CD19 CAR mRNA will express CD19 car protein, and can be used in chimeric antigen receptor T cell immunotherapy (CAR-CD19). The CD19 car is a chimeric antigen receptor. Among them, CD19 is a CD molecule expressed by B cells (i.e. leukocyte differentiation antigen), an important membrane antigen involved in B cell proliferation, differentiation, activation and antibody production, and can also promote BCR signal transduction.