WHO/BS/2017.2321 Collaborative Study to establish the 1st WHO IS for Human Herpes Virus 6B (HHV-6B) DNA for nucleic acid amplification technique (NAT)-based assays

Overview

An international collaborative study was conducted to establish the 1st WHO International Standard for use in the standardisation of Human Herpes virus 6 (HHV-6) nucleic acid amplification technology (NAT) assays. Two candidate freeze-dried HHV-6 virus preparations, species 6B Strain Z-29 (Sample A) and species 6A Strain GS (Sample B), were formulated in 10mM Tris-HCl pH 7.4, 0.5% Human serum albumin (HSA), 2.0% D-(+)-Trehalose dehydrate, and analysed by 26 laboratories from 12 countries, each using their routine NAT-detection assays for HHV-6 viral load determination. A difference of up to 3.08 log10 copies/ mL in the quantitative mean potency estimates were reported across the laboratories for each of the candidates and their liquid equivalents, as well as for 5 clinical samples included for a limited commutability assessment. The agreement between the laboratories was improved when the potencies were expressed relative to either of the candidate preparations. The evaluations of both candidates were very similar however of the two candidates, Sample A is most appropriate for use as an International Standard for HHV-6 DNA detection assays that are primarily employed for HHV-6B associated conditions. The results from the accelerated thermal degradation stability studies performed at 3 months and 6 months have demonstrated that the candidate material (15/266) is stable at temperatures used for storage (-20°C) and temperatures 4°C, 20°C, 37°C and 45°C reflecting ambient temperature fluctuations encountered during global shipment. Further real-time stability analyses will ensue to assess the long-term stability of the candidate. Based upon the the returned dataset, it is proposed that candidate Sample A (NIBSC code 15/266) be established as the 1st WHO International Standard for HHV-6B DNA for nucleic acid amplification technique (NAT)-based assays with an assigned potency of 7.75 log10 IU/ mL per ampoule.