Cross-protection of Lactococcus lactis-displayed HA2 subunit against homologous and heterologous influenza A viruses in mice
Authors: Xiaojue Peng
Jiexiu Ouyang
Han Lei
Daxian Zhao
Huifeng Jiao
Journal: Archives of Virology (2015)
Discipline: MICROBIOLOGY
Keywords: influenza vaccine; universal vaccine; HA2 subunit; Lactococcus lactis; Spax
Affiliations: College of Medicine, Southwest Jiaotong University, 611756, Chengdu, China. ., Department of Biotechnology, College of Life Science, Nanchang University, 330031, Nanchang, Jiangxi, China.

Abstract:  Current influenza vaccines provide strain-specific protection against homologous subtypes and need to be updated annually. Therefore, it is essential to develop a universal vaccine that would induce broadly cross-protective immunity against homologous and heterologous influenza A viruses. The highly conserved HA2 subunit is a promising candidate for developing a universal influenza vaccine. Here, we hypothesized that the HA2 subunit could be displayed on the surface of Lactococcus lactis (L. lactis), using Spax as an anchor protein (L. lactis/pNZ8008-Spax-HA2) and that L. lactis/pNZ8008-Spax-HA2 would have immunogenicity by oral administration without the use of adjuvant in the mouse model. To address this hypothesis, we show that oral vaccination of mice with L. lactis/pNZ8008-Spax-HA2 elicited significant humoral and mucosal immune responses. Importantly, L. lactis/pNZ8008-Spax-HA2 provided 100% protection against homologous H5N1 or heterologous H1N1 virus challenge. These results suggest that an HA2 subunit presented on the surface of L. lactis is an effective universal vaccine candidate against influenza A viruses in the poultry industry and in humans. 

Retracted: No

PubPeer comments:
 Brought to my attention by a reader. This paper is one of a set of six papers that all share the same authors, were all published in 2014-2015, and that all share very similar plots. No matter what animal species (mouse, chicken, or ferret) or number of animals per group (6-25), the body weight loss in unprotected animals was all very similar (around 25% loss at day 6), while the protected animals all show a dip in body weight around 6 days, followed by an increase. In addition, the error bars (standard deviations in all papers) are unexpectedly small for these types of measurements. Could the authors please provide some explanation for these similarities? The 6 papers are the following: * Han Lei et al. Virology 476 (2015) 189u2013195, DOI: 10.1016 j.virol.2014.12.017, https: pubpeer.com publications E932C6D86F69113141665259EB4C79 * Han Lei et al. Arch Virol (2015) 160:3011u20133019, DOI: 10.1007 s00705-015-2587-8, https: pubpeer.com publications 4E88CDED2683B085DE9D52B7AD7700 * Han Lei et al. BMC Veterinary Research (2015) 11:85, DOI: 10.1186 s12917-015-0399-4, https: pubpeer.com publications B407285D6C4C238DC25A4FA0F28991 * Han Lei et al. Virus Research 196 (2015) 56u201359, DOI: 10.1016 j.virusres.2014.11.009, https: pubpeer.com publications 889BA6B1AE96E94614521AA9583E87 * Han Lei et al. Microb Cell Fact (2015) 14:111, DOI: 10.1186 s12934-015-0287-4, https: pubpeer.com publications A13874959B0962999C5A01039B8D02 * Han Lei et al. Journal of Medical Virology (2014), DOI: 10.1002 jmv.23983, https: pubpeer.com publications BFBF1A36BD6B9C54611A9727DA0206 And here are the graphs: ![file] ![file] ![file] ![file] ![file] , 
 Dear Elisabeth M Bik, Thank you very much for your comments. On behalf of all authors, I would like to address your concerns. Virus challenge is a gold-standard method for evaluating immune protection of viral vaccine candidate. Animal mode will be monitored for survival and body weight change for 14 days at post challenge, the criteria of virus challenge is that negative controls would be died within 6-8 days and the endpoint is body weight loss exceeded 25% relative to the weight at the time of challenge inoculation. Therefore, in our studies, different animal models such as mice, chickens or ferrets adapted influenza viruses with different virus dose are chosen for virus challenge experiment for investigating different L. lactis based oral or intranasal vaccine. Unprotected animals that you mentioned are negative controls such as PBS group and L lactis containing empty plasmid group were died within 6-8 days at post animal adapted influenza virus in our publications. Meanwhile, the body losses of these negative controls exceeded 25% would be euthanasia at post challenge, because these negative controls did not produce protective immunity. In contrast, the body weight of animal model vaccinated with L lactis based vaccine would increase on days 6-8 at post challenge, because they could produce protective immunity supported by antibody responses and HI assay. Thus, days 6-8 is a critical time point for virus challenge. The error bars in our publications is unexpectedly small as you mentioned, because the values of standard deviations are derived from statistical software based on our original data at post challenge. Thank you very much for your interests. Please let us know if you have any questions. ,