Single-cell transcriptomic analysis of NK cell dynamics in myeloma patients reveal persistent reduction of cytotoxic NK cells from diagnosis to relapse

Natural killer (NK) cells mediate the cytotoxic immune response against multiple myeloma and are important effector cells in immune therapies through antibody-dependent cellular cytotoxicity. Here, we used single-cell transcriptomics, flow cytometry and functional assays to investigate the bone marrow NK cell compartment of myeloma patients at diagnosis, during treatment and after relapse. The bone marrow of myeloma patients is characterized by a reduction in conventional cytotoxic NK cells that persists throughout treatment. We show in 20% of newly diagnosed myeloma patients that an altered balance between cytotoxic and cytokine-producing NK cells translates into a reduced cytotoxic ability in response to therapeutic antibodies. The relative loss of cytotoxic NK cells persists at relapse and is accompanied by an expansion of IFN-responsive NK cells. These findings reveal previously unappreciated alterations in bone marrow NK cell composition and highlight the importance of understanding the bone marrow immune system in patients receiving immunotherapies. Statement of significance The bone marrow of multiple myeloma patients is characterized by a persistent reduction in cytotoxic CD56dim NK cells, accompanied by inferior in vitro responses to therapeutic antibodies at diagnosis and an increase in IFN-responsive NK cells at relapse. These findings highlight the importance of understanding the BM microenvironment in multiple myeloma patients receiving immunotherapies. ### Competing Interest Statement M.D. is on the advisory board of Sanofi and GSK. F.G. received honoraria from and is on the advisory board of Janssen, Takeda, GSK, BMS/Celgene, Oncopeptides, Sanofi, Amgen, Pfizer, Roche and Abbvie. V.H.J.v.d.V. is an inventor on the EuroFlow-owned patent PCT/NL2013/0505420 (Methods, reagents, and kits for detecting minimal residual disease). The related patent is licensed to Cytognos (Salamanca, ES), who pays royalties to the EuroFlow Consortium. V.H.J.v.d.V. reports Laboratory Services Agreements with Agilent Technologies, Navigate, Cytognos, Janssen and BD Biosciences. S.Z. receives research support from Janssen and Takeda and is on the advisory boards for Janssen, BMS, Takeda, Oncopeptides and Sanofi without receiving personal fees. N.W.C.J.v.d.D. has received research support from Janssen Pharmaceuticals, AMGEN, Celgene, Novartis, Cellectis and BMS, and serves in advisory boards for Janssen Pharmaceuticals, AMGEN, Celgene, BMS, Takeda, Roche, Novartis, Bayer, Adaptive, and Servier, all paid to institution. A.B. received honoraria and/or is on the advisory board of Amgen, Sanofi, BMS and Janssen. P.S. consults for and receives research support from BMS/Celgene and Janssen.