A cationic liposome-DNA complexes adjuvant (JVRS-100) enhances the immunogenicity and cross-protective efficacy of pre-pandemic influenza A (H5N1) vaccine in ferrets

Abstract

Influenza A (H5N1) viruses continue to pose a public health threat. As inactivated H5N1 vaccines are poorly immunogenic, adjuvants are needed to improve the immunogenicity of H5N1 vaccine in humans. Here, we investigated the immunogenicity and cross-protective efficacy in ferrets of a clade 2.2-derived vaccine with addition of JVRS-100, an adjuvant consisting of cationic liposome-DNA complexes (CLDC). After the first vaccination, significantly higher levels of hemagglutination-inhibition (HAI) and neutralizing antibody titers were detected in ferrets immunized with adjuvanted vaccine compared to unadjuvanted vaccine. Following a second dose of adjuvanted vaccine, HAI antibody titers of ≥ 40 were detected against viruses from multiple H5N1 clades. HAI antibodies against newly isolated H5N2 and H5N8 viruses were also augmented by JVRS-100. Ferrets were challenged with a heterologous H5N1 virus. All ferrets that received two doses of adjuvanted vaccine exhibited mild illness, significantly reduced nasal wash virus titers and protection from lethal challenge. In contrast, ferrets that received unadjuvanted vaccine showed greater weight loss, high viral titers and 3 of 6 animals succumbed to the lethal challenge. Our results indicate that the addition of JVRS-100 to H5N1 vaccine enhanced immunogenicity and cross-protection against lethal H5N1 virus disease in ferrets. JVRS-100 warrants further investigation as a potential adjuvant for influenza vaccines.

Keywords: Antibody response; CLDC adjuvant; Cross-protection; Ferrets; Influenza A (H5N1) vaccine.

Fig. 1

Serum HAI and MN antibody responses of ferrets immunized with BH/05 split vaccine with or without JVRS-100. Ferrets were immunized i.m with one or two doses of JVRS-100 alone (15 μg/ferret), vaccine alone (7.5 μg HA/ferret), or vaccine with JVRS-100 (7.5 μg HA+15 μg JVRS-100/ferret). Sera were collected 4 weeks after the first dose (black dots) and 2 weeks after the second dose (open dots), and then tested individually for HAI (A) and MN (B) antibodies against the homologous virus. Antibody titers are expressed as the reciprocal of the highest serum dilution inhibiting agglutination of 1% horse erythrocytes by 4 HAU of virus, or neutralizing 100 TCID₅₀ amount of virus. Solid bars represent geometric mean titers (GMTs) of 6 ferrets per group. Dashed lines indicate the HAI and MN titer of 40. A responder is defined by neutralizing antibody titers≥20. *p<0.01 compared to BH/05 vaccine alone group.

Fig. 2

JVRS-100 adjuvanted clade 2.2 H5N1 vaccine significantly improves survival and morbidity against a heterologous clade 2.1.3.2 H5N1 virus infection. Groups of 6 ferrets were immunized i.m. with two doses of JVRS-100 alone (15 μg/ferret), vaccine alone (7.5 μg HA/ferret), or vaccine with JVRS-100 (7.5 μg HA+15 μg JVRS-100/ferret). Two months after the second dose, ferrets were challenged i.n. with 10⁶ EID₅₀ of the heterologous IN/05 H5N1 virus. Ferrets were monitored daily for weight loss and survival for 14 days. *p<0.01 compared to BH/05 vaccine alone group.