Probing serum transplant immunomes by epitope profiling. (A) Binding of individual epitope-mimicking phage clones to serum antibodies of myeloma patients MM023, MM031, and MM041 in clinical remission as well as to polyclonal control IgG. A nonselected random peptide phage was used as a control. Phage binding was measured by ELISA. (B) Inhibition of phage-antibody interaction by cognate peptide. GST-THMWVWDVSPEL blocks the binding of phage THMWVWDVSPEL to MM031 antibodies. Naked GST was used as a control. (C) Epitope-directed serum reactivity in the pre- and post-HSCT period. Here, we show reactivity against epitope-mimic THMWVWDVSPEL with serum antibodies of patient MM031 and of epitope-mimic ALRMPTMKTFIP with serum antibodies of patient MM023 at different time points before and after allogeneic HSCT. (D) Cross-reactivity of epitope-mimics (selected on serum transplant immunomes) with sera from myeloma patients (before and after allogeneic HSCT), healthy donors, and other hematological patients after allogeneic HSCT. A color key was used to depict binding strength in the heat map. Crosses (×) indicate the selections from which each mimic derives. Ab, antibody; CP, control patient (patients who underwent HSCT due to other hematological diseases); HD, healthy donor; MM, MM patient.