The effect of immunization schedule with the malaria vaccine candidate RTS,S/AS01E on protective efficacy and anti-circumsporozoite protein antibody avidity in African infants.

BACKGROUND: The malaria vaccine RTS,S induces antibodies against the Plasmodium falciparum circumsporozoite protein (CSP) and the concentration of Immunoglobulin G (IgG) against the repeat region of CSP following vaccination is associated with protection from P. falciparum malaria. So far, only the quantity of anti-CSP IgG has been measured and used to predict vaccination success, although quality (measured as avidity) of the antigen-antibody interaction shall be important since only a few sporozoites circulate for a short time after an infectious mosquito bite, likely requiring fast and strong binding. METHODS: Quantity and avidity of anti-CSP IgG in African infants who received RTS,S/AS01E in a 0-1-2-month or a 0-1-7-month schedule in a phase 2 clinical trial were measured by enzyme-linked immunosorbent assay. Antibody avidity was defined as the proportion of IgG able to bind in the presence of a chaotropic agent (avidity index). The effect of CSP-specific IgG concentration and avidity on protective efficacy was modelled using Cox proportional hazards. RESULTS: After the third dose, quantity and avidity were similar between the two vaccination schedules. IgG avidity after the last vaccine injection was not associated with protection, whereas the change in avidity following second and third RTS,S/AS01E injection was associated with a 54% risk reduction of getting malaria (hazard ratio: 0.46; 95% confidence interval (CI): 0.22-0.99) in those participants with a change in avidity above the median. The change in anti-CSP IgG concentration following second and third injection was associated with a 77% risk reduction of getting malaria (hazard ratio: 0.23, 95% CI: 0.11-0.51). CONCLUSIONS: Change in IgG response between vaccine doses merits further evaluation as a surrogate marker for RTS,S efficacy. TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT00436007 .

Validation of an enzyme-linked immunosorbent assay for the quantification of human IgG directed against the repeat region of the circumsporozoite protein of the parasite Plasmodium falciparum.

BACKGROUND: Several pre-erythrocytic malaria vaccines based on the circumsporozoite protein (CSP) antigen of Plasmodium falciparum are in clinical development. Vaccine immunogenicity is commonly evaluated by the determination of anti-CSP antibody levels using IgG-based assays, but no standard assay is available to allow comparison of the different vaccines. METHODS: The validation of an anti-CSP repeat region enzyme-linked immunosorbent assay (ELISA) is described. This assay is based on the binding of serum antibodies to R32LR, a recombinant protein composed of the repeat region of P. falciparum CSP. In addition to the original recombinant R32LR, an easy to purify recombinant His-tagged R32LR protein has been constructed to be used as solid phase antigen in the assay. Also, hybridoma cell lines have been generated producing human anti-R32LR monoclonal antibodies to be used as a potential inexhaustible source of anti-CSP repeats standard, instead of a reference serum. RESULTS: The anti-CSP repeats ELISA was shown to be robust, specific and linear within the analytical range, and adequately fulfilled all validation criteria as defined in the ICH guidelines. Furthermore, the coefficient of variation for repeatability and intermediate precision did not exceed 23%. Non-interference was demonstrated for R32LR-binding sera, and the assay was shown to be stable over time. CONCLUSIONS: This ELISA, specific for antibodies directed against the CSP repeat region, can be used as a standard assay for the determination of humoral immunogenicity in the development of any CSP-based P. falciparum malaria vaccine.

Immunogenicity and safety of two tetravalent (measles, mumps, rubella, varicella) vaccines coadministered with hepatitis a and pneumococcal conjugate vaccines to children twelve to fourteen months of age.

