Conference reportUtilization of serologic assays to support efficacy of vaccines in nonclinical and clinical trials: Meeting at the Crossroads
Introduction
On May 5–6, 2009, in Bethesda, MD, the Division of Microbiology and Infectious Diseases, National Institute of Allergy and Infectious Diseases (NIAID) hosted a workshop on the use of serologic assays to support vaccine efficacy in clinical studies. The purpose of this meeting was to provide a forum for the exchange of ideas among researchers and clinicians and to identify some common themes across pathogens and technologies regarding the development and use of immunoassays. Participants in the meeting were those involved in vaccine or immunotherapeutic development programs that have been evaluated in clinical trials as well as those that are expected to enter Phase I clinical trials in the near future. Also attending were regulatory reviewers involved in evaluation of clinical and nonclinical assay data.
Generation of clinical data demonstrating efficacy and safety remains the gold standard for assessing candidate vaccines protecting against infectious diseases; however, efficacy studies for some products may be unfeasible because of statistical limitations (e.g., disease incidence is too low or variable) or because of ethical considerations (e.g., alternative vaccines or therapeutics are available). The primary purpose of this meeting was to review some vaccines that have been licensed recently and to extract some of the lessons learned which could facilitate the use of serologic assays to evaluate current and future candidate vaccines. The serologic data and experiences associated with vaccine evaluations were presented in three sessions (Table 1): (1) general concepts when using immunoassays to evaluate efficacy, (2) specific vaccines for which humoral correlates have been used for vaccine licensure, and (3) evolving issues related to humoral correlates of protective immunity with respect to new vaccine evaluations. The final session was a panel discussion with participation from the audience that addressed issues and questions raised during the meeting. This summary represents a distillation of the presentations and discussions, uniting the common themes and issues that appeared throughout the meeting.
One issue raised early in the meeting was the lack of clarity of terminology. For many terms, no definitions are universally accepted; this lack of clarity can itself hinder effective communication. In order to facilitate interpretation, we have defined our usage; however, these should not be considered consensus definitions. “Correlate” is a variable that is statistically related to a clinical endpoint, while a “protective correlate” or “predictive correlate” is a correlated variable that, based on additional evidence, is reasonably likely to predict the clinical endpoint [1], [2], [3]. We avoid using the term “surrogate”, as its definition indicates that the measured variable (serologic data, in our case) can totally explain and replace a defined clinical endpoint [1]. “Immunoassays” is a broad term representing measurement of any number of biologic processes associated with immune function. The scope of this meeting was limited to serologic assays which identify and quantify antibodies, rather than assays that assess the cellular activities and functions. Serologic assays include both binding assays (e.g., enzyme linked immunosorbent assays (ELISAs) and hemagglutination inhibition (HI) assays) and functional assays (e.g., bactericidal, opsonophagocytic, neutralization assays). Assay “standardization” is defined as the establishment of an assay methodology within and across laboratories that utilizes a common standard operating protocol (SOP), defining reagent requirements as well as procedures, and generates comparable data sets. Assay “harmonization” is defined as the identification, through an iterative experimental process, of critical parameters that affect assay performance, and the development of related SOPs that conform in those critical variables, leading to the generation of comparable data sets within and across laboratories.
Several common themes emerged and are the focus of this report.
- 1.
Clinical and laboratory testing strategies aimed at defining a protective correlate should be based on an understanding of the biology of a pathogen, the host interactions, and the natural protective responses. This knowledge can lead to the selection of relevant assays which are the most likely to be predictive of clinical benefit.
- 2.
The intended use of the assay needs to be clearly defined before selecting and optimizing the methodology. The assay must be designed to yield data appropriate for the question being asked. Assays need to be of sufficient quality and perform reliably to yield usable data, and the assay format must be practical. “Data are only as good as the quality of the assay used to generate them.” (D.L. Burns presentation).
- 3.
Changes in immunoassays are expected during the vaccine development process. For any particular assay, there is an evolution in the quality, purpose, and degree of standardization. The most rigorous requirements are for assays where the resultant data will be used to consider vaccine licensure and to define correlates of protection. Additionally, the assay itself sometimes must be changed or replaced as the knowledge base increases, the experience with the candidate vaccine matures, and new technologies are developed.
- 4.
