Fluorescein hapten (FITC)

Fluorescein hapten on cell surface-bound conjugates is a synthetic therapeutic target utilized in adapter-mediated immunotherapy, most notably in universal chimeric antigen receptor (CAR) T-cell systems. In this approach, a fluorescein molecule (typically fluorescein isothiocyanate or FITC) is chemically conjugated to a ligand that specifically targets a tumor-associated antigen, such as the folate receptor or PSMA (Lu et al., 2015, Bioconjugate Chemistry). Once the conjugate binds to the cancer cell surface, the fluorescein moiety acts as a neo-antigen or hapten that is recognized by anti-fluorescein CAR-T cells (Lee et al., 2016, Scientific Reports). This modular strategy allows a single CAR-T cell product to be redirected against various tumor types simply by switching the fluorescein-labeled adapter molecule (Kim et al., 2018, Journal of Hematology & Oncology). Furthermore, the system provides a safety switch, as the activity and expansion of the CAR-T cells are dependent on the administration and dosage of the fluorescein-labeled adapter (Low et al., 2009, Accounts of Chemical Research). Clinical candidates like EC17 (folate-FITC) have been developed to bridge immune effectors to folate receptor-positive malignant cells.

Other names

Fluorescein isothiocyanateFITC haptenFluorescein-labeled conjugateFluorescein-labeled adapterFluorescein-labeled cell surface conjugate

The fluorescein-labeled adapter binds to a tumor-specific antigen, effectively coating the tumor cell with fluorescein haptens. Anti-fluorescein CAR-T cells then recognize these haptens via their chimeric receptors, leading to T-cell activation, cytokine release, and directed cytotoxic lysis of the tumor cell (Lee et al., 2016; Lu et al., 2015).