Mookkan Prabakaran

Monoclonal Antibodies against the Fusion Peptide of Hemagglutinin Protect Mice from Lethal Influenza A Virus H5N1 Infection

ABSTRACT The HA2 glycopolypeptide (gp) is highly conserved in all influenza A virus strains, and it is known to play a major role in the fusion of the virus with the endosomal membrane in host cells during the course of viral infection. Vaccines and therapeutics targeting this HA2 gp could induce efficient broad-spectrum immunity against influenza A virus infections. So far, there have been no studies on the possible therapeutic effects of monoclonal antibodies (MAbs), specifically against the fusion peptide of hemagglutinin (HA), upon lethal infections with highly pathogenic avian influenza (HPAI) H5N1 virus. We have identified MAb 1C9, which binds to GLFGAIAGF, a part of the fusion peptide of the HA2 gp. We evaluated the efficacy of MAb 1C9 as a therapy for influenza A virus infections. This MAb, which inhibited cell fusion in vitro when administered passively, protected 100% of mice from challenge with five 50% mouse lethal doses of HPAI H5N1 influenza A viruses from two different clades. Furthermore, it caused earlier clearance of the virus from the lung. The influenza virus load was assessed in lung samples from mice challenged after pretreatment with MAb 1C9 (24 h prior to challenge) and from mice receiving early treatment (24 h after challenge). The study shows that MAb 1C9, which is specific to the antigenically conserved fusion peptide of HA2, can contribute to the cross-clade protection of mice infected with H5N1 virus and mediate more effective recovery from infection.

Development of epitope-blocking ELISA for universal detection of antibodies to human H5N1 influenza viruses.

Background Human infections with highly pathogenic H5N1 avian influenza viruses have generally been confirmed by molecular amplification or culture-based methods. Serologic surveillance has potential advantages which have not been realized because rapid and specific serologic tests to detect H5N1 infection are not widely available. Methodology/Principal Findings Here we describe an epitope-blocking ELISA to detect specific antibodies to H5N1 viruses in human or animal sera. The assay relies on a novel monoclonal antibody (5F8) that binds to an epitope comprising amino acid residues 274–281 (CNTKCQTP) in the HA1 region of H5 hemagglutinin. Database search analysis of publicly available sequences revealed that this epitope is conserved in 100% of the 163 H5N1 viruses isolated from humans. The sensitivity and specificity of the epitope-blocking ELISA for H5N1 were evaluated using chicken antisera to multiple virus clades and other influenza subtypes as well as serum samples from individuals naturally infected with H5N1 or seasonal influenza viruses. The epitope-blocking ELISA results were compared to those of hemagglutinin inhibition (HI) and microneutralization assays. Antibodies to H5N1 were readily detected in immunized animals or convalescent human sera by the epitope-blocking ELISA whereas specimens with antibodies to other influenza subtypes yielded negative results. The assay showed higher sensitivity and specificity as compared to HI and microneutralization. Conclusions/Significance The epitope-blocking ELISA based on a unique 5F8 mAb provided highly sensitive and 100% specific detection of antibodies to H5N1 influenza viruses in human sera.

Gastrointestinal Delivery of Baculovirus Displaying Influenza Virus Hemagglutinin Protects Mice against Heterologous H5N1 Infection

