Expression of single-domain antibody in different systems.

Camelid single-domain antibodies (sdAbs, VHHs, or Nanobodies®) are types of antibody fragments that are composed of the heavy-chain variable domain only. These VHHs possess unique structural and functional features, as they are small in size and exhibit thermal stability and high solubility. Compared to conventional antibodies, VHHs can be manufactured in microorganisms to significantly save on cost, labor, and time since VHHs lack the Fc domain with its N-linked oligosaccharide. Until now, VHHs have been expressed in several kinds of production systems, ranging from prokaryotic cells, yeasts, fungi, insect cells, and mammalian cell lines, to plants. In this review, we focus on the recent production of VHHs, introduce different platforms, and summarize the current state of this area and its future trends. Finally, the first potential VHH product, produced in Pichia pastoris, will probably be available on the market in 2018; thus, it is of great importance to give this antibody fragment timely attention. This is the first review concerning the production of VHHs in laboratory settings.