Bone marrow-free sequencing of M protein genes in monoclonal gammopathies.

In patients with monoclonal gammopathies, M proteins are patient-unique, can cause potentially fatal organ damage and can be used to track the B cell/plasma cell tumor after therapy. The presence of circulating tumor cells and the possibility to analyze the antibody repertoire through next generation sequencing (NGS) and proteomics approaches may provide a window of opportunity to identify patients’ specific M protein genes in the peripheral blood, without invasive bone marrow investigations. Mononuclear cells from peripheral blood were subjected to single-molecule real-time sequencing of the M protein (SMaRT M-Seq) to obtain the circulating repertoire of the affected light chain isotype in a cohort of patients with monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM) and AL amyloidosis. Tryptic digestion peptides from urinary proteins were subjected to mass spectrometry analysis to identify or confirm the clonal light chain sequence from the obtained circulating repertoire. SMaRT M-Seq on matched bone marrow samples to identify the bona fide clonal light chain sequence was performed for confirmatory purposes.