Christopher A. Todd

Optimization and validation of the TZM-bl assay for standardized assessments of neutralizing antibodies against HIV-1.

The TZM-bl assay measures antibody-mediated neutralization of HIV-1 as a function of reductions in HIV-1 Tat-regulated firefly luciferase (Luc) reporter gene expression after a single round of infection with Env-pseudotyped viruses. This assay has become the main endpoint neutralization assay used for the assessment of pre-clinical and clinical trial samples by a growing number of laboratories worldwide. Here we present the results of the formal optimization and validation of the TZM-bl assay, performed in compliance with Good Clinical Laboratory Practice (GCLP) guidelines. The assay was evaluated for specificity, accuracy, precision, limits of detection and quantitation, linearity, range and robustness. The validated manual TZM-bl assay was also adapted, optimized and qualified to an automated 384-well format.

Utilization of Immunoglobulin G Fc Receptors by Human Immunodeficiency Virus Type 1: a Specific Role for Antibodies against the Membrane-Proximal External Region of gp41

ABSTRACT Receptors (FcγRs) for the constant region of immunoglobulin G (IgG) are an important link between humoral immunity and cellular immunity. To help define the role of FcγRs in determining the fate of human immunodeficiency virus type 1 (HIV-1) immune complexes, cDNAs for the four major human Fcγ receptors (FcγRI, FcγRIIa, FcγRIIb, and FcγRIIIa) were stably expressed by lentiviral transduction in a cell line (TZM-bl) commonly used for standardized assessments of HIV-1 neutralization. Individual cell lines, each expressing a different FcγR, bound human IgG, as evidence that the physical properties of the receptors were preserved. In assays with a HIV-1 multisubtype panel, the neutralizing activities of two monoclonal antibodies (2F5 and 4E10) that target the membrane-proximal external region (MPER) of gp41 were potentiated by FcγRI and, to a lesser extent, by FcγRIIb. Moreover, the neutralizing activity of an HIV-1-positive plasma sample known to contain gp41 MPER-specific antibodies was potentiated by FcγRI. The neutralizing activities of monoclonal antibodies b12 and 2G12 and other HIV-1-positive plasma samples were rarely affected by any of the four FcγRs. Effects with gp41 MPER-specific antibodies were moderately stronger for IgG1 than for IgG3 and were ineffective for Fab. We conclude that FcγRI and FcγRIIb facilitate antibody-mediated neutralization of HIV-1 by a mechanism that is dependent on the Fc region, IgG subclass, and epitope specificity of antibody. The FcγR effects seen here suggests that the MPER of gp41 could have greater value for vaccines than previously recognized.

Development and implementation of an international proficiency testing program for a neutralizing antibody assay for HIV-1 in TZM-bl cells

Recent advances in assay technology have led to major improvements in how HIV-1 neutralizing antibodies are measured. A luciferase reporter gene assay performed in TZM-bl (JC53bl-13) cells has been optimized and validated. Because this assay has been adopted by multiple laboratories worldwide, an external proficiency testing program was developed to ensure data equivalency across laboratories performing this neutralizing antibody assay for HIV/AIDS vaccine clinical trials. The program was optimized by conducting three independent rounds of testing, with an increased level of stringency from the first to third round. Results from the participating domestic and international laboratories improved each round as factors that contributed to inter-assay variability were identified and minimized. Key contributors to increased agreement were experience among laboratories and standardization of reagents. A statistical qualification rule was developed using a simulation procedure based on the three optimization rounds of testing, where a laboratory qualifies if at least 25 of the 30 ID50 values lie within the acceptance ranges. This ensures no more than a 20% risk that a participating laboratory fails to qualify when it should, as defined by the simulation procedure. Five experienced reference laboratories were identified and tested a series of standardized reagents to derive the acceptance ranges for pass-fail criteria. This Standardized Proficiency Testing Program is the first available for the evaluation and documentation of assay equivalency for laboratories performing HIV-1 neutralizing antibody assays and may provide guidance for the development of future proficiency testing programs for other assay platforms.

International technology transfer of a GCLP-compliant HIV-1 neutralizing antibody assay for human clinical trials.

