WHO/BS/2018.2343 Preparation and evaluation of the 2nd WHO International Standard for human immunodeficiency virus 2 (HIV-2) for Nucleic acid AmplificationTechniques (NAT)

Overview

This report describes the preparation and collaborative evaluation of the candidate for a higher titre replacement 2nd WHO International Standard for Human Immunodeficiency Virus 2 (HIV2) for use in the standardisation of Nucleic acid Amplification Techniques (NAT). The freeze dried candidate comprised the same HIV-2 CAM2 cultured strain diluted in pooled negative human plasma as used to formulate the 1st (current) standard. This candidate material was evaluated alongside the current 1st WHO International Standard for HIV-2 (08/150), liquid frozen high and low titre preparations from the same stock and a clinical HIV-2 positive specimen. In this study 15 participating laboratories from 11 countries collaborated to evaluate the suitability and potency using their routine NAT assay(s) for HIV-2. A variety of qualitative and quantitative assays were utilised, the qualitative assays were mostly commercial whereas the quantitative assays were predominantly laboratory developed which showed greater variability. Agreement between laboratories was improved when potencies of high titre samples were expressed relative to the current and candidate reference materials; this was not observed for all low titre sample potencies. The overall mean reported estimates for the candidate 2 nd IS (sample 2 in the study) from qualitative assays was 5.26 Log10 NAT detectable units/mL and from quantitative assays was 5.40 Log10 IU/mL with standard deviations 0.28 and 0.32 respectively. The mean estimate across both qualitative and quantitative assays is 5.46 Log10 IU/mL when expressed relative to the current standard. Inter-laboratory variation on the whole was greater than the intra-laboratory variation