FMC63 scFv (single-chain variable fragment) is a recombinant protein derived from the variable regions (VH and VL) of the anti-CD19 monoclonal antibody FMC63, linked by a flexible peptide spacer (e.g., (Gly鈧凷er)鈧?. It specifically binds to the B-cell surface antigen CD19 with high affinity (KD ~1-10 nM) and is a key targeting component in FDA-approved CAR-T therapies, such as Kymriah庐. The humanized FMC63 scFv retains potent antigen recognition while minimizing immunogenicity, making it highly effective in treating B-cell malignancies, including acute lymphoblastic leukemia (ALL) and non-Hodgkin lymphoma (NHL). Ongoing research focuses on optimizing its affinity, stability, and functionality to enhance the safety and efficacy of CAR-T cell therapies.