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Selectively getting rid of B cells is the therapeutic goal with many Leukemia and Lymphoma. It stands to reason that anti-CD19 antibodies would target B cell, which ~ exclusively and specifically express the CD19 molecule. In turn, anti-CD19 antibody-bound B cells are the target of Natural killer cell-mediated Antibody-dependent cell-mediated cytotoxicity, i.e., how antibodies that specifically bind to B cells could be used to get rid of them in B cell malignancies.

In practical terms, the success of such an antibody-mediated approach depends on the antibody’s Biological half-life within the body. Since much of the injected Antibody is simply eliminated, not all of the injected bolus is going to be therapeutically useful. This is why such Rx approaches typically require multiple shots.

On the other hand, Chimeric antigen receptor (CAR) essentially endows a T cell with additional Monoclonal antibody -like functionality. Here, such antibody-like specificity is ‘grafted’ onto the T cell by genetically engineering it to express a CAR that specifically binds the CD19 molecule expressed on the surface of B cells.

Even if, much like injected antibodies, some or many of such genetically engineered CAR-T cells are simply eliminated from the body shortly after injection, cells can replicate but molecules like antibodies can’t. Essentially CAR-T cells can a) replicate in the body to make more copies of themselves, and b) thus stick around longer. Thus, the CAR-T cell approach to target malignant B cells is more effective because it uses a replication-capable cell compared to antibodies which can’t replicate.

https://www.quora.com/Why-is-chimeric-antigen-receptor-better-than-just-injecting-anti-CD19-antibodies/answer/Tirumalai-Kamala

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