Use of VLP to Test Antibody Responses in Clinical Samples
Hemagglutination inhibition antibody (HAI) titer is the accepted immunological correlate for influenza vaccines.8 This assay measures the ability of sera to block agglutination of red blood cells by influenza viruses mediated by the HA
protein (this property of VLP HA is tested as a release requirement: Table 3) and the accepted correlates for protection are
Achievement of Seroconversion: Lower 95% CI must have >40% of subjects with a >4-fold increase in titer and a minimum final
titer of >40.
Achievement of HAI titer >40: Lower 95% CI must have >70% of subjects with a minimum final titer of >40.
The stability of HA in VLP suggests that this might be used as a source of HA to standardize HAI measurement by multiple laboratories.
Serum samples were obtained from rabbits immunized with a trivalent seasonal VLP and the sera were tested for HAI titer to
the H3N2 and H1N1 component using influenza virus and VLP as the source of HA. Figure 6 shows that sera from four rabbits
had equivalent H3N2 HAI titers when virus or VLP were used as the source of HA in the assay. For H1N1, three of the four rabbit
sera gave higher HAI titers when measured with VLP and the fourth serum gave equivalent titers with virus and VLP. These results
suggest that VLP can be used as an alternative source of HA to measure HAI titers in clinical samples.
Figure 6. Measurement of hemagglutination inhibition (HAI) titer comparing influenza virus and VLP as the source of HA for
H3N2 and H1N1
Our influenza VLP vaccine technology has been shown to be safe and to elicit HAI and NAI antibodies in several clinical trials
totaling more than 5,000 subjects. Release testing of this vaccine has involved both standard assays (SRID)used to confirm
potency of the influenza vaccine, allowing dose confirmation by regulatory authorities, and unique assays (particle size,
NA activity) developed to ensure the physical, chemical, and biological stability of this vaccine. These assays have demonstrated
the stability of VLPs over a 12-month period with preservation of functional HA and NA, which suggests that VLP can be used
to standardize clinical assays that provide immunological correlates of protection.
STEVEN PINCUS is the head of analytical and quality operations, SARATHI BODDAPATI is a senior scientist, formulation development, JINGNING LI is a scientist, analytical development, and TRAVIS SADOWSKI is a senior manager, quality control, all at Novavax Inc., Rockville, MD, 240.268.2032, email@example.com
1. Clinical trials performed include a) a two part 2009 pandemic H1N1 A/Calif/04 study in healthy adults (18–64 yrs) with
an n=1000; dose ranging study with 5, 15, and 45µg HA dose injected IM in Stage A followed by an expanded safety Stage B study
with an n=3550 and a 15µg HA dose; b) seasonal trivalent vaccine with more than 1,000 subjects performed in three different
trials with 2008–9 seasonal trivalent strains in healthy adults (age: 18–49; A/Bris/59; A/Bris/10; B/Flor/04), 2009–10 seasonal
trivalent in healthy older adults (age: >60; A/Bris/59; A/Bris/10; B/Bris/60) and 2005–6 seasonal trivalent (age: 18-49; A/NC;
A/NY; B/Jiangsu) and c) H5N1 prepandemic A/Indonesia/05 study in healthy adults (18–40) in more than 200 subjects.
2. Pushko R, Tumpey TM, BeF, Knell J, Robinson R, Smith G. Influenza virus-like particles composed of the HA, NA and M1 proteins
of H9N2 influenza virus induce protective immune responses in BALB/c mice. Vaccine. 2005:23:5751–9.
3. Williams MS. Single-radial-immunodiffusion as an in vitro potency assay for human inactivated viral vaccines. Vet Microbiol.
4. Nayak B, Kumar S, DiNapoli JM, Paldura A, Perez DR, Collins PL, Samal SK. Contributions of the avian influenza virus HA,
NA and M2 surface proteins to the induction of neutralizing antibodies and protective immunity. J Virol. 2010:84:1489–1503.
5. DiNapoli JM, Nayak B, Yang L, Finneyfrock BW, Cook A, Anderson H, T, et al. Newcastle disease virus-vectored vaccines
expressing the hemagglutinin or neuraminidase protein of H5N1 highly pathogenic avian influenza virus protect against viral
challenge in monkeys. J Virol. 2010:84:1489–1503.
6. Huber VC, Peltola V, Iverson AR, McCullers JA. Contribution of vaccine-induced immunity toward either the HA or NA component
of influenza virus limits secondary bacterial complications. J Virol. 2010:84:4105–8.
7. Gillim-Ross L, Subbarao K. Can immunity induced by human influenza virus N1 neuraminidase provide some protection from
avian influenza H5N1 virus? PLoS Med. 2007:4:e91:226–8.
8. Stephenson I, Wood JM, Nicholson KG, Charlett A, Zambon MC. Detection of anti-H5 responses in human sera by HI using horse
erythrocytes following Mf59-adjuvanted influenza A/Duck/Singapore/97 vaccine: Virus Res. 2004:103:91–5.