Multiple myeloma (MM) is an incurable blood cancer with clinically defined precursor states, monoclonal gammopathy of undetermined significance (MGUS) and smouldering myeloma (SMM), allowing us to study the evolution of the immune compartment alongside tumour progression. We aimed to generate a comprehensive overview of the bone marrow (BM) NK cell compartment and investigate how the development of MM from precursor states impacts this repertoire. 

Flow cytometric analysis of over 300 patient BM aspirates revealed a stepwise increase in the proportion of CD56^bright NK cells, with significantly increased frequencies in MM patients when compared to both MGUS and SMM patients (p<0.0001), that correlated with tumour burden. We generated an integrated scRNAseq data set of BM and peripheral blood to analyse over 100,000 NK cells from 206 subjects, including samples from healthy donors and individuals with MGUS, SMM and MM. We resolved NK1, NK2 and NK3 subsets as well as identified a subset of NK cells found only in BM samples that we termed BM-NK. In addition to XCL1 and GZMH, expressed by the classical CD56^bright population, this subset had high expression of CD69, CXCR6 and RGS1. This population was enriched for pathways associated with chemokine responses and reduced cytotoxicity. With disease progression, we found an increase in the proportion of this BM-specific population which was significant between SMM and MM (p=0.008), suggestive of disease-related skewing of the BM NK cell compartment. 

Our results provide a comprehensive analysis of the BM NK cell compartment that enabled us to identify that myeloma progression is accompanied by NK cell alterations. We show for the first time that progression to myeloma is accompanied by an enrichment of BM-specific NK CD56^bright CXCR6+ CD69+ cells. Further work will clarify if these changes in the NK compartment contribute to the loss of host immune control at disease progression.