CD19 is a transmembrane protein found on the cell surface that is involved in establishing intrinsic B cell signaling thresholds through modulating both B cell receptor (BCR)-dependent and independent signaling.1

CD19 is thought to play dual roles in B cell activation:

  • As an adaptor protein to recruit cytoplasmic signaling proteins to the membrane
  • As a signal subunit for the CD19/CD21 complex when bound with the BCR, where antigen-bearing complement enhances B-cell activation via BCR-CD19/CD21 binding

CD19 also has other roles such aiding in the regulation of bone marrow development and plays a role in B cell development from early differentiation events in the bone marrow to late maturation steps in the spleen. CD19 signaling may play a role in controlling the progression of early pre-B to small, resting pre-B cells in the bone marrow by associating with components of the pre-BCR.


Though it is not known if CD19 contributes directly to B cell carcinogenesis, its expression is highly conserved on most B cell tumors. It is expressed at normal to high rates in many malignancies:1

  • 80% of acute lymphoblastic leukemias
  • 88% of B-cell lymphomas
  • 100% of B cell leukemias

CD19 is a marker essential for B-cell proliferation and has high expression across B-cell malignancies including diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), and chronic lymphocytic leukemia (CLL).2

  1. Wang K, Wei G, Liu D. CD19: a biomarker for B cell development, lymphoma diagnosis and therapy. Experimental hematology & oncology. 2012;1(1):1-7.
  2. Levy M, et al. A First-in-Human Phase 1 Study of ABBV-319, an Antibody-Drug Conjugate Composed of a CD19 Antibody Linked to a Potent Propriety Glucocorticosteroid, in Patients with Relapsed or Refractory B-Cell Malignancies. Poster. 64th ASH. December 10-13, 2022. New Orleans, LA.