Min Levine, Ph. D. Influenza Division US Centers for Disease Control and Prevention. June 18, 2015 NIBSC

Transcription

1 Workshop on Immunoassay Standardization for Universal Flu Vaccines Min Levine, Ph. D. Influenza Division US Centers for Disease Control and Prevention June 18, 2015 NIBSC 1

2 Multiple Immune Mechanisms Contribute to the Protection of Influenza Neutralizing antibodies against the HA are generally accepted as primary mediators of protection from infection as current vaccine targets. Other responses including anti-na, anti-m2 Ab and T cell responses can reduce virus load and reduce severity and duration of disease. Li, Rappouli and Xu. Curr Opin Immunol

3 Influenza Universal Vaccines Current influenza vaccines (seasonal or pre-pandemic) are mainly based on head domain of hemagglutinin, which require constant update due to the antigenic drift and antigenic shift of the influenza viruses. Universal vaccines that provides safe, more effective and long-lasting immunity against a broad spectrum of divergent influenza viruses in all ages of people are highly desirable. 3

4 Influenza Universal Vaccines Vaccine antigen design Broadly reactive epitopes (HA stalk, M2, NP etc..) Multi-epitope vaccines Vector delivered vaccine Adjuvants To elicit both humoral and cell-mediated responses. Broaden B cell epitope recognition. Th1 vs Th2 responses. Vaccination regimen Doses: one or multiple doses. Vaccination routes: IN, ID, IM etc. Timing: prime/boost 4

5 Assays for Universal Vaccines 1. New assays need to be developed to evaluate immunogenicity of universal vaccine candidates based on target antigens. 2. Threshold need to be established with new assays for correlate of protection to assess vaccine responses. 5

6 Influenza Virus Neutralization (VN) Assays Detect antibodies that can block influenza virus replication cycle Ludwig et al. 2003, Trends in Molecular Medicine Influenza virus replication cycle depends on the virus strain and cell type, in general around 6-16 hrs.

7 Influenza Virus Neutralization Assay can Detect Different Populations of Antibodies Antibodies to: HA head HA stalk NA 7

8 Influenza Virus Neutralization Assays I Antigens (types and amount): Wild type or reassortant viruses Pseudotype viruses (PV): PV with retroviral vector expressing HA, NA or M2 measures ability of antibody to inhibit expression of reporter gene Chimera viruses-ha stalk based vaccines: Chimeric viruses with exotic HA head domain and NA to which majority of the human are naïve, so HA stalk specific antibodies can be detected H5 head PR8 stalk Cell line (seeding density and timing) MDCK, MDCK-SIAT1,etc. 8

9 Influenza Neutralization Assays II Cycles of virus replication and detection method 2 day assay with NP ELISA readout 96 well Plates high throughput 3 day assay with CPE or HA readout 7 day assay with HA readout Other readout (qpcr etc..) Plaque reduction assay and focus reduction assay 9

10 CDC Microneutralization Assay (MN)--WHO manual 3. Dilute sera 2. Add Sera 1. Treat sera 56 o C 30 min 1 C 4. Add Virus 100 TCID 50 /well Day-1 5. Add Cells 1.5x10 4 cells/well 18 C 6. Fix cells and run NP ELISA Day-2 WHO (2011) Global Influenza Surveillance Network Manual for the laboratory diagnosis and virological surveillance of influenza. 10

11 Influenza Virus Microneutralization Assay Mainly detects Antibodies that Bind around globular head of HA and block virus attachment/entry Target stem region of HA that block membrane fusion Detects a broader spectrum of antibodies than HI More sensitive than HI especially for the detection of an early antibody response and sero-conversion.

12 Influenza Virus Microneutralization Assays Used with a wide ranges of influenza viruses including both influenza A and B viruses. Used in: Sero-epidemiology studies Vaccine immunogenicity studies Sero-diagnosis of novel viruses. Antigenic characterization

13 Standardization of MN assays A number of international collaborative studies were conducted previously: Comparison of serology assays for H3N2 (Stephenson et al., vaccine ) Reproducibility of serology assays for H5N1 (Stephenson et al., EID 2009) Reproducibility of serological assays for pdmh1n1 (Wood et.al, Vaccine ). CONSISE (Consortium for the Standardization of Influenza Seroepidemiology study) consensus protocols were used Inter-lab comparison of MN assays for H5N1, H3N2, pdmh1n1, 2 day ELISA vs 3 day HA based assays. Considerable inter-laboratory variation exists for virus neutralization assays, appropriate calibrated antibody standards for normalization of the original titers can reduce the inter-lab variability (Wagner et al., Vaccine 2012) 13

14 Threshold for Correlate of Protection of MN Although MN is widely used, current limitation of using MN to assess vaccine immunogenicity is the lack of well accepted protective threshold for neutralizing antibodies. HI titers remain a primary end point for immunogenicity and licensure of vaccines. In Europe, quantification of serum antibody responses by VN assay is required for approval of pandemic influenza vaccines. A recent household transmission study reported that an MN titer of 40 was associated with 49% protection against PCR-confirmed H3N2 infection. HI titers of 1:40 were associated with 31% protection against PCR confirmed H1N1 and H3N2 virus infections. (Tsang et al. JID 2014). 14

15 Thank you and Questions 15