WHO/BS/2018.2333 An International Collaborative Study to Establish a WHO International Reference Reagent for CD4 T cell counting

Overview

The World Health Organization (WHO) has recognised the lack of harmonisation in CD4 T cell counting as an issue for HIV patient care. This report describes the evaluation of a freeze-dried preparation of pooled human leukocytes, NIBSC code 15/270, for use as a reference reagent for CD4 T cell enumeration technologies. The material was evaluated by twelve laboratories from eight different countries. Participants used different CD4 T cell counting technologies all of which have shown suitable performance through independent peer-reviewed data. These include single-platform and dual-platform flow cytometry, dedicated CD4 systems and point of care (PoC) technologies. We found that the vast majority of users employ standard flow cytometers for their counting. The material worked well in flow cytometry platforms and with the point of care technology tested. The material could not be read by the dedicated CD4 systems BD FACS Count and BD FACS Presto and was incompatible with one of the commercial lysis reagents used. We conclude this material is fit-for-purpose for use with standard flow cytometry platforms and the point-of-care device Instacount. The issue with the two dedicated CD4 systems will need to be further investigated with the manufacturer in a follow-up study. Red blood cell lysis reagents will need to be independently evaluated in each centre to determine suitability. In addition, we were unable to recruit participants to cover all the technologies used for CD4 T cell counting. Specifically, it would be important to test the material in the PoC device Alere Pima CD4 test commonly used in Sub-Saharan Africa. However, we still feel the material has value. Therefore, we propose that the candidate be established as a WHO reference reagent for CD4 T cell counting. The IFU will state the technologies for which it has been qualified and the expected performance of the material, as obtained by participants in this study. A follow-up study will be organised with manufacturers to allow for testing of the material in a wider breadth of technologies.