Reshaping Antibody Diversity

Abstract

Summary Unlike humans or mice, some species have limited genome encoded combinatorial diversity potential, yet mount a robust antibody response. Cows are unusual in having exceptionally long CDR H3 loops and few V-regions, but the mechanism for creating diversity is not understood. Deep sequencing revealed that ultralong CDR H3s contain a remarkable complexity of cysteines, suggesting that disulfide-bonded mini-domains may arise during repertoire development. Indeed, crystal structures of two cow antibodies reveal that these CDR H3s form a very unusual architecture composed of a β-strand “stalk” that supports a structurally diverse, disulfide-bonded, “knob” domain. Sequence analysis suggests that diversity arises from somatic hypermutation of an ultralong DH with a severe codon bias towards mutation to cysteine. These unusual antibodies can be elicited to recognize defined antigens through the knob domain. Thus, the bovine immune system produces an antibody repertoire composed of CDR H3s of unprecedented length that fold into a diversity of mini-domains generated through combinations of somatically generated disulfides.

Rapid elicitation of broadly neutralizing antibodies to HIV by immunization in cows

“…BnAbs isolated from chronic infection have a number of unusual features that have been selected to cope with the glycan shield including much longer than average HCDR3 loops 10–12 . HCDR3s in most vertebrates have restricted lengths that predominantly encode loops of 12–16 amino acids upon VDJ recombination 9,13–15 . Therefore, in many species, relatively few antibody precursors can be affinity-matured to HIV bnAbs.…”

“…Therefore, in many species, relatively few antibody precursors can be affinity-matured to HIV bnAbs. Cows, however, produce antibodies with HCDR3s that average ~26 amino acids in length with an ultralong subset (10–15% of the repertoire) that can be over 70 amino acids in length 4–6,8,9,16 . Previous work has shown that repeated immunization over multiple years with a non-well-ordered Env trimer in cows can lead to some neutralization breadth in the immunoglobulin-rich colostrum 17–19 , although with relatively low potency.…”

“…To test this hypothesis, we immunized four cows with BG505 SOSIP. The antibody repertoire of cows contains long third heavy chain complementary determining regions (HCDR3) with an ultralong subset that can reach over 70 amino acids in length 4–9 . Remarkably, BG505 SOSIP immunization resulted in rapid elicitation of broad and potent serum antibody responses in all four cows.…”

Broad Neutralizing Antibodies to HIV Env and Other Complex Viral Antigens from Vaccinated Cows

“…Heavy chain camelid antibodies offer the potential for high-level production in conventional bacterial and yeast biofermentation which may lead to large-scale, relatively low-cost production [64]. In contrast, the length of bovine CDRH3 is highly variable and longer (up to 70 amino acids) than those in other species particularly compared to human [16,[65][66][67][68]. The antibodies with ultralong CDRH3 can comprise up to 10-15% of the entire bovine IgG repertoire ( Figure 2) [16].…”

“…However, recent immunization studies in llamas and cows have resulted in induction of BrNAbs. Induction of BrNAbs in these animals is highly informative, as the studies from past 2 decades revealed that the antibodies from these species have unique structure facilitating antibody-antigen interaction through the less accessible epitopes [15,16]. The cows, particularly, produce exceptionally long CDRH3 which could be potentially advantageous in vaccine research developments.…”