A novel promiscuous class of camelid single-domain antibody contributes to the antigen-binding repertoire.
It is well established that, in addition to conventional Abs, camelids (such as Camelus dromedarius and Lama glama) possess unique homodimeric H chain Abs (HCAbs) devoid of L chains. The Ag-binding site of these HCAbs consists of a single variable domain, referred to as VHH. It is widely accepted that these VHHs, with distinct framework-2 imprints evolved within the V(H) clan III-family 3, are exclusively present on HCAbs. In this study, we report the finding of a distinct leader signal sequence linked to variable genes displaying a high degree of homology to the clan II, human VH(4) family that contributes to the HCAb Ag-binding diversity. Although the VHH framework-2 imprints are clearly absent, their VH(4)-D-JH recombination products can be rearranged to the H chains of both classical and HCAbs. This suggests that for these V domains the presence of a L chain to constitute the Ag-binding site is entirely optional. As such, the capacity of this promiscuous VH(4) family to participate in two distinct Ab formats significantly contributes to the breadth of the camelid Ag-binding repertoire. This was illustrated by the isolation of stable, dendritic cell-specific VH(4) single domains from a VH(4)-HCAb phage display library. The high degree of homology with human VH(4) sequences is promising in that it may circumvent the need for "humanization" of such single-domain Abs in therapeutic applications.
Deschacht
Nick
N
Laboratory of Cellular and Molecular Immunology, Vrije Universiteit Brussel, Brussels, Belgium.
De Groeve
Kurt
K
Vincke
Cécile
C
Raes
Geert
G
De Baetselier
Patrick
P
Muyldermans
Serge
S
D000818:Animals; D000941:Antigens / Q000378:metabolism*; D001666:Binding Sites, Antibody / Q000276:immunology*; D001854:Bone Marrow Cells / Q000276:immunology / Q000378:metabolism; D002161:Camelids, New World / Q000276:immunology*; D002162:Camelus / Q000276:immunology*; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism; D007143:Immunoglobulin Heavy Chains / Q000378:metabolism*; D007135:Immunoglobulin Variable Region / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D017434:Protein Structure, Tertiary
D000941:Antigens; D007140:Immunoglobulin Fab Fragments; D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region