Fv, variable fragment –
The Fv fragment is the smallest antibody fragment that retains antigen binding capacity.
It consists of variable fragments of light (VL) and heavy (VH) chains, each of which is stabilized by an intramolecular disulfide bond. However, contacts between VH and VL involve only ionic interactions and therefore the structure of this fragment is very unstable. Structural stability of Fv fragments can be achieved by insertion of interchain disulfide bond.


scFv, single chain Fv in which light and heavy chain fragments are connected by a polypeptide linker –
The linker technology was a key step of success of constructing scfv antibody library. Scfvs have been developed as possible drug candidates in their own right, as well as components or domains of drug candidates. The scFv fragments are the “simplest” target for cloning and expression. However, they frequently exhibit lower stability and, sometimes, lower affinity; during therapeutic use, they are characterized by shorter half- lifetime in blood circulation compared with larger fragments.


(scFv)2, fragment that consists of two scFv molecules connected by a disulfide bond – The (scFv)2 fragments obtained by disulfide bond linking between C-terminal cysteine residues demonstrate better in vivo transport into tissues compared with the scFv-fragments during their use as therapeutic agents.

dsFv, variable fragment stabilized by additional intramolecular disulfide bond –
The bacterial and yeast expression systems are used for expression of small nonglycosylated antibody fragments dsFv.


Fab- and (Fab)2, fragments –
These are identical in their structure with fragments formed during proteolysis of full-length IgG anti- bodies by papain and pepsin, respectively.


VH, heavy chain variable domain –
Single-chain fragment variable (scfv) molecules combine the coding sequence of the variable heavy (VH) and sequence of the variable light chain (VL) domains of an antibody in a single-gene encoded format.


There are antibody derivatives known as “diabodies”, “triabodies”, and “tetrabodies” –
Their molecules consist of two, three, or four identical or different fragments of antibodies of the same or different specificity linked together.


A Single domain antibody (sdAb) was discovered in both camelids and nurse sharks that consist of a lone VH domain, lacking a paired VL, attached to a constant region. The primary advantages of domain antibodies as compared with scFvs are generally better folding and stability characteristics.