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CD19：a validated therapeutic target for B-cell malignancies

CD19 is a B-cell surface protein expressed throughout B-cell development and it is expressed on nearly all B-cell malignancies, including chronic lymphocytic leukemia (CLL), ALL, and many non-Hodgkin lymphomas. This specificity and universal expression for a single cell lineage has made CD19 an attractive target for antibody-based therapy, including bispecific antibodies, ADCs, Fc-engineered antibodies and CAR-T cell therapy. So far, two anti-CD19 CAR-T cell therapies and one bispecific anti-CD19/CD3 antibody have been approved by the FDA to treat hematologic B-cell malignancies. Till May 7, 2020, according to ClinicalTrials.gov, more than 763 clinical trials have been initiated.

To support the development of CD19-targeted antibody-based therapy, ACROBiosystems has developed a comprehensive series of CD19 protein products, including unconjugated CD19, biotinylated CD19 and fluorescent-labeled CD19. These proteins are suitable for immunization, antibody screening, antibody affinity measurement and detection of anti-CD19 CAR expression. The high activity of these proteins has been verified by ELISA, SPR and flow cytometry (FACS). Protocols are offered for free, which can help you save the development cycle.

ACROBiosystems has submitted DMF for its recombinant CD19 to FDA, and filed the DMF number as 034936. If our DMF filed CD19 proteins have been used in your drug development process, you can request that we provide DMF authorization to FDA in support of a submission or filing that you have made to the FDA. Please submit your request to ACROBiosystems by leaving your information here.Request for Authorization

Product List

Cat. No.MoleculeProduct DescriptionStructureOrder Now
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Product Features

Detection of Anti-CD19 CAR Expression by FACS

FACS Analysis of Anti-CD19 CAR Expression
CD9-HP2H5-T1

5e5 of anti-CD19 CAR-293 cells were stained with 100 μL of 1:50 dilution (2 μL stock solution in 100 μL FACS buffer) of PE-Labeled Human CD19 (20-291), His Tag (Cat. No. CD9-HP2H5) and negative control protein respectively (Fig. C and B), and non-transfected 293 cells were used as a control (Fig. A). PE signal was used to evaluate the binding activity (QC tested).



High Affinity Verified by SPR

High Affinity Verified by SPR

Biotinylated Human CD19 (20-291) Protein, His,Avitag™, premium grade (Cat. No. CD9-H82E9) captured on Biotin CAP - Series S sensor Chip can bind FMC63 MAb (mouse lgG2a) with an affinity constant of 0.255 nM as determined in a SPR assay (Biacore 8K) (QC tested).



Higher Binding Affinity than Competitive Products verified by ELISA, FACS and SPR

Higher Binding Affinity than Competitive Products verified by ELISA, FACS and SPR

Binding activity of FITC-Labeled Human CD19, His Tag from two different vendors were evaluated in the ELISA analysis against FMC63 Mab. The result showed that ACRO's FITC-Labeled Human CD19, His Tag has a much higher binding activity than that of the other vendor.

Higher Binding Affinity than Competitive Products verified by ELISA, FACS and SPR

Binding activity of FITC-Labeled Human CD19, His Tag from two different vendors were evaluated in the flow cytometry analysis against anti-CD19-CAR-293 cells. The result showed that ACRO's FITC-Labeled Human CD19, His Tag has a much higher binding activity than that of the other vendor.

Higher Binding Affinity than Competitive Products verified by ELISA, FACS and SPR

Binding activity of Human CD19, His Tag from two different vendors were evaluated by SPR assay against FMC63 MAb. The result showed that ACRO's Human CD19, His Tag can bind FMC63 MAb with an affinity constant of 2.95 nM which is much higher than that of the other vendor.



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FAQ

Q

Why is CD19 considered the gold-standard target for CAR-T therapy in B-cell malignancies?

CD19 is a B-cell lineage-specific type I transmembrane glycoprotein expressed throughout nearly all stages of B-cell development, from pro-B cells to mature B cells, with expression lost only in terminally differentiated plasma cells. This highly restricted expression pattern provides exceptional lineage specificity. As a key signaling component of the B-cell receptor (BCR) complex, CD19 regulates B-cell activation and proliferation and is consistently expressed across chronic lymphocytic leukemia (CLL), B-cell acute lymphoblastic leukemia (B-ALL), and various B-cell non-Hodgkin lymphomas, with minimal tissue-specific loss. This unique expression profile—high and stable expression on malignant cells with limited expression in normal tissues—provides an excellent therapeutic window and favorable safety profile, making CD19 the most clinically validated and widely adopted CAR-T target worldwide. High-quality CD19 antigens with native conformation are essential for CAR discovery and functional evaluation. ACROBiosystems offers highly active recombinant CD19 proteins in multiple formats, including biotinylated and fluorescently labeled versions, with excellent batch-to-batch consistency to support scFv screening, CAR specificity assessment, and preclinical functional validation.
Q

What are the major clinical limitations and relapse mechanisms of single-target CD19 CAR-T therapy?

