A standardized ZAP-70 assay--lessons learned in the trenches

Area of Science:

• Flow cytometry
• Immunophenotyping
• Hematologic malignancies

Background:

• Chronic lymphocytic leukemia (CLL) outcomes vary with laboratory parameters.
• Zeta-associated protein (ZAP-70) levels are a key parameter in CLL.
• A standardized clinical cytometry assay for ZAP-70 is lacking.

Purpose of the Study:

• To develop and validate a standardized flow cytometry assay for ZAP-70 protein expression in CLL.
• To establish reproducible ZAP-70 measurement for clinical use.
• To correlate ZAP-70 levels with clinical outcomes in CLL.

Main Methods:

• Developed a flow cytometry system using 8-peak Rainbow beads for calibration and fixed cell controls.
• Utilized a CD19-PE, CD5-FITC, and ZAP-70-Alexa 647 antibody panel.
• Measured ZAP-70 expression in molecules equivalent fluorescence (MEFL) in normal and CLL samples.

Main Results:

• Established daily assay performance and MEFL-defined ranges for ZAP-70 detection in CLL.
• Defined "negative," "intermediate," and "positive" ZAP-70 staining ranges using a nonparametric approach.
• Validated the assay across multiple institutions, demonstrating reproducibility and correlation with existing methods.

Conclusions:

• Standardization yields a predictable, reliable, and reproducible assay for multisite implementation.
• Rainbow beads and fixed cell controls ensure system calibration and antibody testing.
• Multi-level quality control ensures accurate ZAP-70 detection before reporting patient results.