Selective killing of plasma cell clones using splice-switching oligonucleotides targeting immunoglobulin variable exons

Deregulated proliferation of a plasma cell (PC) clone is accompanied by an excess production of a monoclonal immunoglobulin (mo-Ig) component with unique V(D)J rearrangement features. In systemic Ig light chain (AL) amyloidosis, organ dysfunction is due to the deposition of amyloid fibrils composed of mo-Ig light chains in target tissues. Recent advances in exon skipping therapy using splice-switching antisense oligonucleotides (ASO) prompted us to examine a new antisense strategy targeting the variable (V) exon in myeloma cells. Indeed, we previously observed that the production of truncated Ig light chains, encoded by alternatively spliced mRNAs lacking V exon, heightened endoplasmic reticulum (ER) stress and triggered apoptosis of antibody-secreting plasma cells. We designed ASO hybridizing donor or acceptor V exon splice sites on mo-Ig pre-mRNAs. These compounds were very potent alternative splicing inducers and increased the production of V-domain-less truncated Ig chains. Remarkably, in vitro experiments and tumor xenograft models revealed that myeloma cells were highly sensitive to specific ASO treatment, compared to an irrelevant control-ASO. RNA-seq experiments further confirmed that the production of truncated Ig induced upon ASO treatment provoked a massive myeloma cell death through ER stress-associated apoptosis. In addition, high throughput sequencing of Ig repertoire demonstrated that ASO targeting JH2 or Jκ1 donor splice site induced massive elimination of VDJH2- or VJκ1-rearranged clones respectively, while sparing the others. Collectively, these data provide evidence that ASO targeting V exon on mo-Ig pre-mRNAs can emerge as new weapons to induce selective killing of plasma cell clones.