BACKGROUND: This study compared single-dose tetravalent measles, mumps, rubella, varicella vaccine, Priorix-Tetra, stored refrigerated (GSK+4C) or frozen (GSK-20C), with ProQuad (Merck-20C), when coadministered with hepatitis A vaccine (HAV) and 7-valent pneumococcal conjugate vaccine (PCV7). METHODS: Multicenter, observer-blind phase 2 study in 1783 healthy 12-14 month olds randomized to: GSK+4C (n = 705), GSK-20C (n = 689) or Merck-20C (n = 389), administered concomitantly with HAV (Havrix) and PCV7 (Prevnar). Seroresponse rates and antibody geometric mean concentrations/titers were determined from enzyme-linked immunosorbent assay and neutralization assays. Reactogenicity and safety were assessed. RESULTS: Seroresponse rates (day 42) were >97% for measles and rubella viruses and >92% for mumps virus, in all groups. Noninferiority of both GSK+4C and GSK-20C vaccines versus Merck-20C was demonstrated for seroresponse rates to measles, mumps and rubella viruses (lower 97.5% confidence interval above -5%, -10% and -5%, respectively). For varicella-zoster virus, seroresponse rates were 57.1%, 69.8% and 86.7% in the GSK+4C, GSK-20C and Merck-20C groups, respectively. Noninferiority was not shown for either GSK vaccine (lower 97.5% confidence intervals <-15%). Geometric mean concentration ratios for anti-varicella-zoster virus demonstrated noninferiority (lower 97.5% confidence interval ≥ 0.5) versus Merck-20C for GSK-20C only. Geometric mean concentration ratios for antibodies to HAV and to PCV7 pneumococcal serotypes also met criteria for noninferiority for both GSK groups compared with Merck-20C. GSK vaccine safety was observed comparable to Merck-20C. Localized but not generalized measles/rubella-like rash and grade 3 fever was reported slightly more frequently with GSK vaccines, but antipyretic use was similar. The incidence of subjects experiencing at least 1 serious adverse event was 2.0%, 2.9% and 1.8% in the GSK+4C, GSK-20C and Merck-20C groups, respectively. CONCLUSIONS: Noninferiority of both GSK measles, mumps, rubella, varicella vaccines versus Merck-20C was demonstrated for responses to measles, mumps and rubella viruses but was not fully demonstrated for varicella-zoster virus. The vaccines showed acceptable reactogenicity/safety when coadministered with HAV and PCV7.

Development and technical and clinical validation of a quantitative enzyme-linked immunosorbent assay for the detection of human antibodies to hepatitis B surface antigen in recipients of recombinant hepatitis B virus vaccine.

Pending removal from the market of a commercial assay (the AUSAB [Abbott Laboratories] enzyme immunoassay [EIA]) for the determination of antibodies to hepatitis B surface antigen (HBsAg), a new in-house quantitative enzyme-linked immunosorbent assay (ELISA) to measure antibodies against HBsAg (anti-HBs) was developed (anti-HBs in-house). Specific anti-HBs antibodies were sandwiched between the precoated HBsAg ad and ay subtypes purified from plasma from hepatitis B virus (HBV) human carriers and the recombinant HBsAg adw2 subtype tagged with horseradish peroxidase. The assay was calibrated against the 1st International Reference Preparation for anti-hepatitis B immunoglobulin (lot 1977-W1042). Analytical sensitivity and the limit of quantitation were estimated at 0.43 mIU/ml and 2.0 mIU/ml, respectively. Overall reproducibility was 11.86%, and accuracy was estimated to be 94.89%. More than 4,000 samples from seven clinical trials were tested with the anti-HBs in-house assay and compared to results generated with AUSAB EIA and AUSAB radioimmunoassay (RIA). During the technical validation, the anti-HBs in-house assay was compared to the AUSAB RIA as a reference (n = 919). Overall assessment of concordance and Deming's regression analysis were performed. The coefficient of correlation between the AUSAB RIA and anti-HBs in-house assay was 0.9815 with a slope of 0.9187. The overall agreement between anti-HBs in-house and AUSAB RIA was 97.61%, considering the clinical cutoffs at 3.3 mIU/ml and 1.0 mIU/ml for the respective assays. From a clinical perspective, seroprotection rates and anti-HBs geometric mean antibody concentrations for individual studies calculated with either the in-house assay or the reference assays were similar. Conclusions of individual studies were confirmed. The performance characteristics of the in-house assay are acceptable. There is no evidence that use of the new assay would lead to different clinical conclusions from the reference method.