Single Heavy Chain Antibodies
The discovery of a unique type of antibody, found only in Camelidae, has enabled the development of novel ligands for bioprocessing. The camelid antibody lacks the light chains found in all classical antibodies and as such has only one single variable domain (VHH) by which antigens are bound, and two constant domains (CH2 and CH3). Figure 1 illustrates the structure of the classical antibody and the camelid heavy chain antibody.
The single domain VHH is the smallest intact and functional antigen-binding fragment (12 kDa) derived from a fully functional immunoglobulin. Consequently, it offers improved affinity, stability, and solubility. Its small size and unique 3-D structure enables VHH fragments to recognize novel epitopes that are inaccessible to classical VH-VL pairs. In addition to being able to modify them easily, both at gene and protein level, VHH fragments have been successfully cloned and expressed in microbial systems, therefore making them ideal candidates for application as affinity ligands for biotechnological processes.
BAC has developed CaptureSelect, a technology based on camelid VHH molecules, with which a range of products for affinity purification has been developed.
Expression of the ligands in Saccharomyces cerevisiae and selection of versatile characteristics allows the fragments to be custom made for almost any biotherapeutic purification challenge.
The mRNA encoding VHH fragments is isolated from the peripheral blood lymphocytes of immunized llama through amplification using polymerase chain reaction techniques. The DNA is cloned into Saccharomyces cerevisiae creating VHH libraries, which are screened for ligands that bind to the target molecules.