Heterogeneity and Differentiation Patterns of pDC Cells in pDC-AML: A Novel Perspective from Single-Cell RNA Sequencing

Background: Plasmacytoid dendritic cells (pDCs), being a primary source of natural type I interferon (IFN-I), have pivotal roles in orchestrating the immune response. Typically, only less than 1% pDCs can be detected in the total bone marrow or peripheral blood nuclear cells. However, the uncontrollable proliferation of transformed pDCs is a remarkable characteristic of blastic plasmacytoid dendritic cell neoplasm (BPDCN). Recently, an abnormal amplification of pDCs in myeloid neoplasms has also been reported in MDS/AML patients (pDC-AML/MDS). This abnormal increase in pDCs could potentially promote disease progression. In this study, we utilized single-cell RNA-sequencing (scRNA-seq) to examine the characteristics of pDCs in pDC-AML. Method: Our study employed a mixed retrospective and prospective design. 85 patients diagnosed with PDC-AML/MDS/BPDCN, including 1 pDC-MDS, 17 pDC-AML, 50 non-pDC-AML (AML patients without pDCs expansion), 17 BPDCN from Tongji Hospital of Huazhong University of Science and Technology in Wuhan, China, between July 2014 and June 2023. scRNA-seq using 10x Genomics platform were performed on bone marrow (BM) samples from 8 pDC-AML patients and 1 BPDCN patient. Furthermore, we expanded our dataset by integrating publicly available scRNA-seq data of BM samples from 5 BPDCN patients, 5 non-pDC-AML patients, and 5 healthy donors (HD). Result: The median pDCs proportion of pDC-AML/MDS was 8.0% (range 2.5-52.0%). As of June 2023, The median overall survival (OS) of patients with pDC-MDS/AML was 10.5 months shorter than non-pDC-AML (21.5 months; P＜0.05). In addition, the prognosis of pDC-AML/MDS patients can only be significantly improved after receiving allogenic hematopoietic stem cell transplantation, showing a similar OS to that of non-pDC-AML patients. To further clarified the role of pDCs in these patients, we performed scRNA-seq and acquired 126,693 cells across all samples (8 pDC-AML, 6 BPDCN, 5 non-pDC-AML and 5 HD), and identified 13 clusters based on their transcriptional profile in the overall UMAP (Figure 1 A). Firstly, our single-cell sequencing data revealed significant differences in the proportions of bone marrow pDCs across pDC-AML, HDs, non-pDC-AML, and BPDCN patients. Notably, pDC proportions were significantly elevated in pDC-AML and BPDCN patients. Further differential expression analysis revealed striking differences in the transcriptomes of pDCs across these four groups. When comparing pDC-AML to HDs, we identifi