Fig. 1

Schematic illustration of mAb, HcAb, nanobody, and multivalent nanobody. (a) The application of nanobodies, it has a favorable role for imaging and therapy. (b) Classical mAb is composed of two identical light (L) chains and heavy (H) chains. Each heavy or light chain contains two functional domains, i.e., variable region (VR) and one constant region (CR). The difference is that light chain has only one constant region, whereas heavy chain has three or four constant regions. (c) HcAb naturally lacks light chains and CH1 domains. Its variable fragment is the nanobody. (d) Nanobody consists of four framework regions and three complementarity-determining regions. (e) Nanobodies can be produced in a bivalent format, either bivalent-monospecific or bivalent-bispecific. Furthermore, the addition of a third nanobody that binds to serum albumin (anti-Alb) can form multivalent constructs; all these formats can prolong the half-life of nanobodies in the bloodstream