Antigen escape is the primary mechanism underlying treatment failure and long-term relapse following single-target CD19 CAR-T therapy. Under the selective immune pressure exerted by CD19-directed CAR-T cells, tumor cells can evade immune surveillance through multiple mechanisms, including downregulation of CD19 expression, genetic alterations resulting in complete antigen loss, and even lineage switching from B-cell to myeloid phenotypes. Clonal evolution and antigen heterogeneity progressively enrich CD19-negative tumor populations, ultimately leading to treatment resistance and disease relapse. These mechanisms remain the greatest obstacle to durable clinical responses. Accurate characterization of tumor antigen expression and early identification of antigen escape risk are therefore critical for improving long-term therapeutic outcomes.
Q

How are multi-target strategies being used to overcome antigen escape in CD19 CAR-T therapy?

Multi-target CAR-T strategies have become the leading approach to overcoming CD19 antigen escape, with CD19/CD22 dual-target CAR-T therapies representing the most clinically advanced platform. CD22 is co-expressed with CD19 in most B-cell malignancies and often remains detectable even after CD19 loss, making it an ideal complementary target. Current designs primarily include dual CAR systems, which express two independent CAR receptors within a single T cell, and tandem CAR (TanCAR) constructs, which incorporate two antigen-binding domains into a single CAR molecule. By simultaneously targeting two antigens, these approaches substantially reduce the likelihood of dual-antigen loss and improve treatment durability. Development of multi-target CAR-T therapies relies on high-quality paired antigens for cross-binding analysis and specificity assessment. ACROBiosystems provides highly active recombinant CD19 and CD22 proteins to support structural optimization, functional characterization, and antigen escape studies.
Q

What are the latest research directions and emerging applications of CD19 CAR-T therapy?

CD19 CAR-T therapy has evolved beyond conventional treatment of hematologic malignancies toward multiple innovative directions. Current research focuses include multi-target CAR designs, combination therapies, allogeneic off-the-shelf CAR-T platforms, strategies to enhance in vivo persistence, and approaches to reduce treatment-related toxicities. Beyond oncology, CD19 CAR-T therapy has demonstrated remarkable potential in autoimmune diseases such as systemic lupus erythematosus (SLE) and systemic sclerosis by selectively eliminating pathogenic B cells and inducing long-term drug-free remission. In addition, in vivo CAR-T technology has emerged as a promising frontier, enabling direct genetic programming of T cells within the patient without ex vivo cell manufacturing, thereby simplifying production and expanding clinical accessibility. These rapidly evolving applications require comprehensive target tools for research and development. ACROBiosystems offers recombinant CD19 proteins in multiple formats, including unlabeled, biotinylated, and fluorescently labeled versions, supporting applications ranging from animal immunization and antibody discovery to CAR quality control, pharmacokinetic studies, and translational research in both oncology and autoimmune diseases.
Q

How are high-quality recombinant CD19 proteins produced to meet CAR-T research and clinical QC requirements?

High-quality recombinant CD19 protein is essential for accurate CAR-T screening, reliable functional validation, and standardized clinical quality control. Its production requires strict control of four key aspects: expression system, structural integrity, purification process, and quality assessment. First, mammalian expression systems are preferred to preserve native CD19 glycosylation patterns and spatial conformation, enabling accurate representation of the cell-surface antigen. Second, maintaining the complete extracellular domain is critical to avoid structural disruption and ensure precise CAR recognition. In addition, advanced purification processes are required to minimize aggregates, host cell impurities, and endotoxin levels, ensuring high purity and reliable assay performance. Finally, comprehensive characterization using approaches such as SPR, FACS, and SEC-MALS is essential to confirm biological activity and batch-to-batch consistency. Leveraging advanced mammalian expression and protein engineering platforms, ACROBiosystems develops high-quality recombinant CD19 proteins under the stringent Star Standard quality system. Featuring native conformation, high biological activity, and excellent batch consistency, these products support CAR library screening, affinity evaluation, flow cytometry-based detection, and clinical-stage quality control, accelerating the development of high-performance CD19 CAR-T therapies.
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