Human bone marrow resident natural killer cells have a unique transcriptional profile and resemble resident memory CD8+ T cells

Human lymphoid tissues harbor, in addition to CD56bright and CD56dim natural killer (NK) cells, a third NK cell population: CD69+CXCR6+ lymphoid tissue (lt)NK cells. The function and development of ltNK cells remain poorly understood. In this study we performed RNA sequencing on the CD56bright and CD56dim NK cells (from bone marrow and blood), and the ltNK cells (from bone marrow). In addition, the blood derived CD56dim, and bone marrow derived ltNK cells were further subdivided into a NKG2A+ and NKG2A- fraction. Paired blood and bone marrow samples of 4 healthy donors were included. When comparing the NKG2A fractions, only 3 genes (of 9382 genes included) had a significantly differential expression. Therefore, we pooled the expression data proportionally from the NKG2A+ and NKG2A- fractions in subsequent analyses. In ltNK cells, 1353 genes were differentially expressed compared to circulating NK cells. Several molecules involved in migration were downregulated in ltNK cells: S1PR1, SELPLG and CD62L. By flow cytometry we confirmed that the expression profile of adhesion molecules (CD49e-, CD29low, CD81high, CD62L-, CD11c-) and transcription factors (Eomeshigh, Tbetlow) of ltNK cells differed from their circulating counterparts. LtNK cells were characterized by enhanced expression of inhibitory receptors TIGIT and CD96 and low expression of DNAM1 and cytolytic molecules (GZMB, GZMH, GNLY). Their proliferative capacity was reduced compared to the circulating NK cells. By performing gene set enrichment analysis we identified DUSP6 and EGR2 as potential regulators of the ltNK cell transcriptome. Remarkably, comparison of the ltNK cell transcriptome to the published human spleen-resident memory CD8+ T (Trm) cell transcriptome revealed an overlapping gene signature. Moreover, the phenotypic profile of ltNK cells resembled that of CD8+ Trm cells in bone marrow. Together, we provide a comprehensive molecular framework of the conventional CD56bright and CD56dim NK cells as well as the tissue-resident ltNK cells and provide a core gene signature which might be involved in promoting tissue-residency. Overall design: mRNA sequencing of NK cell populations isolated from blood: CD56bright, NKG2A+ CD56dim and NKG2A- CD56dim, and bone marrow: CD56bright, CD56dim, NKG2A+ ltNK, and NKG2A- ltNK. Each sample has 4 biological replicates.

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Melsen JE, Lugthart G, Vervat C, Kielbasa SM, van der Zeeuw SAJ, Buermans HPJ, van Ostaijen-Ten Dam MM, Lankester AC, Schilham MW