ABSTRACT The recent outbreaks of influenza A H5N1 virus in birds and humans have necessitated the development of potent H5N1 vaccines. In this study, we evaluated the protective potential of an immediate-early promoter-based baculovirus displaying hemagglutinin (BacHA) against highly pathogenic avian influenza (HPAI) H5N1 virus infection in a mouse model. Gastrointestinal delivery of BacHA significantly enhanced the systemic immune response in terms of HA-specific serum IgG and hemagglutination inhibition (HI) titers. In addition, BacHA vaccine was able to significantly enhance the mucosal IgA level. The inclusion of recombinant cholera toxin B subunit as a mucosal adjuvant along with BacHA vaccine did not influence either the systemic or mucosal immunity. Interestingly, an inactivated form of BacHA was able to induce only a negligible level of immune responses compared to its live counterpart. Microneutralization assay also indicated that live BacHA vaccine was able to induce strong cross-clade neutralization against heterologous H5N1 strains (clade 1.0, clade 2.1, and clade 8.0) compared to the inactivated BacHA. Viral challenge studies showed that live BacHA was able to provide 100% protection against 5 50% mouse lethal doses (MLD50) of homologous (clade 2.1) and heterologous (clade 1) H5N1. Moreover, histopathological examinations revealed that mice vaccinated with live BacHA had only minimal bronchitis in lungs and regained their body weight more rapidly postchallenge. Furthermore, immunohistochemistry results demonstrated that the live BacHA was able to transduce and express HA in the intestinal epithelial cells in vitro and in vivo. We have demonstrated that recombinant baculovirus with a white spot syndrome virus (WSSV) immediate-early promoter 1 (ie1) acted as a vector as well as a protein vaccine and will enable the rapid production of prepandemic and pandemic vaccines without any biosafety concerns.

Protective immunity against influenza H5N1 virus challenge in mice by intranasal co-administration of baculovirus surface-displayed HA and recombinant CTB as an adjuvant

The increasing number of recent outbreaks of HPAI H5N1 in birds and humans brings out an urgent need to develop potent H5N1 vaccine regimens. Here we present a study on the intranasal vaccination of recombinant baculovirus surface-displayed hemagglutinin (BacHA) or inactivated whole H5N1 viral (IWV) vaccine with a recombinant cholera toxin B subunit (rCTB) as a mucosal adjuvant in a BALB/c mouse model. Two groups of mice were vaccinated with different doses (HA titer of log 2(4) or log 2(8)) of either HA surface-displayed baculovirus or inactivated whole viral vaccine virus adjuvanted with different doses (2 mug or 10 mug) of rCTB. The vaccinations were repeated after 28 days. HA specific serum IgG and mucosal IgA antibodies were quantified by indirect ELISA, and serum neutralizing antibody titer were estimated by hemagglutination inhibition (HI) assay and virus neutralization titer assay. Functional protective efficacy of the vaccine was assessed by host challenge against HPAI H5N1 strains. The results revealed that mice co-administered with log 2(8) HA titer of BacHA vaccine and adjuvanted with 10 mug of rCTB had a significantly enhanced serum IgG and mucosal IgA immune response and serum microneutralization titer compared with mice administered with unadjuvanted log 2(4) or log 2(8) HA titer of BacHA alone. Also vaccination with 10 mug of rCTB and log 2(8) HA titer of BacHA elicited higher HA specific serum and mucosal antibody levels and serum HI titer than vaccination with log 2(8) HA titer of inactivated H5N1 virus adjuvanted with the same dose of rCTB. The host challenge study also showed that 10 mug rCTB combined with log 2(8) HA titer of BacHA provided 100% protection against 10MLD(50) of homologous and heterologous H5N1 strains. The study shows that the combination of rH5 HA expressed on baculovirus surface and rCTB mucosal adjuvant form an effective mucosal vaccine against H5N1 infection. This baculovirus surface-displayed vaccine is more efficacious than inactivated H5N1 influenza vaccine when administered by intranasal route and has no biosafety concerns associated with isolation, purification and production of the latter vaccine.

Combination Therapy Using Chimeric Monoclonal Antibodies Protects Mice from Lethal H5N1 Infection and Prevents Formation of Escape Mutants

Background Given that there is a possibility of a human H5N1 pandemic and the fact that the recent H5N1 viruses are resistant to the anti-viral drugs, newer strategies for effective therapy are warranted. Previous studies show that single mAbs in immune prophylaxis can be protective against H5N1 infection. But a single mAb may not be effective in neutralization of a broad range of different strains of H5N1 and control of potential neutralization escape mutants. Methods/Principal Findings We selected two mAbs which recognized different epitopes on the hemagglutinin molecule. These two mAbs could each neutralize in vitro escape mutants to the other and in combination could effectively neutralize viruses from clades 0, 1, 2.1, 2.2, 2.3, 4, 7 and 8 of influenza A H5N1 viruses. This combination of chimeric mAbs when administered passively, pre or post challenge with 10 MLD50 (50% mouse lethal dose) HPAI H5N1 influenza A viruses could protect 100% of the mice from two different clades of viruses (clades 1 and 2.1). We also tested the efficacy of a single dose of the combination of mAbs versus two doses. Two doses of the combination therapy not only affected early clearance of the virus from the lung but could completely prevent lung pathology of the H5N1 infected mice. No escape variants were detected after therapy. Conclusions/Significance Our studies provide proof of concept that the synergistic action of two or more mAbs in combination is required for preventing the generation of escape mutants and also to enhance the therapeutic efficacy of passive therapy against H5N1 infection. Combination therapy may allow for a lower dose of antibody to be administered for passive therapy of influenza infection and hence can be made available at reduced economic costs during an outbreak.

