Evaluating Vaccine Effectiveness Using Serologic Assays

1. Evaluating Vaccine Effectiveness Using Serologic Assays Cara R. Fiore, Ph D Office of Vaccines Research and ReviewCenter for Biologics Evaluation and Review U. S. Food and Drug Administration Vaccines Europe, Brussels December 2011

2. Objectives • Background: • Office of Vaccines Research and Review • Vaccine regulation, serological assay validation • Example: two vaccines licensed using immunogenicity data to infer effectiveness 2

3. CBER Regulation of Biologics • Biologics for human use (e.g. vaccines, blood and blood products, cell and gene therapies) • Per authority of: • Public Health Service Act, Section 351 (1944) • Federal Food, Drug and Cosmetic Act (1938) • Regulations: Title 21 of the Code of Federal Regulations (CFR) 5

4. OVRR Regulates:Vaccines for Infectious Disease Indications Live attenuated preparations of bacteria or viruses Inactivated or killed whole organisms Polysaccharides (+/- protein conjugates) Purified proteins, inactivated toxins, VLPs DNA vaccines Vectored vaccines 6

5. Pre IND Development of Preventive Vaccines Phase 1Phase 2Phase 3Phase 4 SafetySafety, Effectiveness Safety, Immunogenicity Initial product characterization Preclinical Safety & Immunogenicity Optimization of Manufacturing Process Process Validation Assay Development & Assay Validation (EOP2) Final Product Specifications Final Formulation/Dosage 7

6. Assay Validation • ICH Q2 (R1) recognized standard guideline • Detection Limit • Linearity • Quantitation Limit • Range • Accuracy • Precision • Repeatability • Intermediate Precision • Specificity • Robustness INTERNATIONAL CONFERENCE ON HARMONISATION OF TECHNICAL REQUIREMENTS FOR REGISTRATION OF PHARMACEUTICALS FOR HUMAN USE. ICH HARMONISED TRIPARTITE GUIDELINE. VALIDATION OF ANALYTICAL PROCEDURES: TEXT AND METHODOLOGY Q2(R1). Current Step 4 version. Parent Guideline dated 27 October 1994.(Complementary Guideline on Methodology dated 6 November 1996 incorporated in November 2005) 8

7. What are Clinical Serological Assays Used For? • Clinical – Immunogenicity and Effectiveness (inferred efficacy) • E.g.- Demonstration of non-inferiority of relevant immune response • Comparison to current standard of care • Comparison to sera from an efficacy trial with a clinical endpoint • Non-Interference with concomitant vaccines • Is there an acceptable correlate of protection? • CMC – Immunogenicity • Bridging manufacturing changes • New facility • Continued/additional product development • Lot consistency 9

8. Clinical Assay Considerations • Assay selection • Functional vs antibody binding • Scientific rationale and practical advantages • Assay validation should demonstrate that it is suitable for its intended purpose • Revalidation may be necessary if: • Drift in method performance • Predefined expiry • Change in procedure, equipment, or other factors 10

9. Immunological Endpoints to Infer Effectiveness • Clinical end-point efficacy studies are the Gold Standard • Why/When to use serological assay: • Clinical efficacy study not possible • Burden of disease too low • New population (age group) • (Animal Rule vaccines) 11

10. Challenges of Assay Design • Goals: • Measure meaningful immunologic biomarker • Reproducible and reliable • Reagents must be attainable • Reagents must be qualifiable • Adequate characterization, standardization and validation • Goals may be challenging for biological/ functional assays 12

11. Example 1: Meningococcal Conjugate Vaccines Serologic Assays as a Measurement of Vaccine Effectiveness • Anti-polysaccharide IgG antibody • Serum bactericidal activity (SBA) assay Meningococcal anti-PS antibody measured by ELISA does not always correlate with functional antibody measured by complement-mediated SBA 13

12. Meningococci Plate on MH agar Antibody Dilutions (human sera) Incubate Complement (human) hSBA + + Antibody titer = highest dilution that results in killing of ≥ 50% cfu of target strain Survival of meningococci 14

13. Serum Bactericidal Activity (SBA) • Data support use of SBA as an immunological correlate for demonstrating effectiveness of meningococcal conjugate vaccines • Measures the antibody dependent complement mediated killing of the specific meningococcal strain in vitro • Critical factors - defined and adequately controlled: • Complement – • Human (h) vs. rabbit (r) • individual vs. pooled source • Target strain • Assay conditions 15

14. Factors Considered in Identifying SBA as the Primary Assay for Serologic Evaluation of Meningococcal Vaccines • Disease Pathogenesis –individuals who lack terminal complement components (complement deficiency) are at high risk of recurrent meningococcal disease • Natural History/Seroepidemiology - inverse correlation between age specific disease rates and prevalence of bactericidal activity • Historical studies of US military recruits • Antibodies that kill N. meningitidis in the presence of active complement (complement mediated bactericidal activity) were associated with protection from disease(Goldschneider et al. 1969.) • Bactericidal Antibodies Play a Critical Role in Protection Against Meningococcal Disease 16

15. Highest incidence of disease occurred at the lowest bactericidal antibody prevalence The incidence of meningococcal disease was inversely proportional to the age-specific prevalence of bactericidal antibodies to the Mn-specific strain Adapted from Pollard et al. Vaccine 2001; 19: 1327-1346; and Goldschneider I, J Exp Med 1969;129:1307-1326 17

