Streamlining basophil activation testing to enable assay miniaturization and automation of sample preparation

Abstract

Background: Numerous studies have demonstrated the capabilities of the basophil activation test (BAT) but various parameters such as a lack of standardization and a time consuming and labor intensive workflow continue to hinder the field to fully leverage the capabilities of this technique. When pediatric patients have to be considered, an additional limitation is related to blood volume consumption.

Objectives: This work aimed at developing and characterizing a simplified and standardized whole-blood based BAT prototype procedure and at further assessing the feasibility of automating and miniaturizing the developed assay into a 96 well plate format.

Methods: A dry and room temperature stable reagent technology was used to simplify and standardize BAT. Under optimized conditions, EDTA anticoagulated whole blood samples of non-allergic and allergic donors (<24 h old) together with calcium containing buffer were added to ready-to-use dry reagent tubes or 96 well plates (negative controls, positive controls and allergen tests) containing a 5 color compensation-free antibody panel (CD45-KrO/CD3-PC7/CRTH2-A647/CD203c-PE/CD63-PB). Upon mixing and incubation at 37 °C for 15 min, erythrocytes were lysed and samples were analyzed by flow cytometry without further washing steps. While it is important to precisely control the incubation time to minimize the assay variability, herein, a 15 min incubation time was chosen as it provides a suitable compromise for both the magnitude of basophil activation and the quality of the staining. A Biomek NXP robotic platform (Beckman Coulter) was used for automation and both CD203c and CD63 levels were monitored to characterize basophil reactivity.

Results: This streamlined BAT protocol is no-wash, compensation free and only requires 4 pipetting steps to be completed. The assessment of assay performance characteristics showed wide applicability, satisfactory repeatability and a high degree of standardization as demonstrated by very low intra-assay and inter-operator variabilities (CVs < 10%). Leveraging these technical foundations, it was then proven that this new BAT procedure can easily be transposed into the 96 well plate format, thereby benefiting from a miniaturized format and full automation capabilities. When considering 8 dilution points to characterize the ex vivo basophil reactivity of a given whole blood sample, we found that as little as 5 μL of blood per point could be used.

Conclusions: A whole blood based and simplified procedure for BAT is proposed. It relies on a dry antibody formulation technology and requires only a few manual steps to be completed. This procedure can also be transposed in a 96 well plate format, fully automated and miniaturized, when sample volume reduction, throughput increase or unattended sample preparation is required.

Trial registration: ClinicalTrials.gov NCT03265262.

Keywords: Assays miniaturization; Automated workflow; Basophil activation test; Flow Cytometry; Whole blood; ex vivo functional assay.