Baculovirus as Vaccine Vectors

Application of viral vectors derived from human viruses to mediate immune response in animals and humans has been greatly hampered by the problems associated with pre-existing immunity and associated toxicities. Among few non-human viral vectors, baculovirus has now evolved as a novel tool for vaccine vector development. With broad tissue tropism and expanded bio-safety profile suitably supplemented with intrinsic immunostimulatory properties, baculovirus has now attained a niche position in the arena of vaccine development. Recombinant envelope-modified baculovirus equipped with novel shuttle promoters for in vivo transduction has shown promising results in several animal models. Baculovirus mediated induction of systemic and mucosal immune responses through intranasal or oral administration has now open an entirely new way for the development of new generation vaccines. Gaining additional insight into the baculovirus biology and its interaction with non-native hosts will certainly promote this human-friendly virus as a potential vector for clinical applications.

Neutralizing Epitopes of Influenza Virus Hemagglutinin: Target for the Development of a Universal Vaccine against H5N1 Lineages

ABSTRACT The nature of influenza virus to randomly mutate and evolve into new types with diverse antigenic determinants is an important challenge in the control of influenza infection. Particularly, variations within the amino acid sequences of major neutralizing epitopes of influenza virus hemagglutinin (HA) hindered the development of universal vaccines against H5N1 lineages. Based on distribution analyses of the identified major neutralizing epitopes of hemagglutinin, we selected three vaccine strains that cover the entire variants in the neutralizing epitopes among the H5N1 lineages. HA proteins of selected vaccine strains were expressed on the baculovirus surface (BacHA), and the preclinical efficacy of the vaccine formulations was evaluated in a mouse model. The combination of three selected vaccine strains could effectively neutralize viruses from clades 1, 2.1, 2.2, 4, 7, and 8 of influenza H5N1 viruses. In contrast, a vaccine formulation containing only adjuvanted monovalent BacHA (mono-BacHA) or a single strain of inactivated whole viral vaccine was able to neutralize only clade 1 (homologous), clade 2.1, and clade 8.0 viruses. Also, the trivalent BacHA vaccine was able to protect 100% of the mice against challenge with three different clades (clade 1.0, clade 2.1, and clade 7.0) of H5N1 strains compared to mono-BacHA or inactivated whole viral vaccine. The present findings provide a rationale for the development of a universal vaccine against H5N1 lineages. Furthermore, baculoviruses displaying HA will serve as an ideal choice for a vaccine in prepandemic or pandemic situations and expedite vaccine technology without the requirement of high-level-biocontainment facilities or tedious protein purification processes.

Rapid Detection of H5N1 Subtype Influenza Viruses by Antigen Capture Enzyme-Linked Immunosorbent Assay Using H5- and N1-Specific Monoclonal Antibodies

