CD69 expression as an index of T-cell function: assay standardization, validation and use in monitoring immune recovery

Background CD69 is a surrogate marker of T-cell responsiveness to mitogen and Ag stimulus and can be used as a measure of T-lymphcyte activation. Quantitative flow cytometric determination of CD69 expression on T lymphocytes has several advantages over traditional lymphocyte proliferation assays, but this method has not yet been standardized for clinical applications. Methods We qualified a commercially available assay using the manufacturers procedures for measurement of T-cell response to a mitogen (PHA), superantigen (Staphylococcus endotoxin B; SEB) and Ca2+ ionophore (phorbyl myrisiate acetate; PMA) with peripheral blood from healthy volunteers. Following this, we tested the usefulness of the assay in determining T-cell responses to PHA and SEB for six immunocompromised patients. Results Healthy volunteers showed 17-fold increases in T-cell CD69 Ab bound per cell (ABC) with PHA stimulation compared with the baseline. SEB was also an effective T-cell activating agent, increasing CD69 ABC by 5-fold, comparable with results obtained with PMA stimulation. PHA- andSEB-stimulated T-cell CD69 ABC for patients 100 days post-BM transplant were generally below 1 SD of that from healthy volunteers. SEB-stimulated T-cell CD69 expression was significantly depressed for CD8(+) T cells while CD4(+) T-cell responses to SEB were generally within I SD of the mean for healthy volunteers. Discussion These results suggest that quantitative measurement of CD69 surface expression by flow cytometry is a useful diagnostic tool for detailed assessment of T-lymphocyte and subset activation.