A standardized flow cytometry procedure for the monitoring of regulatory T cells in clinical trials

International audience; Background: Quantification of regulatory T cells (Tregs) is crucial in immunomonitoring in clinical trials as this cell population has been shown to be involved in a wide range of diseases, including cancers, auto-immune diseases, infections, and allergies. Human Tregs are defined as CD4 1 CD25 1 CD127 low FoxP3 1 cells, and the standardization of their staining by flow cytometry is a challenge, especially in multicenter clinical trials, notably because of the intracellular location of FoxP3.Method: A flow cytometry staining procedure was settled and standardized to measure human Tregs in peripheral whole blood using precoated dried antibodies in ready-to-use tubes. It was compared with reference methods and implemented and validated to be suitable with different cytometer platforms.Results: The standardized protocol developed with dried antibodies and reduced volumes of whole blood allows an optimal identification of Tregs. Compared with classical staining procedure, it reduces the number of steps required, in a very fast and simple technique. The accuracy of the method was confirmed by a multi-center comparison with different cytometer brands.Conclusions: Our results highlight the reliability of this high-standard protocol that could become a reference method for the monitoring of Tregs in clinical trials.