Johan Lantto

A divalent antibody format is required for neutralization of human cytomegalovirus via antigenic domain 2 on glycoprotein B

Glycoprotein B (gB) of human cytomegalovirus (HCMV) is the dominating protein in the envelope of this virus and gives rise to virus-neutralizing antibodies in most infected individuals. We have previously isolated a neutralizing human antibody specific for antigenic domain 2 (AD-2) on gB, a poorly immunogenic epitope, which nevertheless is capable of eliciting potent neutralizing antibodies. In order to define parameters important for the neutralization of HCMV via gB, we have investigated the virus-neutralizing capacity and the kinetics of the interaction with AD-2 of the monomeric and dimeric forms of a single chain variable fragment (scFv) corresponding to this antibody. We demonstrate here that neutralization of HCMV via AD-2 on gB can be mediated by dimeric scFv, while monomeric fragments cannot mediate neutralization of the virus, despite a slow dissociation from the intact glycoprotein. This finding is discussed in the context of possible mechanisms for antibody-mediated virus neutralization.

Non‐germ‐line encoded residues are critical for effective antibody recognition of a poorly immunogenic neutralization epitope on glycoprotein B of human cytomegalovirus

The capability of the antibody (Ab) repertoire to mount a response to appropriate epitopes on infectious agents will strongly affect the ability of the immune system to provide protection against disease. Certain epitopes may be poor inducers of immunity but are nevertheless able to promote biologically important protection when recognized by the immune repertoire. We have investigated the recognition by Ab of one such poorly immunogenic target, antigenic domain 2 (AD‐2) on human cytomegalovirus glycoprotein B. To date, only two well‐characterized human monoclonal Ab reactive with this epitope are known. To define parameters important for establishment of a human paratope recognizing this epitope, we created variants of the variable genes utilized by one of these Ab and used phage display technology to select Ab fragments with retained antigen specificity. We show here that residues in the first complementarity determining region of both the heavy and the light chain are involved in determining the AD‐2 specificity and, in addition, that key mutations in the germ‐line sequence are required for effective interaction with this epitope. Thus, the products of the human germ‐line IGHV3–30 and IGKV3–11 genes, the only V genes that have been demonstrated to participate in an AD‐2 specific Ab response, do not have the intrinsic features required for high‐affinity recognition of this epitope. We propose that the inability of the human germ‐line gene‐encoded Ab repertoire to directly recognize this and possibly other antigenic determinants results in their poor immunogenicity in vivo. This may favor responses to other epitopes, which have a high‐affinity imprint in the human germ‐line Ab repertoire.

Uneven distribution of repetitive trinucleotide motifs in human immunoglobulin heavy variable genes

Insertions and deletions of entire codons have recently been discovered as a mechanism by which B cells, in addition to conventional base substitution, evolve the antibodies produced by their immunoglobulin genes. These events frequently seem to involve repetitive sequence motifs in the antibody-encoding genes, and it has been suggested that they occur through polymerase slippage. In order to better understand the process of codon deletion, we have analyzed the human immunoglobulin heavy variable (IGHV) germline gene repertoire for the presence of trinucleotide repeats. Such repeats would ensure that the reading frame is maintained in the case of a deletional event, as slippage over multiples of three bases would be favored. We demonstrate here that IGHV genes specifically carry repetitive trinucleotide motifs in the complementarity-determining regions (CDR) 1 and 2, thus making these parts of the genes that encode highly flexible structures particularly prone to functional deletions. We propose that the human IGHV repertoire carries inherent motifs that allow an antibody response to develop efficiently by targeting codon deletion events to the parts of the molecule that are likely to be able to harbor such modifications.

Chain Shuffling to Modify Properties of Recombinant Immunoglobulins

Combinatorial libraries and selection of variants from such libraries have proven to be a successful approach for identifying molecules with novel or improved properties. The importance of antibody (Ab) molecules in basic and applied research, as well as the extensive knowledge of how they interact with their antigen (Ag) targets, have made them favorite targets for modification by this approach. The binding site of Abs can be described as a set of modules that together make up the Ag-binding site. These modules may be defined either as the heavy-chain (HC) and light-chain (LC) variable domains (VH and VL respectively) or as the six individual complementarity-determining regions (CDRs) or hypervariable loops, which act together to form this structure. The variable CDRs reside in a relatively fixed framework region (FR) that makes up the basic structure and fold of the protein. (Less)