages of 3, 6, 9, and 12 months. By the age of 6 months, 68% of the infants had developed T-cell responses against enterovirus antigens by lymphocyte proliferation test, whereas only 30% had serological evidence of an enterovirus infection. By this age, only 7% of the infants had adenovirus specific T-cell responses and 3% had serologically verified adenovirus infection. Enterovirus specific T-cell responses correlated with the lack of enterovirus antibodies in cord blood and the number of sibs reflecting protection by maternal antibodies and the rate of exposures, respectively. T-cell responses cross-reacted between different enterovirus serotypes. The results show that enterovirus infections occur frequently in infancy and induce T-cell immunity. Cellular immunity may be a more sensitive indicator of neonatal enterovirus infections than antibodies.

Enhanced spontaneous antibody response after coronary artery bypass surgery

PURPOSE

Cells spontaneously secreting immunoglobulins can be seen in the blood one week after open-heart surgery. The purpose of this study was to measure the antibody specificities of activated cells.

METHODS

Immune responses were studied preoperatively and on the seventh postoperative day in 18 patients undergoing elective coronary artery bypass surgery. The number of cells secreting adenovirus, measles, rubella and tetanus antigen specific antibodies spontaneously and induced by pokeweed mitogen PWM (ASCs) as well as the total number of cells secreting IgG, IgM and IgA (ISCs) were studied using an enzyme-linked immunospot (ELISPOT) assay. Spontaneous as well as phytohaemagglutinin (PHA)- and pokeweed mitogen (PWM)-induced lymphocyte proliferation was also measured.

RESULTS

The number of cells spontaneously secreting IgG, IgM and IgA antibodies was increased on the seventh day after coronary bypass surgery, against adenovirus, measles, rubella and tetanus as well as the total number of cells secreting immunoglobulins IgG, IgM and IgA (P < 0.05/0.001). By contrast, only slight fluctuation was seen in the numbers of cells secreting antibodies after PWM stimulation. Spontaneous lymphocyte proliferation was also increased, PHA proliferative responses were depressed and PWM responses were not changed on the seventh postoperative day compared with preoperative values.

CONCLUSION

Coronary artery bypass surgery caused marked polyclonal B cell activation demonstrated by an increase of cells producing spontaneously antibodies against virus antigens and tetanus toxoid. This activation could not be intensified by PWM stimulation.

Virus-specific, antibody-secreting cells during upper respiratory infections

The humoral immune response of 18 army recruits with febrile upper respiratory infection (URI) was studied by enumerating virus-specific, antibody-secreting cells in the peripheral blood. Diagnosis was based on viral antigen detection in nasopharyngeal specimens, virus isolation from throat swabs, or on antibody measurement from paired serum samples. At the time of the sample collection, three viruses, including adenovirus, influenza A, and influenza B, were found mainly to cause URIs among the recruits, and ELISPOT assay for enumeration of the specific antibody-secreting cells was selected for these viruses. Of the 36 patients with febrile URI studied, viral diagnosis was made in 18 cases, which included 11 patients with adenovirus infection, three with influenza A, and four with influenza B. The first blood sample was collected at the first signs of URI and the second and third samples at 2-week intervals. The adenovirus-positive patients developed a strong IgG class antibody-secreting cell response against the homologous virus, which peaked at the first sample and decreased steeply by the second and third samples. In the influenza A and B patients, the response was similar kinetically to that seen in adenovirus-positive patients. In those cases where also IgA and IgM class antibody-secreting cells were determined, the IgG response dominated. The ELISPOT method has potential also as a diagnostic tool for respiratory infections.

Integrin alpha v beta 5 selectively promotes adenovirus mediated cell membrane permeabilization

Human adenovirus type 2 (Ad2) enters host cells by receptor-mediated endocytosis, an event mediated by the virus penton base binding to cell surface integrins alpha v beta 3 and alpha v beta 5. While both alpha v integrins promote virus internalization, alpha v beta 5 is involved in the subsequent event of membrane permeabilization. Cells transfected with the beta 5 or beta 3 subunit, expressing either alpha v beta 5 and alpha v beta 3, respectively, were capable of supporting Ad2 infection to varying degrees. In this case, cells expressing alpha v beta 5 were significantly more susceptible to Ad2-induced membrane permeabilization, as well as to Ad2 infection, than cells expressing alpha v beta 3. Adenovirus-mediated gene delivery was also more efficient in cells expressing alpha v beta 5. These results suggest that the interaction of alpha v beta 5 with Ad2 penton base facilitates the subsequent step of virus penetration into the cell. These studies provide evidence for the involvement of a cellular receptor in virus-mediated membrane permeabilization and suggest a novel biological role for integrin alpha v beta 5 in the infectious pathway of a human adenovirus.

Comparison of ion-exchange high-performance liquid chromatography columns for purification of Sendai virus integral membrane proteins

The recovery and separation of the integral membrane proteins, the haemagglutinin-neuraminidase (HN) and the fusion protein (F), from a Sendai virus detergent extract were compared on three different ion-exchange high-performance liquid chromatography (IE-HPLC) columns: Mono Q, TSK DEAE-NPR and Zorbax BioSeries SAX. The detergent, either 1-O-n-octyl-beta-glucopyranoside (octylglucoside) or decyl polyethylene glycol-300 (decyl PEG-300), used for extraction of HN and F proteins from the virions, was also present in the elution buffers at a concentration of 0.1%. Recovery of HN and F proteins was primarily dependent on the detergent present in the eluent, resulting in yields of HN varying from 18 to 28 and 56 to 67%, when octylglucoside and decyl PEG-300, respectively, were used. The highest yield for HN protein was obtained by separation on either a Mono Q or a TSK DEAE-NPR column with decyl PEG-300 as the additive. Yields of F protein were lower, and the highest recovery of 46% was found in the presence of decyl PEG-300 by separation on the Mono Q column. Analysis of the fractions by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and by size-exclusion HPLC indicated that the HN protein eluted in the presence of decyl PEG-300 from the Mono Q and the TSK DEAE-NPR columns was obtained in pure form, while the F protein was slightly contaminated with HN. Analysis of the fractions with monoclonal antibodies directed against conformational epitopes of HN and F proteins indicated that after IE-HPLC the conformation of the proteins is largely retained.