Liquid Biopsy Based Single-Cell Transcriptome Profiling Characterizes Heterogeneity of Disseminated Tumor Cells from Lung Adenocarcinoma

The advent of rapid and inexpensive sequencing technology allows scientists to decipher intra-tumor heterogeneity spatially and temporally for resolving the evolutionary history of tumor and the underlying mechanism. However, studies on characterizing heterogeneity of disseminated tumor cells (DTCs) in liquid biopsies are rare because of the rarity and low viability of DTCs as well as a large number of non-tumor cells. Here, high-throughput single-cell transcriptome sequencing technology and rare DTC enrichment method are employed to decipher the heterogeneity and distinct molecular signatures of DTCs in malignant pleural effusion (MPE) from lung adenocarcinoma. Single-cell transcriptomes of 8213 MPE-derived cells are acquired for bioinformatics analysis. In these cells from MPE, five main cell populations including tumor, mesothelial, monocyte, T and B cells are identified with specific markers for each group. Tumor cells present in MPE are further divided into four distinct subgroups that are found to be associated with immune response, cell proliferation, apoptosis, and cell adhesion, respectively. Based on the single-cell dataset of MPE-derived DTCs, 19 tumor-specific markers are identified that are also highly expressed at RNA and protein levels in tumor tissues as candidate markers for detection of extraordinarily rare circulating tumor cells in the blood.