Functional Maturation of the Human Antibody Response to Rotavirus

Abstract

Infant Abs induced by viruses exhibit poor functional activity compared with those of adults. The human B cell response to rotavirus is dominated by use of the VH1–46 gene segment in both adults and infants, but only adult sequences are highly mutated. We investigated in detail the kinetic, structural, and functional advantage conferred by individual naturally occurring somatic mutations in rotavirus-specific human Abs encoded by the immunodominant VH1–46 gene segment. Adult Abs achieved enhanced binding through naturally occurring somatic mutations in the H chain CDR2 region that conferred a markedly prolonged off-rate and a desirable increase in antiviral potency. Three-dimensional cryoelectron microscopy studies of Ag-Ab complexes revealed the mechanism of viral inhibition to be the binding of high-affinity Abs at the viral RNA release pore in the double-layer particle. These structure-function studies suggest a molecular basis for the poor quality of Abs made in infancy following virus infection or immunization.

Immunodominance of the VH1–46 Antibody Gene Segment in the Primary Repertoire of Human Rotavirus-Specific B Cells Is Reduced in the Memory Compartment through Somatic Mutation of Nondominant Clones

“…A limited number of variable gene segments is used in the primary response to RV, especially the V H 1-46 gene segment that encodes the BCR in over a quarter of all VP6-specific cells, even though this segment represents Ͻ4% of the random repertoire. The dominance of this V H gene segment appears to stem from the fact that the HCDR1 and HCDR2 loops specified by V H 1-46 exhibit an optimal Ab-combining site for loops on the surface of VP6 with a high level of shape complementarity and resulting optimal affinity for a primary response (26). Our original report on RV-specific B cell repertoire also suggested V H 1-46 gene usage in B cells sorted to be VP7 specific (15).…”

“…These unusual features of the RV repertoire may have important implications for understanding the mechanism underlying the relatively poor quality and duration of immunity to RV infection. Affinity maturation, enhanced by somatic mutations, is a critical factor in functional maturation of the human B cell response to RV (26). Also, secretory IgA is thought to be a significant effector molecule in RV immunity at the intestinal mucosal surface (3,27,28).…”

Potent High-Affinity Antibodies for Treatment and Prophylaxis of Respiratory Syncytial Virus Derived from B Cells of Infected Patients

“…The results presented here further support the utility of an anti-G Ab in reducing viral load in both prophylactic and postinfection treatment mouse models. Accordingly, we hypothesize potential clinical benefit from supplying affinity-matured human Ab from adults to infants, who are less efficient at generating such Abs themselves (52). The novel Abs described here may provide attractive candidates for testing of this hypothesis in clinical trials.…”

Differential Accessibility of a Rotavirus VP6 Epitope in Trimers Comprising Type I, II, or III Channels as Revealed by Binding of a Human Rotavirus VP6-Specific Antibody

“…RV6-25 and another anti-VP6 human antibody previously isolated from our laboratory, designated RV6-26, are closely related genetically as they are encoded by the same heavy chain variable gene segment (15). However, RV6-26 has been shown to inhibit virus replication following transfection into cells, whereas the RV6-25 antibody that is the subject of the current studies did not inhibit virus replication after transfection (18). It was of interest to determine the pattern of binding of RV6-25 to DLPs, in order to begin to determine the structural basis for the difference in the ability of these genetically related antibodies to inhibit RV.…”

“…Representative antibodies encoded by the V H 1-46 gene segment were expressed and characterized (18). For example, the monoclonal antibody (MAb) RV6-26 was shown to inhibit virus replication when introduced into cells, whereas MAb RV6-25, another human VP6-specific antibody encoded by V H 1-46, was unable to do so.…”