Recombinant Adenovirus Vector-Based Vaccines for Emerging Influenza Viruses

Ahmed Omar Hassan, Purdue University

Abstract

Since 1996, there have been several reports of human infections with avian influenza A viruses of subtypes H5N1, H7N7, H7N9, and H9N2. Although human-to-human transmission has been infrequent and limited, genetic reassortment between avian and human/porcine influenza viruses or mutations in some of the genes leading to virus replication in the upper respiratory tract in humans could result in the generation of a novel pandemic influenza virus strain that could infect and transmit effectively among the human population which would have little or no immunity to the new virus. Since the first case of human infection in March 2013, continued reports of H7N9 cases highlight a potential pandemic threat. Highly immunogenic vaccines to this virus are urgently needed to protect vulnerable populations who lack protective immunity. We evaluated the feasibility of an egg- and adjuvant-independent human adenovirus vector-based, hemagglutinin H7 subtype influenza vaccine (HAd-H7HA) that has demonstrated enhanced cell-mediated immunity (CMI) as well as serum antibody responses in a mouse model. Most importantly, this vaccine provided complete protection against homologous A/(H7N9) viral challenge suggesting its potential utility as a pandemic vaccine. ^ In a pandemic scenario, it is difficult to predict the virus that is going to cause the pandemic. Current vaccines do not provide effective cross protection against antigenically distinct strains of H5, H7, and H9 influenza viruses. Hence, newer vaccine approaches with the potential to induce both humoral and cellular immune responses that confer protection against a broad range of influenza viruses emerging from avian reservoirs are needed. ^ To enhance the breadth of protective efficacy against avian influenza viruses, we developed an egg-independent adenovirus (Ad) based multi-epitope (ME) vaccine approach by including the relatively conserved immunogenic domains of H5N1 influenza virus [M2 ectodomain (M2e), HA fusion domain (HFD), T cell epitope of nucleoprotein (TNP) and HA ?-helix domain (H?D)]. Immunization of mice with ME vaccine formulations led to the development of humoral immune responses against M2e, H?D and HFD domains and a cell-mediated immune response against the TNP domain. There was significant reduction in lung viral titers when immunized mice were challenged with antigenically distinct H5, H7, or H9 avian influenza viruses suggesting that the ME vaccine approach provided broad protection against avian influenza viruses. Since the nature of the next pandemic influenza virus is unknown, this vaccine approach could significantly lower morbidity, hinder transmission, and prevent mortality in a pandemic situation before a strain-matched vaccine becomes available. ^ There still exist some limitations for the use of human Ad type C5 (HAd5) including the preexisting vector immunity that consists of the HAd5-specific neutralizing antibodies and HAd5-specific CD8⁺ T cells. This vector immunity leads to reduced vector uptake with reduced transgene expression and elimination of transduced cells as well. Bovine adenovirus type 3 (BAdV-3)-based vectors represents a promising alternative to overcome the vector immunity hurdle. BAdV-3 E1 region shares functional homology with E1 of HAd5. Sequence analysis of the BAdV-3 E1 region revealed the presence of a novel 155R open-reading frame (ORF) that is not observed in other Ads, on the lower strand antiparallel to a portion of the E1B region. The 155R gene products in BAdV-3-infected cells were identified by Northern blot, RT-PCR followed by sequencing, and Western blot analysis using the155R-specific antibody. 155R seems to be a late protein and is present in purified BAdV-3 particles. Replication kinetics of BAdV mutants with either one (BAdV/155R/mt1) or two (BAdV/155R/mt2) stop codons in the 155R ORF were comparable to that of BAdV-3, indicating that 155R is not essential for virus replication in cell culture. These results suggest that 155R deleted BAdV-3 vectors could be generated in a cell line that fully complements BAdV-3 E1 functions.^

Degree

Ph.D.

Advisors

Suresh K. Mittal, Purdue University.

Subject Area

Pathology|Virology|Epidemiology

COinS