Anti-CAR Whitlow Linker [1B4A1]

The anti-CAR Whitlow linker peptide 1B4A1 clone has been developed to detect cells expressing Whitlow linker-containing CARs with different antigen specificities, including those harbouring the widely employed anti-CD19 FMC63-derived scFv as well as other scFvs, such as those targeting B-cell maturation antigen (BCMA) or CD33. It has been demonstrated to have a mean KD of […]

Contributors

Inventor Institute
Erik Kimble, Jocelyn Wright Fred Hutchinson Cancer Center
Cat. #: 162439
Unit size: 1 mg
Application: Flow cytometry, IHC, WB
Target: Chimeric antigen receptor Whitlow scFv peptide linker
Clone: 1B4A1
Host: Mouse
Class: Monoclonal
Primary citation: Kimble et al. 2025.J Immunother Cancer. 2025 Nov 18;13(11):e013123. PMID: 41253498
Product description: The anti‑CAR Whitlow linker peptide 1B4A1 clone is a murine monoclonal antibody that detects cells expressing Whitlow linker‑containing CARs with different antigen specificities, including those harbouring the widely employed anti‑CD19 FMC63‑derived scFv as well as other scFvs, such as those targeting BCMA or CD33. It has been demonstrated to have a mean K_D of 0.2 to 1 µM when tested for binding kinetics against FMC63‑Whitlow scFv protein and the Whitlow peptide (no binding to G4S4 peptide was found). 1B4A1 has also been demonstrated to stain engineered T cells expressing 1H7‑ or FMC63‑Whitlow, but not 1H7‑ or FMC63‑G4S by FACS analysis. This clone has also been shown to detect commercial CAR T cells in the blood of patients undergoing treatment with Whitlow‑linker CAR T cells (liso‑cel, axi‑cel, brexu‑cel, ide‑cel), but not in patients treated with G4S‑linker products (tisa‑cel and cilta‑cel). Finally, 1B4A1 is able to detect Whitlow‑linker CAR T cells in situ in archival biopsies from patients treated with commercial CAR T‑cell therapies (liso‑cel, axi‑cel, ide‑cel).
Conjugation: Unconjugated
Isotype: IgG2a
Immunogen: Synthetic Whitlow peptide
Target background: While CAR T-cell therapies have revolutionized the treatment of B-lineage malignancies, high-resolution tracking of CAR-engineered cells within the tumor microenvironment (TME) remains a significant technical challenge, particularly in archival formalin-fixed paraffin-embedded (FFPE) tissues. To address this, murine monoclonal antibodies (mAbs) have been developed to specifically target the Whitlow linker, a synthetic peptide commonly utilized in the scFv domains of multiple FDA-approved CAR products (e.g., axi-cel, liso-cel). Because this linker is absent in native human tissue and conserved across various antigen specificities, these mAbs provide a universal tool for the in situ identification, selection, and functional analysis of CAR-expressing cells. This methodology enables a more precise evaluation of CAR T-cell infiltration, persistence, and correlation with clinical outcomes or toxicities.

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Table with Kd values of antibodies
Scientific figure containing flow cytometry histograms

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