Durvalumab Combined with Immunomodulatory Drugs (IMiD) Overcomes Suppression of Antitumor Responses due to IMiD-induced PD-L1 Upregulation on Myeloma Cells.

We previously showed that the interaction of programmed death-ligand 1 (PD-L1) on multiple myeloma (MM) cells with PD-1 not only inhibits tumor-specific cytotoxic T-lymphocyte activity via the PD-1 signaling pathway but also induces drug resistance via PD-L1-mediated reverse signals. We here examined the regulation of PD-L1 expression by immunomodulatory drugs (IMiDs) and antimyeloma effects of the anti-PD-L1 antibody durvalumab in combination with IMiDs. IMiDs induced PD-L1 expression on IMiD-insensitive MM cells and plasma cells from patients newly diagnosed with MM. Gene-expression profiling analysis demonstrated that not only PD-L1, but also a proliferation-inducing ligand (APRIL), was enhanced by IMiDs. PD-L1 induction by IMiDs was suppressed by using the APRIL inhibitor recombinant B-cell maturation antigen (BCMA)-Ig, the antibody against BCMA, or an MEK/ERK inhibitor in in vitro and in vivo assays. In addition, its induction was abrogated in cereblon (CRBN)-knockdown MM cells, whereas PD-L1 expression was increased and strongly induced by IMiDs in Ikaros-knockdown cells. These results demonstrated that PD-L1 upregulation by IMiDs on IMiD-insensitive MM cells was induced by (i) the BCMA-APRIL pathway via IMiD-mediated induction of APRIL and (ii) Ikaros degradation mediated by CRBN, which plays a role in inhibiting PD-L1 expression. Furthermore, T-cell inhibition induced by PD-L1-upregulated cells was effectively recovered after combination treatment with durvalumab and IMiDs. PD-L1 upregulation by IMiDs on MM cells might promote aggressive myeloma behaviors and immune escape in the bone marrow microenvironment.