Effective identification and utilization of available collaborative resources promote assay evolution, improve testing efficiency, and facilitate generation of comparable data over time. Among these resources are standardized critical laboratory reagents and methods, inter-laboratory harmonization efforts, and multidisciplinary teams that include statistical expertise.
Section snippets
Understanding the pathogen and the immune response to vaccines
Ideally, vaccine developers formulate a product that elicits a protective immune response specific for the target pathogen. Rational vaccine design requires the best possible understanding of the nature of the immune response to the pathogen and the cascade of immunological events that culminate in protection [4]. Identification of the important types of response (e.g., humoral or cellular, specific isotype or subclass of immunoglobulin) and the kinetics of response to the initial and
Cell-mediated immunoassays and other assays
Although the meeting focused on antibody assays, immunological assays to measure cell-mediated immune (CMI) responses are also critically important to the assessment of many vaccines. Elkins noted that the state of knowledge related to CMI assays is less mature than for serum antibody assays. Analogous to the discussion above comparing functional and binding assays, many investigators believe that CMI-related assays are inherently better than antibody assays for many products; however, direct
Summary and conclusions
This meeting was organized to bring together investigators from diverse disciplines who are working with different pathogens at various stages of vaccine development. The goal was to encourage communication and explore common experiences with the development, implementation, and potential interpretation of data from serologic assays. One of the overarching goals of the meeting was to facilitate efficient immunoassay development for candidate vaccines by learning lessons from more mature
Acknowledgements
This meeting was funded by the Division of Microbiology and Infectious Diseases, National Institute of Allergy and Infectious Diseases, and National Institutes of Health.
References (92)
- et al.
Bactericidal antibody is the immunologic surrogate of protection against meningococcal disease
Vaccine
(2009) Relative importance of complement-mediated bactericidal and opsonic activity for protection against meningococcal disease
Vaccine
(2009)- et al.
International Bordetella pertussis assay standardization and harmonization meeting report. Centers for Disease Control and Prevention, Atlanta, Georgia, United States, 19-20 July 2007
Vaccine
(2009) - et al.
Low levels of antipertussis antibodies plus lack of history of pertussis correlate with susceptibility after household exposure to Bordetella pertussis
Vaccine
(2003) - et al.
Levels of anti-pertussis antibodies related to protection after household exposure to Bordetella pertussis
Vaccine
(1998) - et al.
Prediction of pertussis vaccine efficacy using a correlates of protection model
Vaccine
(2008) - et al.
A search for serologic correlates of immunity to Bordetella pertussis cough illnesses
Vaccine
(1998) - et al.
Influenza vaccine: the challenge of antigenic drift
Vaccine
(2007) Vaccination and antigenic drift in influenza
Vaccine
(2008)- et al.
Correlates of protection: novel generations of influenza vaccines
Vaccine
(2008)
Correlates of immunity to respiratory syncytial virus (RSV) associated-hospitalization: establishment of minimum protective threshold levels of serum neutralizing antibodies
Vaccine
Estimating the protective concentration of anti-pneumococcal capsular polysaccharide antibodies
Vaccine
Serological criteria for evaluation and licensure of new pneumococcal conjugate vaccine formulations for use in infants
Vaccine
Comparison of neutralising antibody assays for detection of antibody to influenza A/H3N2 viruses: an international collaborative study
Vaccine
Preparation of a respiratory syncytial virus human reference serum for use in the quantitation of neutralization antibody
Biologicals
Testing human sera for antibodies against avian influenza viruses: horse RBC hemagglutination inhibition vs. microneutralization assays
J Clin Virol
Increased sensitivity for detecting avian influenza-specific antibodies by a modified hemagglutination inhibition assay using horse erythrocytes
J Virol Methods
Surrogate endpoints and FDA's accelerated approval process
Health Aff (Millwood)
A framework for assessing immunological correlates of protection in vaccine trials
J Infect Dis
Evaluating a surrogate endpoint at three levels, with application to vaccine development
Stat Med
Lessons learned from a review of the development of selected vaccines. National Vaccine Advisory Committee
Pediatrics
