PD-L1+ aneuploid circulating tumor endothelial cells (CTECs) exhibit resistance to the checkpoint blockade immunotherapy in advanced NSCLC patients

Combined detection of aneuploid circulating tumor-derived endothelial cells and circulating tumor cells may improve diagnosis of early stage non-small-cell lung cancer

BACKGROUND

Many tumor-derived endothelial cells (TECs) are shed into the blood and turn into circulating TECs (CTECs). Rare circulating non-hematologic aneuploid cells contain CTCs and CTECs, which are biologically and functionally different from each other. CD31 is one of the most representative endothelial cell (EC) markers, yet CD31 alone is not sufficient to detect malignant CTECs due to the existence of abundant normal ECs in circulation. Aneuploidy of chromosome 8 (CEP8) is an important criterion for the identification of malignant cells. Combined in situ phenotypic and karyotypic characterization, which includes an examination of both protein expression and aneuploid chromosomes, has demonstrated its unique advantage for both effective distinguishing and comprehensive detection of CTCs and CTECs.

METHODS

A total of 98 subjects were recruited in the current study, including healthy donors and patients with benign disease and early-stage non-small-cell lung cancer (NSCLC). SE-iFISH was performed to quantitatively analyze diverse subtypes of aneuploid CD31⁺ CTECs and CD31^- CTCs classified upon the ploidy of chromosome 8 and tumor marker expression in the specimens collected from the recruited subjects.

RESULTS

CD31^- CTCs primarily consist of triploid CTCs with a small cell size (≤5 µm) and large hyperploid CTCs (≥ pentaploid), whereas CD31⁺ CTECs are mainly comprised of large hyperploid cells. Enumeration of the total numbers of both CTCs and CTECs might help identify malignant nodules with a high sensitivity, whereas quantification of tetraploid CTCs and CTECs specifically exhibited a high specificity for the identification of malignant nodules.

CONCLUSIONS

Combined detection of the specific subtypes of aneuploid CD31⁺ CTECs and CD31^- CTCs may help to effectively identify malignant nodules with a higher sensitivity and specificity in early stage NSCLC patients.

Aneuploid Circulating Tumor-Derived Endothelial Cell (CTEC): A Novel Versatile Player in Tumor Neovascularization and Cancer Metastasis

Hematogenous and lymphogenous cancer metastases are significantly impacted by tumor neovascularization, which predominantly consists of blood vessel-relevant angiogenesis, vasculogenesis, vasculogenic mimicry, and lymphatic vessel-related lymphangiogenesis. Among the endothelial cells that make up the lining of tumor vasculature, a majority of them are tumor-derived endothelial cells (TECs), exhibiting cytogenetic abnormalities of aneuploid chromosomes. Aneuploid TECs are generated from “cancerization of stromal endothelial cells” and “endothelialization of carcinoma cells” in the hypoxic tumor microenvironment. Both processes crucially engage the hypoxia-triggered epithelial-to-mesenchymal transition (EMT) and endothelial-to-mesenchymal transition (EndoMT). Compared to the cancerization process, endothelialization of cancer cells, which comprises the fusion of tumor cells with endothelial cells and transdifferentiation of cancer cells into TECs, is the dominant pathway. Tumor-derived endothelial cells, possessing the dual properties of cancerous malignancy and endothelial vascularization ability, are thus the endothelialized cancer cells. Circulating tumor-derived endothelial cells (CTECs) are TECs shed into the peripheral circulation. Aneuploid CD31⁺ CTECs, together with their counterpart CD31^- circulating tumor cells (CTCs), constitute a unique pair of cellular circulating tumor biomarkers. This review discusses a proposed cascaded framework that focuses on the origins of TECs and CTECs in the hypoxic tumor microenvironment and their clinical implications for tumorigenesis, neovascularization, disease progression, and cancer metastasis. Aneuploid CTECs, harboring hybridized properties of malignancy, vascularization and motility, may serve as a unique target for developing a novel metastasis blockade cancer therapy.

The Blood Circulating Rare Cell Population. What is it and What is it Good For?

Blood contains a diverse cell population of low concentration hematopoietic as well as non-hematopoietic cells. The majority of such rare cells may be bone marrow-derived progenitor and stem cells. This paucity of circulating rare cells, in particular in the peripheral circulation, has led many to believe that bone marrow as well as other organ-related cell egress into the circulation is a response to pathological conditions. Little is known about this, though an increasing body of literature can be found suggesting commonness of certain rare cell types in the peripheral blood under physiological conditions. Thus, the isolation and detection of circulating rare cells appears to be merely a technological problem. Knowledge about rare cell types that may circulate the blood stream will help to advance the field of cell-based liquid biopsy by supporting inter-platform comparability, making use of biological correct cutoffs and “mining” new biomarkers and combinations thereof in clinical diagnosis and therapy. Therefore, this review intends to lay ground for a comprehensive analysis of the peripheral blood rare cell population given the necessity to target a broader range of cell types for improved biomarker performance in cell-based liquid biopsy.