CD19 is a cell surface maker of all B cells. it is a surface antigen that the synthetic CAR chimeric antigen receptor can recognize and bind the lymphocyte to the B cell and then the lymphocyte produces perforin and granzyme that dissolve the cell walls of the B cell and it spills out into the circulation.
these leukemias are only a cancer of the antibody producing B cells. so by using the CAR for the surface antigen of the B cells, the entire population of B cells in the body is destroyed. this leaves that patient with no ability to produce antibodies so they have be placed on permanent immunoglobulin replacement therapies for the missing antibodies.
this CAR T cell therapy is not productive in all patients and many do not obtain any benefit form the CAR T cell therapies in spite of the fact that it is considered by many to be a cure for cancer.