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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Vaccines and Related Biological Products Advisory Committee Meeting 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

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

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

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

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

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

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

Challenges Practical challenges: Clinical assay 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

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

Using serologic endpoints to infer vaccine efficacy: 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

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