Chemotherapy-induced developmental trajectories of monocytes in breast cancer

Relevance . Monocytes are circulating immune cells which are traditionally divided into three subsets. The contribution of each subset to breast cancer pathogenesis is controversial. Moreover, there is no data regarding the programming of monocyte subsets towards antitumor activity induced by chemotherapy. Aim . To study the trajectories of monocyte subsets and transcriptomic changes in blood monocytes during neoadjuvant chemotherapy (NAC). Materials and Methods . Mononuclear cells were purified from the peripheral blood of nine triple-negative breast cancer (TNBC) patients before NAC and on the 3rd and 21st day after the first NAC cycle (AC regimen). Total cell concentration and viability (Calcein/DRAQ7) were assessed by flow cytometry. Single-cell RNA sequencing was performed on a Genolab M platform (GeneMind Biosciences) using the 10x Genomics technology for fixed samples. Data were analyzed using Seurat, SingleR, and the dynverse R package for trajectories. Results and Discussion . The trajectory analysis indicated that monocytes were clustered into three subsets: classical, non-classical, and intermediate. Classical monocytes were characterized by high expression of CD14 , CSF3R , S100A8 , S100A9 , VCAN , LYZ , SELL , and GRN genes, whereas non-classical monocytes expressed FCGR3A , MTSS1 , TCF7L2 , CSF1R , SPN , EVL , and LYN . The developmental trajectories of monocytes were significantly affected by chemotherapy. Transcriptionally, classical monocytes were subdivided into two clusters: one characterized by proliferative signals and the other by stress signals. By day 21st after NAC, developmental trajectories of monocytes and their subset composition were observed to recover. Chemotherapy promoted the pro-inflammatory activity of monocytes. Conclusion . Peripheral blood monocytes of TNBC patients are capable of recovering their subset composition after NAC by the 21st day after the first cycle of chemotherapy.