The Collaboration for AIDS Vaccine Discovery/Comprehensive Antibody – Vaccine Immune Monitoring Consortium (CAVD/CA-VIMC) assisted an international network of laboratories in transferring a validated assay used to judge HIV-1 vaccine immunogenicity in compliance with Good Clinical Laboratory Practice (GCLP) with the goal of adding quality to the conduct of endpoint assays for Human Immunodeficiency Virus I (HIV-1) vaccine human clinical trials. Eight Regional Laboratories in the international setting (Regional Laboratories), many located in regions where the HIV-1 epidemic is most prominent, were selected to implement the standardized, GCLP-compliant Neutralizing Antibody Assay for HIV-1 in TZM-bl Cells (TZM-bl NAb Assay). Each laboratory was required to undergo initial training and implementation of the immunologic assay on-site and then perform partial assay re-validation, competency testing, and undergo formal external audits for GCLP compliance. Furthermore, using a newly established external proficiency testing program for the TZM-bl NAb Assay has allowed the Regional Laboratories to assess the comparability of assay results at their site with the results of neutralizing antibody assays performed around the world. As a result, several of the CAVD/CA-VIMC Regional Laboratories are now in the process of conducting or planning to conduct the GCLP-compliant TZM-bl NAb Assay as an indicator of vaccine immunogenicity for ongoing human clinical trials.

Implementation of Good Clinical Laboratory Practice (GCLP) guidelines within the External Quality Assurance Program Oversight Laboratory (EQAPOL)

The EQAPOL contract was awarded to Duke University to develop and manage global proficiency testing programs for flow cytometry-, ELISpot-, and Luminex bead-based assays (cytokine analytes), as well as create a genetically diverse panel of HIV-1 viral cultures to be made available to National Institutes of Health (NIH) researchers. As a part of this contract, EQAPOL was required to operate under Good Clinical Laboratory Practices (GCLP) that are traditionally used for laboratories conducting endpoint assays for human clinical trials. EQAPOL adapted these guidelines to the management of proficiency testing programs while simultaneously incorporating aspects of ISO/IEC 17043 which are specifically designed for external proficiency management. Over the first two years of the contract, the EQAPOL Oversight Laboratories received training, developed standard operating procedures and quality management practices, implemented strict quality control procedures for equipment, reagents, and documentation, and received audits from the EQAPOL Central Quality Assurance Unit. GCLP programs, such as EQAPOL, strengthen a laboratorys ability to perform critical assays and provide quality assessments of future potential vaccines.

P15-04. Development and implementation of an international proficiency testing program for a neutralizing antibody assay for HIV-1 in TZM-bl cells

Background Recent advances in assay technology led to major improvements in how HIV-1 neutralizing antibodies are measured. A luciferase reporter gene assay performed in TZM-bl (JC53bl-13) cells has been optimized, and many performance parameters of this assay have been validated. Because this assay has been adopted by multiple laboratories world-wide, an external proficiency testing program was developed to qualify laboratories to perform a Good Clinical Laboratory Practice (GCLP) compliant neutralizing antibody assay for HIV/AIDS vaccine clinical trials.

Optimization and validation of the HIV-1 neutralizing antibody assay in A3R5 cells

Background A3R5 is a highly sensitive cell line for the detection of neutralizing antibodies (Nabs) against tier 2 strains of HIV-1. This cell line is particularly useful for the detection of weak Nab responses in preclinical and clinical trials of candidate HIV-1 vaccines. All methods used for endpoint analyses in clinical trials should be validated and demonstrably fit for purpose, in compliance with ICH Q2 (R1) guidelines. Here we describe the optimization/qualification and validation of the HIV-1 Nab Assay in A3R5 cells.

The effect of antipyretics on immune response and fever following receipt of inactivated influenza vaccine in young children

BACKGROUND Antipyretics reduce fever following childhood vaccinations; after inactivated influenza vaccine (IIV) they might ameliorate fever and thereby decrease febrile seizure risk, but also possibly blunt the immune response. We assessed the effect of antipyretics on immune responses and fever following IIV in children ages 6 through 47 months. METHODS Over the course of three seasons, one hundred forty-two children, receiving either a single or the first of 2 recommended doses of IIV, were randomized to receive either oral acetaminophen suspension (n = 59) or placebo (n = 59) (double-blinded) or ibuprofen (n = 24) (open-label) immediately following IIV and every 4-8 h thereafter for 24 h. Blood samples were obtained at enrollment and 4 weeks following the last recommended IIV dose. Responses to IIV were assessed by hemagglutination inhibition assay (HAI). Seroprotection was defined as an HAI titer ≥1:40 and seroconversion as a titer ≥1:40 if baseline titer <1:10 or four-fold rise if baseline titer ≥1:10. Participants were monitored for fever and other solicited symptoms on the day of and day following IIV. RESULTS Significant differences in seroconversion and post-vaccination seroprotection were not observed between children included in the different antipyretic groups and the placebo group for the vaccine antigens included in IIV over the course of the studies. Frequencies of solicited symptoms, including fever, were similar between treatment groups and the placebo group. CONCLUSIONS Significant blunting of the immune response was not observed when antipyretics were administered to young children receiving IIV. Studies with larger sample sizes are needed to definitively establish the effect of antipyretics on IIV immunogenicity.