From the Guidelines
CD19 is a marker primarily for B lymphocytes, a type of white blood cell involved in the immune system's adaptive response. It appears early in B cell development and remains present throughout most stages of B cell maturation, disappearing only when B cells differentiate into plasma cells [ 1 ]. CD19 functions as a co-receptor that enhances B cell receptor signaling, playing a crucial role in B cell activation, proliferation, and antibody production. In clinical settings, CD19 is used to identify B cells in flow cytometry for diagnosing B cell malignancies like leukemias and lymphomas, monitoring immune status, and evaluating the effectiveness of B cell-targeted therapies [ 1 ]. The presence of CD19 on most B cell malignancies has made it an important therapeutic target, with treatments like CAR-T cell therapy specifically designed to target CD19-positive cells in conditions like B-cell acute lymphoblastic leukemia and certain lymphomas [ 1 ].
Some key points to consider about CD19 include:
- It is a reliable B-cell biomarker [ 1 ]
- It is retained on cells that have undergone neoplastic transformation [ 1 ]
- Increased expression of CD19 has been found on most B-cell tumors, including B-cell ALL, chronic lymphocytic leukemia, and B-cell lymphomas [ 1 ]
- CD19 CAR T-cell therapies include tisagenlecleucel, axicabtagene ciloleucel, brexucabtagene autoleucel, and lisocabtagene maraleucel [ 1 ]
Overall, CD19 is a critical marker for identifying and targeting B cell malignancies, and its presence has significant implications for the diagnosis, treatment, and management of these conditions [ 1 ].
From the FDA Drug Label
KYMRIAH is a CD19-directed genetically modified autologous T cell immunotherapy which involves reprogramming a patient’s own T cells with a transgene encoding a chimeric antigen receptor (CAR) to identify and eliminate CD19-expressing malignant and normal cells The CAR is comprised of a murine single-chain antibody fragment which recognizes CD19 and is fused to intracellular signaling domains from 4-1BB (CD137) and CD3 zeta.
CD19 is a marker for B cells. KYMRIAH targets and eliminates CD19-expressing malignant and normal B cells. 2
From the Research
CD19 Marker
- CD19 is a marker for B-lymphocytes and is nearly ubiquitously expressed on these cells 3, 4
- It is also expressed on B-cell malignancies, making it a target for therapies such as CAR T cells, monoclonal antibodies, antibody-drug conjugates, and bispecific T cell engagers or antibodies 3, 4, 5, 6
- CD19 expression is retained following exposure to these agents, and patients can be successfully re-challenged with anti-CD19 therapies of a different drug class upon disease relapse post-CAR T cells 3
- The optimal patient selection and sequencing of these novel therapies has not yet been established, and further data is needed to elucidate sequencing and the impact these agents may have on CAR T-cell therapy 3, 4, 5
CD19 Expression
- CD19 is expressed on the surface of B cells from the early stages of development until maturity 4
- It is not expressed on hematopoietic stem cells or plasma cells 4
- CD19 expression can be dim or lost in some cases of B-cell malignancies, but this does not necessarily predict nonresponse or recurrence after CAR T-cell therapy 7
- Prior therapy with CD19-directed agents, such as blinatumomab, can be associated with a higher rate of failure to achieve remission or subsequent loss of remission with antigen escape 7