Phage-phenotype imaging of myeloma plasma cells by phage display

Multiple myeloma (MM) is a malignant disease based on differentiated plasma cells (PCs) in the bone marrow (BM). Flow cytometry and fluorescence microscopy, used to identify a large combination of clusters of differentiation (CDs), are applied for MM immunophenotyping. However, due to the heterogeneous MM immunophenotypes, more antibody panels are necessary for a preliminary diagnosis and for the monitoring of minimal residual disease (MRD). In this study, we evaluated the use of phage clones as probes for the identification of several PCs immunophenotypes from MM patients. First, A 9-mer M13-pVIII phage display library was screened against an MM.1 cells line to identify peptides that selectively recognize MM.1 cells. Then, the most representative phage clones, with amino acid sequences of foreign peptides closer to the consensus, were labelled with isothiocyanate of fluorescein (FITC) and were used to obtain a fluorescent signal on cells in ex-vivo samples by fluorescence microscopy. Selected phage clones were able to discriminate different MM immunophenotypes from patients related to CD45, CD38, CD56, and CD138. Our results highlight the possibility of using a phage-fluorescence probe for the simultaneous examination of the presence/absence of CDs associated with disease usually detected by combination of anti-CD antibodies. The design of a multi-phage imaging panel could represent a highly sensitive approach for the rapid detection of immunophenotype subtypes and the subsequent characterization of patient disease status.