A Bivalent Live-Attenuated Vaccine for the Prevention of Equine Influenza Virus

Abstract

Vaccination remains the most effective approach for preventing and controlling equine influenza virus (EIV) in horses. However, the ongoing evolution of EIV has increased the genetic and antigenic differences between currently available vaccines and circulating strains, resulting in suboptimal vaccine efficacy. As recommended by the World Organization for Animal Health (OIE), the inclusion of representative strains from clade 1 and clade 2 Florida sublineages of EIV in vaccines may maximize the protection against presently circulating viral strains. In this study, we used reverse genetics technologies to generate a bivalent EIV live-attenuated influenza vaccine (LAIV). We combined our previously described clade 1 EIV LAIV A/equine/Ohio/2003 H3N8 (Ohio/03 LAIV) with a newly generated clade 2 EIV LAIV that contains the six internal genes of Ohio/03 LAIV and the HA and NA of A/equine/Richmond/1/2007 H3N8 (Rich/07 LAIV). The safety profile, immunogenicity, and protection efficacy of this bivalent EIV LAIV was tested in the natural host, horses. Vaccination of horses with the bivalent EIV LAIV, following a prime-boost regimen, was safe and able to confer protection against challenge with clade 1 (A/equine/Kentucky/2014 H3N8) and clade 2 (A/equine/Richmond/2007) wild-type (WT) EIVs, as evidenced by a reduction of clinical signs, fever, and virus excretion. This is the first description of a bivalent LAIV for the prevention of EIV in horses that follows OIE recommendations. In addition, since our bivalent EIV LAIV is based on the use of reverse genetics approaches, our results demonstrate the feasibility of using the backbone of clade 1 Ohio/03 LAIV as a master donor virus (MDV) for the production and rapid update of LAIVs for the control and protection against other EIV strains of epidemiological relevance to horses.

Equine Influenza Virus and Vaccines

“…Importantly, its safety, immunogenicity, and protective efficacy profile was also observed in horses, suggesting the feasibility of implementing this LAIV for the control of FC-1 EIV in horses [ 183 ]. Since the OIE currently recommends that both FC-1 and FC-2 EIV should be incorporated in any EIV vaccine, a year later, Blanco-Lobo et al developed a FC-2 monovalent EIV LAIV and, also, the first bivalent EIV LAIV for the protection against FC-1 and FC-2 EIV based on the use of reverse genetics approaches [ 216 ]. To that end, Blanco-Lobo et al used the internal genes of the Ohio/03 LAIV as a MDV [ 183 ] and the HA and NA of A/equine/Richmond/1/2007 H3N8 (Rich/07), a representative FC-2 EIV, to generate the FC-2 EIV LAIV [ 216 ].…”

“…Since the OIE currently recommends that both FC-1 and FC-2 EIV should be incorporated in any EIV vaccine, a year later, Blanco-Lobo et al developed a FC-2 monovalent EIV LAIV and, also, the first bivalent EIV LAIV for the protection against FC-1 and FC-2 EIV based on the use of reverse genetics approaches [ 216 ]. To that end, Blanco-Lobo et al used the internal genes of the Ohio/03 LAIV as a MDV [ 183 ] and the HA and NA of A/equine/Richmond/1/2007 H3N8 (Rich/07), a representative FC-2 EIV, to generate the FC-2 EIV LAIV [ 216 ]. To generate the bivalent EIV LAIV, Blanco-Lobo et al used a previously described approach to generate a bivalent canine influenza virus (CIV) LAIV [ 217 ] that consisted of mixing the two FC-1 and FC-2 monovalent EIV LAIV and demonstrate how vaccination of horses with the bivalent EIV LAIV was safe and able to protect, upon a single intranasal dose administration, against challenge with both FC-1 A/equine/Kentucky/1/1991 H3N8 and FC-2 Rich/07 H3N8 EIV in horses [ 216 ].…”

A New Master Donor Virus for the Development of Live-Attenuated Influenza B Virus Vaccines

“…If this is the case, updating the MDV of IAV (A/Ann Arbor/6/60 H2N2) and IBV (B/Ann Arbor/1/1966) to different and more contemporary strains backbones, could solve this problem and provide with more effective LAIV for the treatment of both IAV and IBV infections. We have previously shown how the ts, ca, and att mutations of the US MDV A/Ann Arbor/6/60 H2N2 were able to confer a similar phenotype to other IAV strains, including PR8 [ 61 , 62 ] and pH1N1 [ 63 ], A/canine/NY/dog23/2009 H3N8 [ 64 , 65 , 66 ], and A/equine/Ohio/1/2003 H3N8 [ 67 , 68 ] viruses. Likewise, we have also shown that the mutations responsible for the Russian MDV A/Leningrad/17/1957 H2N2 also conferred a similar ts, ca and att phenotype to PR8 [ 62 ] and pH1N1 [ 63 ] IAV.…”

“…We and others have previously shown that introducing the mutations of the US IAV MDV A/Ann Arbor/6/1960 H2N2 LAIV (PB2 N265S and PB1 K391E, D581G, and A661T) [ 59 , 60 ] resulted in the transfer of the ts, ca and att phenotype to other IAV strains, including A/Puerto Rico/8/1934 H1N1 (PR8) [ 61 , 62 ], pandemic A/California/04/2009 H1N1 (pH1N1) [ 63 ], A/canine/NY/dog23/2009 H3N8 [ 64 , 65 , 66 ], and A/equine/Ohio/1/2003 H3N8 [ 67 , 68 ] viruses. Likewise, mutations responsible for the ts, ca and att phenotype of the Russian IAV MDV A/Leningrad/134/17/1957 H2N2 LAIV (PB2 V478L; PB1 K265N and V591I; and NEP M100I) [ 69 ] resulted in the same ts, ca and att phenotype when introduced in PR8 [ 62 ] and pH1N1 [ 63 ] IAV.…”

Immunogenicity of Calvenza-03 EIV/EHV® Vaccine in Horses: Comparative In Vivo Study

“…There are several whole-inactivated virus-based vaccines [ 12 , 13 , 14 , 15 ], subunit vaccines, canarypox vectored vaccines [ 16 ] and modified live viral vaccines that are commercially available ( Table 1 ) [ 17 , 18 , 19 , 20 ]. Reverse genetic-based modified live-attenuated EI vaccines are currently under study [ 21 , 22 ]. Current vaccines are able to reduce clinical signs and viral shedding in vaccinated animals; however, sub-clinical shedding of the virus is a major problem [ 11 ].…”