16. US Licensed Meningococcal Vaccines Menomune 1981 (>2 yo). Quadrivalent PS vaccine, licensed based on efficacy data for A and C only. Not enough disease in W-135 and Y. W-135 and Y were based on 4 fold rise of SBA in 90% of vaccinees. Menactra - Quadravalent (A, C, Y, W-135) PS conjugate • 2005: 11-55yo • 4-fold rise in rSBA non-inferiority to Menomune. • 2007: 2-10 yo • % ≥ 1:8 with hSBA non-inferiority to Menomune • 2011, 9-23mo • % ≥ 1:8 hSBA Menveo - Quadravalent (A, C, Y, W-135) PS conjugate • 2010: 11-55 yo • % ≥ 1:8 with hSBA non-inferiority to Menactra. • 2011: 2-10 yo • % ≥ 1:8 with hSBA non-inferiority to Menactra ACIP recommends MCV4 for 11-18 years of age, as well as others 2-55 years of age at increased risk of meningococcal disease. 18

17. VRBPAC 1999 Vaccines and Related Biological Products Advisory Committee Meeting • VRBPAC agreed that new meningococcal vaccines could be evaluated using immunologic assays • Serum bactericidal activity was an appropriate parameter to evaluate immunogenicity of a new vaccine in age groups for which the current meningococcal vaccine is licensed for use FDA implementation: SBA has been used to evaluate the immunogenicity of new meningococcal vaccines in comparison to currently licensed vaccines 19

18. VRBPAC 2011 • VRBPAC was asked to “comment on the use of hSBA as an immune measure to infer effectiveness of meningococcal conjugate vaccine for children younger than two years old.” The Advisory Committee agreed that data supported the role of functional antibody in protection from meningococcal disease and that vaccine effectiveness can be inferred from serum bactericidal activity measurements in children less than 2 years of age. 20

19. Example 2: Pneumococcal Conjugate Vaccines Serologic Assays as a Measurement of Vaccine Effectiveness • ELISA – Serotype specific IgG • Infants • IgG antibody levels are associated with protection from invasive pneumococcal disease • Good correlation between IgG and pediatric serum OPA titers • Older children and adults • Poor correlation with OPA for many serotypes • Not considered to be an appropriate endpoint in adults. • Opsonophagocytic Antibody (OPA) Assay • OPA measures functional antibodies that play a role in protection against pneumococcus for vaccines directed at capsular antigens 21

20. OPA Methodology • The OPA assay measures the ability of functional antibody to bind and opsonize the target bacteria in the presence of a complement source, engulfment by phagocytic human cell line (HL-60 cells.) • Polysaccharide bound human antibodies activate the complement mediated opsonization through the classical pathyway. • 4 components • Human Sera + pneumococcus + complement + HL-60 cells • OPA titer = reciprocal of the lowest serum dilution that results in complement-dependent killing of 50% of the bacteria in vitro. 22

21. Phagocytic Human Cell Source + Pneumococci Plate on agar + Antibody Dilutions (human sera) Incubate + Complement (human) OPA Antibody titer = highest dilution that results in killing of ≥ 50% cfu of target strain Survival of pneumococci 23

22. US Licensed Pneumococcal Vaccines Pneumovax 23(1983) Multivalent (23) polysaccharide vaccine. • 50 years of age or older and persons aged ≥2 years who are at increased risk for pneumococcal disease. • Efficacy of PS vaccines evaluated in several clinical trials Prevnar - 7 valent polysaccharide conjugate vaccine • 2000: Immunization of infants 2, 4, 6 and 12-15 months of age to prevent invasive pneumococcal disease. • 2002: Immunization of infants and toddlers against otitis media caused by vaccine serotypes . • Clinical endpoint efficacy trail • VRBPAC 2001 – advised that for new pneumococcal vaccines effectiveness could be inferred from non-inferiority studies using ELISA 24

23. Prevnar 13 • 2010: 13 valent polysaccharide conjugate vaccine. • Licensed in 6 weeks through 5 years of age. • Prevention of invasive disease caused by S.pneumoniae serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F and 23F. • Prevention of otitis media caused by S. pneumoniae serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F. • The efficacy was inferred from comparisons to Prevnar 7 using IgG (ELISA) to measured the production of vaccine type (VT)functional antibody. • Under Review in adults ≥ 50 years of age • IgG does not correlate with functional antibody for older children and adults. Therefore, IgG measurement was not considered to be an appropriate endpoint in these age groups. • VRBPAC 2005 – emphasized the need for clinical endpoint studies while acknowledging challenges, accelerate approval reasonable path • OPA - used as the “surrogate endpoint that is reasonably likely… to predict clinical benefit” of Prevnar 13 in adults • VRBPAC November 2011 25

24. Challenges • Practical challenges: • Availability of patient sera: age group, study size, number of different assays • Clinical assay challenges: • Background titers • Functional quality, and robustness of immune responses • Interpretation of results • Study design issues • need for blinding and controls vs. pairing sera pre and post • require dilution of post immune sera 26

25. Summary: Demonstration of Effectiveness • Gold Standard: Clinical endpoint efficacy study • Immunogenicity Assessment: Serologic endpoint: • Non inferiority: Licensure on the basis of a comparison to licensed product • In populations where there is no comparator vaccine, no direct comparison is possible • Accepted correlate of protection • E.g., Menactra® licensed for use in children 9 month to 23 months of age based on the proportion of subjects with hSBA titer ≥ 1:8 27

26. Take Home Message Using serologic endpoints to infer vaccine efficacy: • Ideally, there is a well established correlate of protection • Ideally, we understand the immunologic basis for the correlate of protection • Need to develop an assay that can be well validated and conducted to provide accurate results reliably 28

27. Thanks! Margaret Bash, MD, MPH Elizabeth Sutkowski, Ph D Wellington Sun, MD Nicolette deVore, Ph D cara.fiore@fda.hhs.gov 29