Antibody Fragment

Modality

Antibody Fragments

Types of Antibody Fragments

Conventional antibodies derived fragments:

The ~50 kDa segment known as Fab (antigen binding fragment) is made up of the heavy chain VH and CH1 domains chemically attached to the Ab light chain (VL + CL) by a disulfide bridge, ensuring monovalent and monospecific binding. A major advantage of the various Fab is that linker engineering is not required, which saves time and resources. Fabs are typically conjugated as targeting ligands for therapeutic or diagnostic tool.
The variable domains of an Ab's heavy (VH) and light (VL) chains are joined by a linker peptide to form the single chain variable fragment, or scFv. Because of their small size, scFvs have a short half-life of roughly 0.5-2.0 hours. Similar to Fabs, scFvs are employed in the production of drug conjugates and targeted cancer imaging tracers.

Camelid heavy-chain antibodies derived fragments:

Single domain antibody (sdAb) or heavy-chain variable (VHH), Nanobody (Nb) is the minimum known inartificial antigen-specific binding functional fragment, weighing only ~15 kDa. Nbs are highly stable, durable, and soluble. Furthermore, because of their small size, Nbs can bind epitopes that full-size Abs cannot reach by entering small cavities. Furthermore, Nbs are easily genetically modified to create multivalent and multispecific tools that are effectively expressed on a wide scale using various expression platforms.

Fig 1. Structure of Conventional and Camelid heavy-chain mAb derived fragments

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Reference:

[1] Alonso Villela SM, et al. Production of recombinant scorpion antivenoms in E. coli: current state and perspectives. Appl Microbiol Biotechnol. 2023 Jul;107(13):4133-4152. doi: 10.1007/s00253-023-12578-1.

[2] Khilji SK, et al. Smaller size packs a stronger punch - Recent advances in small antibody fragments targeting tumour-associated carbohydrate antigens. Theranostics. 2023 May 15;13(9):3041-3063. doi: 10.7150/thno.80901.

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