Single domain antibodies: promising experimental and therapeutic tools in infection and immunity

Abstract

Antibodies are important tools for experimental research and medical applications. Most antibodies are composed of two heavy and two light chains. Both chains contribute to the antigen-binding site which is usually Xat or concave. In addition to these conventional antibodies, llamas, other camelids, and sharks also produce antibodies composed only of heavy chains. The antigen-binding site of these unusual heavy chain antibodies (hcAbs) is formed only by a single domain, designated VHH in camelid hcAbs and VNAR in shark hcAbs. VHH and VNAR are easily produced as recombinant proteins, designated single domain antibodies (sdAbs) or nanobodies. The CDR3 region of these sdAbs possesses the extraordinary capacity to form long Wngerlike extensions that can extend into cavities on antigens, e.g., the active site crevice of enzymes. Other advantageous features of nanobodies include their small size, high solubility, thermal stability, refolding capacity, and good tissue penetration in vivo. Here we review the results of several recent proofof-principle studies that open the exciting perspective of using sdAbs for modulating immune functions and for targeting toxins and microbes.

Selection and Characterization of Single Domain Antibodies Specific for Bacillus anthracis Spore Proteins

“…Still, one typically requires a high-throughput screening method such as phage display to isolate target binding elements. SdAbs isolated following rounds of selection typically demonstrate high affinity and target specificity [12,13]. Additionally, though not a universal characteristic, most sdAbs exhibit the ability to refold into active detection elements following denaturation [14].…”

New agents in HSC mobilization

“…Nanobodies have garnered significant interest as potential therapeutics owing to their ease of production as recombinant proteins, small size, high solubility, good thermal stability and good in vivo tissue penetration (Reviewed in [48]). The single-domain CXCR4-specific nanobody referred to as "L8" mobilized equivalent numbers of CD34 + cells in Cynomolgus monkeys and with similar kinetics to AMD3100 [49].…”

Camelid single-domain antibody fragments: Uses and prospects to investigate protein misfolding and aggregation, and to treat diseases associated with these phenomena

“…The long CDR3 of cAb-Lys3 (blue) protrude into the active site of HEWL (Figure adapted from Ref. [50]). …”

“…Moreover, the long CDR3 can form a protruding loop, allowing V H Hs to bind unique conformational epitopes, such as cryptic epitopes, clefts or cavities that are generally inaccessible to conventional VHeVL pairs [50] ( Fig. 2, left part, #).…”