| In multiple myeloma, clonally expanded malignant plasma cells elaborate copious amounts of antibody (a.k.a paraprotein) in the serum. The target specificities of these paraproteins are unknown. Given accumulating evidence for the role of antigenic stimulation in lymphomagenesis, it is important to identify the antigens in question. Without a clinical basis to suspect particular sources, there is currently no method to identify the antigenic stimuli. We have developed a method to overcome this limitation. Using phage-displayed peptide combinatorial libraries, we have characterized the cognate epitope sequences to which paraproteins bind. We then used these epitope motifs to search the protein databases to identify antigen candidates using a bioinformatics algorithm that we developed (Epitope-Mediated Antigen Prediction). Performing in silico experiments, we have shown that short predicted epitope motifs possess sufficient information to identify antigen targets, when searched singly or in a pairwise fashion. The E-MAP algorithm was validated using predicted epitopes that correctly identified their cognate antigens. E-MAP allows us, for the first time, to identify protein antigens simply from knowledge of an antibody's cognate epitope.; We applied E-MAP to analyze the target specificity of four multiple myeloma patients' paraproteins. Two paraproteins were predicted to target determinants from human cytomegalovirus (HCMV). We validated the predicted immunoreactivity of the respective paraproteins for the AD-2S1 epitope of glycoprotein B and the smallest capsid protein UL48, using a variety of techniques. In immunoassays these patient sera react strongly with HCMV. When serum immunoglobulins are electrophoretically resolved, paraproteins comigrate with the specific immunoreactivity to phage clone epitopes, to synthetic peptides of antigens, and to viral determinants. Other multiple myeloma patients' paraproteins also appear to target determinants of HCMV. The paraproteins of two other patients were predicted to target distinct epitopes on the envelope glycoprotein of a human endogenous retrovirus HERV-K Env. This potential autoantigen has been implicated in a number of malignancies and autoimmune diseases.; Identification of the cognate antigens of different patients' paraproteins may implicate antigenic stimulation in pathogenesis, reveal common risk factors and suggest potential therapeutic interventions. |