ABSTRACT Highly pathogenic avian influenza (HPAI) virus of the H5N1 subtype has caused devastating damage to poultry flocks and sporadic human H5N1 infections. There is concern that this virus subtype may gain transmissibility and become pandemic. Rapid diagnosis and surveillance for H5N1 subtype viruses are critical for the control of H5N1 infection. In this study, we report a robust antigen-capture enzyme-linked immunosorbent assay (AC-ELISA) based on H5- and N1-specific monoclonal antibodies (MAbs) for the rapid detection of H5N1 subtype viruses. The H5 hemagglutinin (HA)-specific MAb (2D9) targets a conformational epitope which recognized multiple clades of H5N1 viruses, including clades 0, 1, 2.1, 2.2, 2.3, 4, 7, and 8. The N1 neuraminidase (NA)-specific MAb (8H12) recognized a linear epitope comprising the sequence AELPF. This epitope was 99% conserved in the NA of 708 analyzed H5N1 viruses, while the epitope was absent in NAs of subtypes N2 through N9. The specificity of the AC-ELISA was examined by using 41 H5N1 HPAI strains from multiple clades, 36 non-H5N1 viruses, and 4 influenza B viruses. No cross-reactivity was observed for any of the non-H5N1 viruses tested. The estimated detection limit was 1 to 2 HA titers. It is concluded that this H5N1 AC-ELISA can simultaneously detect H5 and N1 subtype antigens, eliminating the need for secondary testing for the NA subtype. Implementation of this assay in ELISA-like formats suitable for field use, such as dot ELISA, immunofiltration, or electrochemical biosensor technologies, would provide dual on-site detection of H5 and N1 in clinical or environmental specimens.

Recombinant Baculovirus Associated with Bilosomes as an Oral Vaccine Candidate against HEV71 Infection in Mice

Background Human enterovirus 71 (HEV71) is one of the major pathogen responsible for hand, foot and mouth disease (HFMD). Currently no effective vaccine or antiviral drugs are available. Like poliovirus, EV71 is transmitted mainly by the feco-oral route. To date the majority of the studied EV71 vaccine candidates are administered parenterally. Injectable vaccines induce good systemic immunity but mucosal responses are often unsatisfactory, whereas mucosal vaccines provide both systemic and mucosal immunity. Therefore, oral immunization appears to be an attractive alternative to parenteral immunization. Methodology/Principal Findings In this report, we studied the efficacy of an orally administered vaccine candidate developed using recombinant baculovirus displaying VP1 (Bac-VP1) in a murine model. Gastrointestinal delivery of Bac-VP1 significantly induced VP1-specific humoral (IgG) and mucosal (IgA) immune responses. Further, we studied the efficacy of the Bac-VP1 associated with bilosomes and observed that the Bac-VP1 associated with bilosomes elicited significantly higher immune responses compared to bilosomes non-associated with Bac-VP1. However, mice immunized subcutaneously with live Bac-VP1 had significantly enhanced VP1 specific serum IgG levels and higher neutralizing antibody titers compared with mice orally immunized with live Bac-VP1 alone or associated with bilosomes. Conclusion Bilosomes have been shown to possess inherent adjuvant properties when associated with antigen. Therefore Bac-VP1 with bilosomes could be a promising oral vaccine candidate against EV71 infections. Thus, Bac-VP1 loaded bilosomes may provide a needle free, painless approach for immunization against EV71, thereby increasing patient compliance and consequently increasing vaccination coverage.

Reverse micelle-encapsulated recombinant baculovirus as an oral vaccine against H5N1 infection in mice

Induction of mucosal immunity through oral immunization is an effective way to control influenza infection. In this study, baculovirus displaying influenza hemagglutinin was encapsulated within a reverse micelle structure of phosphatidylcholine and delivered into the gastrointestinal tract of mice to study its efficacy as an oral vaccine against cross-clade H5N1 infection. Mice vaccinated with encapsulated baculovirus displaying HA (En-BacHA) showed significantly enhanced HA specific serum IgG and mucosal IgA antibodies, and higher hemagglutination inhibition (HI) titers, when compared to its non-encapsulated form (BacHA). Estimation of serum neutralizing antibodies also indicated that En-BacHA formulation was able to induce strong cross-clade neutralization against heterologous H5N1 strains (clade 1.0, clade 2.1, clade 4.0 and clade 8.0). Further, mice vaccinated with En-BacHA alone were able to confer 100% protection against 5MLD50 of HPAI heterologous H5N1 strain (clade 1). Inclusion of recombinant cholera toxin B subunit as a mucosal adjuvant in the vaccine formulation did not show any significant effect in both systemic and mucosal immune responses. Oral delivery of encapsulated recombinant H5 HA expressed on baculovirus surface is an effective way to prime the immune system against H5N1 infection in mice and will have no biosafety concerns associated with their production or administration.