A Porcine Adenovirus with Low Human Seroprevalence Is a Promising Alternative Vaccine Vector to Human Adenovirus 5 in an H5N1 Virus Disease Model Ami Patel1,2, Suresh Tikoo 3 , Gary Kobinger1,2* 1 National Microbiology Laboratory, Public Health Agency of Canada, Canadian Science Centre for Human and Animal Health, Winnipeg, Canada, 2 Department of Medical Microbiology, University of Manitoba, Winnipeg, Canada, 3 Vaccine and Infectious Disease Organization, University of Saskatchewan, Saskatoon, Canada Abstract Human adenovirus 5 (AdHu5) vectors are robust vaccine platforms however the presence of naturally-acquired neutralizing antibodies may reduce vector efficacy and potential for re-administration. This study evaluates immune responses and protection following vaccination with a replication-incompetent porcine adenovirus 3 (PAV3) vector as an alternative vaccine to AdHu5 using an avian influenza H5N1 disease model. Vaccine efficacy was evaluated in BALB/c mice following vaccination with different doses of the PAV3 vector expressing an optimized A/Hanoi/30408/2005 H5N1 hemagglutinin antigen (PAV3-HA) and compared with an AdHu5-HA control. PAV3-HA rapidly generated antibody responses, with significant neutralizing antibody titers on day 21, and stronger cellular immune responses detected on day 8, compared to AdHu5-HA. The PAV3-HA vaccine, administered 8 days before challenge, demonstrated improved survival and lower virus load. Evaluation of long-term vaccine efficacy at 12 months post-vaccination showed better protection with the PAV3-HA than with the AdHu5-HA vaccine. Importantly, as opposed to AdHu5, PAV3 vector was not significantly neutralized by human antibodies pooled from over 10,000 individuals. Overall, PAV3-based vector is capable of mediating swift, strong immune responses and offer a promising alternative to AdHu5. Citation: Patel A, Tikoo S, Kobinger G (2010) A Porcine Adenovirus with Low Human Seroprevalence Is a Promising Alternative Vaccine Vector to Human Adenovirus 5 in an H5N1 Virus Disease Model. PLoS ONE 5(12): e15301. doi:10.1371/journal.pone.0015301 Editor: Troy D. Randall, University of Rochester School of Medicine, United States of America Received August 21, 2010; Accepted November 10, 2010; Published December 16, 2010 Copyright: 2010 Patel et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Financial support was provided by the Public Health Agency of Canada; Canadian Institutes for Health Research (grant 83142 and team grant 310641 to G.P.K.). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: gary_kobinger@phac-aspc.gc.ca Introduction Experimental adenovirus-based vaccine vectors are promising alternatives to conventional vaccine platforms. In particular, human adenovirus serotype 5 (AdHu5) vectors are well-characterized and are being developed against several infectious disease models including influenza, hepatitis C, dengue and viral hemorrhagic fever viruses [1,2,3,4]. Several candidates have demonstrated unique protective efficacy and can generate robust immune responses in both animal models and clinical trials [4,5,6,7]. Pre-existing immunity against AdHu5 is, however, frequent in the human population and has been associated with undesirable clinical outcomes and the suspension of clinical trials [8,9,10]. One promising alternative is the development and evaluation of rare human, chimpanzee, or other mammalian adenovirus vectors with low seroprevalence in humans. A chimeric simian adenovirus 21 vector protected mice against lethal Ebolavirus challenge and generated robust T-cell responses against the glycopro- tein in nonhuman primates [11]. A bovine adenovirus 3 (BAV3)–based vaccine previously demonstrated successful protection against avian influenza A virus H5N1 challenge in mice and was able to escape pre- existing neutralizing antibodies against AdHu5 [12]. Similarly, a porcine adenovirus 3 (PAV3) vector was successful in several swine vaccination studies against classical swine fever and pseudorabies virus [13,14,15]. PAV3-based vaccines were able to evade pre-existing immunity and provide long-term protection in pigs [14]. The antigenic profile and reported in vivo efficacy as an animal vaccine makes the PAV3 vector a promising alternative adenovirus vector for human administration. Due to their genetic diversity and the availability of several significantly different isolates, avian influenza H5N1 viruses provide a valuable and challenging disease model for evaluating broad immune responses generated by potential adenovirus vectors. The external hemagglutinin (HA) glycoprotein mediates receptor binding, fusion, and can generate both strong antibody and cell-mediated immune responses [16] which can be directly assayed and provide useful comparison of adenovirus platforms. Highly pathogenic avian influenza H5N1 viruses have spread throughout domestic and aquatic bird populations in South East Asia and the World Health Organization (WHO) has confirmed 500 clinical cases of H5N1 cross-transmission into humans. Despite the limited incidence of human-to-human-transmission, high mortality rates (.60%) and continuous evolution of the virus represent a concern for future influenza pandemics [17,18]. The emergence of pandemic swine-like H1N1 influenza A virus isolates in early 2009 highlights the need to generate cross-protective and lasting immune responses against diverging human and zoonotic influenza viruses. In addition to evaluation of different adenovirus platforms, the development of improved influenza vaccines would also help in better preparation against emerging pandemic viruses and could reduce the impact of infection on public health. This study evaluates the protective efficacy following lethal homologous challenge of a replication-incompetent porcine PLoS ONE | www.plosone.org 1 December 2010 | Volume 5 | Issue 12 | e15301