Jason Hockley

EUVAC.NET collaborative study: evaluation and standardisation of serology for diagnosis of pertussis.

As part of the new EUVAC.NET contract with ECDC (Pertussis Work Area 4), a collaborative study was organised in July-December 2010. Two well-defined reference preparations with high and low IgG antibodies to pertussis toxin (PT), were sent to participants. The purposes of this study were to assess current laboratory performance of serological assays for pertussis; to compare in-house reference preparations that are currently used by participants for the serological assay; and to identify needs for standardisation of the serological assay. Reference Laboratories in Europe currently performing serological assays for the diagnosis of pertussis by measuring antibody to PT, were invited to participate in the study. A total of 17 laboratories/countries participated in this study. Results were reported from a total of 9 participants who used in-house ELISA assays and 10 participants who used commercial kits. All participants using in-house ELISA with purified PT coating plates distinguished the 2 preparations and gave results that were comparable to the expected values. A total of 6 commercial kits included in the study showed different results. The kits coated with mixture antigens did not appear to be able to give results that were correlated to the WHO reference preparations.

Anti-therapeutic antibodies and their clinical impact in patients treated with the TNF antagonist adalimumab.

HighlightsECL‐based assays for measurement of adalimumab and adalimumab antibodies.Performance of ECL antibody assay not significantly improved by acid dissociation.Negative correlation between levels of antibody and free adalimumab.Negative correlation between adalimumab level and disease activity scores. Abstract Patients treated with the TNF antagonist adalimumab develop anti‐therapeutic antibodies (ATA), the prevalence of which varies depending on the assay used. Most assays are compromised due to the presence of adalimumab in the clinical samples. Our objective was to develop an antibody assay, applicable for clinical testing, which overcomes the limitation of therapeutic interference and to further determine the relationship between ATA development, adalimumab levels and disease activity in patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA) or ankylosing spondylitis (AS). Use of an electrochemiluminescence platform permitted development of fit‐for‐purpose immunoassays. Serum samples from patients, taken prior to and at 12 and 24 weeks of treatment, were retrospectively analysed for levels of adalimumab and ATA. Overall, the antibody prevalence was 43.6% at 12 weeks and 41% at 24 weeks of treatment. Disruption of immune complexes by acid dissociation, a strategy often adopted for this purpose, only marginally increased the antibody prevalence to 48.7% and 46% at 12 and 24 weeks respectively. We found that antibody formation was associated with decreasing levels of circulating adalimumab, but no direct effect on disease activity was evident as assessed using DAS28 for RA patients and BASDAI for PsA and AS patients. However, a negative correlation of free adalimumab trough levels with disease activity scores was observed. Data showed that adalimumab levels can serve as an indicator of ATA development which can then be confirmed by ATA testing. Monitoring of both therapeutic and antibodies should be considered during adalimumab therapy to allow clinicians to personalise treatments for maximal therapeutic outcomes.

Establishment of the first International Standard for human anti-typhoid capsular Vi polysaccharide IgG.

Vi capsular polysaccharide (Vi) conjugate vaccines prevent Typhoid in infants and young children. Several Vi-conjugate vaccines are being developed and an International Standard (IS) for human anti-Vi IgG is required to compare their immunogenicity. The suitability of 16/138 as an IS for human anti-Vi IgG was assessed alongside U.S. reference reagent Vi-IgGR1, 2011, previous candidate IS 10/126 and individual sera. 16/138 is a pool of post-vaccination sera from volunteers receiving either Vi Tetanus Toxoid conjugate vaccine or plain Vi vaccine. Seven laboratories tested the samples in the VaccZyme Human Anti-Salmonella typhi Vi IgG ELISA (Binding Site, n = 7), a biotinylated Vi ELISA (n = 7) and in-house ELISAs (n = 7). Valid estimates were obtained for the potency of all samples when either 16/138 or Vi-IgGR1, 2011 were used as a reference in the VaccZyme ELISA. The commutability of 16/138 and Vi-IgGR1, 2011 was evident for the VaccZyme ELISA and in-house ELISAs based on a coating of native Vi and a protein. The WHO Expert Committee on Biological Standardization established 16/138 as the first IS for anti-Vi capsular polysaccharide IgG (human) with 100 IU per ampoule and assigned potencies of 163 IU per vial of Vi-IgGR1, 2011 and 54 IU per ampoule of 10/126.

Establishment of the World Health Organization First International Standard for Factor XII, Plasma, Human

Until recently, the role of factor XII (FXII) in hemostasis was not considered to be important since patients with FXII deficiency do not present with bleeding. The activation of FXII by agents including mast cells and platelet polyphosphates suggests that it may have a role in thrombogenesis. The inhibition of FXII therefore presents an option for antithrombotic therapy, and antibodies and inhibitors are already in development. Assays for FXII will be required to support these technologies, and an international standard (IS) for FXII would be useful for the development of these methods and for the clinical monitoring of patients. The purpose of this study was to develop an IS for FXII, with values for functional activity (FXII:C) and antigen (FXII:Ag). Double-spun normal plasma was pooled, filled into siliconized glass ampoules, and freeze-dried to prepare the candidate material. Data from 20 laboratories using the one-stage clotting assay were used to assign the functional activity value in units (u). The antigen value was calculated using data from eight laboratories that carried out antigen assays. Each laboratory was requested to collect two local normal plasma pools. Units of activity and antigen were calculated relative to these pools, as is usual for new coagulation factor analytes. The amount of activity or antigen in 1 ml of normal plasma from each pool was taken to be 1 unit. A total of 566 donors were used across the pools for the FXII:C study and 216 donors for the FXII:Ag study. The overall geometric mean per ampoule for FXII:C was 0.86 u and for FXII:Ag was 0.80 u. The inter-laboratory variation was 10 and 11%, respectively (expressed as the geometric coefficient of variation). Based on these data, the candidate was deemed suitable for use as an IS for FXII. In 2017, the candidate was established by the World Health Organization (WHO) Expert Committee on Biological Standardization as the WHO first IS for blood coagulation FXII, Plasma (National Institute for Biological Standards and Control code 15/180). The values assigned were 0.86 international units (IU) of functional activity (FXII:C) per ampoule and 0.80 IU/ampoule of antigen (FXII:Ag).