Variant CD44 expression is enriching for a cell population with cancer stem cell-like characteristics in human lung adenocarcinoma

Abstract

Background: Preliminary studies have identified cancer stem cells (CSCs) in various cancers and there are several ongoing clinical studies targeting these cells. CD44 (standard or variant isoforms) and/or aldehyde dehydrogenase (ALDH) expression is the most commonly used markers for the identification of CSCs. The goal of the current study was to examine the ability of CD44v, either alone or in combination with ALDH, to identify CSCs within human lung cancer cells lines.Methods: We examined several lung adenocarcinoma cell lines for the ability of CD44v and/or ALDH expression to enrich for cells with CSC characteristics such as in vitro differential proliferation rate, chemotherapeutic-resistance, tumorsphere formation, and in vivo tumorigenicity. We also compared their in vivo secondary tumor formation, and histological characteristics of their xenograft tumors, and examined their expression of PD-L1, EGFR, xCT, and reactive oxygen species (ROS).Results: Both CD44vhigh/ALDHhigh and CD44vhigh/ALDHlow cells were enriched in cells with CSC characteristics, with the CD44vhigh/ALDHlow cells being more proliferative and more resistant to chemotherapeutics, whereas CD44vhigh/ALDHhigh cells were more efficient in forming tumorspheres in vitro, in making primary xenograft tumors, and in propagating secondary tumors in vivo. Applying stricter sorting gates to select for cells with the highest CD44v/ALDH expression caused the CD44vhigh/ALDHlow cells to lose their high proliferation rates and chemotherapeutic resistance ability, but enriched for the tumorsphere-forming cells among the CD44vhigh/ALDHhigh and CD44vhigh/ALDHlow cells. CD44vhigh expression was associated with PD-L1 and xCT expression in both H1650 and HCC827 cells. This association was not modified by ALDH expression in the H1650 cell line. However, in the HCC827 cell line, ALDH expression was negatively associated with PD-L1 and positively associated with xCT expression.Conclusion: Lung adenocarcinoma cells with high CD44v expression are enriched for CSCs. Addition of ALDH as an enrichment marker bestowed some CSCs characteristics to CD44vhigh/ALDHlow cells and others to CD44vhigh/ALDHhigh cells. We propose that lung adenocarcinoma contains different CSCs, each of them endowed with different CSC characteristics.

The Extrinsic and Intrinsic Roles of PD-L1 and Its Receptor PD-1: Implications for Immunotherapy Treatment

“…PD-L1 expression has been shown to correlate with the cancer stem cell (CSC)-like characteristics including the expression of CD44 and/or CD133 at high levels on tumor cells. Human head and neck (177), lung (178), and colorectal (179) cancer cells that have CSC-like characteristics (CD44 high /CD133 high ) were shown to preferentially express PD-L1 compared to CD44 low /CD133 low cancer cells in immunocompromised mouse models either inoculated with a patient-derived xenograft or human cancer cell lines mixed with Matrigel R , respectively. In breast and lung cancer cells CD44 was shown to be a key regulator of PD-L1 expression following shRNA-directed knockdown of CD44 in vitro and in vivo using a metastatic breast cancer xenograft mouse model (180).…”

Tumor-Intrinsic PD-L1 Signaling in Cancer Initiation, Development and Treatment: Beyond Immune Evasion

“…For example, bladder cancer cells with surface expression of PD-L1 exhibited signatures of immune evasion as well as increased stemness ( 93 ). PD-L1 has been shown to be preferentially expressed on CD44 high CSCs in lung cancer cells ( 94 ). Selective expression of PD-L1 was observed on CD44 + head and neck tumor cells compared with CD44 − tumor cells ( 95 ).…”

A Virus-Like-Particle immunotherapy targeting Epitope-Specific anti-xCT expressed on cancer stem cell inhibits the progression of metastatic cancerin vivo

“… 12 High levels of xCT mRNA and protein correlate with significant reduction in distal metastases-free and overall survival. 13,14 xCT expression is upregulated in breast CSC (BCSC) 15 and other solid tumor stem cells, 16–21 and several studies show that xCT physically interacts with the well-known stem cell proteins, CD44 and MUC1. 6,20–23 The frequency of xCT expression on a variety of CSC suggests that therapies targeting xCT may be effective in treating many tumors with high stem cell frequencies including gastrointestinal 23 and pancreatic 24 cancers.…”