Used in immunotherapy research, particularly in the development of CAR-T cell therapies targeting B-cell malignancies. Serves as a critical antigen for antibody binding and immune cell activation studies. Employed in protein-protein interaction assays, ELISA, and flow cytometry to detect anti-CD19 antibodies or engineered immune cells. Supports quality control in biopharmaceutical manufacturing by enabling detection and quantification of CD19-specific therapeutics. The His tag facilitates easy purification and immobilization on nickel-based surfaces for analytical or diagnostic platforms.