Molecular mimicry of the unidentified antigen of myeloma antibody IgE-ND

Accurate identification of paraprotein antigen targets by epitope reconstruction

We describe the first successful clinical application of a new discovery technology, epitope-mediated antigen prediction (E-MAP), to the investigation of multiple myeloma. Until now, there has been no reliable, systematic method to identify the cognate antigens of paraproteins. E-MAP is a variation of previous efforts to reconstruct the epitopes of paraproteins, with the significant difference that it provides enough epitope sequence data so as to enable successful protein database searches. We first reconstruct the paraprotein's epitope by analyzing the peptides that strongly bind. Then, we compile the data and interrogate the nonredundant protein database, searching for a close match. As a clinical proof-of-concept, we apply this technology to uncovering the protein targets of para-proteins in multiple myeloma (MM). E-MAP analysis of 2 MM paraproteins identified human cytomegalovirus (HCMV) as a target in both. E-MAP sequence analysis determined that one para-protein binds to the AD-2S1 epitope of HCMV glycoprotein B. The other binds to the amino terminus of the HCMV UL-48 gene product. We confirmed these predictions using immunoassays and immunoblot analyses. E-MAP represents a new investigative tool for analyzing the role of chronic antigenic stimulation in B-lymphoproliferative disorders.

Probing the specificity of human myeloma proteins with a random peptide phage library

Human myeloma proteins (HMPs) from 10 patients with multiple myeloma (MM) were used to affinity-select peptides from a random phage-display peptide library. Binding peptides were identified for the 10 analysed antibodies (eight, immunoglobulin G (IgG), and two, immunoglobulin A (IgA)). The specificity of the binding was confirmed by competitive experiments using phages and chemically synthesized peptides. Interestingly, some phage-displayed peptides were immuno-selected with HMPs isolated from different patients. Sequence alignments and homology searches revealed a significant homology with human proteins (e.g. neural cell adhesion proteins) and pathogen-derived proteins (e.g. herpes simplex virus capsid proteins). The selected peptides could be useful as targeting agents for myeloma cells expressing surface immunoglobulins.

Specific destruction of hybridoma cells by antigen-toxin conjugates demonstrate an efficient strategy for targeted drug therapy in leukemias of the B cell lineage

Many types of leukemia including multiple myeloma remain essentially incurable despite recent developments in immuno- and chemotherapy. The effectiveness of these therapies might be greatly enhanced by targeting cell surface proteins unique to the malignant clone, which for leukemias of the B cell lineage means clonotypic surface immunoglobulin (sIg). As this immunoglobulin (Ig) is necessarily epitope specific, we are developing ligand-toxin conjugates (LTCs) as a strategy for delivering toxins and other drugs to clonotypic tumor cells. Here we report in vitro studies that illustrate the effectiveness of this approach. LTC comprising the DNP hapten conjugated to ricin A toxin (DNP-RTA) were shown to specifically and effectively kill anti-DNP secreting murine hybridoma (U7.6) cells but not other hybridoma cells (1B12), a murine erythroleukemia cell line (Friend's Leukemia or) normal mouse spleen cells. In addition to direct toxicity, LTC treatment negatively affected the growth characteristics of the few surviving cells as reflected in decreased growth index and an increase in growth inhibition over 72 h post treatment. Interestingly, U7.6 cells that survived one or two LD90 dose(s) of LTC showed no alteration in their dose response to a subsequent attack of LTC indicating that this treatment strategy may not induce drug resistance. These data suggest that LTC therapy may be a new and effective strategy for specific destruction of tumor cells such as myeloma plasma cells and could be extended to other tumors where clonotypic receptors can be identified.

Analysis of IgE antibodies from a patient with atopic dermatitis: biased V gene usage and evidence for polyreactive IgE heavy chain complementarity-determining region 3

To better understand V gene usage, specificity, and clonal origins of IgE Abs in allergic reactions, we have constructed a combinatorial Ab library from the mRNA of an adult patient with atopic dermatitis. Sequence analysis of random clones revealed that 33% of clones used the IGHV6-1 H chain V gene segment, the only member of the V(H)6 gene family. IGHV6-1 is rarely used in the expressed adult repertoire; however, it is associated with fetal derived Abs. Features of the V(H)6 rearrangements included short complementarity-determining region 3, frequent use of IGHD7-27 D gene, and little nucleotide addition at the D-J junction. There was also a low level of mutation compared with V(H)1, V(H)3, and V(H)4 rearrangements. The library was expressed as phage-Fab fusions, and specific phage selected by panning on the egg allergen ovomucoid. Upon expression as soluble IgE Fabs, 12 clones demonstrated binding to ovomucoid, skim milk, and BSA by ELISA. Nucleotide sequencing demonstrated that the IGHV6-1 V gene segment encoded each of the 12 multiply reactive IgE Fabs. A cyclic peptide was designed from the complementarity-determining region 3 of several of these clones. The cyclic peptide bound both self and nonself Ags, including ovomucoid, human IgG, tetanus toxoid, and human and bovine von Willebrand factor. These results suggest that some IgE Abs may bind more than one Ag, which would have important implications for understanding the multiple sensitivities seen in conditions such as atopic dermatitis.