A meningococcal polysaccharide vaccine and course of the group A meningococcal epidemic in Finland
Scand J Infect Dis
Haemophilus influenzae type b capsular polysaccharide vaccine in children: a double-blind field study of 100,000 vaccinees 3 months to 5 years of age in Finland
Pediatrics
Efficacy, safety and immunogenicity of heptavalent pneumococcal conjugate vaccine in children. Northern California Kaiser Permanente Vaccine Study Center Group
Pediatr Infect Dis J
Immunity to disease caused by Hemophilus influenzae type b. II. Specificity and some biologic characteristics of “natural”, infection-acquired, and immunization-induced antibodies to the capsular polysaccharide of Hemophilus influenzae type b
J Immunol
Prevention of pneumococcal infection by immunization with capsular polysaccharides of Streptococcus pneumoniae: current status of polyvalent vaccines
J Infect Dis
Human immunity to the meningococcus. I. The role of humoral antibodies
J Exp Med
The protective level of serum antibodies to the capsular polysaccharide of Haemophilus influenzae type b
J Infect Dis
Prevention of Haemophilus influenzae type b infections in high-risk infants treated with bacterial polysaccharide immune globulin
N Engl J Med
Evaluation of bacterial polysaccharide immune globulin for the treatment or prevention of Haemophilus influenzae type b and pneumococcal disease
J Infect Dis
Functional characterization of human IgG, IgM, and IgA antibody directed to the capsule of Haemophilus influenzae type b
J Infect Dis
Measurement of human serum IgG antibodies or a surrogate is sufficient to standardize (predict efficacy) vaccines
Dev Biol Stand
Immune responses to polysaccharide and conjugate vaccines
Requirements for meningococcal polysaccharide vaccine (Requirements for Biological Substances No. 23). WHO Technical Report Series No. 594
Standardization and a multilaboratory comparison of Neisseria meningitidis serogroup A and C serum bactericidal assays. The Multilaboratory Study Group
Clin Diagn Lab Immunol
Serological basis for use of meningococcal serogroup C conjugate vaccines in the United Kingdom: reevaluation of correlates of protection
Infect Immun
A modified enzyme-linked immunosorbent assay for measurement of antibody responses to meningococcal C polysaccharide that correlate with bactericidal responses
Clin Diagn Lab Immunol
Age-related disparity in functional activities of human group C serum anticapsular antibodies elicited by meningococcal polysaccharide vaccine
Infect Immun
Naturally acquired passive protective activity against Neisseria meningitidis Group C in the absence of serum bactericidal activity
Infect Immun
Acellular vaccine efficacy trials
Pediatr Infect Dis J
Collaborative study for the evaluation of enzyme-linked immunosorbent assays used to measure human antibodies to Bordetella pertussis antigens
Clin Diagn Lab Immunol
The prospect of vaccination against group A beta-hemolytic streptococci
Curr Infect Dis Rep
Studies on immunity to streptococcal infections in man
AMA Am J Dis Child
Streptococcal infections
Cross-protection against homologous drift variants of influenza A and B after vaccination with split vaccine
Intervirology
Antigenic variation of human RSV strains isolated in Japan
J Med Virol
Cited by (0)
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Margaret C. Bash and Drusilla L. Burns, US Food and Drug Administration, Rockville, MD 20852, United States; Jan Callahan, Callahan Associates, La Jolla, CA 874 92037, United States; James B. Dale, University of Tennessee Health Science Center, Memphis, Memphis, TN 38104, United States; Morven S. Edwards, Baylor College of Medicine, Houston, TX 77030, United States, United States; Karen L. Elkins, US Food and Drug Administration, Rockville, MD 20852, United States; Carl E. Frasch, Frasch Biologics Consulting, Martinsburg, WV, United States; Steven W. Hildreth, Sanofi Pasteur, Swiftwater, PA 18370, United States; Katrin Jansen, Pfizer Inc., Pearl River, NY 10965, United States; Robert C. Kohberger, Blair and Associates, Greenwich, CT 06831, United States; Michael Kalos, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, United States; Karen C. Meysick, US Food and Drug Administration, Rockville, MD 20852, United States; ChrisAnna M. Mink, Harbor-UCLA Medical Center, Torrance, CA 90502, United States; Moon Nahm, University of Alabama, Birmingham, AL 35294, United States; Brian D. Plikaytis, Centers for Disease Control and Prevention, Atlanta, GA 30333, United States; David S. Stephens, Emory University School of Medicine, Atlanta, GA 30322, United States; Kanta Subbarao and Christopher Taylor, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892, United States; Edward E. Walsh, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, United States.