Versican proteolysis predicts immune effector infiltration and post-transplant survival in myeloma

High-dose alkylator-based conditioning followed by autologous stem-cell transplantation (ASCT) is a therapeutic mainstay for eligible patients with multiple myeloma. However, post-transplant relapses are common and prognostic biomarkers are scarce. Relapses are characterized by the influx of regulatory myeloid cells and dysfunctional T effectors. We have shown that myeloma-infiltrating myeloid cells produce versican (VCAN), a large matrix proteoglycan with tolerogenic activities. VCAN proteolysis by a-disintegrin-and-metalloproteinase-with-thrombospondin-motifs (ADAMTS) proteases generates versikine, a bioactive fragment (matrikine) that regulates Batf3-dendritic cells, known to control CD8+-attracting chemokine networks. Here we demonstrate that intense VCAN proteolysis predicts CD8+ infiltration post-transplant and paradoxically portends significantly inferior survival outcomes. Our data suggest that VCAN proteolysis promotes the influx of CD8+ effectors that are rendered overwhelmingly dysfunctional and/or frankly immunoregulatory (CD8+ Treg) at the tumor site. Thus, complex immunosuppressive circuits orchestrated through VCAN accumulation and turnover generate conditions favorable for myeloma tumor regrowth and point to a readily-assayed biomarker to identify the patients at risk for relapse and early death. The dismal outcomes associated with VCAN proteolysis may be rationally overcome through immunotherapies such as checkpoint inhibition (e.g., anti-TIGIT), tumor vaccines or anti-myeloid (e.g., anti-CSF-1R) approaches.